Part II — VV ECMO · Chapter 7
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Evidence search date: 6 September 2026. Two source documents held in the project library were read in full for this chapter: the 2024 Perfusion review of mechanical ventilation during ECMO, and the 2022 Intensive Care Medicine summary of anticoagulation management. Both are cited directly.
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The circuit is running. What is set, what is stopped, what is started, and what is checked — in the first minutes, the first hours, and the first day?
There is a specific reason this chapter is not an administrative appendix to Chapter 6.
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Evidence — the first three days are the ones that count
In a pooled individual patient data analysis of earlier studies of mechanical ventilation during ECMO for ARDS, totalling 545 patients, driving pressure during the first three days of ECMO was the sole independent risk factor for mortality (Serpa Neto A, et al. Intensive Care Med 2016, as reported in Szuldrzynski K, et al. Perfusion 2024).
Separately, a retrospective analysis across three high-volume ECMO centres found higher PEEP during the first days of ECMO associated with reduced mortality (Schmidt M, et al. Crit Care Med 2015, as reported in the same review).
Certainty: moderate. Observational and pooled-observational data, vulnerable to confounding by severity — a sicker lung tolerates less. But the signal is consistent, and it is specific to the early period.
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The implication is uncomfortable and useful: the ventilator settings chosen in the first hour of ECMO may matter more than most of what follows. This chapter is organised around that.
The physiological reasoning for each of these is in Chapter 6 and is not repeated here.
| Action | Setting | Why |
|---|---|---|
| Establish flow | Increase to the target, or to maximum sustainable flow — chatter and erratic flow define the ceiling | Chapter 6. Effective flow relative to cardiac output sets arterial saturation |
| FdO₂ | 1.0 | Standard for emergent VV initiation; weaned later |
| Sweep gas | Deliberately low — commonly about half the blood flow | To avoid abrupt CO₂ correction. See the Danger below |
| Temperature | Set the heat exchanger to normothermia unless hypothermia is intended | A circuit outside the body is a large heat-exchange surface; patients cool fast, and shivering raises VO₂ (Chapter 2) |
| Anticoagulation | Continue the infusion started around cannulation, to an early target | See Starting Anticoagulation below |
| Blood gases | Arterial, pre-oxygenator and post-oxygenator | Establishes the three-point baseline every later interpretation depends on (Chapters 2 and 6) |
| Echo and radiograph | Confirm cannula position; screen for complications | Chapter 5. The distal cannula is radiolucent, so the radiograph is not the answer on its own |
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Danger — the two things that go wrong in the first ten minutes
Abrupt CO₂ correction. The membrane can normalise a PaCO₂ of 100 mmHg within minutes; cerebral vasoconstriction and a rapid CSF pH shift follow. Correct over roughly 4–8 hours (Chapter 6). This is what the low starting sweep is for. Resist the urge to fix the first blood gas.
Hypotension. VV ECMO is haemodynamically neutral by construction — the same volume is drained and returned to the venous compartment. So hypotension at initiation is not the circuit doing something to the circulation. It has other causes, and they need naming rather than treating reflexively with flow.
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| Cause | Mechanism | Response |
|---|---|---|
| Dilution by the prime | An adult circuit prime is roughly 500–700 mL (Chapter 3), delivered as a bolus of non-oxygen-carrying fluid | Expect a fall in haemoglobin and in platelets. Anticipate it rather than discovering it |
| Sedation and neuromuscular blockade | Given at or around cannulation; removes sympathetic drive | Vasopressor, titrated — not fluid by reflex |
| Blood–surface contact | Inflammatory activation on first exposure to the circuit | Usually transient; supportive |
| Unmasked hypovolaemia | Drainage reveals a volume state that positive-pressure ventilation was concealing | Judicious volume — with the warning below |
| Tamponade, pneumothorax, bleeding | Procedural complications of cannulation | Echo immediately. Chapter 5 |
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Pitfall — the fluid the patient spends the next week losing
The reflex at initiation is to give volume: the pressure is low, the circuit chatters, and fluid fixes both in the moment. Chapter 6 gave the counter-argument — higher-than-necessary flow requires greater volume expansion, worsening extravascular lung water and complicating later diuresis and sedation reduction (Shekar K, et al. J Thorac Dis 2020).
The de-resuscitation problem of day five is created on day zero. Use vasopressor for vasoplegia, volume for hypovolaemia, and be able to say which one you are treating.
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