Extracorporeal Membrane Oxygenation (ECMO)

ECMO (extracorporeal membrane oxygenation, also called extracorporeal life support, ECLS) is a temporary circuit. It drains venous blood, runs it through a pump and a membrane oxygenator, and sends it back into the body. Venovenous (VV) ECMO supports gas exchange only. Venoarterial (VA) ECMO supports gas exchange and circulation. It is a bridge. It buys time for recovery or for a definitive therapy.

Key Components

Flow Path

1. Patient: venous blood drains through the drainage cannula.
2. Pump: the centrifugal pump moves blood at the set flow.
3. Oxygenator: gas exchange and temperature control happen here. Sweep gas carries CO₂ away.
4. Return: blood goes back into a vein (VV) or an artery (VA).
5. Sampling: pressures and blood gases before and after the oxygenator show each stage.

What It Does

What It Depends On

• Cannula size and position: the cannula caps achievable flow and sets the drainage pressure.
• Native cardiac output and lung function: decide how much blood skips the circuit's oxygenator.
• Hemoglobin: oxygen content depends on it just as much as on flow (see Calculations).
• Volume status and intrathoracic pressure: shift the drainage pressure and the risk of suck-down.
• Native LV contractility (VA): sets the pulse pressure and decides whether the LV distends.

Cannulation Concept

VV ECMO is commonly set up one of two ways. One is a dual-lumen cannula. The other is separate drainage and return sites. Peripheral VA runs through femoral or axillary vessels. A femoral arterial cannula needs a distal perfusion catheter in the same limb. The ECMO team picks the configuration, based on the underlying cause and the vascular anatomy.

Mode Settings to Know

• VV ECMO: you set flow, sweep and FdO₂. The ventilator goes to lung-rest levels (see Setup, Settings & Targets).
• VA ECMO: flow, the MAP target and the LV assessment drive the settings. Pulse pressure shows native contractility.
• ECPR: cannulation happens during CPR, under the local ECPR protocol. Keep external compressions going through the whole cannulation. ELSO recommends that.

Indications

• VV ECMO, hypoxemic failure: PaO₂/FiO₂ below 80 mmHg after optimal care, including a trial of prone positioning if no contraindication (ELSO VV guideline).
• VV ECMO, hypercapnic failure: pH below 7.25 despite optimal ventilation (rate 35 breaths/min, plateau pressure 30 cmH₂O or less).
• VV ECMO, bridge: bridge to lung transplantation or primary graft dysfunction after lung transplant.
• EOLIA entry criteria (very severe ARDS): with optimized ventilator settings, PaO₂/FiO₂ below 50 mmHg for more than 3 hours, PaO₂/FiO₂ below 80 mmHg for more than 6 hours, or pH below 7.25 with PaCO₂ of at least 60 mmHg for more than 6 hours.
• VA ECMO: refractory cardiogenic shock with a potentially reversible or surgically correctable cause, massive pulmonary embolism, fulminant myocarditis, post-cardiotomy shock, bridge to decision, transplant or durable LVAD, and ECPR under local criteria (ELSO VA guideline). VA ECMO is a bridge, not destination therapy. Plan the route from the start: recovery, decision, transplant or durable LVAD. Routine early VA ECMO in infarct-related shock did not lower mortality in randomized trials. Selection is individual (see Key Evidence).

Contraindications

ECPR Candidacy (Example Criteria)

ELSO's adult ECPR interim guideline lists these as example inclusion criteria. Agree on local criteria in advance. The trial populations are narrow, and resources are limited.

• Age under 70 years, witnessed arrest, and bystander CPR started within 5 minutes.
• Initial rhythm of VF, pVT or PEA, with ECMO flow established within 60 minutes (the "low-flow interval").
• End-tidal CO₂ above 10 mmHg during CPR before cannulation.
• No known life-limiting comorbidity, and no more than mild aortic valve incompetence.

Key Evidence

Initial Settings

• VV lung-rest ventilator: plateau pressure below 25 cmH₂O (acceptable up to 30), PEEP at least 10 cmH₂O, set rate 4 to 15 breaths/min, and FiO₂ as low as keeps saturation adequate (ELSO VV Table 3).
• Sweep: set the starting rate per protocol and adjust slowly to reach the PaCO₂ and pH target.
• Flow: increase toward at least 60% of cardiac output, within what the cannula and drainage pressure allow.
• Anticoagulation: start per the local protocol and adjust to the target in the Anticoagulation section.

Sizing and Positioning

• Cannulation guidance: ELSO recommends ultrasound for percutaneous cannulation (ELSO VA guideline).
• Distal perfusion catheter: with femoral arterial return, place it at cannulation. Where flow can be measured, aim for at least 100 mL/min (ELSO VA guideline).
• Cannula size: sets the flow ceiling. The ECMO team chooses size and sites (typical; follow institutional protocol).

Normal

• Drainage (pre-pump) pressure: negative. It gets more negative as flow rises or volume falls. Watch for a rapid swing.
• Pre- and post-oxygenator pressures: watch the difference, the oxygenator pressure drop. It changes slowly. A rising drop suggests clot.
• Arterial pulse pressure (VA): reflects native LV ejection. Lost pulsatility suggests the LV is not ejecting.
• Paired blood gases: compare pre- and post-oxygenator samples to estimate recirculation.

Positioning and Mobility

• Keep a femoral cannulated limb straight. Avoid hip flexion beyond the limit the cannula site sets.
• Check distal pulses, Doppler signals or capillary refill every hour, and after any move.
• Mobilize as far as the cannula setup and team consensus allow.

Daily Checklist

1. Confirm mode (VV or VA), cannula sites and flow direction.
2. Review flow, pressures, oxygenator pressure drop and any upward trend.
3. Review sweep, FdO₂, ventilator settings and the most recent blood gases.
4. Assess MAP, pulse pressure, vasoactive support, lactate and urine output.
5. Inspect cannula sites and limb perfusion.
6. Review anticoagulation, Hb, platelets, fibrinogen, plasma free Hb and electrolytes.
7. Assess neuro status, sedation depth and mobility plan.

Strategy and Targets

Hemolysis

• Causes: high flow, suck-down, pump-head or oxygenator clot, and cannula shear.
• Tests: plasma free hemoglobin, LDH, haptoglobin and bilirubin, plus dark or red urine.
• Action: check the circuit and pump, reduce flow to the lowest effective level, and call the ECMO team about circuit change.

Bleeding and Transfusion Goals

Bleeding risk climbs on long runs with anticoagulation. Acquired von Willebrand syndrome (loss of large multimers) and fibrinogen changes increase it (ELSO VA guideline). The ELSO 2021 anticoagulation guideline sets these blood product goals.

Antithrombin and HIT

Consider antithrombin replacement when heparin requirement runs high and anticoagulation targets are still missed. Routine antithrombin monitoring is not established (ELSO guidance 2021). With heparin-induced thrombocytopenia, reach for a direct thrombin inhibitor under local protocol.

Sequestration by the circuit differs from drug to drug. ECMO dosing data are thin, so titrate to effect and check the medication page.

Readiness Criteria

• VA: MAP above 65 mmHg, pulse pressure above 10 mmHg, and mixed venous saturation adequate at 2 to 2.5 L/min of ECMO flow (ELSO VA guideline).
• VV: SpO₂ above 92% or PaO₂ at least 70 mmHg while FdO₂ and sweep are reduced (ELSO VV guideline).
• Cause treated: echo, chest X-ray and labs show the reason for ECMO has improved.

Weaning Steps

1. VA ECMO: reduce flow in serial steps, with echo and hemodynamic assessment at each stage, until about 0.5–1.0 L/min is reached (ELSO ECPR interim guideline). Protocol sets the lowest flow used before decannulation.
2. VV ECMO: reduce FdO₂ from 1.0 to 0.21 in steps of about 20%, keeping SpO₂ above 92%. Then reduce sweep by 0.5 to 1 L/min toward 1 L/min, checking an ABG at each step.
3. Off-sweep challenge (VV): trial off sweep gas for 2 to 3 hours or longer, with SpO₂ and ABG monitoring (ELSO VV guideline).
4. Hypothermia ECLS: attempt weaning once core temperature is above 35°C and echo shows improved LV ejection. Reduce flow to 50%, then 25% of adequate cardiac output (ELSO guidance 2025).

Failure Criteria: Step Back Up

• Falling MAP, rising lactate or falling mixed venous saturation during a trial.
• Worsening LV function, falling pulse pressure or new pulmonary edema on echo or chest X-ray.
• SpO₂ falling as FdO₂ or sweep is reduced.

Removal and Post-Removal Care

• The surgical or ECMO team does the decannulation. Large-bore cannulas come out surgically (ELSO VA guideline).
• Check hemostasis, distal pulses and limb perfusion after removal, and continue monitoring per team protocol.
• After decannulation, ELSO recommends a vessel ultrasound to check for thrombosis (ELSO VA guideline).

Before You Move

1. Confirm console battery and backup power for the planned transport time, per the manufacturer and your program.
2. Confirm gas supply and cylinder duration for the full trip.
3. Secure every line: drainage, return, ventilator, monitoring and infusions. Tape or dress cannula sites.
4. Carry the spare equipment your program requires, including clamps and backup supplies.
5. Confirm that a trained ECMO team member or trained RN travels with the patient.
6. Brief the receiving team on mode, flows, sweep, anticoagulation and recent alarms.

If You Are Not the Device Specialist

• Watch: flow, drainage pressure, SpO₂, MAP and limb perfusion.
• Never touch: pump speed, sweep, FdO₂, or clamps, unless the ECMO team has ordered it.
• Call: the ECMO team at the first sign of flow change, bleeding or limb change.
• Arrest: start CPR per your local ECLS protocol and keep the circuit intact.
• ECPR candidates: note the time of arrest, the time CPR started and the ETCO₂ during CPR. Report all three to the receiving ECPR team. ELSO example criteria use these numbers: low-flow time under 60 minutes, ETCO₂ above 10 mmHg.

During Transport

• Hold the console at the set flow. Position the circuit so tubing is not kinked or stretched.
• Recheck cannula sites, limb perfusion and lines after every move, bump or position change.
• Expect alarms during movement. Stop. Assess the patient, then the circuit.

Air Medical and Altitude

Altitude changes the gas volumes in the lungs and in the circuit. How you respond is program-specific. Before departure, follow your air medical program's ECMO altitude plan, agreed with the ECMO team.

Handoff

• Mode, cannula sites and flow.
• Sweep, FdO₂, ventilator settings and latest gases.
• Anticoagulation agent, target, and recent bleeding or transfusion.
• Recent alarms, complications and limb checks.
• Goals of care and the weaning or escalation plan.

Pediatric and Neonatal

• VA flow: ELSO pediatric cardiac failure guidance aims for a cardiac index of 2.5–3 L/min/m². That is about 100–150 mL/kg/min in infants and 70–100 mL/kg/min in larger children.
• Shunt physiology: single-ventricle physiology with a systemic-to-pulmonary shunt may need higher flow. In neonates, that is about 150–200 mL/kg/min (ELSO pediatric guidance).
• Scope: this page does not cover pediatric or neonatal respiratory ECMO. For those, use the specialist center and ELSO guidance.
• Pediatric drug doses are weight-based. See weight-based dosing, and shock in children for the pediatric approach to cardiogenic shock.

Pregnancy and Peripartum

• Unique indications: peripartum cardiomyopathy, amniotic fluid embolism and eclampsia syndromes (ELSO 2025 pregnancy guideline).
• Gas goals: pH above 7.3, PaCO₂ 30–40 mmHg, PaO₂ above 70 mmHg.
• Heparin: it does not cross the placenta. Pause circuit heparin for anyone suspected of being in labor or bleeding.
• Cardiac arrest: in an experienced center, cannulate during or right after resuscitative hysterotomy. CPR continues throughout.

Accidental Hypothermia

• Indication: hypothermic cardiac arrest. ECLS is considered mainly when core temperature is below 30°C and HOPE-estimated survival is at least 10% (ELSO guidance 2025). Temperature alone does not decide eligibility.
• Rewarming: up to 5°C per hour, until 30°C or return of circulation. Keep the venous-to-arterial temperature gradient at 4°C or less (ELSO guidance 2025).
• Cannulation: for emergency access, femoral-femoral VA with a distal perfusion cannula is preferred. Do not delay for CT.

Other

Age is not, on its own, an absolute contraindication to VA ECMO (ELSO VA guideline). Weigh prognostic scores and local criteria with the ECMO team.

Systematic Walk-Through

1. Indication: VV for lungs or VA for heart and lungs?
2. Mode and cannulas: where are they, and which flow is set?
3. Settings: flow, sweep, FdO₂, ventilator and MAP target.
4. Anticoagulation: agent, target and latest results.
5. Complications: limb, bleeding, hemolysis, neurologic and LV status.
6. Today's goal: wean, adjust, mobilize or escalate.

Pearls

• On VV ECMO, the usual reasons SaO₂ stays low despite high flow are recirculation and high native cardiac output (ELSO VV guideline).
• On VA ECMO, pulse pressure is your bedside sign of native LV contraction.
• Anti-Xa can read falsely low when plasma free hemoglobin runs high.
• Protect the lungs during VV ECMO: the circuit does the gas exchange.
• For a femoral arterial cannula, distal perfusion is the first line of protection.