Time poor: rushing decreases the accuracy and reliability of blood pressure measurement technique in pregnancy

Abstract

Background: In pregnancy, absolute blood pressure (BP) limits define preeclampsia. Therefore, BP in pregnancy should be measured accurately and in accordance with accepted guidelines. Accuracy of BP readings determined by rate of cuff deflation was analyzed. This study also investigated the compliance of clinical staff at Royal Prince Alfred Hospital, Australia, to guidelines for BP measurement.

Methods: The study was an observational trial of 98 normotensive antenatal or recently postnatal patients. Two BP readings were taken, each with fast (>5 mm Hg/sec) and slow (<or=2 mm Hg/sec) descent of mercury and compared by Bland-Altman analysis. Also, BP techniques used by junior doctors, specialist obstetricians, and midwives were compared using a 9-point scale.

Findings: Australian national guidelines recommend slow descent of mercury. Fast descent underestimated the systolic BP by 9 mm Hg (95% confidence interval [CI], -23 to +5 mm Hg) (p < 0.001). Fast descent measured the diastolic BP within 2 mm Hg (95% CI, -10 to +14 mm Hg) (not different, p = 0.151). Accuracy of fast cuff deflation was 28% for systolic BP and 50% for diastolic BP for <5 mm Hg, and respectively, 64% and 68% for <10 mm Hg, 84% and 80% for <15 mm Hg and 91% and 87% for <20 mm Hg. Compliance with guidelines was greatest for specialists and midwives (p = 0.001) and their most commonly missed feature (76% to 100%) was slow cuff deflation.

Interpretation: Rapid cuff deflation underestimates the systolic BP compared to accepted guidelines (<or=2 mm Hg/sec). Medical and midwifery staff may not follow accepted guidelines for BP measurement, particularly with regard to rate of cuff deflation. Potential misdiagnosis and under-treatment of patients with hypertension may compromise pregnancy outcomes.