Fetal effects of prophylactic ephedrine and maternal hypotension during regional anesthesia for cesarean section.

The purpose of this study was to evaluate the effects of a prophylactic intravenous bolus of ephedrine on the incidence and severity of maternal hypotension and on neonatal outcome. Term healthy parturients (n = 122) scheduled for elective repeat cesarean section under regional anesthesia were studied. Ninety-two women received 10 mg ephedrine as a prophylactic intravenous bolus prior to intrathecal epidural local anesthesia. Thirty parturients who served as controls did not receive prophylactic ephedrine. Maternal blood pressures, Apgar scores, and umbilical cord blood acid-base status were evaluated. Sixty-three of 92 women (69%) who received intravenous prophylactic ephedrine prior to regional anesthesia developed hypotension compared to 21 (70%) controls. The mean (+/- SD) lowest systolic blood pressure was similar in both groups (95.6 +/- 12.9 vs. 96 +/- 8.9 mmHg; P = 0.86). The mean (+/-SD) fetal pH was significantly lower with prophylactic ephedrine than controls (7.24 +/- 0.07 vs. 7.28 +/- 0.05; P = 0.001). The frequency of umbilical artery blood pH < 7.20 was 10.6% for the ephedrine group vs. 3.2% for controls (P = 0.024). Among newborns of hypotensive mothers, the frequency of umbilical artery blood pH < 7.20 was 30.2% and 4.6% for the ephedrine and control groups, respectively (P = 0.018). Intravenous prophylaxis with ephedrine did not significantly decrease the frequency of hypotension in women receiving regional anesthesia and resulted in a greater proportion of umbilical artery blood pH values < 7.20.

Prediction of the severity of meconium aspiration syndrome.

OBJECTIVE: Meconium aspiration syndrome is associated with increased neonatal morbidity and mortality. We sought to determine whether the need for neonatal mechanical ventilation or prolonged ventilation (> or = 3 days) was predictable from antepartum, intrapartum, and immediate neonatal events. STUDY DESIGN: Between 1987 and 1989, 8003 of 43,906 (18%) live infants had meconium-stained amniotic fluid; 82 of these infants had clinical and radiographic evidence of meconium aspiration, and of these 82, 39 (48%) required mechanical ventilation. Predictors of ventilation or prolonged ventilation were determined by means of stepwise logistic regression. RESULTS: Predictors of neonatal ventilation included fetal tachycardia, interval from meconium detection to delivery, low 5-minute Apgar score, respiratory distress necessitating intubation in the delivery suite, and delivery by cesarean section. Sensitivity was 72%, and specificity was 64%; the model was incorrect in 32% of the cases. Predictors of prolonged ventilation were ominous fetal heart rate tracing, umbilical arterial pH < 7.20, birth weight > 90th percentile, nulliparity, and Apgar score > 4 at 1 minute and < or = 6 at 5 minutes. Sensitivity was 67%, and specificity was 91%; prolonged ventilation was incorrectly predicted in 17% of the cases. CONCLUSIONS: Use of these models to determine the need for mechanical ventilation or prolonged ventilatory assistance will enhance identification of infants at risk of severe meconium aspiration and will lead to early transfer to the neonatal intensive care unit for intense observation and management.

Acid-base significance of meconium discovered prior to labor.

Although the significance of meconium in the amniotic fluid diagnosed during labor remains problematic, there is little information regarding the significance of meconium discovered prior to labor. The present study consisted of 40 term pregnancies with meconium found at amniocentesis for lung maturity (n = 7) or elective cesarean section (n = 33) and 40 uncomplicated, control pregnancies with clear amniotic fluid at elective cesarean section. The mean umbilical artery (UA) blood pH was 7.26 in the meconium group and 7.28 in the control group. Overall, the frequency of fetal acidemia (UA pH < 7.20) was 15% (6 of 40) of the infants in the meconium group versus 8% (3 of 40) in the control group (p = 0.24). All nine of these infants had a respiratory acidosis defined as a UA blood pH less than 7.20 with normal bicarbonate and elevated carbon dioxide pressure. Importantly, none of the neonates had metabolic acidemia and all had uncomplicated hospital courses. All of the pregnancies reported were promptly delivered because of meconium and we therefore cannot recommend nonintervention when meconium is diagnosed in the antepartum period. Meconium discovered prior to labor is not necessarily a marker of immediate or chronic fetal compromise.

Pathologic fetal acidemia.

There is no clearly established umbilical artery pH cutoff to be used for defining pathologic fetal acidemia (ie, the threshold associated with major neonatal morbidity or mortality). Classically, a pH cutoff of less than 7.20 has been used. Our goal was to define this pH cutoff more precisely. There were 3506 term newborns (2500 g or greater) with an umbilical artery pH of less than 7.20; these newborns were divided into five pH groups. Eighty-seven (2.5%) had a pH of less than 7.00, 95 (2.7%) a pH of 7.00-7.04, 290 (8.3%) 7.05-7.09, 798 (22.8%) 7.10-7.14, and 2236 (63.8%) 7.15-7.19. Two-thirds (66.7%) of the newborns with an umbilical artery pH less than 7.00 had a metabolic component in their acidemia, compared with 13.7% or less in all other pH groups. Significantly more (P less than .05) newborns in the less-than-7.00 pH group had low (less than 3) 1- and 5-minute Apgar scores compared with the other four pH groups. In addition, neonatal death was significantly more common (P = .03) in newborns with a pH less than 7.00, and seven (50%) of the 14 deaths occurred in this group. The statistically significant pH cutoff for all seizures was less than 7.05 (P = .004), and for unexplained seizures was less than 7.00 (P = .01). Eight (67%) of the 12 unexplained seizures occurred in this latter pH group. Thus, a more realistic pH cutoff for defining pathologic fetal acidemia would appear to be less than 7.00.

Intrapartum asphyxia in pregnancies complicated by intra-amniotic infection.

Intra-amniotic infection has been reported to be associated with intrapartum asphyxia; however, the criteria used to define asphyxia have been imprecise. In the present study of 123 women with intra-amniotic infection and 6769 women without infection, the mean umbilical artery pH was 7.28 in both groups. The frequency of acidemia (umbilical artery pH less than 7.20) was not significantly different between the infection group and controls (15 versus 10%; P = .12). Likewise, there was no significant difference between the groups when a lower umbilical artery pH value (less than 7.15) was used to define acidemia. None of the infants from infected mothers had metabolic acidemia with a pH of less than 7.15 and none had a pH of less than 7.00. Significantly more (P less than .05) infants in the infected group did have low 1-minute (20 versus 5%) and 5-minute (3 versus 1%) Apgar scores of 6 or less, criteria often used to define asphyxia. However, none of the newborns from the infected group had recently proposed criteria for the diagnosis of birth asphyxia (ie, leading to neurologic impairment) such as metabolic acidemia, seizures in the immediate newborn period, and low Apgar scores (3 or less). Birth asphyxia is rarely associated with intra-amniotic infection, and in the absence of other signs of fetal jeopardy such as an ominous fetal heart rate pattern, an immediate cesarean to prevent asphyxia does not appear justified once the diagnosis of chorioamnionitis is made.