Relative bradycardia in hypotensive trauma patients: a reappraisal.
BACKGROUND
The inability to mount tachycardia (T) after trauma-related hypotension is labeled relative bradycardia (RB). The objective of this study was to examine RB incidence and prognosis in a large cohort of patients.


METHODS
The Los Angeles County Trauma System database, consisting of five Level I and eight Level II trauma centers, was queried for all adult (>14 years) hypotensive (systolic blood pressure [SBP] <or=90) trauma patients admitted between 1998 and 2005. RB was defined as SBP <or=90 with heart rate (HR) <or=90, and T was defined as SBP <or=90 with HR >90. Demographics, injury severity, mechanism, and outcomes were compared between the RB and T groups. Multivariate logistic regression was used to determine significant risk factors for mortality.


RESULTS
Of 130,906 adult trauma patients, 7,123 (5.4%) were hypotensive. After excluding patients dead on arrival and those with missing data, 3,727 patients were identified. RB was observed in 1,630 (44%) of patients, whereas T was observed in 2,097 patients (56%). RB patients were older (39.8 +/- 18.6 years vs. 35.3 +/- 17.0 years, p < 0.0001), less severely injured (injury severity score 18.0 +/- 14.2 vs. 20.5 +/- 15.3, p < 0.0001), more hypotensive (SBP 64.7 +/- 31.6 vs. 76.2 +/- 15.1, p < 0.0001), and had less abdominal trauma (abdomen abbreviated injury score 2.9 +/- 1.2 vs. 3.2 +/- 1.1, p < 0.0001) than their tachycardic counterparts. In addition, the mortality was significantly higher in the RB group compared with the T group (30.1% vs. 22.6%, p < 0.0001). Overall, RB had a higher mortality among all subgroups except older patients (age >or=55; 27.7% vs. 35.2%, p = 0.045) and patients with a higher Glasgow coma scale score (>or=12; 5.3% vs. 11.2%, p < 0.0001). Logistic regression identified RB as an independent risk factor for mortality (odds ratio, 1.60; 95% confidence interval, 1.33-1.94; p < 0.0001). When RB was further divided into two groups, observed mortality for HR <60 and HR 60 to 90 was 62.4% and 9.7%, respectively.


CONCLUSIONS
RB was common in hypotensive adult trauma patients; overall, it was associated with increased mortality. Patients older than 55 years and with a higher Glasgow coma scale score demonstrated decreased mortality with RB. When RB was further divided, a HR between 60 and 90 demonstrated a significant lower mortality compared with a HR <60 and to T.