cardio-pulmonary bypass

Technology rules the world…..• A physician at the bedside of a child dying of an

intracardiac malformation as recently as 1952 could only pray for a recovery. Today correction is routine.

• And about 2,000 such surgeries performed every 24 hours worldwide these days.

CARDIOPULMONARY Bypass

Vidya V SMSc Nursing Student

• Why do we bypass the cardiac and pulmonary system?

• How is it possible??• How does the tissues supplied if the heart is

not pumping?• We know if the heart stops beating, the

person dies. Then how CPB saves the pt??• Taken out blood clots easily, then how could

the whole blood is bypassed without clotting?

Definition• Cardiopulmonary bypass is a form of extra

corporeal circulation.• It temporarily takes over the function of the

heart and lungs during surgery maintaining the circulation of blood and oxygen content of the body.

• Heart–lung machine

Goals of CPBThe CPB circuit has 4 major functions

• Diversion of blood from heart to provide blood less & stable surgical field.

• Circulation of blood. • Oxygenation & carbon dioxide elimination.• System cooling and rewarming.

History • The first operation – 5th April 1951- Dr. Clarence

Dennis (University Of Minnesota) following 4 years of experiment with dogs.

• The first successful open heart procedure on a human using bypass machine – 6th May 1953,

John Gibbon (Philadelphia) correction of ASD in an 18 year old girl.

BIRTH OF THE OPEN HEART ERA !

Surgical procedures in which cardiopulmonary bypass is used

• Coronary artery bypass surgery.• Cardiac valve repair and/or replacement.• Repair of large septal defects.• Repair and/or palliation of congenital heart

defects.• Transplantation. • Repair of some large aneurysms. • Pulmonary thrombectomy.

On pump

Off pump

On pump

Bypass system • Removes & pumps blood.

Cardioplegia • Stops beating of the heart

BYPASS SYSTEM• Basic bypass system– Blood drained from the venous system using

gravity through,• Cannulas in SVC & IVC• Single cannula in RA in to the venous reservoir.

• It is pumped into the membrane oxygenator .• Returned to the systemic circulation via a cannula

usually placed in distal ascending aorta.

Basic CPB

Beyond the basics………

Basic components of CPB

• Venous cannula

• A venous reservoir

• An oxygenator

• A heat exchanger

• The main pump

• An arterial filter

• Aortic cannula

• Accessory pumps and devices

Basic components of CPBVenous cannula & venous reservoir

Venous cannulas • Made of flexible plasticsSize (According to )• Pt size• Anticipated flow rate • Index of catheter: flow index

For an average adult • 30F SVC + 34F IVC • Single 42F (Single cavoatrial)

Venous cannulation

❶ ❷

Venous reservoir Venous blood enters the circuit by gravity into a reservoir placed 40-70cm below the level of heart.

The amount of blood drained is determined by, CVP, Resistance in cannula, tubing, and connectors & Absence of air with in the system.Volume Adult-4000-5000mlPaediatrics-3500-4000mlInfants-1000-1500ml

Basic components of CPB(contd..)

Main pumpRoller pump/ peristaltic pump

Rotating motor-driven pumps – Peristaltic "massage“ of tubing gently propels the blood through the tubing.

Main pumpCentrifugal pump

Blood flow is produced by centrifugal force, and is thought to produce less blood damage.

In CPB there are 4 pumps:1. To pump the oxygenated blood to patient.2. To induce negative pressure to operate the

cardiotomy suction system.3. To deliver the cardioplegic solution to perfuse the

coronary arteries during open operations involving the aortic root.

4. To actively vent the left heart.

Basic components of CPB(contd..)

Heat exchanger Whole body hypothermia has been widely used to reduce metabolic demand and to protect vital organs.

For every 1 °C decrease in brain temperature, cerebral metabolic rate decreases by 7%.

Basic components of CPB(contd..)Oxygenator• This serves as the lung and is designed to

expose the blood to oxygen. • Disposable & membrane is permeable to gas

but impermeable to liquid blood. • Blood flows on one side of the membrane

while oxygen on the other.

Oxygenator…• The rate of oxygen addition is similar to that of

normal respiration.• Blood flow is 3-5 liters/min and gas flow is between 40-60% of blood flow.

Basic components of CPB(contd..)

Arterial filter • To prevent systemic embolization• Filters and bubble traps• Remove Particulate Matter (Bone, Tissue, Fat,

Blood Clots etc.)• Pore Size : 30 – 40 micro meter.

Basic components of CPB(contd..)

Aortic cannulaIt is usually the narrowest part of the extracorporeal circuit.

• High flow • High pressure gradients• High velocity of flow • Turbulence

Basic components of CPB(contd..)

Accessory pumps and devicesConsiderations in the selection of tubing and connectors. • Minimization of blood trauma• Prime volume• Resistance to flow• Avoidance of leaks

Desirable tubing characteristics• Transparency• Resilience • Flexibility• Kink resistance• Hardness • Toughness

• Inertness• Smooth and non-

wettable inner surface• Tolerance of heat

sterilization • Blood compatibility

Tubing• Medical grade polyvinyl chloride (PVC)

(e.g., Tygon) • Silicone or latex rubber tubing is sometimes

used in roller pumps.• New formulations of PVC are being developed

for use in roller pumps.

Cardiotomy Suction System• 2 handheld suckers, connecting

tubing, one roller pump, and a combined blood filter and a reservoir unit.

• Return blood spilled in the operative field directly into the perfusion circuit.

LV VentingVENTRICULAR VENTING :• LV venting done to keep the operative field clear • Maintain Low LA & pulmonary venous pressure • Remove air from cardiac chamber.• Blood from LV goes to reservoir bag

Cardioplegia• A separate circuit for infusing a solution into the

heart to produce cardioplegia (i.e. to stop the heart from beating), and to provide myocardial protection(i.e. to prevent death of heart tissue).

Cardioplegic Solutions

Each ml contains:• Potassium chloride – 59.65 mg• Magnesium chloride – 162.65mg• Procaine hydrochloride – 13.64mgDOSE:• Adult:30ml/kg• Paeds:20ml/kg• Neonates:10ml/kg

del Nido Cardioplegia

500mL RL with,• MgSO4 - 2mL• KCl - 6.5mL• NaHCO3 - 6.5mL• Xylocaine - 3.3mL• Mannitol - 8.5mL

Monitoring

Assess venous outflowIs bypass complete ???• Appropriate flow• Appropriate MAP• Empty heart with CVP 2-5cm H2O.

Discontinue drug and fluid administration.Discontinue ventilation and inhalation drugs to the pt lung.

Monitoring venous drainKink

Airlock

Non-cardiac suction

Reservoir is not positioned

low enough

Bleeding

Causes poor venous return

Precaution• If venous return is poor check cannulas for

proper placement, kink, airlock etc.• The pump flow should be slowed until the

program is resolved.• Search for evidence of SVC obstruction

High CVP Facial engorgement

Assess arterial inflow

• Is Arterial blood is oxygenated?• Is the flow is appropriate?• Evidence of arterial dissection (persistent low

MAP in presence of high inflow line pressure and falling of reservoir level).

Causes of aortic cannula high line pressure

• Kink in the arterial cannula or line• Cannula improperly positioned• Cannula too small• Arterial systemic blood pressure very high• Aortic dissection• Blockage in arterial filter

Continuous monitoring during CPB

• Reservoir level• Blood flow @ proper rate or flow rate• Pressure line / arterial line pressure• Arterial blood pressure • Oxygen saturation• Temperature• ECG• Venous oxygen saturation• Central venous pressure

Intermittent monitoring during CPB

• Blood gas • Urine output : Urine output is monitored using

a freely draining urinary catheter.

• Electrolyte

Monitoring devices • Anesthesia monitor• Ventilator parameters• CPB machine parameters and alarms• Cardioplegia system alarms• CVP pressure • Pulse oxymetry • Urine output • Arterial line pressure monitor

Management of CPB &

Management of pt on CPB

Before Surgery – Pt Mx• Routine preoperative care.• NPO• Antiseptic bath• Autoclaved clothes• High risk consent• Various investigation reports should be attached to the patient

file.• Articles needed in the surgery should be ready with the client.• Pre operative vitals monitoring and recording.• Make sure that patient has no allergy to

heparin/shell fish.

Management of Pt• Information from the patient's chart is

obtained regarding the proposed surgical procedure and relevant history.

• Equipment is then selected appropriate to surgical and patient needs.

• Blood grouping and matching done.• Arranged for blood.

Before Sx - Management of Tubing

• CPB circuit must be primed with fluid and all air expunged before connection to the patient.

• The circuit is primed with a crystalloid solution and sometimes with blood products .

• The patient must be fully anti-coagulated with an anticoagulant such as heparin.

• The circuit may be briefly flushed with filtered 100% carbon dioxide to displace room air.

During surgery

• Patient is prepared.• Circuits kept in a secure area with sealed ports

and vents to maintain sterility of the blood-contacting surfaces.

• Sequence of circuit done in a consistent manner.

• Heat exchanger and cardioplegia delivery system are turned on and tested.

Preparation for bypass• Full anticoagulation (heparin 300IU/kg)• Bypass circuit primed with crystalloid, heparin

+/- mannitol just before aortic cannulation.• Prepare and pressurize cardioplegia to

300mmHg.

Anticoagulation-heparin

• Heparin is given soon after the chest is opened.

• After a control activated clotting time(ACT) is obtained, a loading dose of 300 IU/Kg heparin is given through central venous line.

During Surgery

• When the surgeon is ready to begin CPB, the heart–lung machine console is positioned near the operating table.

• Pump should be placed to minimize tubing lengths to the cannulation sites to reduce Prime volume Pressure gradient (resistance to flow) Blood trauma

Connection of patient to circuit

• After administration of systemic heparin • Verify CPB circuit for any visible gas bubbles.• Arterial and venous lines are clamped at the

pump and table. • The surgeon or assistant divides the

arterial/venous recirculation loop.

• Upon instruction from the surgeon, CPB begins by removing the clamp(s) on the arterial line and activating the systemic pump speed control.

• After removal of the arterial line clamp at the field, the perfusionist should manually palpate or observe pulsation on an arterial flow line pressure monitor.

Establishing extracorporeal blood flow

• Full CPB flow can be established in most cases within 30 seconds.

• Starts flow in the systemic pump before releasing the venous line.

• As the volume of perfusate in the CPB reservoir decreases, the venous line clamp or occluder is released.

During bypass

• Turn off ventilator • Propofol 6mg/kg/hr OR midazolam OR volatile

agent on bypass machine• MAP maintained at 50-70mmHg by altering

SVR• Pressure maintained with vasopressors and

vasodilators• Hypothermia to 28-34˚C used

Performing the Correction

Coming off bypass• Warm to 37˚C• K+ 4.5-5.0• HCT >20%• Normal acid-base status• HR 70-100/min (ideally SR)• 100% O2• Venous line progressively clamped

• Heart gradually fills.• Start inotropes if inadequate cardiac output• Protamine (3mg/kg)• Restart volatile and opioid• Removal of aortic cannula is the final step.

Protamine

• Once bypass is terminated, and after removal of venous cannula,protamine is given to reverse heparin, usually during a 5-10 min period.

• The reversing dose is approximately 1.3mg of protamine for 100 U of heparin.

Bypass catastrophes

• Supply failure - pump stops working• Inadequate anticoagulation - circuit clots• Oxygenation failure - hypoxaemia and ischemia• Disconnection, empty reservoir - RV distension,

increased PAP - cardiovascular collapse• Gas emboli - into system circulation• Aortic dissection - renal failure, bowel ischaemia,

paraplegia, cardiac tamponade, limb ischemia, stroke

• Hemolysis

Other Complications

• Capillary leak syndrome.

• 1.5% at risk of developing ARDS.

• Post-perfusion syndrome ("pump-head").

After Surgery

• Preparing the ICU environment for the patient.• Make sure the functioning of equipment.• To warm the patient after surgery , a

hyperthermia blanket is placed on the bed.• All the emergency equipments including IABP

machine and all the emergency drugs should be available.

• After receiving the patient baseline vitals should be checked.

After Surgery• Closely monitor the hemodynamic parameters of the

patient.• Clotting time,Hct. ,Na,K,ABG should be monitored

frequently.• Look for any signs of complications.• Closely monitor the IV fluid input and urine output,

chest drainage.• Document all the findings.• Once the patient is stabilized, an ECG and upright chest

X ray are routinely performed.

Complications• Swelling of the brain• Infections• Arrhythmia• Kidney stress• Blood vessel damage• Need for transfusion• Low output syndrome• Weight gain• Release of cytokines leading to a variety of physiologic events• Difficulty planning out complex actions• Irritability

Newer modifications

• Centrifugal pumps• Diffusion oxygenator • Heparinized oxygenator• Mini CPB• Octopus

Off pump surgeries

• The off pump technique is very similar to the conventional Coronary Artery Bypass Grafting (CABG) procedure. OPCAB still utilizes a medial sternotomy, however the important difference is that the cardiopulmonary bypass pump is no longer employed.

Extracorporeal membrane oxygenation (ECMO)

• Partial CPB that diverts a fraction of systemic venous return (maximum 75%) to an oxygenator and thus temporarily supports the heart and lung function.

INDICATIONS FOR ECMO• Preoperative cardiopulmonary support.• Management of failure to wean from the

cardiopulmonary bypass.• Resuscitation after cardiac arrest in the post

operative period.

CARDIAC PUZZLE……….

Intra cardiac surgeries are cardiac puzzles, an effective CPB determines the win and the lose.

Thank you