Traditional teaching is that we bleed whole blood, and it takes time to pull volume out of the interstitial space to replace it. Therefore, the initial hematocrit should be normal when a fresh, bleeding trauma patient rolls through the doors.
An observation I have made over the years is that this is not necessarily so. A few patients have low initial hemoglobin or hematocrit readings, and they tend to be bleeding briskly from somewhere. A paper to be presented at next week’s AAST meeting in Chicago shows just that.
The authors retrospectively reviewed 198 trauma patients requiring emergency surgery at a Level I trauma center. Patients with lower initial hematocrits tended to have lower systolic blood pressure, lower GCS, lose more blood, and require infusion of more blood products during surgery. They also had a higher ISS and mortality. The biggest jump in these indicators occurred when the Hct dropped below 37.
Bottom line: A low hematocrit on the first blood drawn during trauma resuscitation is more helpful that previously thought. Be sure to check those lab values early, and if the hematocrit value is in the mid-30s or lower, start looking for significant sources of bleeding.
Reference: The initial hematocrit matters in trauma: a paradigm shift? AAST 2011 Annual Meeting, Paper 38.