Evaluation of a continuous noninvasive blood pressure monitor in obstetric patients undergoing spinal anesthesia

Abstract

A noninvasive blood pressure monitor (Finapres) that continuously displays the arterial waveform using the Penňaz methodology has recently been introduced into clinical practice. We compared this device with an automated oscillometric blood pressure monitor (Dinamap 1846SX) in 20 patients during spinal anesthesia for nonemergency cesarean section according to a procedure suggested by the Association for the Advancement of Medical Instrumentation. After administration of the spinal anesthetic, the Finapres monitor produced systolic, mean, and diastolic pressure measurements greater than those of the Dinamap monitor (6.6±12.5, 3.3±10.4, and 7.2±9.8 mm Hg, respectively). In most patients, the Finapres measurements were similar to those determined by the Dinamap; however, in 4 patients, mean systolic differences were greater than 20 mm Hg. These patients did not differ from the others in age, height, weight, or baseline blood pressure, and the pressure values recorded by the Finapres monitor were substantially higher than those measured by auscultation in the labor room. In 30% of the patients, the offset between Dinamap and Finapres blood pressure measurements changed markedly over the course of the surgical procedure. The Finapres monitor occasionally stopped working and had to be restarted. In 1 patient (not included in this analysis), the Dinamap monitor was unable to determine the blood pressure due to patient shivering; this did not appear to interfere with the Finapres. We conclude that the Finapres monitor does not consistently provide blood pressure information equivalent to that of the Dinamap in obstetric patients undergoing spinal anesthesia. When the Finapres monitor is used, pressure measurements should be verified periodically by using an auscultatory or oscillometric blood pressure methodology to rule out the presence of large differences, particularly in systolic pressure. The extreme systolic blood pressure discrepancies noted in 20% of the patients studied warrant further evaluation.