Abdominal girth: an unreliable measure of intra-abdominal bleeding.

The measurement of abdominal girth in an attempt to detect intra-abdominal bleeding may be dangerously misleading. It is an inaccurate measure of intra-abdominal collection of fluid. The results show that measurements are heavily biased by the expectations of observers, with the result that a considerable change in girth is likely to be ignored. The error caused by observer bias is much greater than the distension which actually occurs when fluid collects in the abdomen over a short period.