Initial hematocrit in trauma: a paradigm shift?

After severe trauma and hemorrhage, it is generally assumed that the rate of fluid shift from the interstitial space into the vasculature is relatively slow and that initial hematocrit (Hct) does not reflect estimated blood loss. This study challenges that idea and tests the hypothesis that initial Hct correlates with signs of shock and hemorrhage in trauma patients.

Data were retrospectively reviewed from 198 trauma patients requiring emergency surgery at a Level I center from July 2009 to April 2010. Patients were divided into quartiles based on the initial Hct measured within 10 minutes of arrival. Categorical data were compared using χ(2) test or Fisher's exact test, as appropriate. Normally distributed data were compared using Student's t test or analysis of variance. Nonparametric data were compared with a Mann-Whitney U test or Kruskal-Wallis test. Post hoc analysis was conducted using the Bonferroni correction or paired Mann-Whitney U tests.

The study population was 83% male, aged 35 ± 1 years (mean ± SE), with 71% penetrating injuries. Lower initial Hct correlated with hypotension (p < 0.001), acidosis (p = 0.003), altered mental status (p < 0.001), Injury Severity Score (p < 0.001), Revised Trauma Score (p < 0.001), estimated blood loss (p < 0.001), and usage of packed red blood cells (p < 0.001), fresh frozen plasma (p = 0.003), crystalloid (p = 0.021), and vasopressors (p < 0.001).

Admission Hct correlates with signs of shock and hemorrhage in trauma patients requiring emergency surgery because fluid shifts rapidly from the interstitial space into the vasculature. This finding of a rapid Hct change contradicts the current teaching in most trauma textbooks.