Marlene Eng

Maternal cardiovascular dynamics VI. Cesarean section under epidural anesthesia without epinephrine

Abstract Hemodynamic measurements were carried out in 13 normal term pregnant women undergoing cesarean section under epidural anesthesia without epinephrine. Only minor alterations in maternal cardiovascular function were encountered. Following the administration of anesthesia, there was a transient decline in blood pressure, but it remained constant throughout the surgical procedure. The maximum rise in cardiac output was found immediately following delivery, but it was only 1.46 L. per minute (25 per cent above control values). No significant heart rate changes occurred, and the stroke volume rose by a maximum of only 19 c.c. (28 per cent above control values) at 10 minutes post partum. This hemodynamic stability has not been achieved previously with other anesthetic techniques.

Respiratory function in pregnant obese women

Lung volumes and other ventilatory variables were measured in 10 women with a mean age of 28 years, a mean height of 163 cm., and weights which were 50 to 140 per cent above the normal. Measurements were made during the last trimester of pregnancy and after the second month postpartum. Mean values of lung volumes in liters during these two time periods were: vital capacity (VC), 3.7 and 3.92; expiratory reserve volume (ERV), 0.79 and 0.94; functional residual capacity (FRC), 2.06 and 2.14; and forced expiratory volume at one second (FEV1) 3.2 and 3.3. Mean blood gas values were as follows: pH, 7.44 during both times; PaCO2, 29.7 and 35 torr; standard bicarbonate, 22 and 28.8 mEq; base excess, -4.2 and 0.03 PaO2 breathing air, 85 and 86 and breathing 100 per cent oxygen, 527 and 515 torr; AaDO2, 162 and 167 torr. We conclude that, with the exception of FRC, pregnant obese women who are 50 to 140 per cent overweight develop respiratory changes similar to those seen in normal-weight gravidas. These findings suggest that obesity of this magnitude does not exaggerate changes in ventilation induced by pregnancy as generally believed. Why in this obese population the decrease in FRC during pregnancy did not occur to the same degree as that seen in normal-weight gravidas cannot be defined from our study. Evidence is presented for a ventilation/perfusion imbalance in obese subjects which is not corrected during pregnancy.

Maternal cardiovascular dynamics: V. Cesarean section under thiopental, nitrous oxide, and succinylcholine anesthesia

Abstract Serial hemodynamic measurements were carried out in 17 normal pregnant women undergoing repeat cesarean section at term under thiopental, nitrous oxide, and succinylcholine anesthesia. The peak cardiac output reached 7 L. per minute (41 per cent over control values) 10 minutes after delivery. A maximum arterial pressure of 131/82 mm. Hg was found just prior to delivery (18 per cent above control values). The peripheral resistance showed little change except for a slight decline post partum. The hemodynamic fluctuations were found to be significantly smaller than those previously reported during cesarean section under subarachnoid block anesthesia and during labor and vaginal delivery under local and caudal anesthesia. From the hemodynamic data presently available, cesarean section under balanced anesthesia should be considered as an alternate method for delivering the infant of the seriously ill pregnant cardiac patient (Classes III and IV).

Effect of pudendal, spinal, and peridural block anesthesia on the second stage of labor☆

Abstract The second stage of labor was studied in 42 patients before and after conduction anesthesia. Intrauterine pressure and superimposed voluntary effort were measured and compared before and after induction of anesthesia. Voluntary effort increased progressively during the second stage in patients receiving pudendal block. Patients having peridural block showed a slight drop in voluntary effort. Patients with spinal block had a mean reduction in voluntary effort after the block. Patients receiving peridural block showed a mean decrease in uterine contraction intensity, but no change was seen in contraction intensity after pudendal or spinal block. Record review of 3,265 primigravid term patients revealed an increased length of the second stage and an increased incidence of forceps deliveries in patients with spinal and peridural anesthesia when compared with pudendal anesthesia.

Experiences with the use of ketamine for parturition. I. Primary anesthetic for vaginal delivery.

Ketamine was used as the sole anesthetic agent for vaginal delivery in 80 women. Complete analgesia occurred in 78, partial analgesia in one, and one had no effects. Administered intravenously immediately before delivery in doses of 12.5 to 25 mg. (0.2 to 0.4 mg./kg.) with a dosage limit of 100 mg., ketamine administration resulted in no significant maternal or newborn complications.

Uterine Blood Flow and Oxygen Uptake during Maternal Hyperventilation in Monkeys at Cesarean Section

The effect of maternal hyperventilation during nitrous oxide and succinylcholine anesthesia was studied in seven pigtailed macaques near term during cesarean section. An average maternal arterial pH of 7.66 and an average carbon dioxide tension of 13 torr were achieved. Uterine blood flow, cardiac output, arterial blood pressure, and blood gases were measured during hyperventilation and control periods immediately before and after hyperventilation. Average uterine blood flow and uterine oxygen consumption remained relatively constant during all three periods. There were a small reduction in cardiac output and a significant increase in total peripheral resistance during hyperventilation. The pH of uterine venous blood rose significantly and in the two cases studied umbilical arterial pH also increased. These observations do not support the contention that maternal hyperventilation results in uterine vasoconstriction, and the criteria used do not suggest untoward effects on the fetus.

Maternal and fetal responses to halothane in pregnant monkeys.

Maternal cardiac output, blood pressure, heart rate, fetal blood pressure, heart rate and respiratory blood gases, and uterine blood flow were measured in six pregnant monkeys during halothane–nitrous oxide and oxygen anesthesia and compared to these same parameters observed during nitrous oxide and oxygen anesthesia. Halothane 1.5% was associated with a decrease in maternal arterial pressure (54%), heart rate (10%), cardiac output (17%), total peripheral resistance (40%), and uterine blood flow (28%). Mean fetal heart rate decreased 18% and mean fetal blood pressure 22%. These changes in fetal hemodynamics were probably related to a direct depression of the fetal cardiovascular system and its usual compensatory mechanism as well as the fetal asphyxia secondary to the decrease in uterine blood flow.

Spinal anesthesia and ephedrine in pregnant monkeys

Abstract A study of the maternal and fetal effects of spinal hypotension and its treatment with ephedrine was made in 6 pregnant monkeys whose activity was controlled with succinylcholine and nitrous oxide. During spinal hypotension, mean maternal arterial blood pressure decreased 54 per cent; cardiac output, 18 per cent; total peripheral resistance, 47 per cent; and uterine blood flow, 30 per cent. Fetal P O2 decreased from a mean of 27.1 ± 6.4 to 15.4 ± 7.8. Fetal pH decreased from a mean of 7.34 ± 0.04 to 7.22 ± 0.05, and fetal P CO2 increased from 41.6 ± 6.1 to 50.9 ± 10.4 mm. Hg. Ephedrine was effective in restoring these changes in the maternal cardiovascular system toward prespinal levels and preventing further deterioration of the fetus.

Maternal acid-base status during cesarean section under thiopental, N2O, and succinylcholine anesthesia

Abstract Maternal acid-base status was evaluated in 17 normal term pregnant women undergoing repeat cesarean section under thiopental, nitrous oxide, and succinylcholine anesthesia. Little change in maternal acid-base status was noted during the surgical procedure. The induction and maintenance of anesthesia for operation prior to delivery resulted in a very mild acidosis (pH 7.42 to 7.37) which was due to a slight increase in arterial carbon dioxide tension and a slight decline in bicarbonate. The dosages of thiopental used (2.5 to 4 mg. per kilogram of body weight) did not affect the fetal outcome. However, it appears that prolonging nitrous oxide-oxygen anesthesia at concentrations of 70 to 30 per cent results in a high incidence of fetal depression (Apgar 5 or less at one minute) at delivery but not fetal acidosis as shown by cord blood evaluation. The 5 minute Apgar score in 13 of the 14 newborns recorded was 7 or above. Balanced anesthesia is safe for cesarean section so long as the time from induction to delivery is not prolonged.

A Comparison of the Effects of the Inhalation of 4% and 8% Fluroxene in the Pregnant Primate

A comparison was made of the effects of inhalation of 4% fluroxene (n = 5) and 8% fluroxene (n = 5) in pregnant monkeys. Measurements of maternal arterial blood pressure, heart rate, cardiac output, total peripheral resistance, uterine blood flow, fetal heart rate and arterial blood pressure, and maternal and fetal blood gas levels were made. Inhalation of 4% fluroxene for 20 minutes produced little change in maternal hemodynamics and was well tolerated by the fetus. Fluroxene 8% inhaled for a similar 20‐minute‐period produced a significant decrease in maternal blood pressure (‐27%), total peripheral resistance (‐32%), and uterine blood flow (‐27%) and lowered the level of maternal fetal exchange.