Relative bradycardia in patients with traumatic hypotension

Tachycardia is considered a physiologic response to traumatic hypotension. The inability of the heart to respond to shock with tachycardia has been described as paradoxical bradycardia or relative bradycardia. The incidence and clinical significance of this condition in major trauma is not known. The objective of this study was to examine the incidence and prognostic significance of tachycardia and relative bradycardia in patients with traumatic hypotension. Relative bradycardia is defined as a systolic pressure < or = 90 mm Hg and a pulse rate < or = 90 beats per minute.

This is a retrospective study conducted at a large Level I academic trauma center during a 4-year period. Seventeen demographic and injury severity factors were analyzed for their possible role in tachycardic or bradycardic response in hypotensive patients. Incidence and mortality were derived for each subpopulation. Bivariate analysis of the association of incidence and mortality with each risk factor was performed. Factors with p values < 0.2 were included in stepwise logistic regression analyses that identified significant risk factors and derived adjusted relative mortality risks between tachycardic and bradycardic hypotensive patients.

Excluding transfers and patients dead on arrival, 10,833 major trauma patients were seen during the study period. Seven hundred fifty patients (6.9%) had systolic blood pressure < or = 90 mm Hg; 533 patients had tachycardia (overall incidence of 4.9%, or 71.1% of hypotensive patients), and 217 patients had bradycardia (overall incidence of 2.0%, or 28.9% of hypotensive patients). The overall crude mortality was 29.2% among tachycardia patients and 21.7% among bradycardia patients (crude relative risk = 1.34; 95% confidence interval = 1.00-1.81; p = 0.047). The adjusted relative mortality risk between the two groups was 1.23 (95% confidence interval = 0.84-1.73; p = 0.284). Multivariate analysis showed that patients with relative bradycardia in the subgroups with Injury Severity Scores > or = 16, chest Abbreviated Injury Scale scores > or = 3, or abdominal Abbreviated Injury Scale scores > or = 3 had significantly better survival than patients with similar injuries presenting with tachycardia.

Relative bradycardia in hypotensive trauma patients is a common hemodynamic finding. Mortality among tachycardic patients was more predictable than among bradycardic patients using commonly used demographic and injury indicators. The presence of relative bradycardia in some subgroups of patients with severe injuries seems to be associated with better prognosis than the presence of tachycardia.