Comparison of non-invasive blood pressure versus radial arterial catheter measurement in an intensive care setting

Introduction

Many critical care patients are haemodynamically unstable and have clinical therapy directed by measurements, such as blood pressure. Surprisingly, there appears a failure to appreciate that indirect devices (non-invasive blood pressure [NIBP]) may be inaccurate in critically ill patients. This is substantiated by several manufacturer's legal disclaimers advising against the use of NIBP devices except in normotensive patients with normal heart rates and rhythms.

Objectives

To evaluate the accuracy of NIBP measurements in the ICU and to investigate sources of error in arterial blood pressure measurements.

Methods

In 47 ICU patients blood pressure was auscultated using a mercury sphygmomanometer and then measured using two NIBP devices (GE Marquette) and Dinamap (Critikon) The arterial line fidelity was validated using a return to flow technique and its harmonic/damping characteristics analysed using a recorded flush test. The non-invasive methods were then compared using standard statistical analysis with the arterial catheter measurements.

Results

The mercury sphygmomanometer was the most accurate when compared with the arterial line. Both automated devices had unacceptable ranges in the intensive care setting with both algorithms markedly overestimating at low blood pressures. Of the 29 waveforms analysed, 62% of the arterial waveforms had inadequate dynamic responses.

Conclusions

The sphygmomanometer gave acceptable readings versus the arterial catheter. Both NIBP algorithms were inaccurate and unreliable in the intensive care setting, with a tendency to over-read at low arterial pressures and under-read at high arterial pressures. Damping characteristics of the arterial catheters are frequently unfavourable.

Figure 1

(abstract P71)

Figure 2

(abstract P71)