PROSPECTIVE CROSSOVER STUDY OF THE EFFECT OF PHLEBOTOMY AND INTRAVENOUS CRYSTALLOID ON HEMATOCRIT

Objective: To compare the changes in hematocrit (Hct) between phleboto mized and nonphlebotomized individuals given IV crystalloid. Methods: A prospective, crossover volunteer study was performed comparing Hct c hanges immediately and 30 minutes after IV crystalloid bolus in 20 hea lthy adults with and without prebolus phlebotomy. In the control porti on, volunteers were given a 15-mL/kg bolus of normal saline over 30 mi nutes with Hct determination before (H1), immediately after (H2), and 30 minutes after (H3) crystalloid infusion. At least 7 days later, the same subjects were phlebotomized 1 unit of blood and then administere d a 15-mL/kg IV bolus of normal saline 30 minutes later. Hcts were obt ained before (H4) and 30 minutes after (H5) phlebotomy (immediately pr ior to crystalloid infusion). Hcts were also obtained immediately afte r (H6) and 30 minutes after (H7) crystalloid infusion. A post-hoc test performance analysis was then performed to determine the Hct drop thr esholds that would yield the maximal sensitivity and specificity for 5 00 mL of blood loss (via phlebotomy) in this population. Results: The Hct (%) drops in the nonphlebotomized individuals receiving IV fluids averaged 4.5 +/- 1.3 immediately and 3.2 +/- 1.3 30 minutes after infu sion. These drops were different (p < 0.05) from the Hct drop in indiv iduals receiving IV fluids after phlebotomy, which averaged 6.6 +/- 1. 5 and 5.7 +/- 1.1, respectively Post-hoc analysis revealed that Hct dr ops of 5.4 immediately, or 4.3 at 30 minutes after infusion, had a sen sitivity of >90% and a specificity of 75% for identification of patien ts in the phlebotomy group. Conclusions: The practice of measuring ser ial Hcts may be helpful to identify trauma patients with occult blood loss. A prospective clinical trial is needed to validate these Hct dro p thresholds (immediate and 30 minutes postinfusion) in crystalloid-re suscitated trauma patients.