Hypotension begins at 110 mm Hg: redefining "hypotension" with data

Clinicians routinely refer to hypotension as a systolic blood pressure (SBP) < or =90 mm Hg. However, few data exist to support the rigid adherence to this arbitrary cutoff. We hypothesized that the physiologic hypoperfusion and mortality outcomes classically associated with hypotension were manifest at higher SBPs.

A total of 870,634 patient records from the National Trauma Data Bank with emergency department SBP and mortality data were analyzed. Patients (140,898) with severe head injuries, a Glasgow Coma Score < or =8, and base deficit (BD) <5, or missing data items were excluded from analysis. Admission BD, as a measure of metabolic hypoperfusion, was evaluated in 81,134 patients and mortality was plotted against SBP.

Baseline mortality was <2.5%. However, at 110 mm Hg, the slope of the mortality curve increased such that mortality was 4.8% greater for every 10-mm Hg decrement in SBP. This effect was consistent to a maximum of 26% mortality at a SBP of 60 mm Hg. Hypoperfusion (change in the slope of BD curve) began to increase above baseline of 4.5 at a SBP 118 mm Hg.

Taking the BD and mortality measurements together, this analysis shows that a SBP < or =110 mm Hg is a more clinically relevant definition of hypotension and hypoperfusion than is 90 mm Hg. This analysis will also be useful for developing appropriately powered studies of hemorrhagic shock.