Five pregnant ewes and their singleton fetuses were instrumented at 115 to 120 days' gestation (term, 145 days) for heart rate, blood pressure, uterine blood flow, and arterial blood gas sampling. In separate studies, cocaine was given to the ewe or fetus as a 0.5-, 1.0-, or 2.0-mg/kg intravenous bolus, and cardiovascular and arterial blood gas values were obtained for 60 minutes after the injection. The results showed that maternal administration of cocaine produced dose-dependent increases in maternal blood pressure and decreases in uterine blood flow. Uterine vascular resistance increased by 52%, 96%, and 168%, respectively. These responses were accompanied by marked fetal hypoxemia, hypertension, and tachycardia. Direct cocaine administration to the fetus produced smaller increases in fetal heart rate and blood pressure than those observed following maternal cocaine injection, and no significant changes in fetal arterial blood gas values. The conclusions are (1) cocaine alters fetal oxygenation by reducing uterine blood flow and impairing oxygen transfer to the fetus; and (2) fetal cardiovascular changes to maternal administration of cocaine may reflect fetal hypoxemia, increased fetal levels of cocaine or fetal catecholamines, or a combination of these events. ( JAMA 1987;257:957-961)

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=JAMA&articleId=364565&pdfFileName=jama_257_7_027.pdf

Effect of cocaine on uterine blood flow and fetal oxygenation.

Thirty-eight healthy women undergoing elective Caesarean section under spinal anaesthesia at term were allocated randomly to receive boluses of either phenylephrine 100 micrograms or ephedrine 5 mg for maintenance of maternal arterial pressure. The indication for administration of vasopressor was a reduction in systolic pressure to < or = 90% of baseline values. Maternal arterial pressure (BP) and heart rate (HR) were measured every minute by automated oscillometry. Cardiac output (CO) was measured by cross-sectional and Doppler echocardiography before and after preloading with 1500 ml Ringer lactate solution and then every 2 min after administration of bupivacaine. Umbilical artery pulsatility index (PI) was measured using Doppler before and after spinal anaesthesia. The median (range) number of boluses of phenylephrine and ephedrine was similar; 6 (1-10) vs 4 (1-8) respectively. Maternal systolic BP and CO changes were similar in both groups, but the mean [95% CI] maximum percentage change in maternal HR was larger in the phenylephrine group (-28.5 [-24.2, -32.9]%) than in the ephedrine group (-14.4 [-10.6, -18.2]%). As a consequence atropine was required in 11/19 women in the phenylephrine group compared with 2/19 in the ephedrine group (P < 0.01). Mean umbilical artery pH [95% CI] was higher in the phenylephrine group (7.29 [7.28-7.30]) than in the ephedrine group (7.27 [7.25-7.28]). The results of the present study support the use of phenylephrine for maintenance of maternal arterial pressure during spinal anaesthesia for elective Caesarean section.

Randomized trial of bolus phenylephrine or ephedrine for maintenance of arterial pressure during spinal anaesthesia for Caesarean section.

BACKGROUND Because ephedrine infusion (2 mg/min) does not adequately prevent spinal hypotension during cesarean delivery, the authors investigated whether adding phenylephrine would improve its efficacy. METHODS Thirty-nine parturients with American Society of Anesthesiologists physical status I-II who were scheduled for cesarean delivery received a crystalloid preload of 15 ml/kg. Spinal anesthesia was performed using 11 mg hyperbaric bupivacaine, 2.5 microg sufentanil, and 0.1 mg morphine. Maternal heart rate and systolic blood pressure were measured at frequent intervals. A vasopressor infusion was started immediately after spinal injection of either 2 mg/min ephedrine plus 10 microg/min phenylephrine or 2 mg/min ephedrine alone. Treatments were assigned randomly in a double-blind fashion. The infusion rate was adjusted according to systolic blood pressure using a predefined algorithm. Hypotension, defined as systolic blood pressure less than 100 mmHg and less than 80% of baseline, was treated with 6 mg ephedrine bolus doses. RESULTS Hypotension occurred less frequently in the ephedrine-phenylephrine group than in the ephedrine-alone group: 37% versus 75% (P = 0.02). Ephedrine (36+/-16 mg, mean +/- SD) plus 178+/-81 microg phenylephrine was infused in former group, whereas 54+/-18 mg ephedrine was infused in the latter. Median supplemental ephedrine requirements and nausea scores (0-3) were less in the ephedrine-phenylephrine group (0 vs. 12 mg, P = 0.02; and 0 vs. 1.5, P = 0.01, respectively). Umbilical artery pH values were significantly higher in the ephedrine-phenylephrine group than in the group that received ephedrine alone (7.24 vs. 7.19). Apgar scores were similarly good in both groups. CONCLUSION Phenylephrine added to an infusion of ephedrine halved the incidence of hypotension and increased umbilical cord pH.

Phenylephrine added to prophylactic ephedrine infusion during spinal anesthesia for elective cesarean section.

Systemic and uterine responses to α-adrenergic stimulation in pregnant and nonpregnant ewes

URATION of general anesthesia prior to D delivery is an important factor influencing the depression of the infant born by cesarean section. In a study of 173 elective cesarean sections performed under nitrous oxide-succinylcholine anesthesia (with or without thiopental induction) , Finster and Poppers1 found a mean anesthesia duration of 22.7 minutes in neonates with 1-minute Apgar scores of 6 or less as compared to 17.1 minutes in neonates scoring 7 or better.

F. C. Greiss

Papers

Effects of sympathomimetic drugs and angiotensin on the uterine vascular bed.