Published May 20 in the
NEJM to coincide with the ATS meeting is the (latest) Guerin et al study of Prone Positioning in ARDS. The editorialist
was impressed. He thinks that we should start proning patients similar to those in the study. Indeed, the study results are
impressive: a 16.8% absolute reduction in mortality
between the study groups with a corresponding P-value of less than 0.001. But before we switch our tastes from sunny
side up to over easy (or in some cases, over hard - referred to as
the "turn of death" in ICU vernacular) we should consider some general principles as
well as about a decade of other studies of prone positioning in ARDS.
First, a general principle:
regression to the mean. Few, if
any, therapies in critical care (or in medicine in general) confer a mortality
benefit this large. I refer the reader (again) to our study of delta inflation which tabulated over 30 critical care trials in the top 5
medical journals over 10 years and showed that few critical care trials show mortality
deltas (absolute mortality differences) greater than 10%. Almost
all those that do are later refuted.
Indeed it was our conclusion that searching for deltas greater than or
equal to 10% is akin to a fool's errand, so unlikely is the probability of
finding such a difference. Jimmy T.
Sylvester, my attending at JHH in late 2001 had already recognized this. When the now infamous sentinel trail of intensive insulin therapy (IIT) was published, we discussed it at our ICU
pre-rounds lecture and he said something like "Either these data are
faked, or this is revolutionary." We
now know that there was no revolution (although many ICUs continue to practice as if there had been one). He
could have just as easily said that this is an anomaly that will regress to the
mean, that there is inherent bias in this study, or that "trials stopped early for benefit...."
