ECMO in adults: what is its role?

Abstract

I N this issue of the Journal, Voelckel e t al . 1 report on two cases of blunt thoracic trauma with severe acute respiratory failure (ARF) in which extracorporeal membrane oxygenation (ECMO) was successfully employed. In the first case, a 29 yr old man involved in a motor vehicle accident sustained a haemopneumothorax and severe bilateral pulmonary contusions. Within seven hours post injury, his oxygenation had deteriorated (PaO2=21 mm Hg; FIO 2 1.0) and ECMO was subsequently used for support of oxygenation. In the second case, a 12 yr old boy was hit by a falling tree and sustained a pneumothorax and bilateral pulmonary contusions. His oxygenation subsequently deteriorated and a tracheobronchial disruption was ultimately diagnosed. The patient was immediately placed on ECMO for respiratory support as well as to facilitate repair of the tracheobronchial injury. Both patients made full recoveries and left hospital. The first report of the use o f ECMO for ARF was by Hill in 1972. 2 Since that time, numerous studies and case reports s-8 have been published on its use in patients with severe ARF of various aetiologies including those with trauma related respiratory failure. In these reports, ECMO is variably described using the synonyms Extracorporeal Lung Assist (ECLA or ELA) and /o r Extracorporeal Life Support (ECLS), all of which refer to the same process. The results for ECMO in neonates with ARF have been positive with survival rates as high as 90% in patients with meconium aspiration syndrome. Overall, survival rates in neonates have been approximately 80%. 9 The UK collaborative randomized trial of neonatal ECMO 1~ revealed an overall survival of 59%, but when patients with congenital diaphragmatic hernia (a group with a notoriously poor outcome) were excluded, the overall rate increased to 80% also. Therefore, ECMO has become a standard therapy in neonates with severe ARF. In adults however, results have been variable and much less encouraging. ECMO has been employed primarily for ARF in patients with the Acute Respiratory Distress Syndrome (ARDS). Several published reports 3-s including the NIH-sponsored randomized controlled trial of ECMO ha adults with ARF 11 have failed to demonstrate a benefit in adults. The N I H study demonstrated survival rates of only 10% in both the ECMO and control groups. Of the 90 patients studied, there were six posttraumatic patients, none of whom survived. Although there were various case reports of the successful use of ECMO in adult patients over the ensuing years after the NIH trial, a report in 1986 of the use of ECMO solely for CO s removal (extracorporeal CO s removal or ECCO2R ) revealed promising results (48.8% survival in 43 adults with ARDS) and renewed interest in the use of ECMO for ARF. 12 However, a subsequent randomized trial of ECCO2R demonstrated no survival benefit of this therapy. Is The therapeutic principle of ECMO is to ensure adequate oxygenation by partially or totally replacing the lungs' function in gas exchange thus allowing minimization of mechanical ventilation and its attendant risks of O 2 toxicity as well as baroand volutrauma. This may provide a window to support the lungs' healing process. Generally, it should be remembered that ECMO is an adjunct to oxygenation and ventilation and not a therapy in itself. The ECMO circuit consists of three main components: pumps, oxygenators, and heat exchangers, but also requires cannulae for vascular access, filters, pressure gauges and in-line oxygen saturation monitors as well as personnel for constant monitoring of the patient and system, a detailed protocol, and an experienced team. Blood flow can generally be directed in one of two directions: veno-venous or veno-arterial. Venous blood is withdrawn, O 2 is added and /o r CO s is removed, and then reinfused into the patient. ECMO usually provides approximately 30-50% of the cardiac output but in situations of cardiac failure, veno-arterial access can be employed to bypass a larger percent-