SYSTEMIC VASCULAR-RESISTANCE INDEX DETERMINED BY THORACIC ELECTRICAL BIOIMPEDANCE PREDICTS THE RISK FOR MATERNAL HYPOTENSION DURING REGIONAL ANESTHESIA FOR CESAREAN DELIVERY

OBJECTIVE: Our purpose was to evaluate the predictive value of the bas eline systemic vascular resistance index for the development of matern al hypotension during regional anesthesia for cesarean delivery. STUDY DESIGN: Patients receiving a standardized spinal or epidural anesthet ic for nonemergency cesarean delivery were studied prospectively. Hemo dynamic data were obtained noninvasively with an NCCOM-3 cardiac outpu t monitor (Borned Medical Manufacturing, Irvine, Calif.), which uses t horacic electrical bioimpedance to estimate stroke volume and cardiac output. Measurements obtained were indexed to body surface area. The s ystemic vascular resistance index was calculated from mean arterial pr essure and thoracic electrical bioimpedance-derived cardiac index. Hem odynamic data obtained were analyzed to identify statistically signifi cant predictors of maternal hypotension. RESULTS: Maternal hypotension occurred in 24 of 42 (57%) patients studied. The incidence of hypoten sion did not differ between the types of anesthesia: spinal 17 of 27 ( 62%) versus epidural 7 of 15 (47%, p = 0.48). The mean interval to the onset of hypotension was 12.2 minutes (SD 2.2 minutes, range 2 to 24 minutes). Mean (SD) baseline maternal systolic blood pressure was high er in patients who had hypotension (145 torr [4]) than those who did n ot (129 torr [4], p = 0.01). The mean (SD) baseline systemic vascular resistance index was higher in patients who had hypotension (633 [SD 3 6] dyne . cm . sec(-5)/m(2)) than those who did not (454 [SD 29] dyne . cm . sec(-5)/m(2); p = 0.001). With receiver-operator characteristic curves, a baseline systemic vascular resistance index of 500 had a se nsitivity of 83%, a specificity of 78%, a positive predictive value of 83%, and a negative predictive value of 78% for maternal hypotension (odds ratio 17.5, 95% confidence interval 3.1 to 109.4). A baseline sy stolic blood pressure of 140 torr had a sensitivity and specificity of 42% and 72%, respectively (odds ratio 1.9, 95% confidence interval 0. 4 to 8.8). CONCLUSIONS: Baseline systemic vascular resistance index ob tained by noninvasive cardiac output monitoring with thoracic electric al bioimpedance and systolic blood pressure are useful to predict the risk for maternal hypotension with regional anesthesia. Patients with increased baseline systemic vascular resistance index or systolic bloo d pressure are at increased risk for hypotension.