VA ECMO: Physiology and Configurations

Steven Conrad, MD PhD, MCCMProfessor, LSU Health Sciences Center in ShreveportECLS Director, University Health System Shreveport

Disclosures

• No financial disclosures• Discussion of off-label use of medical devices

ECLS – extracorporeal life support

VA ECMO

VV ECMO

Hybrid VA/VV

EDCD

ECPR

ECCO2R

Acute circulatory failure

Acute respiratory failure

CO2 retention states

Cardiac arrest

Combined failure

Organ donation

ECMO – extracorporeal membrane oxygenation

Venous drainageCentral circulation

Pump-driven flowCentrifugal

Gas exchangeOxygen and CO2

Blood returnVenous (VV) or

arterial (VA)

ECLS Configuration (VA)

Heart/Lungs

SystemicCirculation

System

Pump

+-

Decreased pulmonary flow

Mixed venous

Decreased aortic rootblood flow

Combinedflow

Venovenous (VV) configuration

Heart/Lungs

SystemicCirculation

System

Full cardiac output

Mixed venous

Aorticblood

Mild hypoxemia

Recirculation

Venous admixture

+

Hollow Fibers: Artificial Alveoli

Quadrox DO2 transfer

Gas transfer

Quadrox D

Overview of physiology during VA support

• Cardiopulmonary bypass– Reduction in RV preload– Reduction in pulmonary blood flow– Reduction in pulsatility

• Increases systemic perfusion– Combination of native cardiac output and extracorporeal flow

• Heterogeneity of perfusion– Arterial cannulation site dependent– Competing circulations– Regional hypoxemia

• Imposed afterload– LV dilatation

Venoarterial support

• Functions of heart and lungs replaced (CP bypass)• Total bypass

– Not usually achieved in VA ECLS

• Partial bypass– VA perfusate mixes with aortic blood– Blood gases and oxygen content represent mixture of blood for

these two sources– Systemic blood flow is the sum of extracorporeal flow plus

remaining blood from heart/lungs

Hemodynamics in VA support

• Blood flow is created by the pump and the heart– Function of venous drainage and vascular tone

• Pulsatility is a provided by the heart– Pump flow is non-pulsatile– Some pulsatility should be maintained (e.g. 10 mmHg)

• Avoids dilated LV and stagnation in aortic root

• VA support decreases preload and increases afterload• Wean inotropes and pressors as tolerated by perfusion

– Mixed venous > 70% even if MBP low is OK– MAP at least 70 may be better for renal perfusion

VA ECMO flow patterns

Pulsatile blood flow

• ECLS circuit produces non-pulsatile flow– Pulsatility diminished

with VA ECLS– Inadequate flow

(<40 – 60) results in organ dysfunction and shock

– Pulsatility is protective when compared with non-pulsatility but only at low flow

Determining adequacy of support

• Flow range– 2.5 L/min/m2

– 50 ml/kg/min• Metabolic assessment

– Venous drainage oxygen saturation (70 – 75%, > 65%)– Lactate

• Peripheral perfusion assessment– NIRS

• Clinical assessment– Urine output– Mental status

Determining adequacy of cardiac rest

• LV support– Pulse pressure– Arterial waveform (dicrotic notch)– Echocardiography (TTE, TEE)– CXR

• If pulmonary involvement, may need decompression or hybrid support

• RV support– PA tracing (+/-) [pressure = flow vs resistance]– Liver and renal function– Splanchnic and peripheral congestion: edema, ascites,– Echocardiography

Left ventricular function in VA ECLS

• ECLS system drains ~ 80% from RA, 20% or more goes to lungs and LA

• Inadequate LV function with inability to eject against systemic pressure results in distension of LA and LV– Cardiac support with severe LV dysfunction– Respiratory support with myocardial stunning

• PDA can decompress LV in neonates• LV decompression may be required

Managing LV dilatation

• Enhancing cardiac ejection– Inotropic drugs

• Afterload reduction– Vasodilators– IABP– Impella®

• Venting– Atrial septostomy– Transpulmonary

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Femoral cannulation for VA

VA: Venoarterial access via the femoral vessels

VA: Venoarterial access via the neck vessels

Central cannulation

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Native Lung in ECLS

• VA support (no lung dysfunction)– Normal function during bypass– Normal x-ray appearance– High ventilation-perfusion ratio

• Due to low blood flow• Low end-tidal CO2• Lower ventilation with adquate PEEP

Native Lung in ECLS

• Lung dysfunction– Reduced airway pressure during ECLS

• Pulmonary consolidation (white-out)• Period of little or no lung function• VA and VV modes• Total ECLS dependence

– Maintain elevated PEEP • Reduces consolidation

Oxygen delivery in ECLS

• VA ECLS– Mixture of two sources:

• Native lung blood flow (CO)• Extracorporeal blood flow

• VV ECLS – Native cardiac output (CO)

• *Native lung blood flow ‘preconditioned’ by membrane lung

Circuit Lungs

Circuit

Lungs

𝐷𝐷𝑂𝑂2 = 𝐶𝐶𝑂𝑂 × 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑂𝑂2∗

𝐷𝐷𝑂𝑂2 = 𝐶𝐶𝑂𝑂 × 𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑂𝑂2 + 𝑄𝑄𝐸𝐸𝐶𝐶𝐸𝐸𝐸𝐸 × 𝐶𝐶𝑂𝑂2 (100%)

Femoral VA ECMO with respiratory failure

• When cardiac function is minimal or absent

• Oxygenated blood able to reach the aortic root

• Myocardium and brain receive oxygenated blood

Femoral VA ECMO with respiratory failure

• When cardiac function is present

• Oxygenated blood not able to reach the aortic root against LV ejection

• Hypoxic myocardium and brain

Saturation during VVA ECMO

• Hybrid VV + VA ECMO• Femoral and IJ approach• Some cardiac function• Poor to absent lung function• VA blood provides distal aortic

blood oxygenation• VV return provides aortic root

and arch oxygenation• Suitable for respiratory failure

requiring partial cardiac support

Indications for VA ECMO

• Failure to wean from CPB• Cath lab complications, failed IABP• Support for high risk interventions • Low cardiac output (cardiomypathy, ischemic)• Acute reversible right heart failure (PE, RCA MI)• Severe chronic PHTN as bridge to transplant• Intractable arrhythmia (medication, ablation)• Profound vasodilatory septic shock• Acute CV collapse unknown origin• Sudden cardiac death (ECPR)

Contraindications to VA ECMO

• Aortic insufficiency• Known irreversible or untreatable heart / lung disease• Adults with severe PVD and vascular access issues • Major intracranial hemorrhage (acute)• Severe or progressive chronic lung injury• Irreparable cardiac disease• Irreversible process (malignancy, end stage lupus, etc)

Weaning

• Maximum recovery• Echocardiography• Pacemakers / defibrillators back on • Milrinone, other inotropes? • Gradual illing – (Don’t suddenly fill a resting and recovering

LV). First need to remove LV vent, if in. • As flow weaned, watch parameters:

– MVO2 (No ASD), Lactate, U.O., Mental Status, pH• Determine optimal hemoglobin for each patient• When at low flow, open bridge if in use• Trial off, decannulate

ECMO without myocardial recovery

• Rapid placement on ECMO• Stabilize, evaluate

– Find treatable problem– Find irreversible or irreparable problem

• Convert to VAD• Lungs must be OK to use femoral VA (VAV an option for

combined support) and must recover to place VAD

Summary

• VA ECMO is the mode of ECLS required for cardiac support

• VA ECMO is not truly ideal for either cardiac or pulmonary support

• Only mode that can maintain systemic perfusion in ventricular failure

• VA ECMO is a combination of competing circulations• Pulmonary failure introduces regional differences in

arterial saturations and oxygen delivery