All About extra corporeal membrane oxygenation
What is ECMO?
ECMO or extra corporeal membrane oxygenation is a type of prolonged mechanical cardiopulmonary support that is usually delivered in the intensive care unit. ECMO is performed by clinicians with training and experience in its initiation, maintenance, and discontinuation.
How does it function?
During ECMO, blood is drained from the native vascular system, circulated outside the body by a mechanical pump and re-infused into the circulation. While outside the body, the blood passes through an oxygenator and heat exchanger. In the oxygenator, hemoglobin becomes fully saturated with oxygen, while carbon dioxide (CO2) is removed. Oxygenation is determined by flow rate, whereas CO2 elimination can be controlled by adjusting the rate of countercurrent gas flow through the oxygenator.
What are the types of ECMO?
ECMO can be venovenous (VV) or venoarterial (VA):
· In VV ECMO, blood is extracted from the vena cava or right atrium and returned to the right atrium. It provides respiratory support, but the patient is dependent upon his/her own hemodynamics.
· In VA ECMO, blood is extracted from the right atrium and returned to the arterial system, bypassing the heart and lungs. It provides both respiratory and hemodynamic support. The additional benefit of hemodynamic support comes with additional risks.
VV ECMO is used in patients with respiratory failure, while VA ECMO is used in patients with cardiac failure.
Which patients are suitable candidates for ECMO?
ECMO is indicated for patients with severe, but potentially reversible, acute respiratory or cardiac failure that is unresponsive to conventional management.
What is the procedure?
Once it has been determined that ECMO will be initiated, the patient is anticoagulated. Cannulae are then inserted and the patient is connected to the ECMO circuit. The blood flow is increased until respiratory and hemodynamic parameters are satisfactory. Once the initial respiratory and hemodynamic goals have been achieved, blood flow is maintained, ventilator support is minimized, and vasoactive drugs are decreased to minimal levels.
The patient's readiness for weaning from ECMO should be evaluated frequently. Prior to discontinuing ECMO permanently, one or more trials should be done during which the patient is off ECMO. Such trials provide an opportunity to the clinician to determine whether conventional supportive care is sufficient for the patient.
What are the complications?
Bleeding is the most common complication (30-40%) of ECMO. Thromboembolism and cannula complications are rare (<5%).
What are the contraindications?
The only absolute contraindication to ECMO is a pre-existing condition, which is incompatible with recovery (severe neurologic injury, end stage malignancy). Relative contraindications include uncontrollable bleeding and very poor prognosis from the primary condition. Results in respiratory failure are better when ECMO is instituted within 7 days of intubation.
Have studies been conducted in cardiac arrest?
VA ECMO can provide acute support in cardiogenic shock or cardiac arrest in adults. Assuming that the brain function is normal or only minimally impaired.
ECMO is provided until the patient recovers or receives a long-term ventricular assist device as a bridge to cardiac transplantation. Observational studies and case series have reported survival rates of 20 to 50 percent among patients who received ECMO for cardiac arrest, severe cardiogenic shock, or failure to wean from cardiopulmonary bypass following cardiac surgery.
In two observational studies, ECMO performed for cardiac arrest was associated with increased survival compared to conventional cardiopulmonary resuscitation (Crit Care Med. 2011;39(1):1-7 and Lancet 2008;372(9638):554-61).
In a systematic review of adults with refractory out of hospital cardiac arrest, survival was 22% in the 833 patients who received ECMO during resuscitation and half of these had good neurological recovery (Resuscitation 2016;101:12-20).
Which is the largest study in cardiac arrest?
A systematic review and meta-analysis of cohort studies comparing mortality in patients treated with and without ECLS support in the setting of refractory cardiac arrest and cardiogenic shock complicating acute myocardial infarction was conducted by Ouweneel et al (Intensive Care Med. 2016 Dec;42(12):1922-1934).
Purpose: Veno-arterial extracorporeal life support (ECLS) is increasingly used in patients during cardiac arrest and cardiogenic shock, to support both cardiac and pulmonary function. We performed a systematic review and meta-analysis of cohort studies comparing mortality in patients treated with and without ECLS support in the setting of refractory cardiac arrest and cardiogenic shock complicating acute myocardial infarction.
Methods: We systematically searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials and the publisher subset of PubMed updated to December 2015. Thirteen studies were included of which nine included cardiac arrest patients (n = 3098) and four included patients with cardiogenic shock after acute myocardial infarction (n = 235). Data were pooled by a Mantel-Haenzel random effects model and heterogeneity was examined by the I (2) statistic.
Results: In cardiac arrest, the use of ECLS was associated with an absolute increase of 30 days survival of 13 % compared with patients in which ECLS was not used (95 % CI 6-20 %; p < 0.001; number needed to treat (NNT) 7.7) and a higher rate of favourable neurological outcome at 30 days (absolute risk difference 14 %; 95 % CI 7-20 %; p < 0.0001; NNT 7.1). Propensity matched analysis, including 5 studies and 438 patients (219 in both groups), showed similar results. In cardiogenic shock, ECLS showed a 33 % higher 30-day survival compared with IABP (95 % CI, 14-52 %; p < 0.001; NNT 13) but no difference when compared with TandemHeart/Impella (-3 %; 95 % CI -21 to 14 %; p = 0.70; NNH 33).
Conclusions: In cardiac arrest, the use of ECLS was associated with an increased survival rate as well as an increase in favourable neurological outcome. In the setting of cardiogenic shock there was an increased survival with ECLS compared with IABP.