cardiopulmonary bypass - s. ghosh, et. al., (cambridge, 2009) ww.pdf

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Cardiopulmonary Bypass


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Cardiopulmonary Bypass

Edited by

Sunit Ghosh

Florian Falter

David J. Cook


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CAMBRIDGE UNIVERSI Y PRESS

Cambridge, New York, Melbourne, Madrid, Cape own, Singapore,São Paulo, Delhi, Dubai, okyo

Cambridge University Press

Te Edinburgh Building, Cambridge CB2 8RU, UK

Published in the United States of America byCambridge University Press, New York

www.cambridge.orgInformation on this title: www.cambridge.org/9780521721998

© S. Ghosh, F. Falter and D. J. Cook 2009

his publication is in copyright. Subject to statutory exceptionand to the provisions of relevant collective licensing agreements,no reproduction of any part may take place without the writtenpermission of Cambridge University Press.

First published 2009

Printed in the United Kingdom at the University Press, Cambridge

A catalog record for this publication is available from theBritish Library

ISBN 978-0-521-72199-8 Paperback

Additional resources for this publication atwww.cambridge.org/9780521721998

Cambridge University Press has no responsibility for the persistence oraccuracy of URLs for external or third-party Internet websites referredto in this publication, and does not guarantee that any content on suchwebsites is, or will remain, accurate or appropriate.

Every effort has been made in preparing this publication to provideaccurate and up-to-date information which is in accord with acceptedstandards and practice at the time of publication. Although case historiesare drawn from actual cases, every effort has been made to disguise theidentities of the individuals involved. Nevertheless, the authors, editorsand publishers can make no warranties that the information containedherein is totally free from error, not least because clinical standards areconstantly changing through research and regulation. Te authors,editors and publishers therefore disclaim all liability for direct orconsequential damages resulting from the use of material contained inthis publication. Readers are strongly advised to pay careful attention toinformation provided by the manufacturer of any drugs or equipmentthat they plan to use.


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v

1. Equipment and monitoring 1

Victoria Chilton and Andrew Klein

2. Circuit setup and safety

checks 23

Simon Colah and Steve Gray

3. Priming solutions for

cardiopulmonary bypass

circuits 36

George Hallward and Roger Hall

4. Anticoagulation, coagulopathies,

blood transfusion and

conservation 41

Liza Enriquez and LindaShore-Lesserson

5. Conduct of cardiopulmonary

bypass 54

Betsy Evans, Helen Dunningham andJohn Wallwork

6. Metabolic management during

cardiopulmonary bypass 70

Kevin Collins and G. Burkhard

Mackensen

7. Myocardial protection and

cardioplegia 80

Constantine Athanasuleas and GeraldD. Buckberg

8. Weaning from cardiopulmonary

bypass 92

James Keogh, Susanna Price and BrianKeogh

9. Mechanical circulatory

support 106

Kirsty Dempster and Steven Tsui

10. Deep hypothermiccirculatory arrest 125

Joe Arrowsmith and Charles W. Hogue

11. Organ damage during

cardiopulmonary bypass 140

Andrew Snell and Barbora Parizkova

12. Cerebral morbidity in adult

cardiac surgery 153

David Cook

13. Acute kidney injury (AKI) 167

Robert C. Albright

14. Extracorporeal membrane

oxygenation 176

Ashish A. Bartakke and Giles J. Peek

15. Cardiopulmonary bypass in

non-cardiac procedures 187

Sukumaran Nair

Index 199

Contents

List of contributors vii Preface ix


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vii

Contributors

Robert C. Albright Jr DO

Assistant Professor of Medicine, Divisionof Nephrology and Hypertension, MayoClinic, Rochester, Minnesota, USA

Joe Arrowsmith MD FRCP FRCA

Consultant Cardiothoracic Anaesthetist,

Papworth Hospital, Cambridge, UK

Constantine Athanasuleas MD

Division of Cardiothoracic Surgery, Univer-sity of Alabama, Birmingham, Alabama, USA

Ashish A Bartakke MD (Anaesthesia),

MBBS

ECMO Research Fellow, Glenfield Hospital,Leicester, UK

Gerald D. Buckberg MDDistinguished Professor of Surgery, Dep-artment of Cardiothoracic Surgery, DavidGeffen School of Medicine at UCLA, LosAngeles, California, USA

Victoria Chilton BSc CCP

Senior Clinical Perfusion Scientist, AlderHey Children’s Hospital, Liverpool, UK

Simon Colah MSc FCP CCP

Senior Clinical Perfusion Scientist, Cam-bridge Perfusion Services, Cambridge, UK

Kevin Collins BSN CCP LP

Staff Perfusionist, Duke University MedicalCenter, Durham, North Carolina, USA

David Cook MD

Associate Professor, Department of Anesthe-siology, Mayo Clinic, Rochester, Minnesota,USA

Kirsty Dempster CCP


Helen Dunningham BSc CCP


Liza Enriquez MD

Fellow, Department of Anesthesiology,Montefiore Medical Center, Albert EinsteinCollege of Medicine, New York, USA

Betsy Evans MA MRCS

Registrar in Cardiothoracic Surgery, Pap-worth Hospital, Cambridge, UK

Steve Gray MBBS FRCA

Consultant Cardiothoracic Anaesthetist,Papworth Hospital, Cambridge, UK

Roger Hall MBChB FANZCA FRCA


George Hallward MBBS MRCP FRCA

Clinical Fellow in Cardiothoracic Anaes-thesia, Papworth Hospital, Cambridge, UK

Charles W. Hogue MD

Associate Professor of Anesthesiology andCritical Care Medicine, Te Johns Hopkins

Medical Institutions and Te Johns HopkinsHospital, Baltimore, Maryland, USA

Brian Keogh MBBS FRCA

Consultant Anaesthetist, Royal Brompton &Harefield NHS rust, UK

James Keogh MBChB FRCA

Clinical Fellow in Paediatric CardiothoracicAnaesthesia, Royal Brompton & HarefieldNHS rust, UK

Andrew Klein MBBS FRCA



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List of contributors

G. Burkhard Mackensen MD PhD FASE

Associate Professor, Department of Anes-

thesiology, Duke University Medical Center,Durham, North Carolina, USA

Sukumaran Nair MBBS FRCS

Consultant Cardiothoracic Surgeon, Pap-worth Hospital, Cambridge, UK

Barbora Parizkova MD

Clinical Fellow in Cardiothoracic Anaes-thesia, Papworth Hospital, Cambridge, UK

Giles J Peek MD FRCSConsultant in Cardiothoracic Surgery &ECMO, Glenfield Hospital, Leicester, UK

Susanna Price MBBS BSc MRCP EDICM

PhD

Consultant Cardiologist and Intensivist,Royal Brompton & Harefield NHS rust, UK

Linda Shore-Lesserson MD

Professor, Department of Anesthesiol-

ogy, Montefiore Medical Center, AlbertEinstein College of Medicine, New York,USA

Andrew Snell MBChB, FANZCA

Clinical Fellow in Cardiothoracic Anaes-thesia, Papworth Hospital, Cambridge,UK

Steven Tsui MBBCh FRCS

Consultant in Cardiothoracic Surgery/Di-rector of ransplant Services, PapworthHospital, Cambridge, UK

John Wallwork MA MBBCh FRCS FRCP

Professor, Department of CardiothoracicSurgery, Papworth Hospital, Cambridge,

UK


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Preface

Tis book has been written to provide an easily readable source of material for the everydaypractice of clinical perfusion. For the past few years there has been a dearth of books, otherthan large reference tomes, relating to cardiopulmonary bypass. We hope that newcomersto the subject will find this book useful, both in the clinical setting and in preparation forexaminations, and that more experienced perfusionists and medical staff will find it useful forpreparing teaching material or for guidance.

We would like to thank everyone who helped in the preparation of the manuscript, par-ticularly those who contributed their expertise by writing chapters for this book.

S. Ghosh , F. Falter and D. J. Cook


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1Cardiopulmonary Bypass, ed. S. Ghosh, F. Falter and D. J. Cook. Published by Cambridge University Press.© Cambridge University Press 2009.

Equipment and monitoringVictoria Chilton and Andrew Klein

Te optimum conditions or cardiothoracic surgery have traditionally been regarded as a“still and bloodless” surgical field. Cardiopulmonary bypass (CPB) provides this by incor-

porating a pump to substitute or the unction o the heart and a gas exchange device, the“oxygenator,” to act as an artificial lung. Cardiopulmonary bypass thus allows the patient’sheart and lungs to be temporarily devoid o circulation, and respiratory and cardiac activitysuspended, so that intricate cardiac, vascular or thoracic surgery can be perormed in a saeand controlled environment.

HistoryIn its most basic orm, the CPB machine and circuit comprises o plastic tubing, a reservoir,an oxygenator and a pump. Venous blood is drained by gravity into the reservoir via a cannulaplaced in the right atrium or a large vein, pumped through the oxygenator and returned into

the patient’s arterial system via a cannula in the aorta or other large artery. ransit throughthe oxygenator reduces the partial pressure o carbon dioxide in the blood and raises oxygencontent. A typical CPB circuit is shown in Figure 1.1.

Cardiac surgery has widely been regarded as one o the most important medical advanceso the twentieth century. Te concept o a CPB machine arose rom the technique o “cross-circulation” in which the arterial and venous circulations o mother and child were connectedby tubing in series. Te mother’s heart and lungs maintained the circulatory and respiratoryunctions o both, whilst surgeons operated on the child’s heart (Dr Walton Lillehei, Minne-sota, 1953, see Figure 1.2a). Modern CPB machines (see Figure 1.2b) have evolved to incor-porate monitoring and saety eatures in their design.

John Gibbon (Philadelphia, 1953) is credited with developing the first mechanical CPBsystem, which he used when repairing an atrial secundum deect (ASD). Initially, the technol-ogy was complex and unreliable and was thereore slow to develop. Te equipment used in atypical extracorporeal circuit has advanced rapidly since this time and although circuits varyconsiderably among surgeons and hospitals, the basic concepts are essentially common to allCPB circuits.

Tis chapter describes the standard equipment and monitoring components o the CPBmachine and extracorporeal circuit as well as additional equipment such as the suckers usedto scavenge blood rom the operative field, cardioplegia delivery systems and hemofilters (seeables 1.1 and 1.2).

TubingTe tubing in the CPB circuit interconnects all o the main components o the circuit. A varietyo materials may be used or the manuacture o the tubing; these include polyvinyl chloride

Chapter

1


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Chapter 1: Equipment and monitoring

3

to slide over one another more easily, thus increasing the exibility o the PVC. However, onedisadvantage is that PVC tubing stiffens during hypothermic CPB and tends to induce spal-

lation; that is, the release o plastic microparticles rom the inner wall o tubing as a result opump compressions.

Other materials used to manuacture perusion tubing include latex rubber and siliconerubber. Latex rubber generates more hemolysis than PVC, whereas silicone rubber is knownto produce less hemolysis when the pump is completely occluded, but can release more par-ticles than PVC. As a result o this, and because o PVC’s durability and accepted hemolysisrates, PVC is the most widely used tubing material. Te arterial roller pump boot is the mainexception to this, as the tubing at this site is constantly compressed by the rollers themselves,leading to the use o silicone tubing or this purpose.

Arterial cannulaeTe arterial cannula is used to connect the “arterial limb” o the CPB circuit to the patientand so deliver oxygenated blood rom the heart-lung machine directly into the patient’s arte-rial system. Te required size is determined by the size o the vessel that is being cannulated,

Figure 1.2b. Cardiopulmonarybypass machine (reproducedwith kind permission of SorinGroup).


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as well as the blood ow required. Te ascending aorta is the most common site o arterialcannulation or routine cardiovascular surgery. Tis is because the ascending aorta is readily

accessible or cannulation when a median sternotomy approach is used and has the lowestassociated incidence o aortic dissection (0.01–0.09%). Afer sternotomy and exposure, thesurgeon is able to assess the size o the aorta beore choosing the most appropriately sizedcannula (see able 1.4).

Table 1.1. Components of the CPB machine and the extracorporeal circuit

Equipment Function

Oxygenator system, venous reservoir,oxygenator, heat exchanger

Oxygenate, remove carbon dioxide and cool/re-warm blood

Gas line and FiO2 blender Delivers fresh gas to the oxygenator in a controlled

mixture

Arterial pump Pumps blood at a set ow rate to the patient

Cardiotomy suckers and vents Scavenges blood from the operative field and ventsthe heart

Arterial line filter Removes microaggregates and particulatematter >40 μm

Cardioplegia systems Deliver high-dose potassium solutions to arrest theheart and preserve the myocardium

Cannulae Connect the patient to the extracorporeal circuit

Table 1.2. Monitoring components of the CPB machine and the extracorporeal circuit

Monitoring device Function

Low-level alarm Alarms when level in the reservoir reaches minimumrunning volume

Pressure monitoring (line pressure, blood cardioplegiapressure and vent pressure)

Alarms when line pressure exceeds set limits

Bubble detector (arterial line and blood cardioplegia) Alarms when bubbles are sensed

Oxygen sensor Alarms when oxygen supply to the oxygenator fails

Sa O

2 , S

v O

2 , and hemoglobin monitor Continuously measures these levels from the

extracorporeal circuit

In-line blood gas monitoring Continuously measures arterial and venous gases fromthe extracorporeal circuit

Perfusionist Constantly monitors the cardiopulmonary bypassmachine and the extracorporeal circuit

Table 1.3. Tubing sizes commonly used in different parts of the extracorporeal circuit (adults only)

Tubing size Function

3/16˝ (4.5 mm) Cardioplegia section of the blood cardioplegia delivery system

1/4˝ (6.0 mm) Suction tubing, blood section of the blood cardioplegia delivery system

3/8˝ (9.0 mm) Arterial pump line for ow rates


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Venous cannulaeVenous cannulation or CPB allows deoxygenated blood to be drained rom the patient intothe extracorporeal circuit. Te type o venous cannulation used is dependent upon the opera-tion being undertaken. For cardiac surgery that does not involve opening the chambers o

the heart, or example, coronary artery bypass grafs (CABG), a two-stage venous cannula isofen used. Te distal portion, i.e., the tip o the cannula, sits in the inerior vena cava (IVC)and drains blood rom the IVC through holes around the tip. A second series o holes in thecannula, a ew centimeters above the tip, is sited in the right atrium, to drain venous bloodentering the atrium via the superior vena cava (SVC).

An alternative method o venous cannulation or CPB is bicaval cannulation – this usestwo single-stage cannulae that sit in the inerior and superior vena cavae, respectively. Te twosingle-stage cannulae are connected using a Y-connector to the venous line o the CPB circuit.Bicaval cannulation is generally used or procedures that require the cardiac chambers to beopened, as the two separate pipes in the IVC and SVC permit unobstructed venous drainageduring surgical manipulation o the dissected heart and keep the heart completely empty oblood (see Figure 1.4).

Te emoral veins may also be used as a cannulation site or more complex surgery. In thisinstance, a long cannula, which is in essence an elongated single-stage cannula, may be passedup the emoral vein into the vena cava in order to achieve venous drainage.

As with arterial cannulation, the size o the cannulae will depend on the vessels being can-nulated as well as the desired blood ow. It is important to use appropriately sized cannulae inorder to obtain maximum venous drainage rom the patient so that ull ow can be achievedwhen CPB is commenced.

Pump headsTere are two types o pumps used in extracorporeal circuits:1. Tose that produce a ow – roller pumps.

2. Tose that produce a pressure – centriugal pumps.

Figure 1.4. Commonly used venous cannulae: (a) Y-connector to connect single-stage cannulae; (b) single-stagecannula; (c) two-stage cannula. RA, right atrial; SVC, superior vena cava; IVC, inferior vena cava.


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Roller pumpsInitial technology developed in the mid twentieth century used non-pulsatile roller pumps inCPB machines. Tis technology has not changed greatly over the past 50 years.

Roller pumps positively displace blood through the tubing using a peristaltic motion.wo rollers, opposite each other, “roll” the blood through the tubing. When the tubing is

Figure 1.5. (a) Line drawing of a roller pump; (b) a roller pump. (Reproduced with kind permission fromSorin Group.)


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intermittently occluded, positive and negative pressures are generated on either side o thepoint o occlusion. Forward or retrograde ow o blood can be achieved by altering the direc-

tion o pump head rotation; thus roller pumps are commonly used as the primary arterialow pump as well as or suction o blood rom the heart and mediastinal cavity during CPBto salvage blood. Roller pumps are relatively independent o circuit resistance and hydrostaticpressure; output depends on the number o rotations o the pump head and the internal diam-eter o the tubing used (see Figure 1.5a,b).

Tis type o positive displacement pump can be set to provide pulsatile or non-pul-satile (laminar) ow. Debate over the advantages and disadvantages o non-pulsatile orpulsatile perusion during cardiopulmonary bypass still continues. Non-pulsatile per-usion is known to have a detrimental effect on cell metabolism and organ unction. Temain argument in avor o pulsatile perusion is that it more closely resembles the pattern

o blood ow generated by the cardiac cycle and should thereore more closely emulatethe ow characteristics o the physiological circulation, particularly enhancing owthrough smaller capillary networks in comparison to non-pulsatile perusion. Te increasedshear stress rom the changing positive and negative pressures generated to aid pulsatile per-usion may, however, lead to increased hemolysis. Roller pumps have one urther disadvantage:sudden occlusion o the inow to the pump, as a result o low circulating volume or venous can-nula obstruction, can result in “cavitation,” the ormation and collapse o gas bubbles due to thecreation o pockets o low pressure by precipitous change in mechanical orces.

Centrifugal pumpsIn 1973, the Biomedicus model 600 became the first disposable centriugal pump head orclinical use. Te Biomedicus head contains a cone with a metal bearing encased in an outerhousing, orming a sealed unit through which blood can ow. When in use the head is seatedon a pump drive unit. Te cone spins as a result o the magnetic orce that is generated whenthe pump is activated. Te spinning cone creates a negative pressure that sucks blood into theinlet, creating a vortex. Centriugal orce imparts kinetic energy on the blood as the pumpspins at 2000–4000 rpm (this speed is set by the user). Te energy created in the cone createspressure and blood is then orced out o the outlet. Te resulting blood ow will depend onthe pressure gradient and the resistance at the outlet o the pump (a combination o the CPBcircuit and the systemic vascular resistance o the patient). Flow meters are included in all

centriugal pumps and rely on ultrasonic or electromagnetic principles to determine bloodow velocity accurately (see Figure 1.6a–c).Despite extensive research, there is little evidence to show any benefit o one type o pump

over another in clinical practice. Centriugal pumps may produce less hemolysis and plateletactivation than roller pumps, but this does not correlate with any difference in clinical out-come, including neurological unction. Tey are certainly more expensive (as the pump headis single use) and may be prone to heat generation and clot ormation on the rotating suracesin contact with blood. In general, they are reserved or more complex surgery o prolongedduration, during which the damage to blood components associated with roller pumps maybe theoretically disadvantageous.

ReservoirsCardiotomy reservoirs may be hardshell or collapsible. Hardshell reservoirs are most com-monly used in adult cardiac surgery; collapsible reservoirs are still used by some institutions


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or pediatric and adult cases. Hardshell reservoirs usually comprise o a polycarbonate hous-ing, a polyester depth filter and a polyurethane de-oamer. Te reservoir component o theCPB circuit thereore provides high-effi ciency filtration, de-oaming and the removal o or-eign particles (see Figure 1.7).

Te reservoir acts as a chamber or the venous blood to drain into beore it is pumped intothe oxygenator and permits ready access or the addition o uids and drugs. A level o uid ismaintained in the reservoir or the duration o CPB. Tis reduces the risks o perusion acci-dents, such as pumping large volumes o air into the arterial circulation i the venous returnto the CPB machine rom the patient is occluded or any reason.

Blood that is scavenged rom the operative field via the suckers is returned to the reservoir.Te salvaged blood is mixed with air and may contain tissue debris. It is thereore vital or thisblood to be filtered through the reservoir beore being pumped to the patient. Te reservoir

is constantly vented to prevent the pressure build-up that could occur i the suckers were lefrunning at a high level or the duration o the procedure. Te salvaged blood rom the ventsthat the surgeon uses to prevent the heart rom distending during CPB also returns to thereservoir.

Figure 1.6. (a) Centrifugal pump. (b) Schematicdiagram of centrifugal pump. (c) Schematic cutthrough centrifugal pump. (a, b Reproduced withkind permission from Sorin Group.)


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Oxygenators

Te present success o cardiac surgery relies heavily on extracorporeal perusion techniquesemploying an effi cient gas exchange mechanism: the oxygenator. Te requirements o the oxy-genator include effi cient oxygenation o desaturated hemoglobin and simultaneous removalo carbon dioxide rom the blood. Te oxygenator thereore acts as an artificial alveolar-pulmonary capillary system.

Gas exchange is based on Fick’s Law o Diffusion:

Diffusion coefficient Partial pressure differenceVolume of Gas diffused

Distance to travel

Te oxygenator provides an interace o high surace area between blood on one side andgas on the other. Te distance gas has to travel across the interace is minimized by construct-ing the membrane rom very thin material.

In the early 1950s, attempts were made to oxygenate the blood using techniques suchas cross circulation between related humans, or using animal lungs or patients undergoingopen heart surgery. In 1955, DeWall and Lillehei devised the first helical reservoir to be used;this was an early orm o the bubble oxygenator. One year later, in 1956, the rotating discoxygenator was developed. In 1966, DeWall introduced the hardshell bubble oxygenator withintegral heat exchanger. Subsequently, Lillehei and Lande developed a commercially manu-actured, disposable, compact membrane oxygenator.

Currently, most commonly used oxygenators are membrane oxygenators with a micro-porous polypropylene hollow fiber structure. Te membrane is initially porous, but proteins

in blood rapidly coat it, preventing direct blood/gas contact. Te surace tension o the bloodalso prevents plasma water rom entering the gas phase o the micropores during CPB andprevents gas leakage into the blood phase, thus reducing microemboli. However, afer severalhours o use, evaporation and condensation o serum leaking through micropores leads to

Figure 1.7. Reservoir in CPB circuit.


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reduced effi ciency and thereore the majority o these types o oxygenators must be changedafer about 6 hours.

Te majority o oxygenators consist o a module or gas exchange with an integratedheat exchanger. An external heater–cooler pumps temperature-controlled water into theheat exchanger, which is separated rom the blood by a highly thermally conductive mat-

erial. Tis is biologically inert, to reduce the risk o blood component activation. Te exter-nal heater–cooler has digital regulating modules to allow precise control o temperaturethrough thermostat-controlled heating and cooling elements within the console. Con-trolled cooling and re-warming o the patient are crucial to ensure an even distribution o

Figure 1.8. Schematic cut through an oxygenator.


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temperature throughout the body and to prevent damage to blood components, proteinsand tissues.

Te Cobe Duo (Cobe Cardiovascular CML-Duo) adult cardiovascular membrane oxy-genator comprises o a microporous polypropylene pleated sheet that has a prime volume oapproximately 250 ml and works on the principle o diffusion. Blood first passes over an inte-gral heat exchanger, changes temperature and then moves into the oxygenator compartment.Gas supplies o oxygen, air and carbon dioxide are delivered to the membrane in controlledquantities. Tis “sweep” gas ows inside the fibers and has a higher concentration o oxygenthan venous blood on the outside o the fibers, enabling oxygen to move along a concentrationgradient across the membrane into the blood to create equilibrium. Carbon dioxide, which ispresent in a high concentration in the venous blood, moves in the opposite direction, acrossthe membrane into the gas phase (see Figures 1.8 and 1.9). Te exhaust gases are scavenged

rom outlet ports on the back o the oxygenator.

Gas supply systemTe gas supply system provides a source o oxygen, air and carbon dioxide to the oxygenator.A blender mixes piped oxygen and air to the concentration set by the user, and the gas is deliv-ered at a rate set on a ow meter (see Figure 1.10). Flow meters may be digital or mechanicalrotameters. An oxygen analyzer is included in the gas circuit to continuously display the con-centration o oxygen delivered in order to prevent the inadvertent administration o a hypoxicmixture. An anesthetic vaporizer may be incorporated, along with a means o scavengingwaste gases.

Filters and bubble trapsTere are numerous filters that can be used within the extracorporeal circuit. Tese rangerom 0.2 μm gas line filters to 40 μm arterial line filters (see able 1.5).

Table 1.5. Filtration devices used within the cardiopulmonary bypass circuit

Filter type Application and specication

Gas line Removes 99.999% of bacteria found in the gas stream minimizingcross-contamination between the patient and the equipment

Pre-CPB 0.2 μm filter is used during the priming and re-circulation phase. It isdesigned for the removal of inadvertent particulate debris and microbialcontaminants and their associated endotoxins

Arterial line Designed to remove microemboli >40 μm in size from the perfusate duringextracorporeal circulation. This includes gas emboli, fat emboli andaggregates composed of platelets, red blood cells and other debris

Leukodepletion Reduces the levels of leukocytes, either from the arterial line or cardioplegiasystem, and excludes microemboli >40 μm

Cardioplegia Blood cardioplegia: >40 μm filter. Crystalloid cardioplegia: >0.2 μm filter. Lowpriming volume filter for cell-free solutions. Removes inadvertent particulatedebris and microbial contaminants and their associated endotoxins

Blood transfusion Designed to reduce the levels of leukocytes and microaggregates from 1

unit of packed red blood cells or whole blood

Cell salvage Designed for the filtration of salvaged blood to remove potentially harmfulmicroaggregates, leukocytes and lipid particles

Adapted from Pall product specifications 2007.


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Tere are a number o reasons or venting the heart during CPB:

to prevent distension o the heart;•

to reduce myocardial re-warming;•

to evacuate air rom the cardiac chambers during the de-airing phase o the procedure;•

to improve surgical exposure; and•to create a dry surgical field, especially during the distal coronary anastamosis phase o•CABG surgery.

Tere are complications associated with all sites used or venting, most commonly relatingto injury to tissues at the site. Venting via the lef ventricular (LV) apex, however, is associatedwith particularly serious consequences including:

damage to the LV wall due to excessive suction;•

LV wall rupture i inadequately closed at the end o the bypass period; and•embolization through air entrained into the LV.•

Active venting with high levels o suction can lead to air being introduced into the arte-rial side o the CPB circuit due to a small percentage o air sucked into the venous side o thereservoir and oxygenator passing through the circuit into the arterial side. Tereore, suctionpressure and duration should be kept to a minimum.

Cardioplegia delivery systemsOne o the major concerns during cardiac surgery is protection o the heart during the

operation. Myocardial protection is discussed more ully in Chapter 7. During the periodin which the heart is devoid o blood supply, the myocardial cells continue to utilize high-energy phosphates (adenosine triphosphate, AP) to uel metabolic reactions anaerobi-cally. his results in depletion o energy reserves and the build up o products o anaero-bic metabolism, such as lactic acid. hese processes decrease myocardial contractilityin the period immediately ollowing restoration o blood low and myocardial unctionremains compromised until AP reserves are restored and the products o anaerobicmetabolism decline in concentration. Preservation o myocardial unction during theischemic period, that is, during the period in which the aorta is cross-clamped, is bestachieved by putting the heart into a state o hibernation using a solution – genericallytermed “cardioplegia.” he purpose o cardioplegia is to cause rapid diastolic cardiacarrest. his produces a still, laccid heart, which acilitates surgery and also is the statein which myocardial metabolism is almost at its lowest levels. Further reduction in themetabolic state o the heart is achieved by cooling using cold cardioplegia and also by corecooling o the body.

Te common constituent o all cardioplegia solutions is a high concentration o potassium,as this produces diastolic cardiac arrest. Te other constituents o cardioplegia vary widelyrom normal saline solution to blood mixed with complex antioxidants. Te delivery o cardi-oplegia may be as a single bolus, intermittent boluses or continuous inusion or combinationso all three. Te administration techniques have progressed rom un-monitored pressurizeddelivery into the root o the aorta; current practice is discussed more ully in Chapter 7. Te

delivery sites or the cardioplegia vary according to surgical preerence and the operationbeing perormed and include: directly into the aortic root, the coronary ostia, the saphe-nous vein graf or retrograde via the coronary sinus. Te ow rates and pressures thatthe cardioplegia solution is delivered at will vary depending on the mode o delivery.


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Figure 1.11 (a) Double-lumen aortic root cannula, which can be used to deliver cardioplegia and as an aortic rootvent. (b) Retrograde cardioplegia delivery cannula. (c) Schematic drawing of antegrade and retrograde cardioplegiadelivery. (Reproduced with kind permission from Edwards Lifesciences.)


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Figure 1.12 Cardioplegiadelivery system: allows mixing ofblood and cardioplegia solutionand warming or cooling of solu-tion before application.

Table 1.7. Cardioplegia delivery systems

ManufacturerIntegrated heatexchanger Air trap removal Delivery system

Sorin Yes Yes Blood cardioplegia 4:1 ratiovia roller pump

Medtronic Yes Yes Blood cardioplegia 4:1ratio via roller pump (canalso be used with a syringedriver for the potassiumsolutions)

Lifeline-Delhi Yes Yes Blood cardioplegia 4:1 ratiovia a roller pump

Aeon Medical Yes Yes Blood cardioplegia 4:1 ratiovia a roller pump

Different types o cannulae are available or delivery o cardioplegia via the various sites(see Figure 1.11).

Many different designs o cardioplegia delivery systems are available (see Figure 1.12).Almost all o the systems allow delivery o warm and cold solutions and allow the mixing ocrystalloid solutions with blood (see able 1.7). Te systems also allow the monitoring o thecardioplegia inusion line pressure. Tis is essential when delivering cardioplegia into small vessels and the coronary sinus to prevent damage.

HemoltersAlso known as ultrafilters or hemoconcentrators, these contain semipermeable membranes(hollow fibers) that permit passage o water and electrolytes out o blood. Tey are normally


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connected to the CPB circuit at a high pressure port or line, such as the systemic ow line, toprovide a driving orce or blood through the device. Tis allows blood to be filtered beorebeing returned to the patient. Fluid removal is usually 30 to 50 ml/minute, and depending onthe membrane used, molecules o up to 20 000 Daltons are removed. Hemofiltration may be

used during or afer CPB, mainly to manage hyperkalemia or acidosis, but also to concentratethe blood i the hematocrit (HC) is low and circulating volume is adequate (see Figure 1.13).

MonitoringExtracorporeal perusion techniques require a large amount o vigilance rom the entire teaminvolved in the patient’s care. Setup and saety eatures during CPB are discussed in moredetail in Chapter 2.

In-line blood gas analysis and venous saturation/hematocrit monitorsTe theoretical advantages o using continuous in-line blood gas and electrolyte monitoring

during CPB are well established; however, the clinical impact remains controversial. Tesedevices may be divided into those using electrochemical electrodes and cuvettes, which areplaced in the circuit, and those that use light absorbance or reectance, which require sensorsplaced external to the circuit tubing.

Figure 1.13 Hemofilters.(Reproduced with kind permis-

sion from Sorin Group.)


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Figure 1.15 Spectrum Medical in-line real-time saturation and Hb monitoring system.

AlarmsIdeally all alarm systems are linked into the computer system o the CPB circuit and directly

regulate or stop the pump ow when appropriate. Te alarm systems used within the circuitaid the perusionist in running a sae pump and are all vital components o the circuit.Te alarms are engaged prior to initiating CPB and are not turned off, or over-ridden, untilthe patient has been weaned rom CPB. Te perusionist, in an analogous ashion to a pilot,is the main saety device or the CPB circuit and constantly monitors all o the parametersassociated with running the pump.

Mini bypass systemTere has been some recent interest in the development o miniature extracorporeal

circuits (see Figure 1.16a ). Tese are designed to reduce oreign surace area, priming volume (as little as 500 ml) and blood-air contact. Tis leads to decreased hemodilution, andthus reduced blood transusion requirements, and may reduce the inammatory responseto CPB.


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Figure 1.16 (a) Mini bypass system. (b) Schematic drawing of mini bypass circuit. (Reproduced with kind permissionfrom Sorin Group.)


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Such circuits usually do not include a reservoir, heat exchanger and cardiotomy suctionbut increasingly incorporate arterial filters (see Figure 1.16b). Research and urther develop-

ment is ongoing, but early trials have been promising, some demonstrating a reduced releaseo vasoactive substances and a reduced activation o the coagulation cascade.

Suggested Further ReadingAnderson KS, Nygreen EL, Grong K,• et al .Comparison o the centriugal and rollerpump in elective coronary bypass surgery: aprospective randomized study with a specialemphasis upon platelet activation. ScandCardiovasc J 2003; 37 : 356–62.

Black S, Bolman RM III. C. Walton Lillehei•and the birth o open heart surgery. J CardSurg 2006; 21 : 205–8.

Driessen JJ, Dhaese H, Fransen G,• et al .Pulsatile compared with non-pulsatileperusion using a centriugal pump orcardiopulmonary bypass during coronaryartery bypass grafing: effects on systemichaemodynamics, oxygenation andinammatory response parameters.Perfusion 1995; 10 : 3–12.

Fried DW. Perormance evaluation o• blood-gas exchange devices. Int AnesthesiolClin 1996; 34 : 47–60.

Gibbon JH Jr. Development o the artificial•heart and lung extracorporeal blood circuit. JAMA 1968; 206 : 1983–6.

Kmiecik SA, Liu JL, Vaadia S,• et al .Quantative evaluation o hypothermia,hyperthermia and hemodilution oncoagulation. J Extra Corpor Technol 2001;33 : 100–5.

Mejak BL, Stammers A, Rauch E,• et al .A retrospective study on perusionincidents and saety devices. Perfusion 2000;15 : 51–61.

Mulholland JW, Shelton JC, Luo XY. Blood•ow and damage by the roller pumpsduring cardiopulmonary bypass. J FluidStruct 2005; 20 : 129–40.

Peek GJ, Tompson A, Killer HM,• et al .Spallation perormance o extracorporealmembrane oxygenation tubing. Perfusion

2000; 15 : 457–66.


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23Cardiopulmonary Bypass, ed. S. Ghosh, F. Falter and D. J. Cook. Published by Cambridge University Press.© Cambridge University Press 2009.

Circuit setup and safety checksSimon Colah and Steve Gray

Assembling the CPB circuit and checking the CPB machine or aults prior to clinical useis an essential part o the provision o extracorporeal perusion. Tis chapter describes the

procedure or “setting up” the CPB system and the saety checks that should be undertakenbeore embarking on a case.

Philip Kay and Christopher Munsch (2004) in “echniques in Extracorporeal Circulation”state: “Cardiopulmonary bypass is a dynamic artificial environment conerring a shock stateon the body with its own potential or severe morbidity and mortality.” Vigilance is thus para-mount to the conduct o cardiopulmonary bypass. Modern perusion systems are designed tooptimize saety. echnological advances have seen the incorporation o automatic alarms andail-sae devices; however, the perusionist’s attention to detail and observance o prebypasschecklists and protocols still underpins sae practice. Human error is a ar greater cause oaccidents than mechanical mishap.

Preparing the CPB circuit and machine, attention to the patient’s clinical details and thesurgical requirements or the procedure all orm part o the process o sae provision o car-diopulmonary bypass. By necessity the preparation o the CPB machine and assembly o thedisposable circuit components should be “ritualistic” ollowing a routine dictated by institu-tional protocols.

CPB machine preparation and circuit setupCPB circuits are made up o a number o disposable items. Principally these are:

the integrated membrane oxygenator/hardshell (or sofshell) venous reservoir:•

cardioplegia set;•

arterial line filter; and•custom tubing pack.•

All components are rigorously checked. In particular, the disposable items are closelyexamined with regard to expiry date and integrity o the packaging.

Tere are many ways to set up a CPB circuit. Departmental preerences and specific patientrequirements dictate the approach. A commonly used sequence or setting up and priming astandard CPB system is outlined in Appendix 2A, together with a synopsis o electronic saetydevices in Appendix 2B, at the end o this chapter.

Securing the gas hoses to the gas source, checking that gas supplies o air and oxygen areunctional and attaching the scavenging line initiates the process. Te CPB machine console

is then powered and temporarily disconnected to ascertain that the power ailure alarm andbackup battery unit are ully unctional. Most operating rooms have an uninterruptible powersupply (UPS), essentially a series o batteries linked to the hospital generator that powers theCPB machine, anesthetic machine, intravenous inusion pumps and other vital equipment

Chapter

2


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Chapter 2: Circuit setup and safety checks

25

Tere are two ways to check the roller heads or occlusion: either check each roller at the “6o’clock” position or together at the “9.15” position, with the circuit pressurized at 250 mmHg

and the arterial line clamped. Any rapid drop in pressure may indicate that connections arenot secure or that an “occlusion” has been incorrectly set. Centriugal pumps are non-occlu-sive and should be gravity filled to ensure good de-airing. Centriugal consoles have inte-grated ow probes that are unidirectional. As they are aferload sensitive, pump speed mustbe set to produce orward ow beore initiating bypass.

Te inow to the sucker pumps is clamped and the rollers are adjusted to avoid collapse othe tubing. Te vent line should have a one-way pressure relie valve in-line to prevent inadvertent air entry into the heart and to prevent cavitation inside cardiac chambers.

emperature probes are placed into the arterial, venous and cardiolegia ports and visual-ized on the LED display. Te level sensor is placed at, or above, 400 ml and the bubble detector

placed on the arterial line distal to the filter. All alarms, pressure ranges, timers and cardiople-gia parameters can now be set in preparation or bypass.

Design and use of a prebypass checklistExperience rom other high-risk industries, such as aviation or maritime, demonstrate thatdisasters are ofen associated with poor checking procedures. Te ormat o the CPB checklistis either written or automated and best signed off by two perusionists. Ideally, the primaryperusionist does the checking whilst the second perusionist works through the list. TeAmerican Society o Extracorporeal echnology and the European Board o CardiovascularPerusion publish an excellent array o perusion guidelines and checklists (see Figure 2.1). Asexpected the list is comprehensive yet targeted, covering all aspects rom sterility to backupcomponents.

Safety concerns prior to, during and after CPBBeore embarking on a case the perusionist should review the patient’s notes. Te mostimportant details are:

planned procedure and likelihood o additional procedures;•

allergies;•

significant comorbid conditions, such as diabetes or renal dysunction; and•metabolic or hematological abnormalities, such as anemia, thrombocytopenia or•hyperkalemia.

Te patient’s blood group should be confirmed and the availability o bank bloodchecked.

Details o the patient’s height and weight are essential to calculate:

dose o heparin (usually 300 mg/kg) required or CPB;•

body surace area (BSA) in square meters, which is required to determine the “ideal”•ow rate at normothermia (BSA × cardiac index) and so to select appropriately sized venous and arterial cannulae; and

predicted HC on initiation o CPB•

Saety issues relating to the pre-, intra- and post-CPB periods are summarized in ables2.1, 2.2 and 2.3, respectively.


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Table 2.1. Pre-CPB safety concerns

Heparin given, activated clotting time (ACT ) >400 seconds

Arterial cannula correctly placed, pulsatile swing on an anaeroid pressure gauge connected to a side arm of thearterial line

Venous reservoir has a safe level of prime, additional uid available to add, low level alarm activated

Oxygen analyzer monitoring gas supply to oxygenator on, alarm activated

Sweep rate appropriate for patient (usually 2–3 l, FiO2 = 0.6)

Venous cannula relatively free of air

Shunt lines are clamped, apart from arterial filter purge line and drug administration manifold line

No clamps on the arterial or venous lines placed by surgical team

Alarm overrides deactivated

Vasopressors prescribed and available

Pre-bypass checklist

Patient: _____________________

ID correct

Chart reviewed

Sterility

Components: integrity and expiry

date

Heart-lung machine

Power connected

Start-up normal

Back-up power

Heater-cooler

Start-up normal

Water connections: flow verified

Water temperature: _______° C/F

Gas supply

Gas lines connected

Flow meter/blender in order

Vaporizer shut off

CO2 flush

Pump

Roller heads not obstructed

Flow meter: calibration & directionTubing holders secure

Occlusion set : ______ mmHg

______cmH20/min

Tubing

Pump tubing condition inspected

Suckers functional and sucking

One-way valves: direction correct

Circuit shunts closed

ID:_____________________

Monitoring

Temperature probes positioned

Pressure transducers calibrated

In/on-line sensors calibrated

Safety & alarms

Low-level alarm engaged

Air detector engaged

Pressure alarm limits set

Temperature alarm limits set

Cardiotomy reservoir vented

Oxygenator

Gas line attached

Heat exchanger integrity inspected

Scavenger attached

Debubbling

Tubing

Oxygenator

Cardioplegia

Arterial filter/bubble trap

Accessories

Tubing clampsHand cranks

Backup circuit components

Anticoagulation

Heparin in: _______time

Patient properly anticoagulated

Ready to start bypass

Signature: ..........................................

Figure 2.1. Prebypasschecklist. The European Board ofCardiovascular Perfusion (EBCP)promotes the use of prebypasschecklists in the practice of clini-cal perfusion. The suggestionsin this checklist are designedas the minimum requirementsfor cardiopulmonary bypassprocedures and each institutionshould adapt this to suit its ownrequirements. The EBCP canaccept no liability whatsoever forthe adoption and practice of thissuggested checklist. (Repro-duced by kind permission of The

European Board of Cardiovascu-lar Perfusion: http://www.ebcp.org)


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Table 2.4. Key factors contributing to a safer perfusion service

Accreditation of training programs

Certification and re-certification of perfusionists

Conferences, yearly appraisals, departmental quality assurance meetings

Reporting of adverse occurrences

Quality in-house training

Electronic data acquisition with associated audit facilities

Departmental protocols, especially outlining procedures in abnormal and emergency situations

Manufacturer product alerts acted on

Equipment maintenance records and quality assurance logs kept

ConclusionSurveys by Jenkins et al . (1997) and Mejak et al . (2000) report the number o pump-relatedincidents to be 1:140 and the likelihood o permanent injury or death o the patient afer suchan incident to be 1:1350. A multitude o healthcare organizations, not least the Institute oMedicine (IOM), have called or a 90% reduction in preventable patient injuries.

Since the introduction o CPB in the early 1950s the ocus on saety has evolvedand improved. oday, the quality o components is excellent. CPB machines incorporate in-built alarms with auto-regulatory eedback systems, together with real-time data acquisition.Yet surveys confirm the mishap rate is slow to all. Accredited training, scrupulous attention

to detail and use o checklists and protocols will hopeully continue to improve saety. Te keyactors contributing to a saer perusion service are summarized in able 2.4.

Appendix 2A: Procedure for setting up and priming astandard heart–lung bypass system(Adapted, with permission, rom London Perusion Science Protocols.)

2A.1: The heart–lung machine and accessories

2A1.1: Connection checks(a) All cables, plugs and sockets are checked(b) All cables should be laid neatly, so that they are not likely to be damaged and where

they are least likely to cause accidents(c) All parts of the apparatus, including heater/chiller and pump light (if it is to be used)

are checked for power(d) Gas lines are fitted to the wall outlets and connections, hoses, mixers and ow meters

are checked for leaks(e) Gas ow to the oxygenator is checked

2A1.2: Pump head checksEach pump head is checked:

(a) For power


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(b) Te rollers and guides are moving(c) Te pump heads are free from foreign bodies

(d) Te pump heads are set to rotate in the correct direction(e) Te ow/rpm settings on the console are accurately calibrated(f) For winding handles(g) Tat the tubing inserts are o the correct size or the tubing to be used

2A1.3: Checks that other electrical safety devices are in working order(a) Battery backup (UPS) is charged(b) Pressure transducers(c) Level detectors

(d) Bubble detectors

2A.2: The setup of disposable heart–lung equipment

2A2.1: The oxygenator(a) Remove packaging and check its integrity and sterility(b) Te oxygenator is examined for obvious faults and debris(c) Te oxygenator is placed securely into its holder(d) Any gas outow cap is removed

(e) Te gas connection is made(f) Remove any venting cap on the reservoir(g) Te CO

2 ush is initiated until priming

(h) Te water connections to the heater/chiller are now made, the heat exchanger and allconnections are checked or leaks with the water running at 37°C

2A2.2: The circuitry(a) Remove packaging and check its integrity and sterility(b) Te circuitry is checked for faults (cracked connectors, kinked tubing, etc.)(c) Check the silicone pump boot and place so it is lying correctly in order to prevent

wear or damage from the tube guides or rollers(d) Check that the pump boot tube is securely held at both the outlet and the inlet.

Rotate the pump to check the tubing is correctly seated(e) Do the same with sucker tubing, checking direction of ow(f) With attention to sterile technique, connect the pump lines to the oxygenator, ensure

they have been connected in the correct direction and not crossed over(g) Te lines should be suffi ciently long so that they may be moved to the neighboring

pump head if necessary(h) Any cuts to tubing should be made cleanly and perpendicular to the length of the

tubing, using a sterile blade

(i) Te outow line should now be connected to the outow port of the oxygenator(j) Te re-circulating lines should now be similarly connected as required by manufac-

turer’s specifications(k) All pressure connections can be made secure using nylon ties


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2A2.3: The cardiotomy reservoir if required(a) Te reservoir can be used or any surgery where intracardiac clot is suspected, where

it is anticipated that large quantities o blood will be used or where the use o autotransusion is anticipated

(b) Te reservoir and its packaging is checked as above and inserted into the appropriateholder

(c) Remove any venting cap and using the 3/8² cardiotomy return, connect thecardiotomy to the oxygenator, ensuring that this return line cannot be kinked orobstructed

(d) Connect the sucker lines and recirculation lines to the cardiotomy reservoir

2A2.4: The cardioplegia system if required(a) Remove packaging and check its integrity and sterility(b) Te circuitry is checked for faults (cracked connections, kinked tubing, etc.)(c) Assemble circuit according to manufacturer’s instructions(d) Ensure all connections (oxygenator, recirculation lines, etc.) are secure and correct(e) Water lines are connected to the cardioplegia administration set heat exchanger.

Water is circulated to ensure that it is ree rom leaks

2A2.5: The centrifugal pump if required(a) Remove packaging and check its integrity and sterility(b) Te relevant ow and drive connectors should be connected to the console(c) Te battery charger should be examined to determine whether or not there is

suffi cient battery backup(d) Te perfusionist should check that the relevant hand-crank mechanism is available in

case of power failure(e) Te drive motor heads must be examined or dirt, as this may impair the unction o

the device, including the possibility o disengagement

2A2.6: Arterial line lters if required(a) Check the filter or sterility, any damage or debris(b) If the filter is to be cut into the arterial line this should be carried out using the

appropriate sterile technique(c) Ensure the filter holder is positioned to prevent the stretching or kinking of lines(d) Position the filter securely in the holder

An air bubble trap would be primed in a similar ashion.

2A2.7: Cell saver if required(a) Remove outer packaging and check its integrity and sterility(b) Open the collection reservoir portion of the set and secure firmly in holder

(c) Connect the vacuum source to the reservoir(d) Te washing portion of the set should only be opened when either enough blood has

been collected to salvage or the perfusionist is confident that enough blood will becollected to salvage


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31

(e) Te washing portion of the set should be assembled neatly() All ports and connections should be checked, closed and tightened where

necessary

2A2.8: Prebypass lters if usedI the circuit contains a prebypass filter there are a number o points the perusionist mustremember:

Te prebypass filter should be removed beore priming the circuit with blood•Te prebypass filter should be removed i the low pressure suction is required beore•the lines have been divided

A ½² × 3/8² connector should be readily available to replace the prebypass filter i

necessary.

2A.3: In-line blood chemistry/gas analyzer (e.g., CDI 500) setupand calibration

2A3.1: Setup of CDI 500 arterial sensor shunt(a) urn off monitor and afer the monitor has sel-tested select the required configura-

tion o the sensor shunt(b) Select calibration

(c) Verify the K* calibration value on the sensor packaging(d) Check that the calibrator’s cable is connected to the monitor(e) Remove blue cap from the base of the sensor shunt and attach to one of the calibra-

tor’s ports(f) Loosen the blue cap on the top of the sensor shunt(g) Initiate calibration by pressing √ twice on the monitor(h) Calibration lasts 10 minutes(i) Afer calibration tighten large luer cap and remove gas filter

2A3.2: Setup of CDI 500 Venous Line Sensor(a) Remove venous sensor rom packaging and cut into venous line(b) Afer the monitor has been switched on and has sel-tested the venous probe can be

connected to the venous sensor

2A.4: Priming the systemTe perusionist should ensure, i possible, that the ollowing patient details are availablerom the anesthetic and surgical staff, to provide a basis on which to decide the primingstrategy:

Height and weight•

Renal status•Hb/HC•

Heart size•Fluid status•


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2A4.1: Standard prime(a) 1 l Hartmann’s solution is checked(b) Preservative-ree heparin should be injected into the liter bag o Hartmann’s solution

(dose per liter o prime as per institutional protocol) and labeled(c) Te Hartmann’s solution is run into the system via a giving set or rapid prime line.

It is important that this heparinized prime runs through the length o the circuit(i.e., all filters are exposed to this heparinized prime). Te prime is delivered via acardiotomy port (i a cardiotomy is in use)

(d) Te reservoir should be inspected or obvious bubbles and tapped to remove them(e) Suffi cient prime should be added to the system to maintain a dynamic priming

volume

() It is most important at this stage that the oxygenator manuacturer’s instructions arecareully adhered to(g) urn off the CO

2 ush

(h) A gravity eed prime is undertaken, with de-bubbling taking place in a logicalashion, beginning with the oxygenator reservoir and progressing to the arterial lineand so on

(i) Te “sash” should be clamped off, the arterial pump switched on and the primere-circulated

(j) Te pressure line may now be connected, via an air-ree isolator to the line pressuregauge and pressure transducer

(k) Te re-circulation lines are securely clamped, and the “sash” primed

(l) It is important to remember that air is easily dragged across the membrane ohollow fiber oxygenators, so the ollowing precautions should be taken toavoid this:

the venous line should be partially occluded so as to offer a resistance, and•thereore maintain a positive pressure as the prime is re-circulatingthe pump should be switched off slowly to avoid the momentum effect•(see below)

(m) When the circuit appears to be clear o bubbles, the re-circulation rate should nowbe increased to around 5 l/minute, to remove any bubbles rom within the oxygenatormembrane with the venous line partially clamped maintaining a post-membrane

pressure o around 80 mmHg. Beore the “sash” is divided, a final check must bemade by both perusionist and surgeon or the presence o bubbles. Beore stoppingthe re-circulation, the pump should be turned down slowly, reducing the chances othe inertia effect o a sudden reduction in ow that would cause air to be draggedacross the membrane

2A4.2: Priming cardioplegia if required(a) Te type, temperature and concentration o blood cardioplegia should be

determined rom the surgeon in advance. Tis inormation should be heldin the hospital’s database (e.g., proportion 4:1, 2:1, etc., the need or any

“hot shots,” etc.)(b) Bags of Ringer’s solution should be carefully prepared. Te vials of cardioplegia

should be carefully checked before injection. Te bags must be labeled clearly as soonas this has been done


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(c) Te cardioplegia circuit is primed with Hartmann’s solution or Ringer’s solution,checking that all air has been purged

(d) During priming, care must be taken that the main prime does not becomecontaminated with cardioplegia

(e) Te cardioplegia pump boots are placed in the raceway and appropriately sizedcollets fitted (if applicable), or a check is made to ensure that the ratio is correctlyprogramed into the pump console

() Te occlusion o the pump is then set as with the arterial pump (see later)

2A4.3: Priming the arterial line lter if required(a) Place clamps either side o the arterial filter beore the oxygenator is

gravity primed(b) Once the circuit is primed, stop the pump, slowly release lower clamp and

allow prime to ow retrogradely through the filter via the bypass line,expelling air through the purge line. Te retrograde ow is provided by theprime in the “sash”

(c) Release the top clamp, start the pump(d) Invert the filter and de-air as normal(e) Clamp the arterial filter bypass loop

2A4.4: Priming centrifugal pump if required

Centriugal pumps differ rom roller pumps in several important respects:Tey are non-occlusive devices•Tey are constant energy devices•

(a) A length o 3/8² PVC tubing is connected to the outlet o the venous reservoir andclamped. A length o 3/8² PVC tubing is also connected to the oxygenator inletport

(b) Te outlet o the membrane compartment is connected to the circuit as with aroller pump

(c) I a “BioPump” bi-directional ow probe is required it should be inserted into thearterial line, at least 6² away rom the nearest connector

(d) Te oxygenator venous reservoir is primed with heparinized Hartmann’s solution,as described in the routine procedure

(e) Te centriugal pump is cut in as required ensuring sterile technique using a sterileblade

() Te clamp on the inlet tube is then slowly released, allowing the prime to slowly fillthe head. Te outlet port o the head (which is tangential to the body o the head)is held uppermost. Te head is thus filled with the priming solution, and as muchair as possible is purged

(g) Te oxygenator is gravity primed as above(h) Te head should again be examined or bubbles and i ound should be manipulated

out o the inlet port back into the venous reservoir

(i) When the outlet o the centriugal head is clamped any air will collect at the centero the casing (low mass). I the pump is then switched off the collected air will travel vertically into the inlet tube. As beore, this air can be manipulated back into the venous reservoir


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2A4.5: Calibrating the ow probesWith the circuit ully primed:(a) Te motor drive is switched off(b) Clamps are positioned some 6² on either side of the probe(c) Calibrate the ow probe as directed by manuacturer’s instructions

2A.5: Setting occlusions

2A5.1: Occlusion of the arterial pump if a roller pump is used:(a) Clamp the arterial line and any re-circulating lines and close the sampling ports

(b) Te pump is carefully turned until the pressure on the gauge is around 300 mmHgand the rate of fall of pressure can be observed

(c) ighten the occlusion until there is no fall of pressure in this high-pressure range(this ensures that there are no other leaks in the circuit and that all clamps arecompetent)

(d) Adjust the occlusion until the fall off of pressure over the lower 260–280 mmHgrange takes approximately 10 seconds

(e) Both rollers must be treated individually. Should the occlusion between rollers beobviously unequal, the pump should be changed

2A5.2: Occlusion of the suction pumps(a) A clamp is placed on the negative side o the sucker boot and the pump is turned

until the boot collapses with the vacuum created(b) Te occlusion should now be “backed off” until the vacuum is cleared(c) Te occlusion setting is then again increased, until the vacuum is just drawn and held(d) In order to check the direction o rotation o the sucker/vent roller pumps, a small

quantity o heparinized saline or other appropriate uid should be used by the scrubnurse to check the suction

Appendix 2B: Electronic safety devices(Adapted, with permission, rom London Perusion Science Protocols.)

2B.1: Level sensorsTe level sensor should be positioned at around the 400 ml mark on the reservoir•

I the option is available, level sensors should be set to slow the pump down beore•stopping itLevel sensors should not be overridden unless it is absolutely necessary•

2B.2: Bubble detectorsPerfusionists must use a gas bubble detector placed in the circuit: it is usual practice to•have the bubble detector on the arterial outlet of the circuit


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2B.3: Pressure alarmsMost modern heart-lung machines have integrated electronic alarms or limits o•pressure during a caseTese limits should be checked and correctly set to appropriate parameters beore each•case

2B.4: Temperature alarmsMost modern heart-lung machines have integrated electronic alarms or limits o•temperature during a case

Arterial blood, venous blood and cardioplegia temperature alarms should be checked•

and correctly set to appropriate parameters beore each caseWhere available the water temperature alarm limits should also be checked and set•

2B.5: Gas alarmsMost modern gas blenders have alarms or gas ailure•

Tese alarms can be checked when the gas lines are connected to the hospital gas•supplyConnecting the lines then disconnecting them individually should trigger the alarm•

2B.6: Electrical failure alarmMost modern heart-lung machines have an integrated alarm that sounds when the•mains power supply fails and UPS is activated. If this occurs, all unnecessary equipmentshould be turned off to conserve the battery.

Suggested Further ReadingAmerican Society o Extra-Corporeal•echnology, Herndon, VA. www.amsect.org

Gravlee GP, Davis RF, Stammers AH,•

Ungerleider RM. CardiopulmonaryBypass Principles and Practice.3rd edition, 2008, LippincottWilliams & Wilkins.

Jenkins OF, Morris R, Simpson JM.•Australian perusion incident survey.Perfusion 1997; 12 : 279–288.

Kay PH, Munsch CM.• Techniques inExtracorporeal Circulation . 4th edition,2004. London: Arnold.

Mejak BL, Stammers A, Rauch E,• et al . Aretrospective study on perusion incidentsand saety devices. Perfusion 2000; 15 :51–61.

Recommendations or Standards o• Monitoring during CardiopulmonaryBypass. Published by the: Society o ClinicalPerusion Scientists o Great Britain &Ireland, Association o CardiothoracicAnaesthetists, Society o CardiothoracicSurgeons in Great Britain & Ireland. July2007.

Wheeldon DR. Saety during•cardiopulmonary bypass. London: FranklinScientic Projects , 1986; 7 : 57–65.


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36 Cardiopulmonary Bypass, ed. S. Ghosh, F. Falter and D. J. Cook. Published by Cambridge University Press.© Cambridge University Press 2009.

Priming solutions forcardiopulmonary bypass circuitsGeorge Hallward and Roger Hall

Te cardiopulmonary bypass (CPB) circuit must be primed with a uid solution, so thatadequate ow rates can be rapidly achieved on initiation o CPB without risk o air embo-

lism. Te optimum composition o the CPB priming solution is still a matter or debate.Currently used “primes” have evolved rom historical concepts o using a solution withsimilar electrolyte content and osmolarity to the intravascular and interstitial compartments,providing a uid that when mixed with blood is capable o maintaining oxygen delivery,carbon dioxide removal and physiological homeostasis.

Prime volumeTe volume o prime required is either based on a standard empirically derived volumegreater than a minimum sae priming volume, or may be guided by the patient’s weight orbody surace area. In practice, the minimum volume required is that which fills both venousand arterial limbs o the circuit and maintains an adequate reserve volume in the venousreservoir to ensure that air is not entrained into the arterial side o the circuit during initia-tion o CPB. Tis volume is determined by both the caliber and length o tubing connectingthe patient to the CPB machine and by the design, and thereore capacity, o the venous res-ervoir and oxygenator. Reduction o the prime volume may thus be achieved by modificationo the circuit.

Te initial hematocrit (HC) achieved afer initiation o CPB is determined by the volumeo the prime in relation to the patient’s pre-CPB HC. In adults, priming volumes are com-monly in the range o 1400–1800 ml, typically representing 30–35% o the patient’s blood volume. In children, especially inants and neonates, even the minimum priming volume is

ofen ar greater than their blood volume, making the use o non-blood-containing primesimpossible.

Acceptable hemodilutionInitiation o CPB inevitably leads to hemodilution by the priming uid. Some degree ohemodilution is beneficial as blood viscosity is reduced, improving microcirculatory ow.Most centers aim or an HC o less than 30% during CPB; however, there is no consen-sus regarding optimal HC. HC is the main determinant o the oxygen-carrying capacityo blood. Teoretically, minimum acceptable HC should meet the oxygen delivery (DO

2 )

required to match systemic O2 consumption (VO

2 ). However, DO

2 is inuenced by pump ow

rate and systemic temperature and VO2 also alters proportionately with temperature. Tere isthus wide variation in practice with regard to the minimum, sae, acceptable HC. Values aslow as 14% have been advocated by some, whilst others have suggested using venous oxygensaturation (S

v O

2 ) rather than a specific HC value as transusion trigger. Experience with

Chapter

3


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Chapter 3: Priming solutions for CPB circuits

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Jehovah’s Witness patients who reuse blood transusions show that cardiac surgery and CPBwith low HCs is not only possible, but is also relatively sae.

Factors affecting the HC during CPB include:patient size;•

preoperative hemoglobin concentration/HC;•

pre-CPB blood loss;•

pre-CPB uid administration;•

CPB prime volume; and•urine output.•

One method o reducing the degree o hemodilution, without using “Bank” blood, is touse autologous blood to partially prime the CPB circuit. Tis method replaces part o the

CPB prime volume with the patient’s own blood thus reducing the degree o hemodilution.Autologous priming can be achieved by either antegrade or retrograde routes. Antegradepriming utilizes partial filling o the venous reservoir with the patient’s own blood romthe venous limb o the CPB circuit on initiation o CPB, but beore institution o CPB owthrough the oxygenator and arterial limb o the circuit. Retrograde priming utilizes retro-grade filling o the venous reservoir via the arterial limb o the CPB circuit, just prior to theinitiation o CPB, displacing the crystalloid prime volume in the arterial line tubing, filterand oxygenator and so partially filling the reservoir with the patient’s blood. Both meth-ods reduce the volume o crystalloid in the prime by replacing it with 400–500 ml o thepatient’s blood. Sae autologous priming relies on good teamwork between perusionist,anesthetist and surgeon to select appropriate patients and to ensure hemodynamic stabil-

ity, usually with the help o vasopressors, during the period o partial exsanguination othe patient.

In general, acceptance o a degree o hemodilution during CPB, the use o autologouspriming, collection and processing o shed mediastinal blood and the return o residual pumpblood at the end o CPB can all lead to a decrease in allogenic blood transusions with theirconsequent risks and uncertain risk/benefit profile.

Priming solutionsTere are many different recipes or priming solutions using crystalloid, colloid or blood asprimary constituents. Historically, blood was used to prime the CPB circuit in an attempt topreserve a high hematocrit; early in the evolution o CPB this was thought to be an importantdeterminant or successul outcome. It later became clear, however, that use o allogenic bloodin the prime may have worsened, rather than improved, outcomes. In 1962, Cooley andcoworkers showed improved outcome by adding 5% dextrose to the prime instead o justblood. Five percent dextrose later ell out o avor or two reasons: firstly, the realization thatmetabolism o glucose leads to a hypotonic solution; and secondly, ears about hyperglycemiaworsening neurological outcome. In part, accumulation o knowledge about the deleteriouseffects o blood primes and acceptance that a lower hematocrit is compatible with good out-comes has led to acceptance o crystalloids as priming solutions. Te introduction o hypo-thermic bypass in the 1960s, the inability o blood banks to support cardiac surgery with large

amounts o whole blood and the prevalence o blood-borne inections were also important inthe shif to “clear” primes. In general, an ideal priming solution should have the same tonicity,electrolyte composition and pH as that o plasma. O these ideal properties the most impor-tant is that o “tonicity,” in order to avoid red cell lysis and the uid shifs rom the extracellular


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to the intracellular compartment that occur with hypotonic solutions. Fluid shifs may occurin any organ or tissue, but the organs most vulnerable to uid accumulation are the brain and

lungs. Intracellular uid gain causes cerebral or pulmonary edema and impairs organ unc-tion. It is important to appreciate that uids which are nominally isotonic but which haveglucose as a major constituent, e.g., 5% dextrose or dextrose/saline, become very hypotonicwhen the glucose is metabolized. For this reason, glucose-containing solutions should not bea major constituent o a prime and only those uids with a near physiological sodium concen-tration should be used.

Suitable solutions used include lactated Ringer’s (Hartmann’s), Ringer’s, normal saline,Plasma-Lyte and Normosol (see ables 3.1 and 3.2). All o these solutions have similar sodiumconcentrations (130–150 mmol/l) and may contain physiological concentrations o potas-sium (Hartmann’s, Plasma-Lyte). Tere are some differences in anion composition, but all

have chloride as a major anionic constituent, the balance in Hartmann’s or Plasma-Lyte beingmade up with lactate or acetate, respectively. Both lactate and acetate are ultimately metabo-lized to bicarbonate in the liver, thus producing a near ideal physiological solution. Hart-mann’s solution is the most commonly used crystalloid in priming uids in the UK, althoughthere is variation in practice amongst different units. Normosol-A and Plasma-Lyte are bal-anced solutions more commonly used in the USA.

Te priming solution has been implicated as one o the potential causes o the disturbanceo pH associated with development o metabolic acidosis on initiation o CPB. Tis acidosisis probably caused by hyperchloremia and is more likely to occur with normal saline, whichhas a higher chloride load than the more “physiological” solutions. Other possible reasons orthis include an increase in unmeasured anions such as acetate and gluconate. Tis metabolic

Table 3.1. Composition of commonly used priming uids

Na+ K+ Cl− Ca2+ Mg2+ HCO3 − pH Other mosmol/l

Dextrose 5% 0 0 0 0 0 0 4.2 Glucose50 g/l

279

Saline 0.9% 154 0 154 0 0 0 5.0 – 308

Hartmann’s 131 5.0 111 2.0 0 29(lactate)

6.5 – 280

Plasmalyte A 140 5.0 98 0 3 27(acetate) 7.4 – 294

29 (glu-conate)

Normasol R 140 5.0 98 0 3 27(acetate)

7.4 – 294

29 (glu-conate)

Bicarbonate1.26%

150 0 0 0 0 150 7.0 – 300

Gelofusine 154 0.4 120 0.4 0 0 7.1–7.7 Gelatine

40 g/l

274

Starch 154 0 154 0 0 0 4.5–5.5 Starch 308

HumanAlbumin 4.5

100–160


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acidosis is a benign phenomenon and probably accounts or much o the base deficit observedwhile on bypass.

Colloid solutions, including 4.5% albumin, gelatins, e.g., gelousine, dextrans and

starches, e.g., hydroxyethyl starch, have been advocated or use in the CPB prime onaccount o their potential to counteract the decrease in colloid oncotic pressure associ-ated with hemodilution o albumin and other circulating plasma proteins during CPB.Tis reduction in colloid oncotic pressure causes movement o water out o the intravas-cular space and into the interstitial and intracellular spaces, contributing to postoperativeedema and subsequent organ dysunction. Tus, using colloids, with their high molecularweight, to maintain oncotic pressure and thereore reduce uid shifs seems an attractivestrategy. Te drawback to this hypothesis is that whilst, in theory, colloid solutions oughtto remain in the intravascular space, in practice the “tight junctions,” which render theendothelial lining impermeable to large molecules, become more permeable on activa-

tion o the systemic inammatory response associated with CPB. Tis may paradoxicallyincrease the amount o extravasated uid, as the high-molecular-weight constituents ocolloid solutions become trapped in the interstitial uid, potentially adding to edema bydrawing more ree uid into the interstitium. Furthermore, some o the constituents ocolloids have undesirable properties: dextrans interere with coagulation, starches mayremain in the body or years, with unknown long-term consequences and albumin solu-tions are in scarce supply and pose inection hazards. Cost and availability are also an issuewith colloid solutions.

Te use o colloid-based primes has not been shown to significantly inuence clinical out-comes such as the duration o ventilatory support and length o intensive care unit (ICU) orhospital stay. None o the types o colloids has been shown to have significant advantages overanother. Albumin may have a beneficial effect as a constituent o the prime: it is thought tocoat the extracorporeal circuit, making it appear less “oreign” to the body’s immune mecha-nisms and so to ameliorate the inammatory response.

Te lack o measurable benefit, potential risks and the significant cost penalty incurredin comparison to crystalloid uids have resulted in colloids no longer being widely used as apriming uid in adult CPB.

Te use o mannitol as a colloidal uid added to the CPB prime is perhaps the one excep-tion to the above discussion. Mannitol is a common constituent o primes, but the indica-tion or its use is or its properties as a potent osmotic diuretic, rather than to simply raisethe oncotic pressure o the prime. Maintenance o urine output both during CPB and in the

immediate postoperative period is desirable to enhance elimination rom the body o the uidload presented by prebypass iv uids, the priming uid volume and cardioplegia solution. Ithas also been postulated that mannitol may help to preserve renal unction and reduce theincidence o post-CPB renal dysunction, although the evidence or this is extremely weak. In

Table 3.2. Commonly used additives

Heparin 1000–2500 U/l of prime to ensure adequate anticoagulation

Bicarbonate 25 mmol/l of prime as buffer when unbalanced priming solutions are used

Mannitol Osmotic diuretic and free radical scavenger

Calcium Needed if citrated blood is added to the prime to prevent chelation of calcium

Steroids To attenuate systemic inammatory response to CPB (evidence weak)


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addition, mannitol is a ree radical scavenger and it is appealing to think that the ree radicalsproduced during periods o hypoperusion, ischemia and reperusion might be “mopped up”

during bypass, thus reducing end-organ damage. However, this concept remains unproven inany clinically relevant way.

Experimental oxygen-carrying solutionsTe idea o using oxygen-carrying solutions as blood substitutes may be an attractive meanso maintaining oxygen delivery. Tey would address the expense, limited supply and diseasetransmission associated with blood transusion. Both hemoglobin-based substitutes and per-uorocarbons have been researched in the context o use in the CPB priming uid, but nonehave yet proven to be both sae and effi cacious as alternatives or oxygen carriage. Despiteseveral decades o research no molecule seems close to being marketed as a viable alternative

to red cells in the clinical arena and it remains to be seen whether there is any uture or theuse o these oxygen-carrying solutions during CPB.

Suggested Further ReadingBunn F, Alderson P, Hawkins V. Colloid•solutions or uid resuscitation. CochraneDatabase Syst Rev 2003; Art NoCD001319(1):1–40.

Cooley DA, Beall AC, Grondin P. Open•heart operations with disposableoxygenators, 5% dextrose prime, andnormothermia. Surgery 1962; 52 :713–19.

Fang WC, Helm RE, Krieger KH,• et al .Impact o minimum haematocrit duringcardiopulmonary bypass on mortality inpatients undergoing coronary artery surgery.Circulation 1997; 96 (suppl II): II-194–99.

Harris EA, Seelye ER, Barratt-Boyes BG.•Respiratory and acid-base changes duringCPB in man. Br J Anaesth 1970; 42 : 912–21.

Hoef A, Korb H, Mehlhorn U,• et al .Priming o cardiopulmonary bypass withhuman albumin or ringer lactate: effect oncolloid osmotic pressure and extravascularlung water. Br J Anaesth 1991; 66 :73–80.

Klein HG, Spahn DR, Carson JL. Red blood•cell transusion in clinical practice. Lancet 2007; 370 (9585):,415–26.

Lilley A. Te selection o priming uids or•cardiopulmonary bypass in the UK andIreland. Perfusion 2002; 17 :315–319.

Liskaser FJ, Bellomo R, Hayhoe M,• et al . Roleo pump prime in etiology and pathogenesis

o cardiopulmonary bypass – associatedacidosis. Anesthesiology 2000; 93 : 1170–3.

Marelli D, Paul A, Samson R,• et al . Doesthe addition o albumin to the prime

solution in cardiopulmonary bypass affectoutcome? A prospective randomized study. J Torac Cardiovasc Surg 1989; 98 (5 Pt1):751–6.

Paone G, Silverman N. Te paradox o on•bypass transusion thresholds in bloodconservation. Circulation 1997; 96 (suppl II):II-205–8.

Rawn JD. Blood transusion in cardiac•surgery: a silent epidemic revisited.Circulation 2007; 116 (22): 2523–4.

Riegger L, Voepel-Lewis , Kulik ,• et al .Albumin versus crystalloid prime solutionor cardiopulmonary bypass in youngchildren. Crit Care Med 2002; 30 (12):2649–54.

Rosengart K, DeBois WJ, Helm RE.•Retrograde autologous priming (RAP) orcardiopulmonary bypass: a sae and

effective means o decreasing hemodilutionand transusion requirements. J ToracCardiovasc Surg 1998; 115 (2): 426–38.

Rosengart K, Helm RE, DeBois WJ. Open•heart operations without transusion using amultimodality blood conservation strategy in50 Jehovah’s Witness patients: implicationsor a “bloodless” surgical technique. J AmColl Surg 1997; 184 : 618–29.

Russell JA, Navickis RJ, Wilkes MM.•Albumin versus crystalloid or pumppr

cardiopulmonary bypass - s. ghosh, et. al., (cambridge, 2009) ww.pdf

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