HEMODYNAMIC-EFFECTS OF SUBARACHNOID FENTANYL IN LABORING PARTURIENTS

Background and Objectives. The subarachnoid administration of fentanyl to laboring parturients may decrease maternal blood pressure. The hem odynamic effects of subarachnoid fentanyl (SAF) in laboring women was studied by impedance cardiography. Methods. Following a 500 mL fluid b olus, 15 healthy women received 25 mu g of SAF for labor analgesia by a combined spinal-epidural technique. Maternal systolic, mean, and dia stolic blood pressure, heart rate, cardiac index, stroke index, and en d-diastolic index were measured before SAF administration (baseline) a nd every 5 minutes for 30 minutes after administration. Prelabor blood pressure values were obtained from the patient's last office visit. D ata were analyzed by analysis of variance at P < .05. Results. Followi ng SAF administration, pain scores decreased and pruritus scores incre ased (based on 100-mm visual analog scales). Maternal systolic, diasto lic, and mean blood pressures, heart rate, and cardiac index decreased significantly by 12, 18, 17, 12, and 14%, respectively, as compared w ith baseline values, with no significant change in stroke index. Cardi ac preload (end-diastolic index) decreased by 10% 25 minutes following SAF administration but otherwise did not significantly change. Compar ed with prelabor blood pressure values, the diastolic pressure decreas ed significantly only 9% at 20 minutes and the mean arterial pressure decreased only 7 and 8% at 20 and 25 minutes, respectively; the systol ic pressure did not change. In 53% of patients, at least one hypotensi ve episode (systolic pressure of less than or equal to 100 mm Hg or a > 30% decrease in systolic pressure) occurred, following SAF administr ation. However, only two of these episodes (systolic pressures of 93 a nd 96 mm Hg) lasted longer than 1 minute, and these were easily treate d with intravenous ephedrine. Conclusions. Vasodilation due to sympath ectomy causes a decrease in preload (end-diastolic index) and in strok e index and an increase in heart rate. Since the end-diastolic index a nd stroke index remained relatively stable and the heart rate decrease d, it was concluded that the observed decrease in blood pressure was n ot due to vasodilation.