Extracorporeal membrane oxygenation for severe acute respiratory failure

Abstract

Extracorporeal membrane oxygenation (ECMO) is a technique for providing life support, in case the natural lungs are failing and are not able to maintain a sufficient oxygenation of the body's organ systems. ECMO technique was an adaptation of conventional cardiopulmonary bypass techniques and introduced into treatment of severe acute respiratory distress syndrome (ARDS) in the 1970s. The initial reports of the use of ECMO in ARDS patients were quite enthusiastic, however, in the following years it became clear that ECMO was only of benefit in newborns with acute respiratory failure. In neonates treated with ECMO, survival rates of 80% could be achieved. In adult patients with ARDS, two large randomized controlled trials (RCTs) published in 1979 and 1994 failed to show an advantage of ECMO over conventional treatment; survival rates were only 10% and 33%, respectively, in the ECMO groups. Since then, ECMO technology as well as conventional treatment of adult ARDS have undergone further improvements. In conventional treatment lung-protective ventilation strategies were introduced and ECMO was made safer by applying heparin-coated equipment, membranes and tubings. Many ECMO centres now use these advanced ECMO technology and report survival rates in excess of 50% in uncontrolled data collections. The question, however, of whether the improved ECMO can really challenge the advanced conventional treatment of adult ARDS is unanswered and will need evaluation by a future RCT.

Figure 1

ARDS patients treated with ECMO in European centres from 1992 to 1998. Data were obtained by a yearly fax survey among the centres. In 1995 the number of centres participating in the survey had almost doubled, as did the number of ECMO therapies. Since 1996 the frequency of ECMO therapies in Europe has been decreasing. Survival rates in ECMO patients have remained constant at above 50% during the past 6 years.

Figure 2

Schematic drawing of a low-flow venovenous ECMO circuit.

Figure 3

Trends in reported survival rates in conventionally (non-ECMO) and ECMO-treated ARDS patients, including data from 51 clinical studies. Reported survival rates in (clear circle) conventionally treated and (filled square) ECMO-treated ARDS patients. The survival rate reported in each study was assigned to the year representing the median of study period or, if the study period was not stated, to the year of report. The data support the view that survival rates in both treatment groups followed a positive trend. Data have been taken from [1,5,8,9,10,12,13,14,15,30,31,39,43,55, 56,63,64,91,92,95,96,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130].

Figure 4

ARDS patients treated with ECMO at the Charité, Virchow Clinic, Berlin. Since 1995/1996 the frequency of ECMO treatment in ARDS patients has been decreasing, although the number of ARDS patients admitted to the centre has remained almost constant.