Extracorporeal Membrane Oxygenation: Anesthetic Considerations

Introduction

• ECMO is an advanced form of temporary mechanical cardiopulmonary support in which venous blood is drained from the patient, circulated through an extracorporeal circuit containing a membrane oxygenator for gas exchange, and returned to the circulation with or without mechanical pumping depending on the clinical indication.
• The primary role of ECMO is supportive rather than curative. By facilitating oxygen delivery, removing carbon dioxide, and, when indicated, providing circulatory support, ECMO preserves systemic perfusion and end-organ function in patients with severe, potentially reversible cardiopulmonary failure, allowing time for physiologic recovery, definitive intervention, or further clinical decision-making.

Rationale

Gas Exchange Support and Reduced Physiological Workload^1,4

• ECMO allows for venous blood to be drained and cycled through a pump outside the body, where it is decarboxylated, oxygenated, and warmed before being infused back into either the venous (VV ECMO) or arterial (VA ECMO) circulation.
• By partially or completely supporting gas exchange or systemic perfusion, ECMO reduces myocardial oxygen consumption and attenuates ventilator-induced lung injury (VILI).
  • VV ECMO reduces mechanical ventilatory stress, minimizing the risk of VILI
  • VA ECMO reduces left ventricular workload and myocardial stress, promoting recovery in reversible cardiac pathology

Functions as a “Bridge” Strategy⁵

• In reversible conditions, ECMO serves as a bridge to recovery by providing additional time for organ healing while preventing further physiologic injury.
• For patients in end-stage cardiopulmonary disease, ECMO serves as temporary support until a donor organ becomes available.
• If it is clinically uncertain whether the heart and/or lungs will recover, ECMO provides time to collect information before deciding the best next step.

Types

VV ECMO^2,6

• Used to support gas exchange only and relies on the patient’s native cardiac function.
• Venous blood is drained from the femoral vein and extracorporeally oxygenated before being returned to the venous system via the right internal jugular vein.

Veno Arterial (VA) ECMO^5,6

• Provides both cardiac and pulmonary support, as well as full hemodynamic and gas-exchange support.
• Venous blood is drained via the femoral vein and artificially oxygenated before being returned to the femoral artery.

Indications

Indications for VV ECMO⁷

• Acute respiratory distress syndrome (ARDS):
  • Severe bacterial or viral pneumonia
  • Aspiration syndromes
  • Alveolar proteinosis
• Extracorporeal assistance to provide lung rest:
  • Airway obstruction
  • Pulmonary contusion
  • Smoke inhalation
• Lung transplant
  • Primary graft failure after lung transplantation
  • Bridge to lung transplant
  • Intraoperative ECMO
• Lung hyperinflation secondary to status asthmaticus
• Pulmonary hemorrhage or massive hemoptysis
• Congenital diaphragmatic hernia, meconium aspiration

Indications for VA ECMO⁵

• Cardiogenic shock or severe cardiac failure due to almost any cause, including but not limited to:
  • Acute coronary syndrome
  • Cardiac arrhythmic storm refractory to other measures
  • Sepsis with profound cardiac depression
  • Drug overdose/toxicity with profound cardiac depression
  • Myocarditis
  • Pulmonary embolism
  • Isolated cardiac trauma
  • Acute anaphylaxis
• Postcardiotomy with inability to wean from cardiopulmonary bypass after cardiac surgery
• Bridge to heart or heart-lung transplant
• Post-heart or heart-lung transplant resulting in primary graft failure
• Bridge to longer-term ventricular assistance device support or decision for chronic cardiomyopathy patients
• Periprocedural support for high-risk percutaneous cardiac interventions

Basic Circuitry and Components⁶

• Standard ECMO circuitry includes a blood pump, oxygenator, drainage and return cannulae, flow and pressure sensors, a heat exchanger for cooling and heating blood, and arterial and venous access (Figure 3).
  • The blood pump propels blood from the patient to the oxygenator membrane, thus creating flow to the system.
• A roller pump drives blood flow through progressive compressions of segments of the drainage cannula tubing, producing unidirectional, continuous flow.
• Centrifugal pumps use a magnetic field generated by the rotation of an axis coupled to a disc to produce unidirectional, continuous blood flow.
  • The oxygenator is a container comprising two chambers separated by an oxygenation membrane. It is here that gas diffusion occurs between the patient’s blood and a gas mixture (fresh gas flow), allowing oxygenation of venous blood and removal of carbon dioxide. (Figure 4).

Anesthetic Considerations

Preanesthetic Considerations^3,6

• The majority of ECMO candidates have cardiopulmonary instability due to severe hypoxemia or hypercapnia, as seen in VV ECMO patients, or cardiogenic shock and low-flow states seen in VA ECMO patients.
  • Evaluate the hemodynamic status
  • Assess vasopressor/inotrope dependence
  • Optimize preload for ECMO flows
  • Review ventilation settings, especially high positive end-expiratory pressure (PEEP)
    • Loss of high PEEP during induction can lead to rapid desaturation and worsening of hemodynamic status.
• Evaluate anticoagulation status before systemic heparinization during ECMO cannulation.
  • Obtain baseline activated clotting time and anti-Xa levels
  • Confirm timing and dose of last heparin bolus to avoid excess anticoagulation and potential for hemorrhage during cannulation
  • Ensure blood products such as packed red blood cells, fresh frozen plasma, platelets, and cryoprecipitate are readily available if needed

Pharmacokinetic Considerations^3,8

• ECMO introduces several clinically relevant alterations in drug pharmacokinetics that complicate medication dosing in critically ill patients.
• Generalized effects of ECMO on pharmacokinetics include increased apparent volume of distribution and drug sequestration within circuit components.
• The degree of drug sequestration is largely dependent on physicochemical properties, particularly lipophilicity and protein binding, thus requiring highly individualized dosing considerations depending on the drug being used (Table 1).

Choice of Induction Agents and Maintenance of Hemodynamic Stability^3,7

• Hemodynamic stability is of paramount importance as is choosing drugs that minimize myocardial depression.
  • Etomidate (0.2-0.3 mg/kg) is the most stable induction agent and ideal for patients in shock.
  • Ketamine (0.5-1 mg/kg) maintains sympathetic tone and is useful in hypotensive patients.
  • Fentanyl must be titrated carefully, as high doses can cause chest wall rigidity.
  • Midazolam may be used as an adjunct agent, but can also prolong sedation in patients with multi-organ dysfunction.
  • Avoid propofol in patients with severe cardiogenic shock unless in very small, carefully titrated doses due to significant depression of cardiac output.

Neuromuscular Blockade^3,7

• Rocuronium or cisatracurium are preferred for neuromuscular blockade
  • Cisatracurium is ideal in ARDS patients due to organ-independent metabolism and minimization of ventilator dyssynchrony