Authors Keywords: blood pressure determination, instrumentation, diagnostic errors, Bland–Altman analysis, ultrasound, natural frequency, damping ratio Abstract

Background: We investigated whether invasive and non-invasive blood pressure (NIBP) measurement technique differences were clinically important.

Methods: We compared invasive and two non-invasive measurement techniques (standard automated oscillometry and a mercury sphygmomanometer with flow detection using Doppler ultrasound). Bland–Altman statistical analysis was employed, and clinically important differences were determined using error grid analysis. Natural frequencies (fn) and damping ratios (ζ) were calculated from monitor photographs of fast flush tests.

Results: Bland–Altman analysis of 195 systolic and 194 mean pressure measurements revealed small mean differences but wide limits of agreement (LOA), which precluded the interchangeability of measurement techniques. However, error grid analysis revealed that 85% and 15% of paired measurements were in the “no risk” and “low risk” zones, respectively. Natural frequencies and damping ratios (mean, range) were 16.5 Hz (4.8–33.0) and 0.38 (0.03–0.74), respectively. Natural frequencies and damping ratios were poorly predictive of error zone location.

Conclusions: This study identified statistically significant differences between invasive and NIBP measurement techniques. Despite the non-interchangeability of techniques, error grid analysis indicated that no patients in our sample would likely have received inappropriate therapy resulting from flawed intra-arterial measurements. In ensuring the accuracy of invasive pressure measurements, fast flush test determination of natural frequencies and damping ratios were unhelpful, mirroring other researchers’ findings. Our findings reinforce recommendations that invasive pressures be checked against a reliable NIBP device. A systolic pressure difference > 15 mmHg should prompt an invasive system review. We propose ultrasound-guided systolic pressure measurement as a reliable method for this purpose.

Author Biographies JF Coetzee, Stellenbosch University

Department of Anaesthesiology and Critical Care, Faculty of Medicine and Health Sciences, Stellenbosch University, South Africa

R Blomerus, Stellenbosch University

Department of Anaesthesiology and Critical Care, Faculty of Medicine and Health Sciences, Stellenbosch University, South Africa

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