Comparison of arterial tonometry with radial artery catheter measurements of blood pressure in anesthetized patients.

BACKGROUND

Arterial tonometry has been introduced for continuous noninvasive measurement of blood pressure. The accuracy of this method depends on the performance of two components: a piezoelectric crystal array and an oscillometric cuff. This study evaluates overall performance of arterial tonometry in terms of the performance of these two components by comparing it with simultaneous recording of blood pressure from an intraarterial catheter.

METHODS

Seventeen adult patients were studied during general anesthesia. Blood pressure was measured with an intraarterial catheter and with an arterial tonometry system. Analog pressure waveforms were sampled at 100 Hz. Blood pressure measurements obtained by oscillometry were recorded by computer. Comparisons of mean blood pressure on a beat-by-beat basis were made with and without correction for the calibration error introduced by oscillometry.

RESULTS

The difference between pairs of blood pressure determined by arterial tonometry and intraarterial measurement was 1.3 +/- 9.4 mmHg (mean +/- SD, bias +/- precision) with 88,158 pairs of measurements. The difference between blood pressure determined by oscillometry and intraarterial measurement was 2.4 +/- 7.5 mmHg (mean +/- SD) with 401 comparisons. After correcting for calibration error, the difference between the tonometry measurements and intraarterial measurements was -1.0 +/- 5.6 mmHg. Continuous episodes of discrepancy from intraarterial measurements in excess of 10 mmHg and lasting 5-60 s occurred 4.6 +/- 0.8 times per hour with tonometry and 12.6 +/- 1.4 times per hour with oscillometry.

CONCLUSIONS

Discrepancies in blood pressure readings by arterial tonometry versus intraarterial measurement result from both the piezoelectric crystal array and the oscillometry used for calibration. Accuracy for individual measurement is inferior to oscillometry alone. The ability to detect significant changes of blood pressure more rapidly than with oscillometry alone is limited by the accuracy of the piezoelectric crystal component but is enhanced by the reduced interval between measurements.