2 The procedure
2.1.1 Extracorporeal membrane oxygenation is a supportive therapy for adults with severe acute respiratory failure from a potentially reversible cause. Extracorporeal membrane systems mimic gas exchange in the lungs by eliminating some carbon dioxide from the blood and adding oxygen.
2.1.2 There are many causes of severe acute respiratory failure, including acute respiratory distress syndrome, pneumonia, and chest trauma.
2.1.3 Conventional treatment involves maximum medical support, including mechanical ventilation. Arteriovenous extracorporeal membrane carbon dioxide removal, also known as pumpless extracorporeal lung assist, can also be used to support gas exchange.
2.2.1 Extracorporeal membrane oxygenation for severe acute respiratory failure in adults aims to reduce ventilator-induced lung injuries and improve patient outcomes.
2.2.2 There are two main types of ECMO: venovenous ECMO (for respiratory support) and venoarterial ECMO (for cardiac and mixed cardiac and respiratory support). In venovenous ECMO desaturated blood is withdrawn from the venae cavae and pumped through an oxygenator, where gas exchange of oxygen and carbon dioxide takes place. The oxygenated blood is then returned to the venous system. In venoarterial ECMO, blood is withdrawn via the venous system and returned to the arterial system. In both systems patients are given a continuous infusion of an anticoagulant, usually heparin, to prevent blood clotting in the external system.
Sections 2.3 and 2.4 describe efficacy and safety outcomes from the published literature that the Committee considered as part of the evidence about this procedure. For more detailed information on the evidence, see the overview, available at http://www.nice.org.uk/guidance/index.jsp?action=download&o=56402
2.3.1 A randomised controlled trial (RCT) of 180 patients treated by ECMO or conventional management reported death or severe disability in 37% (33/90) and 53% (46/87; there was no information about 3 patients) of patients respectively at 6-month follow-up (relative risk [RR] 0.69, 95% confidence interval [CI] 0.05 to 0.97).
2.3.2 A non-randomised comparative study of 245 patients treated by ECMO or conventional treatment reported survival to hospital discharge in 55% (34/62) and 61% (absolute figures not stated) of patients respectively (p = not significant). A non-randomised comparative study of 150 patients treated by ECMO or conventional treatment reported survival rates of 53% (17/32) and 71% (84/118) respectively (p = 0.06). All patients in these studies treated by ECMO had more severe disease than controls.
2.3.3 The RCT of 180 patients treated by ECMO or conventional management reported similar levels of overall health status scores in both groups at 6 months (67.9 versus 65.9; measured on a visual analogue scale from 0 to 100, where a higher score indicates a better health status).
2.3.4 The Specialist Advisers listed key efficacy outcomes as successful weaning from ECMO, successful weaning from ventilation, improved survival and quality of life.
2.4.1 The non-randomised comparative study of 245 patients and the case series of 255 patients both reported that 5% of patients (3/62 in the comparative study, no actual figures were given for the case series) developed disseminated intravascular coagulation.
2.4.2 Vessel perforation during cannulation contributed to the deathof 1 patient out of 68 treated by ECMO in the RCT of 180 patients.
2.4.3 Difficulties and/or injuries during cannulation were reported in 8% (5/62) of patients in the non-randomised comparative study of 245 patients; 1 patient required surgical intervention to repair an injury to the carotid artery.
2.4.4 The non-randomised comparative study of 245 patients and case series of 1473 and 255 patients reported rupture of the ECMO tubing system in 5% (3/62), 4% (64/1473) and 3% (actual numbers not stated) of patients respectively. Of the patients in the non‑randomised comparative study, brain death was diagnosed in 1 patient after resuscitation and reinstitution of ECMO.
2.4.5 The Specialist Advisers listed anecdotal adverse events as air embolism, thromboembolic events, sepsis, multi‑organ failure and mechanical failure.