Hemodynamic effects of subarachnoid fentanyl in laboring parturients

The subarachnoid administration of fentanyl to laboring parturients may decrease maternal blood pressure. The hemodynamic effects of subarachnoid fentanyl (SAF) in laboring women was studied by impedance cardiography.

Following a 500 mL fluid bolus, 15 healthy women received 25 micrograms of SAF for labor analgesia by a combined spinal-epidural technique. Maternal systolic, mean, and diastolic blood pressure, heart rate, cardiac index, stroke index, and end-diastolic index were measured before SAF administration (baseline) and every 5 minutes for 30 minutes after administration. Prelabor blood pressure values were obtained from the patient's last office visit. Data were analyzed by analysis of variance at P < .05.

Following SAF administration, pain scores decreased and pruritus scores increased (based on 100-mm visual analog scales). Maternal systolic, diastolic, and mean blood pressures, heart rate, and cardiac index decreased significantly by 12, 18, 17, 12, and 14%, respectively, as compared with baseline values, with no significant change in stroke index. Cardiac preload (end-diastolic index) decreased by 10% 25 minutes following SAF administration but otherwise did not significantly change. Compared with prelabor blood pressure values, the diastolic pressure decreased significantly only 9% at 20 minutes and the mean arterial pressure decreased only 7 and 8% at 20 and 25 minutes, respectively; the systolic pressure did not change. In 53% of patients, at least one hypotensive episode (systolic pressure of < or = 100 mm Hg or a > 30% decrease in systolic pressure) occurred, following SAF administration. However, only two of these episodes (systolic pressures of 93 and 96 mm Hg) lasted longer than 1 minute, and these were easily treated with intravenous ephedrine.

Vasodilation due to sympathectomy causes a decrease in preload (end-diastolic index) and in stroke index and an increase in heart rate. Since the end-diastolic index and stroke index remained relatively stable and the heart rate decreased, it was concluded that the observed decrease in blood pressure was not due to vasodilation.