How the two ECMO configurations work, who each is for, contraindications, and the physiology a junior must understand before touching the circuit.
At the bedside
Timed steps- 1
Name the failing organ
0 minLungs only with adequate heart function → VV ECMO (gas exchange support). Heart failing (± lungs) → VA ECMO (circulatory + gas exchange support). Do a bedside echo before deciding: severe LV/RV failure on VV may need VA or a hybrid configuration.
- 2
Optimise conventional care first
Before ECMOSevere ARDS: lung-protective ventilation (VT 6 mL/kg PBW, Pplat ≤30, driving pressure ≤15), PEEP titration, neuromuscular blockade, and prone positioning ≥12–16 h/day unless contraindicated. Shock: fluids if responsive, noradrenaline, inotropes, revascularisation, treat arrhythmia.
- 3
Check VV indications (ELSO 2021)
DecideAny of: PaO₂/FiO₂ <80 mmHg after optimal care including a prone trial; hypercapnic failure with pH <7.25 despite RR 35/min and Pplat ≤30; bridge to lung transplant. EOLIA entry (used by many centres): P/F <50 for >3 h, P/F <80 for >6 h, or pH <7.25 with PaCO₂ ≥60 mmHg for >6 h despite optimisation.
- 4
Check VA indications
DecideRefractory cardiogenic shock (SCAI D–E) despite vasopressors/inotropes, with a plan (recovery, durable VAD, transplant or decision): fulminant myocarditis, massive PE with arrest/shock, post-cardiotomy shock, cardiotoxic poisoning (e.g. calcium-channel blocker, aluminium phosphide), refractory VT/VF storm, primary graft failure; and ECPR in selected refractory arrests.
- 5
Screen contraindications
DecideAbsolute: no exit strategy (irreversible disease, not a transplant/VAD candidate). Relative: intracranial haemorrhage or major brain injury, contraindication to anticoagulation, >7 days of high-pressure ventilation (Pplat >30 and FiO₂ >0.9), advanced age or frailty, end-stage malignancy, severe immunosuppression. For VA: significant aortic regurgitation and aortic dissection.
- 6
Call the ECMO centre early
ActDiscuss with the regional ECMO team while the patient is still transportable; calculate RESP (VV) or SAVE (VA) to frame the discussion, not to decide alone.
VV vs VA ECMO at a glance
| Feature | VV ECMO | VA ECMO |
|---|---|---|
| Supports | Gas exchange only | Circulation + gas exchange |
| Typical cannulae | Femoral drainage (23–25 Fr) + internal jugular return (17–21 Fr), or a single dual-lumen bicaval cannula via right IJ | Peripheral: femoral venous drainage (21–25 Fr) + femoral arterial return (15–19 Fr) with a distal perfusion cannula (6–8 Fr); central (post-cardiotomy): RA + aorta |
| Typical blood flow | 60–80 mL/kg/min (adult often 4–6 L/min) | Enough for cardiac index ~2.2–2.5 L/min/m² (adult often 3–5 L/min); use the lowest flow that maintains perfusion |
| Oxygenation target | SaO₂ 85–92% often acceptable (mixing with native venous return) | Normal saturations; check the right radial ABG for differential hypoxia |
| Main physiology problems | Recirculation; hypoxaemia with high cardiac output | LV distension, differential (north–south) hypoxia, limb ischaemia |
| Native heart must | Pump the oxygenated blood through the lungs | Eject at least partly (aortic valve opening) to avoid LV stasis |
Cannula sizes are typical adult ranges; the ECMO team chooses size from ultrasound vessel diameter and target flow.
Common indications
| Mode | Conditions |
|---|---|
| VV | ARDS (viral, bacterial, aspiration), severe asthma, pulmonary haemorrhage/DAH, inhalational injury, chest trauma/contusion, large bronchopleural fistula, bridge to or after lung transplant |
| VA | Selected AMI cardiogenic shock, fulminant myocarditis, massive PE, post-cardiotomy shock, decompensated cardiomyopathy as bridge, refractory arrhythmia, cardiotoxic poisoning, peripartum cardiomyopathy, hypothermic arrest, ECPR |
Calculators for this topic
PaO₂/FiO₂ ratio
Oxygenation ratio with ARDS severity bands (Berlin; PEEP ≥ 5 cmH₂O).
Driving pressure
Plateau pressure − PEEP (volume control, passive patient).
Predicted (ideal) body weight
ARDSNet predicted body weight from height and sex. Use for tidal volume, not for most drug doses.
Tidal volume from predicted body weight
Lung-protective tidal volume (usually 6 mL/kg PBW; range 4-8).
Oxygenation index
OI = FiO₂(%) × mean airway pressure ÷ PaO₂.
References
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Choosing ECMO mode
Step 1 of ~3
Decision pathway from refractory organ failure to VV, VA or no ECMO.
Decision: Realistic exit strategy (recovery, transplant, VAD, or bridge-to-decision)?
Based on Tonna JE, Abrams D, Brodie D, et al; Lorusso R, Shekar K, MacLaren G, et al; Naidu SS, Baran DA, Jentzer JC, et al. Educational use; follow local protocol.
Pathophysiology
Oxygen delivery on ECMO. Circuit O₂ supply = blood flow × (post- minus pre-oxygenator O₂ content). ELSO suggests a VV circuit able to supply at least 240 mL/m²/min of oxygen (rest requirement ~120 mL/m²/min; normal systemic DO₂ ~600 mL/m²/min). Because the circuit only oxygenates the fraction of venous return it drains, SaO₂ on VV depends on the ratio of ECMO flow to native cardiac output — a hyperdynamic septic patient can be hypoxaemic despite a perfectly working oxygenator.
VA physiology. Retrograde femoral arterial flow raises LV afterload. A weak LV may fail to open the aortic valve → LV distension, rising LA pressure, pulmonary oedema and stasis thrombus. If the heart recovers while the lungs are poor, deoxygenated blood ejected by the LV perfuses the coronaries and upper body (differential or north–south hypoxia).
Evidence
Respiratory ECMO
- CESAR (2009, UK): referral to a single ECMO centre (75% actually received ECMO) reduced death or severe disability at 6 months (37% vs 53%). It tested referral to an expert centre, not ECMO itself.
- EOLIA (2018): early VV ECMO vs conventional lung-protective ventilation in very severe ARDS. 60-day mortality 35% vs 46% (RR 0.76; p=0.09), with 28% crossover to rescue ECMO in controls.
- ELSO VV guideline (2021): P/F <80 after optimal care including a prone trial, or pH <7.25 with RR 35 and Pplat ≤30; rest ventilator settings at minimum Pplat ≤25 cmH₂O and PEEP ≥10.
Cardiac ECMO
- ECLS-SHOCK (2023): routine VA ECMO in AMI cardiogenic shock with planned revascularisation did not reduce 30-day mortality (47.8% vs 49.0%) and increased moderate–severe bleeding and peripheral vascular complications.
- ECMO-CS (2023): immediate VA ECMO in rapidly deteriorating or severe CS did not improve the composite outcome vs early conservative therapy with rescue ECMO allowed.
- VA ECMO in AMI-CS is therefore for selected patients rather than routine use (ESC 2023 ACS guideline).
- SCAI SHOCK stages (A–E) give a shared language for escalation: C classic, D deteriorating, E extremis.
Controversies
- Age cut-off: no threshold is defined; risk rises steadily with age.
- Timing: 'early' ECMO (EOLIA criteria) vs rescue — many Indian centres can only offer rescue because of cost.
- Awake ECMO and extubation on VV ECMO: attractive, but evidence is from cohorts.
- VA ECMO in AMI-CS after ECLS-SHOCK: limited to selected patients, arrest and mechanical complications.
- Hybrid configurations (V-AV, V-VA) for mixed failure need expert teams.
🇮🇳 India notes
- ECMO is available mainly in tertiary private and some government institutes in large cities; most district and medical-college ICUs must refer. Build a referral relationship with your nearest ECMO centre before you need it.
- Cost is largely out-of-pocket; insurance and government-scheme coverage for ECMO varies — discuss realistic costs and duration (VV runs often last 1–3 weeks) with families early.
- Indian indications with a strong case for VA ECMO include aluminium phosphide cardiotoxicity, myocarditis, peripartum cardiomyopathy and massive PE; for VV, severe influenza/COVID-19 ARDS, leptospirosis pulmonary haemorrhage and scrub typhus ARDS.
- Leptospirosis pulmonary haemorrhage may need heparin-sparing strategies — a decision for the ECMO centre.
References
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