Are automated blood pressure measurements accurate in trauma patients?

Automated blood pressure (BP) determinations by oscillometry are reported to be as accurate as invasive monitoring for systolic pressures as low as 80 mm Hg. Automated BP devices are widely used by prehospital providers and in hospital operating rooms, emergency departments, and intensive care units, although the accuracy of automated BP has not been demonstrated in trauma patients. We hypothesized that automated BP is less accurate than manual BP in trauma patients. The purpose of this study was to determine the accuracy of automated BP versus manual BP in trauma patients.

A retrospective review of patients who met trauma activation criteria admitted to a Level I trauma center over a 30-month period was conducted. Patients were included if both manual BP and automated BP were measured within 5 minutes of admission. Additional data collected included Injury Severity Score, base deficit, and emergency department resuscitation volume. Statistical analysis was performed using paired t test, chi2, and linear regression analysis. Significance was attributed to a value of p < 0.05.

From January 2000 through June 2002, 388 patients met inclusion criteria. Patients were grouped by manual BP levels: group 1, BP < or = 90 mm Hg (n = 92); group 2, BP 91-110 mm Hg (n = 119); and group 3, BP > or = 110 mm Hg (n = 177). The mean automated BP measurements were significantly higher than the manual measurements in groups 1 and 2 (26 and 16 mm Hg, respectively; p < 0.001). Of the 92 patients with manual BP < or = 90, 45 (49%) had automated BP > or = 100. The base deficit (-5, -3, and -2 for groups 1, 2, and 3, respectively; p < 0.01), Injury Severity Score (30, 25, and 18; p < 0.01), and volume of resuscitative fluid and blood (p < 0.001) all decreased with higher BP group.

Injury severity, degree of acidosis, and resuscitation volume were more accurately reflected by manual BP. Automated BP determinations were consistently higher than manual BP, particularly in hypotensive patients. Automated BP devices should not be used for field or hospital triage decisions. Manual BP determinations should be used until systolic blood pressure is consistently > or = 110 mm Hg.