Lateral positioning for regional analgesia during labour.

Sir,—We were interested to read the editorial by Peek and Firmin1 arguing for the greater use of extracorporeal membrane oxygenation (ECMO) in the management of severe acute lung injury. Their results in Leicester seem impressive (although apparently unpublished elsewhere) and the authors issue a challenge to other units to match their 34% hospital survival rate in a similar group of patients. Unfortunately, however, they do not give enough information to allow this. Values are given for the mean Murray score2 and 2 2 O O I a / P F ratio in their group of 50, but more is needed if this category of patients is to be defined accurately and reproducibly. While a mean 2 2 O O I a / P F ratio of 8.7 provides an approximate indication of the problems with oxygen transfer in these patients, the picture is incomplete. First, it would be helpful to know how long the problems persisted at this level before extracorporeal support was started; was it one or more hours or was the mean calculated from the single worst value for each patient and so based in each case on a single blood-gas result? Second, apart from the Murray score which includes positive end-expiratory pressure (PEEP) as one component, we are given little clue as to mean airway pressure at this time, despite the fact that this is accepted as being a major determinant of arterial oxygenation.3 As long ago as the 1970s the importance of at least some reference to airway pressure was recognized and the American ECMO study entry criteria reflected this by referring to specific levels of PEEP together with defined requirements for