Advanced Pulmonary Monitoring

Transpulmonary-Guided VentilationThom Petty BS RRTLead Ventilation Solutions Specialist Eastern & Midwestern U.S CareFusion Respiratory Technologies - Ventilation

Advanced Ventilator Management1Esophageal BalloonaryObjectivesReview the hazards associated with positive pressure ventilation and the sequelae of Ventilator-Induced Lung Injury.

Identify the limitations of current Respiratory Mechanics.

Discuss the role of chest wall, pleura and abdominal pressures during positive pressure ventilation

Introduce the measurement of Transpulmonary Pressure as a valuable ventilation management tool.

Review two Case Studies highlighting the use of transpulmonary pressures in the management of ventilator settings.Disclaimer

Mechanical Ventilation?So, whats so bad aboutThe Hazard that is Mechanical Ventilation5mechanical ventilation can no longer be seen merely as a supportive therapy in ali and ards, but as a treatment modality capable of significantly influencing the course of pulmonary disease and clinical outcome.Viana M, Jornal de Pediatria, 2004Just What is Positive-Pressure Ventilation?What is it that is actually delivered by the ventilator to the patients lungs?

Volume

Flow

Pressure

The Alveolar StructureAdjacent alveoli and terminal bronchioles share common walls

Interdependence - forces acting upon transmitted to those around it

During Uniform lung expansion - all lung units subjected to similar transpulmonary pressures.

During Non-Uniform lung expansion transpulmonary pressures vary considerably.7The Alveoli Not Grapes on a Straw

Its important to remember that alveoli are not the cluster of grapes at the end of a straw like we envisioned in school. They are more like a sponge sharing common walls and full of holes.8Dynamic Alveolar Mechanics

Healthy alveoli:Small changes in alveolar size Ventilation primarily from changes in the size of the alveolar duct or conformational changes as a result of alveolar folding

Alveoli in Acute Lung Injury:Large changes in alveolar sizeWidespread alveolar recruitment/derecruitment.Significant shear stress-induced lung injuryGross tearing of the alveolar wallInjury to the cell membrane Ultrastructural injuryWilson, J Appl Physiol, 2001Carney, CCM, 2005Steinberg, AJRCCM, 2004

Alveolar InterdependenceWhen an alveolus collapses, the traction forces that are exerted on its walls by adjacent expanded lung units increase as they are applied to a smaller surface area.

These forces will promote re-expansion at the expense of greatly increased and potentially harmful stress at the interface between collapsed and expanded lung units

At a transpulmonary pressure of 30 cmH2O it has been calculated that re-expansion pressures could reach 140 cmH2O.10The Problems with Positive-Pressure VentilationDeparts radically from the physiology of breathing spontaneously. Positive intrathoracic pressures are created during inhalation

Flow is not homogenously distributed throughout the lung:Effectively distributed through compliant lung Attenuated in low-compliant areas

Overdistension of compliant healthy lung and underdistension of non-compliant injured lung

Basic Ventilator Mechanics12Esophageal BalloonaryMechanics 101: Motion of Air EquationPAO = ( VL / CRS) + ( F x RAW )

PAO = Pressure at the Airway OpeningVL = Volume in the LungCRS = Compliance of the Respiratory System (Lung + Pleura) F = Flow Rate of Gas in L/sRAW = Resistance of the Airway and ETT ( pressure / flow)

Lung-Protective VentilationSafer Flow-Blowing

Early LPV TheoryThe macroscopic side-effects of positive-pressure ventilation were easily recognized and understood.Lungs exposed to excessive pressures had more frequent PTX

Early LPV focus was prevention of BarotraumaLungs ventilated to high pressures have a propensity for air leaksKeep PIPs safeCurrent LPV TheoryRecent (and some not-so-recent) research reveals significant microscopic side-effectsIncreased permeability of the alveolar/capillary membraneIncreased production of pro-inflammatory mediators within the lung

Current Lung-Protective Ventilation strategies are directed primarily towards preventing/reducing this microscopic damageSeminal LPV ResearchRelease of ALI Lung Flooding factors in rodents ventilated with three modes:

HiP/HiVHigh Pressure (45 cmH2O)High Volume

LoP/HiVLow Pressure (neg.pres.vent)High Volume

HiP/LoVHigh Pressure (45 cmH2O)Low Volume (chest bound)

Dreyfuss,D ARRD 1988;137:115917More LPV ResearchSix RCTs evaluating the effect of lung-protective ventilation vs conventional approaches1988Amato et al Brazil29 pts: Vt < 6ml/kg, Pplat < 20cmH2O24 pts: Vt = 12ml/kg, PaCO2 35-38 mmHg38% Mortality71% Mortality 1998Stewart et alCanada60 pts: Vt < 8ml/kg, Ppeak < 30cmH2O60 pts: Vt 10-15ml/kg, Ppeak < 50cmH2O50% Mortality at disch47% Mortality at disch1998Brochard et alMultinational58 pts: Vt 6-10ml/kg, Pplat < 25-30 cmH2O58 pts: Vt 10-15ml/kg, PaCO2 38-42 mmHg47% Mortality at 60 days38% Mortality at 60 days1999Brower et alUSA26 pts: Vt 5-8ml/kg, Pplat 5 cmH2O32% Mortality in ICU53% Mortality in ICUCurrent Presumed Mechanism for VILIMechanical Disruption of Pulmonary EpitheliumMechanotransductionCell & Tissue DisruptionUpregulation & release of Cytokines &, Chemokines Subsequent leucocyte attraction and activationPulmonary Inflammation: VILISystemic Spillover:SIRS / MODSMECHANOTRANSDUCTION Conversion of Mechanical Stimiuls into Chemical ReactionSIRS systemic inflammatory Response SyndromeMODS Multi Organ Dysfunction syndromeTake Home Points - VolutraumaCaused by excessive End-Inspiratory VolumesIndicated by elevated end-inspiratory (Plateau) pressuresMay result from a combination of Safe Vt + PEEP

Mechanical and Biochemical in nature

Even safe Vts may severely over-inflate normal alveoli due to heterogenicity of airflow within the lung

QUESTION: How can a clinician determine if elevated Airway Plateau Pressures accurately indicate end-inspiratory volutrauma

Take Home Points - AtelectraumaCaused by repeated closing & re-opening of alveoli during ventilatory phasing

Worsens surfactant dysfunction

Release of inflammatory mediators into alveolar spaces and into the systemic circulation

QUESTION: How can the clinician determine what PEEP is truly necessary to keep the alveoli recruited at end-exhalation

An RTs Working Definition of Lung-Protective Ventilation Maintain acceptable gas exchange while avoiding harmful mechanical ventilation practices.

Need for potentially injurious volumes, FiO2s and pressures must be weighed against the benefits of such gas exchange support.

Lung-Protective ControversiesThe common denominator of the intervention sides of these trials is the use of lower Vt and limited Plateau Pressures.Many attempts have been made to understand the differences in the survival outcomes of these six RCTs as well as to clarify whether a low Vt strategy benefits patients with ALI/ARDS.

A 2002 meta-analysis by Eichacher of the trials revealed:The control arms of the non-beneficial RCTs actually had lower Pplats (a surrogate for end-inspiratory alveolar pressure) than in the two beneficial armsCould the survival benefit of the two non-beneficial RCTs be related to the larger-than-routine Vts in the control arms?Could the differences be related to Pplat rather than Vt?Eichacker PQ, Am J Resp Crit Care Med 2002

Applying Lung-Protective VentilationDriving Vents Better

The Handful of Ventilator SettingsTidal Volume Accurately measuredRespiratory RateAccurately measuredFiO2 Accurately measuredPEEP Measured but not accuratePlateau PressureMeasured but not accurate

The Problem with Airway PressuresA key limitation to mechanical ventilators is that they report peak airway pressures without distinguishing compliance that reflects intrinsic lung mechanics or chest wall and abdominal pressures

Piraino T, Respiratory Care, April 2011

As the Lung InflatesAirway Pressure (Paw) Measured at the circuit wye or ventilator outletReflects both lung and pleural pressures

Peri-pulmonary/Pleural Pressure (Pes) Pressure imposed upon the lungs by the Chest Wall and AbdomenCan be approximated by measuring pressures within the Esophagus

Transpulmonary Pressure (Ptp)The true pressure within the lungPtp = Paw Pes

PawPesPtp27PEEP Measured but not accuratePlateau PressureMeasured but not accurate

The Two Settings we Estimate: PEEPThe Two Settings we Estimate: PEEPPEEP the pressure that is being exerted by the volume of gas that is remaining in the lungs at the end of exhalation (FRC or EELV)

Optimal Lung-Protective PEEP remains undetermined.PEEP > traditional values of 5-12 cmH2O minimize cyclical alveolar collapse and the corresponding shearing injury.Potential adverse consequences including circulatory depression and lung overdistension may outweigh the benefits of higher PEEPs

Use of PEEP < 10cmH2O leads to an increase in mortalityAmato M., 8th World Congress, Sydney, AustraliaDreyfuss, Crit Care Med, 1998Gattinoni, NEJM, 2006Muscedere , Am J Respir Crit Care Med. 1994

The Two Settings we Estimate: PEEP ResearchThree RCTs comparing high PEEP vs Low PEEP in ARDS:

2010 Briele Meta-Analysis Differences in hospital mortality not statically significantSignificant reduction of death in the ICU in the High PEEP group

2004ARDSNetALVEOLIUSA276 pts: Mean PEEP = 14.7cmH2O273 pts: Mean PEEP = 8.9cmH2O25% Mortality at disch27.5% Mortality at disch2008MeadeLOVSMultinational508 pts: Mean PEEP = 15.6cmH2O475 pts: Mean PEEP = 10.1cmH2O36% Mortality at disch40% Mortality at disch2008MercatEXPRESSFrance382 pts: Mean PEEP = 14.6cmH2O385 pts: Mean PEEP = 7.1cmH2O35% Mortality at 60 days39% Mortality at 60 daysLow PEEP/High FiO2 ProtocolFiO2 0.3 0.4 0.4 0.5 0.5 0.6 0.7 0.7 0.7 0.8 0.9 0.9 0.9 1.0PEEP 5 5 8 8 10 10 10 12 14 14 14 16 16 18-24

High PEEP/Low FiO2 ProtocolFiO2 0.3 0.3 0.3 0.3 0.3 0.4 0.4 0.5 0.5 0.5-0.8 0.8 0.9 1.0PEEP 5 8 10 12 14 14 16 16 18 20 22 22 22-24

The Two Settings we Estimate: The High PEEP vs Low PEEP Controversy

The Two Settings we Estimate: Tools for Determining Optimal PEEP Ideal PEEP is defined as:

High enough to induce alveolar recruitment, keeping the lung more aerated at end-exhalation, while not distending goodalveoli Low enough to prevent hemodynamic impairment & overdistension

PEEP TableTable of FiO2 & PEEP combinations to achieve PaO2 or SpO2 in target rangeMaximal PEEP without overdistensionUse of highest PEEP while maintaining Pplat < 30 cmH2OGas ExchangeLowest shunt (highest PaO2), lowest deadspace (lowest PaCO2), best oxygen delivery (CaO2 x C.O.)ComplianceUse of the highest PEEP that results in the highest respiratory-system complianceStress IndexObserve the Pressure/Time Curve during constant flow inhalation for signs of tidal recruitment and overdistensionPressure/Volume CurveSet PEEP slightly higher than Lower Inflection PointImagingComputed tomography, Electrical impedence tomography, UltrasoundEsophageal Pressure MonitoringEstimate the intra-pleural pressure with the measurement of Esophageal Pressure then determine optimal PEEPThe Two Settings we Estimate: Alveolar RecruitabilityBriele benefits of high PEEP in ARDS patients with higher lung recruitabilityARDS patients with low potential for recruitment, the resulting over-distension associated with PEEP increases was harmful

How To Quickly Determine Lung Recruitability:Non-Recruitable If PEEP is and Plateau Pressure then in an equal or greater increment.Recruitable If PEEP is and Plateau Pressure then in a lesser incrementThe Two Settings We EstimatePEEP Measured but not accuratePlateau PressureMeasured but not accurate

The Two We Estimate: Plateau PressurePlateau Pressure is the pressure exerted by the volume of gas in the lungs at end-inhalation.Indicator of lung fullness

Goal: Keep PPLAT < 30 cmH2O

The Two We Estimate: Plateau PressureCheck PPLAT (with a minimum 0.5 second inspiratory pause) at least q 4h and after each change in PEEP or VT

If PPLAT >30 cmH2O: VT by 1ml/kg to minimum of 4 ml/kg.

If PPLAT < 25 cmH2O and VT< 6 ml/kg: VT by 1 ml/kg until PPLAT > 25 cmH2O or VT = 6 ml/kg.

If PPLAT < 30 but patient/ventilator dys-synchrony is evident: VT by 1ml/kg to a VT of 7-8 ml/kg keepng PPLAT < 30 cm

Transpulmonary Guided VentilationUsing the Proper ToolsA Brief History of the Study of Advanced Respiratory Mechanics150 AD - Galen (Greek Physician): Postulated that lungs were expanded by the outward movement of the thorax.

1817 Carson: Attached a water manometer to the trachea of a recently-killed animal and noted an increase in tracheal pressure when the chest was opened. This he attributed to the elastic recoil of the lung.

1847 Ludwig: First to measure pleural pressure in an animal.

1900 Aron: Measured pleural pressure in a human with a chest tube.

1960s Applicability of Esophageal Pressures to measure pleural pressures discovered.Solving The Airway Pressure Problem REMEMBER: Airway pressures do not reflect pressures within the lung but pressures of the entire Respiratory System

To know true Lung Pressure (Transpulmonary Pressure) you must account for the pressures outside of the lung (Pleural or Peripulmonary Pressures)Difficult to directly measure pressure in the pleura

A number of studies have demonstrated reasonable correlation between Esophageal Pressures and Pleural PressuresPleural pressures adjacent to the esophagus transmitted to esophagus.Pressure within the pleural space is not uniformPressure in the dependent & basal regions is greater than in the upper regions of the thoracic cage

Solving The Airway Pressure ProblemPatients on mechanical ventilation are usually supine or semi-recumbentImportant to account for the effect that mediastinal structures such as the heart have on esophageal pressures.Washko (2006) and Talmor (2008)Approximately 2-5 cmH2O be subtracted from the esophageal pressure to more accurately reflect pleural pressures.Stiff Lung or Stiff Abdomen?

30 = 15 + 1530 = 25 + 5PPLAT = PTP + PESGattinoni, Crit Care, Oct 2004;PPLAT = PTP + PES41How Common are Increased Intra-Abdominal Pressures?Malbrain et al, Intensive Care Med (2004) 30:822829

Abdominal PressureTotal PrevalenceMICU PrevalenceSICU Prevalence>12 mmHg58.8%54.4%65%>15 mmHg28.9%29.8%27.5%>20 mmHg8.2%10.5%5.0%13 ICUs, 6 countries, 97 patients

42Can High Intra-abdominal Pressures Really Affect Ventilation?

Rigid Abdomen in ACS S/P Decompressive Laparotomy

43Transpulmonary-Guided Ventilation3 Basic ConceptsFor alveolar recruitment a transpulmonary pressure greater than the opening pressure of the lung must be applied to the lung.

To avoid alveolar collapse after recruitment, a PEEP that is greater than the compressive forces operating on the lung and alveolar ventilation that is sufficient to prevent absorption atelectasis must be provided.

Avoidance of stretch (by maintaining a low plateau pressure) and prevention of cyclic collapse and reopening (by maintaining adequate PEEP and alveolar ventilation) are the physiologic cornerstones of mechanical ventilation in ARDS.

Gattinoni et al,CritCareMed2003Vol.31,No.4(Suppl.)

The Talmor/Ritz StudyARDS survival has improved in recent years with low Vts and the use PEEP but the Optimal level of PEEP remains difficult to determine.

Could the use of Esophageal Pressure measurements enable the clinician to determine a PEEP value that would maintain oxygenation while preventing lung injury due to repeated alveolar collapse and/or overdistention?

Mechanically-ventilated ARDS patients randomly assigned to groups:CONTROL GROUP: PEEP adjusted as per ARDSNet recommendationsPES-GUIDED GROUP: PEEP adjusted to achieve a PTP PEEP of 0 to+10 cmH2O

The ResultsPrimary end point of the study was improvement in oxygenation.Secondary end points - respiratory-system compliance & pt outcomes.

The study reached its stopping criterion and was terminated after 61 patients had been enrolled.

The PaO2/FiO2 ratio at 72 hours was 88 mmHg higher in the Pes-group than in the control group

This effect was persistent through the 24, 48 & 72 hour follow-up time.

Respiratory-system compliance was also significantly improved at 24, 48, and 72 hours in the Pes-guided groupOutcomes

Basing ventilator settings on a maximum allowable airway plateau pressure may leave large portions of the lung under-inflated and at risk of VILI from repeated airway opening and closing.

Estimating pleural pressures from PES and setting PEEP to achieve a target PTP may allow higher PEEP in many patients without overdistending lung regions that are already recruited.A Sampling of Whats in the Journals

Systematic use of Pes has the potential to improve ventilator management in ARF by providing more direct assessment of lung distending pressure.

A Sampling of Whats in the JournalsThe use of airway Plateau Pressures to set ventilation may under-ventilate patients with intra-abdominal hypertension and overdistend the lungs of patients with atelectasis. Thus PTP must be used to accurately set mechanical ventilation in the critically ill.

A Sampling of Whats in the JournalsIncreases in peak airway pressure without a concomitant increase in alveolar distension are unlikely to cause damage.

Critical variable is not PIP but PTP

In patients with a stiff chest wall from non-pulmonary ARDS that may have elevated pleural pressures airway Plateau Pressures may exceed 35 cmH2O without causing alveolar distension

A Sampling of Whats in the JournalsPes can be used to estimate transpulmonary pressures that are consistent with known physiology, and can provide meaningful information, otherwise unavailable, in critically ill patients.

A Sampling of Whats in the JournalsPplat > 25 cmH2O

Static Lung Compliance < 40 ml/cmH2O

P/F Ratio < 300

PEEP > 10 cmH2O to maintain SaO2 > 90%

PaCO2 > 60 mmHg or pH < 7.2 attributable to respiratory acidosis

Wolfson Medical Center, Holon, IsraelOne Hospitals Protocol for Identification of Pes Candidates

5fr or 7fr balloon-tipped catheter or a specialized NG/OG catheter with balloon tip Inserted into the lower third of the esophagus, above the diaphragm.

An approximation of proper placement can be made by measuring the distance from the tip of the nose to the bottom of the earlobe and then from the earlobe to the distal tip of the xiphoid process of the sternum.Esophageal Balloonary: The Catheter

Properly inserted balloon will show simultaneous negative Paw & Pes deflections with a patient-initiated breath during an expiratory hold (Baydur Maneuver).If balloon is inserted too far into the esophagus Pes will deflect positively during a spontaneous inspiration.

PES tracing may show small cardiac oscillations reflective of cardiac activity.PES should be similar (+ 10) to PGA (Bladder Pressure)Measurements should match the patients clinical presentation.

Esophageal Balloonary: Determining Proper Catheter PlacementProperly inserted an inflated balloon may show small cardiac oscillations reflective of cardiac activity.Esophageal Balloonary: Determining Proper Catheter Placement

Increased abdominal pressure and/or decreased chest wall compliance is skewing PAW PLAT

PAW PLAT = 39 cmH2OPTP PLAT = 9 cmH2O

Keep PTP PLAT < 20 cmH2O

Esophageal Numerology: PTP PLATTranspulmonary Pressure at End-Inspiratory Plateau

PAW PEEP = 5 cmH2OPES = 15 cmH2OPTP PEEP = -10 cmH2O

155-101515Esophageal Numerology: PTP PEEPTranspulmonary Pressure at End-Expiratory Plateau

Esophageal Numerology: PTP PEEPTranspulmonary Pressure at End-Expiratory PlateauGoal is to adjust PEEP to maintain PTP PEEP 0 - +2-5 cmH2O

Negative PTP PEEP = pressure outside the lung is greater than pressure inside the lung.

Positive PTP PEEP = pressure inside the lung is greater than pressure outside the lungMay cause end-expiratory overdistension if excessive

Visualizing PTP PEEP

Good indicator of Work of BreathingValues