Incremental analysis of diagnostic peritoneal lavage fluid in adult abdominal trauma

It is uncertain how much diagnostic peritoneal lavage (DPL) fluid must be recovered from abdominal trauma patients to avoid falsely low red blood cell (RBC) counts. A study was carried out to investigate this controversy. A convenience sample of adult abdominal trauma patients in a Level 1 university trauma center who were undergoing DPL with 1 L crystalloid was enrolled. Subjects with grossly positive or colorless effluent were excluded. A blinded prospective experimental design was used. Differences were evaluated among RBC counts collected at 200, 400, 600, and 800 mL of returned fluid using repeated-measures analysis of variance. In 11 patients, mean RBC counts collected at 200 and 400 mL were 24,600 (95% confidence interval [CI], 20,700 to 29,100) and 39,700 (95% CI, 33,200 to 47,100) cells/microL. These were substantially lower than the final mean count of 95,800 (95% CI, 80,000 to 115,800), measured at 800 mL (F = 23.7, P < .0001). Mean counts at 600 mL were less than those obtained at 800 mL but were not statistically different (P = .08). Two of the 11 subjects would have been misclassified (as not requiring surgery) had "early" sampling been used. In abdominal trauma patients, the RBC count of DPL fluid regularly increases as more fluid is recovered. It is important to collect >600 mL of effluent to avoid misleading, low RBC counts and misclassification of patients.