Effect of normal and preeclamptic pregnancies on the oxyhemoglobin dissociation curve.

Hemoglobin affinity for oxygen in whole blood of ten normal nonpregnant women, ten normal pregnant women at first trimester, ten normal pregnant women at second trimester, 24 normal pregnant women at or near term, and 14 pregnant women with preeclampsia at or near term was studied. The mean P-50 values for normal nonpregnant women, normal pregnant women in first trimester, second trimester, and at or near term were 26.7 +/- 0.11 mmHg, 27.8 +/- 0.08 mmHg, 28.8 +/- 0.17 mmHg, and 30.4 +/- 0.20 mmHg, respectively. The mean P-50 of pregnant women with preeclampsia at or near term was 25.1 +/- 0.38 mmHg. It is concluded that in normal pregnant women there was a significant shift of P-50 to the right compared with the normal nonpregnant women (P less than 0.01), and the extent of this shift to the right is directly related to the duration of the pregnancy. In addition, preeclamptic parturients showed a significant shift of P-50 to the left when compared with normal pregnant women at or near term (P less than 0.001).

Neonatal effect of prolonged anesthetic induction for cesarean section.

The relationship of induction-to-delivery and uterine incision-to-delivery intervals to neonatal outcome was studied in 105 parturient women undergoing cesarean section. Sixty patients received general anesthesia and 55 were given spinal anesthesia. During general anesthesia, induction-to-delivery intervals of more than 8 minutes and uterine incision-to-delivery intervals of more than 3 minutes were associated with significantly more instances of neonatal acidosis (umbilical artery pH 7.31 versus 7.22) and a greater incidence of low 1-min Apgar scores (4% versus 73%). In the groups receiving spinal anesthesia, prolongation of uterine incision-to-delivery interval by more than 3 minutes was found to be the only important factor influencing fetal outcome, as determined by an increased acidosis (umbilical artery pH 7.30 versus 7.18) and by depressed Apgar scores (0% versus 62%).

Epidural anesthesia for cesarean section in diabetic parturients: maternal and neonatal acid-base status and bupivacaine concentration.

Acid-base status and blood levels of bupivacaine were determined in 16 diabetic parturients and their infants after epidural anesthesia for cesarean section. The newborn infants were divided into two groups based on umbilical artery pH at birth. Group A consisted of 10 infants who had a pH of less than 7.2 and group B consisted of six infants with a pH of greater than 7.2. Neonatal acidosis was related to both the severity of maternal diabetes and the presence of maternal hypotension after epidural anesthesia. In addition, the half-life to bupivacaine was prolonged in acidotic infants. The placental transfer of bupivacaine, as judged by umbilical vein/maternal vein ratios, was significantly greater in acidotic infants.

Epidural anesthesia for cesarean section: a comparison of bupivacaine, chloroprocaine, and etidocaine.

The authors studied three groups of patients undergoing elective cesarean section during lumbar epidural anesthesia with bupivacaine, 0.75 per cent (15 patients), chloroprocaine, 3 per cent (15 patients) or etidocaine, 1 per cent (ten patients). Excellent sensory and motor block were obtained with chloroprocaine and bupivacaine; sensory anesthesia was inadequate with etidocaine in most patients. Onset of anesthesia, induction--delivery interval, and stay in the recovery room were all longer with bupivacaine when compared with chloroprocaine. Fetal outcomes, as determined by Apgar scores, acid--base status and neurobehavioral testing, were equally good in all groups. At delivery, fetal/maternal concentration ratio of bupivacaine was 0.31 and that of etidocaine, 0.25. The umbilical artery--umbilical vein blood concentration difference for etidocaine was significantly higher than that for bupivacaine. Excellent clinical results were obtained using either bupivacaine, 0.75 per cent, alone, or chloroprocaine, 3 per cent- for induction and maintenance of anesthesia, supplemented with bupivacaine, 0.25 per cent, before removal of the catheter.

Effects of maternal position on epidural anesthesia for cesarean section, acid-base status, and bupivacaine concentrations at delivery.

In 25 patients excellent clinical anesthesia for elective cesarean section was obtained with lumbar epidural block using an average dose of bupivacaine of 130 mg (18 ml of 0.75 per cent solution). Supplemental drugs were not needed. All infants had normal Apgar scores at delivery. Ten patients were kept in a 35--40 degree semi-sitting supine position during induction, while 15 patients were similarly semi-sitting but turned into the left lateral position. Maternal position did not affect the adequacy of the anesthesia or the clinical condition of the infants, but did alter acid-base state and bupivacaine concentrations in the infants. At delivery, the infants whose mothers had been supine had significantly lower pH values in umbilical cord blood than those whose mothers had been in the lateral position. Also, high concentrations of bupivacaine were found in the umbilical vein blood of infants whose mothers were supine.

Acid-base status in diabetic mothers and their infants following general or spinal anesthesia for cesarean section.

Acid-base status was studied in 30 diabetic mothers and their infants and in 30 healthy mothers and their babies after general or spinal anesthesia for cesarean section. A normal acid-base state was found for the diabetic subjects following general or spinal anesthesia. However, the infants of diabetic mothers given spinal anesthesia had an average pH of 7.20 and a base excess value of -5.67 mEq/l in umbilical-artery blood at delivery. These values were significantly lower than those observed in the infants of the other groups, where the average pH was between 7.28 and 7.30 and the base excess between -1.87 mEq/l and 1.00 mEq/l. These findings were significantly related to maternal diabetes and maternal hypotension.

Acidosis, local anesthetics, and the newborn.

Four newborn infants were studied following maternal epidural block with lidocaine or mepivacaine. Each of these neonates, born with a pH of 7.23 or below in the umbilical vein blood, showed an elevated fetal-to-maternal concentration ratio, a possible manifestation of ion trapping of a weak base.

Newborn blood levels of lidocaine and mepivacaine in the first postnatal day following maternal epidural anesthesia.

Distribution and elimination of lidocaine and mepivacaine were studies in 114 subjects after obstetric epidural anesthesia, Epinephrine significantly lowered the concentrations of lidocaine in the mothers' circulations by about 33 per cent, and the concentrations of mepivacaine by about 22 per cent. It also significantly altered their concentrations in the newborns' circulations at delivery and in the first 4 hours after birth. More mepivacaine than lidocaine crossed the placenta. The mepivacaine concentration in the cord blood was 36 to 47 per cent higher, and the mean fetal to maternal ratio for mepivacaine without epinephrine was 0.64, in contrast to 0.52 for the equivalent lidocaine group. Of importance was the long persistance of either drug in the newborns' circulation. Detectable levels of lidocaine and mepivacaine were present until 8 and 24 hours after birth, respectively. Pharmacokinetic models revealed that the long-term rate of disappearance of lidocaine was approximately three times as fast as that of mepivacaine. Computed half-times averaged 3 hours for lidocaine and 9 hours for mepivacaine.

A new method of fetal heart rate monitoring.

A new method of continuous fetal heart rate monitoring, employing for cardiotachometry the fetal electrocardiogram obtained from electrodes placed on the maternal abdomen, was evaluated over a period of 26 months at the Lying-in Division of the Boston Hospital for Women. A total of 2460 hours of intrapartum monitoring were analyzed. This "noninvasive" method of fetal ECG-based monitoring was shown to be as accurate as the direct scalp electrode method and more reliable than indirect ultrasound. Useful fetal monitoring, from very early labor up to the time of delivery, was possible in 91% of 507 patients, using maternal skin electrodes alone. Beat-to-beat variability determinations, possibly of significance in evaluating fetoplacental function in the antepartum period, were precise and without the artifactuality of ultrasonic or phonocardiographic methods.