Abstract:
BACKGROUND: Forearm blood pressures have been suggested as an alternative site to measure blood pressures when the upper arm is unavailable. However there is little evidence utilising clinical populations to support this substitution. OBJECTIVES: To determine agreement between blood pressures measured in the left upper arm and forearm using a singular oscillometric non-invasive device in adult Emergency Department patients. The secondary objective was to explore the relationship of blood pressure differences with age, sex, ethnicity, smoking history and obesity. DESIGN: Single centre comparison study. SETTING: Adult Emergency Department, Tertiary Trauma Centre. PARTICIPANTS: Forty-four participants who met inclusion/exclusion criteria selected sequentially from the Emergency Department arrival board. METHODS: A random assignment of order of measurement for left upper arm and forearm blood pressures was utilised. Participants were eligible if they were aged 18 years or older, had been assigned an Australasian Triage Scale code of 2, 3, 4, or 5, were able to consent, and able to have blood pressures measured on their left arm whilst lying at a 45° angle. The Bland-Altman method of statistical analysis was used, with the level of agreement for clinical acceptability for the systolic, diastolic and mean arterial pressure defined as ±10mmHg. RESULTS: The forearm measure overestimated systolic (mean difference 2.2mmHg, 95% limits of agreement ±19mmHg), diastolic (mean difference 3.4mmHg, 95% limits of agreement ±14.4mmHg), and mean arterial pressures (mean difference 4.1mmHg, 95% limits of agreement ±13.7mmHg). The systolic measure was not significantly different from zero. Evidence of better agreement was found with upper arm/forearm systolic measures below 140mmHg compared to systolic measures above 140mmHg using the Levene's test (p=0.002, F-statistic=11.09). Blood pressure disparity was not associated with participant characteristics. CONCLUSIONS: Forearm measures cannot routinely replace upper arm measures for blood pressure measurement. If the clinical picture requires use of forearm blood pressure, the potential variance from an upper arm measure is ±19mmHg for systolic pressure, although the variability may be close to ±10mmHg if the systolic blood pressure is below 140mmHg.
