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When the lungs or heart fail so badly that a ventilator is not enough, blood can be pumped out of the body, passed through an artificial lung that adds oxygen and removes carbon dioxide, and returned. It buys time for the organs to recover. It used to mean lying still and sedated for weeks; increasingly, patients are awake and some can walk while supported.
The two modes, and why the difference matters
Extracorporeal membrane oxygenation (ECMO) drains venous blood, passes it through a pump and a membrane oxygenator, and returns it to the body. Where it returns the blood defines the mode, and the mode defines what the support is actually doing.
| Venovenous (VV) | Venoarterial (VA) | |
|---|---|---|
| Blood returns to | The venous system, before the right heart | The arterial system, bypassing the heart |
| Supports | Lungs only — gas exchange | Heart and lungs — gas exchange and circulation |
| Typical indication | Severe acute respiratory distress syndrome; bridge to lung transplantation | Refractory cardiogenic shock; failure to wean from bypass; extracorporeal cardiopulmonary resuscitation |
| Cardiac output | Entirely the patient's own | Substantially or wholly the circuit's |
| Haemodynamic effect of physiotherapy | Patient's own circulation responds normally | Circuit flow is fixed; the patient cannot increase output in the usual way |
Cannulation configuration then determines mobility. Femoral cannulation limits hip flexion and in practice restricts the patient to bed. Upper-body configurations — a dual-lumen cannula in the internal jugular vein, or an internal jugular and subclavian arrangement — free the legs and are what make sitting, standing and walking possible.
The evidence for the therapy
CESAR found that referral to an ECMO centre improved survival without severe disability in severe adult respiratory failure, though the trial randomised referral rather than the therapy itself.1 EOLIA randomised patients with very severe acute respiratory distress syndrome to early ECMO or conventional management with crossover permitted; the primary mortality endpoint did not reach statistical significance, but a high crossover rate and subsequent analyses have left most intensive care communities treating it as supportive of ECMO in selected patients.2 The Extracorporeal Life Support Organization guideline is the practical reference for venovenous management.3
Complications and phenomena to understand
- Bleeding and thrombosis. Patients are anticoagulated against a thrombogenic circuit. Bleeding is the commonest complication, cannula sites are a frequent source, and intracranial haemorrhage is the most feared.
- Cannula displacement or decannulation — catastrophic and immediate. This is the single dominant safety consideration in any physiotherapy intervention.
- Recirculation (venovenous). Oxygenated blood returning to the circuit rather than the patient, causing falling saturations despite adequate flows. Position changes can provoke or relieve it.
- Differential hypoxia in peripheral venoarterial support — sometimes called north–south or harlequin syndrome. Oxygenated blood returns retrogradely up the aorta from a femoral cannula while a recovering heart ejects poorly oxygenated blood from failing lungs into the aortic root. The upper body, including the brain and coronary arteries, can be hypoxic while the legs are well oxygenated. Monitoring is from the right upper limb for this reason.
- Limb ischaemia distal to an arterial cannula.
- Haemolysis, infection and circuit failure.
- Intensive-care-acquired weakness and post-intensive-care syndrome — near-universal after a prolonged run, and the reason mobilisation matters. See ICU-Acquired Weakness.
Mobilising a patient on extracorporeal support
Mobilisation on ECMO is feasible and can be done safely, but only with a trained multidisciplinary team, an explicit plan, and a dedicated person whose only job is the cannulae and circuit. It is never attempted opportunistically or single-handed, and the first session for any patient is planned in advance with intensive care and perfusion.
Retrospective cohort and systematic review evidence supports the safety and feasibility of physiotherapy and early mobilisation in selected patients on extracorporeal support, including ambulation in those with upper-body cannulation, with low rates of adverse events in experienced centres.4,5 Established safety-criteria frameworks for mobilising mechanically ventilated patients provide the structure for the decision.6
Before the session
- Confirm cannulation site and configuration, and the permitted hip flexion.
- Confirm circuit flows, anticoagulation status and platelet count with the treating team.
- Agree roles explicitly — airway, cannulae, lines, mobility, and who calls a stop.
- Rehearse the stop plan and have the chair or bed positioned before the patient moves.
During
- Move slowly and in stages; most adverse events occur during transitions.
- Watch flows, circuit line chatter, saturations and the patient simultaneously — which is why one person cannot do this.
- Falling flows with line chatter usually means underfilling or cannula position; stop and reposition rather than persisting.
- In venoarterial support, remember the patient cannot mount a normal cardiac output response to exertion.
Beyond mobility
Respiratory physiotherapy continues on its usual indications — secretion retention, volume loss — with the caveat that in venovenous support the lungs are often deliberately rested at low ventilator settings, and recruitment is not the physiotherapy goal it might otherwise be. Prone positioning is used with ECMO in some centres and is a whole-team procedure with cannula security as the priority.
Awake and ambulatory support
The clearest example of the change in practice is the patient bridged to lung transplantation on extracorporeal support who is awake, extubated, eating and walking on a treadmill while supported. This approach preserves muscle mass and transplant candidacy in a group who would previously have deconditioned to the point of being delisted. It requires upper-body cannulation, a cooperative patient and a centre organised around it — but it has redefined what rehabilitation on ECMO means. See Lung Transplantation.
Role of the physiotherapist
Know the mode and the cannulation before anything else — they determine both what the support is doing and whether the patient can move. Treat cannula security as the organising principle of every intervention. Contribute to the team decision about mobilisation rather than requesting permission for a technique. Recognise differential hypoxia and recirculation as circuit problems rather than physiotherapy problems. And keep the long view: survivors of a prolonged run face months of rehabilitation, and what is preserved during the run determines where that starts.
Evidence summary
Framing. Extracorporeal support has moved from a rescue therapy delivered to deeply sedated, paralysed patients to one in which awake, extubated and ambulatory management is achievable in selected cases.4 That change is largely a rehabilitation change, and physiotherapy is central to it — but it is also the highest-risk mobilisation undertaken in critical care, and the safety margin depends on team structure rather than individual skill.
Evidence — the therapyCESAR supported referral to an ECMO centre for severe adult respiratory failure.1 EOLIA did not meet its primary endpoint but is widely interpreted, with its crossover pattern and post-hoc analyses, as supporting early ECMO in the most severe acute respiratory distress syndrome.2 ELSO guidance codifies venovenous management.3
Evidence — physiotherapyAbrams and colleagues reported the feasibility of early mobilisation including ambulation on extracorporeal support in a retrospective cohort, and systematic review has since found physiotherapy to be safe with low adverse-event rates in experienced centres.4,5 Expert consensus safety criteria for mobilising mechanically ventilated adults provide the decision framework, extended in practice by cannula-specific considerations.6
Clinical reasoningThree facts drive most decisions: the mode determines whether the patient has a functioning circulation of their own; the cannulation site determines whether the legs are available; and right-sided upper-limb monitoring is required in peripheral venoarterial support because differential hypoxia can leave the brain hypoxic while peripheral saturations look reassuring.
Evidence gapsAll physiotherapy evidence in this population is observational and drawn from high-volume specialist centres, so it describes what is achievable there rather than what is safe everywhere. There are no randomised data on mobilisation during extracorporeal support, no established dose, and no validated criteria specific to ECMO as distinct from mechanical ventilation. Long-term functional outcomes in survivors are described but not well predicted.
References & evidence base
- Peek GJ, Mugford M, Tiruvoipati R, et al. Efficacy and economic assessment of conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure (CESAR): a multicentre randomised controlled trial. Lancet 2009;374(9698):1351–1363.
- Combes A, Hajage D, Capellier G, et al. Extracorporeal membrane oxygenation for severe acute respiratory distress syndrome (EOLIA). N Engl J Med 2018;378(21):1965–1975.
- Tonna JE, Abrams D, Brodie D, et al. Management of adult patients supported with venovenous extracorporeal membrane oxygenation (VV ECMO): guideline from the Extracorporeal Life Support Organization (ELSO). ASAIO J 2021;67(6):601–610.
- Abrams D, Javidfar J, Farrand E, et al. Early mobilization of patients receiving extracorporeal membrane oxygenation: a retrospective cohort study. Crit Care 2014;18(1):R38.
- Ferreira DDC, Marcolino MAZ, Macagnan FE, Plentz RDM, Kessler A. Safety and potential benefits of physical therapy in adult patients on extracorporeal membrane oxygenation support: a systematic review. Rev Bras Ter Intensiva 2019;31(2):227–239.
- Hodgson CL, Stiller K, Needham DM, et al. Expert consensus and recommendations on safety criteria for active mobilization of mechanically ventilated critically ill adults. Crit Care 2014;18(6):658.
References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.
Physiotherapy around major chest, cardiac and upper abdominal procedures — from open surgery to bronchoscopic, catheter-based and bedside treatments — aims to reduce chest complications and shorten the return to normal function.
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