J. S. Naulty

Effect of diluent volume on analgesia produced by epidural fentanyl

Injection of opioids into the epidural space produces postoperative analgesia by acting on receptors in lamina 11, IV, and V of the substantia gelatinosa (1). Morphine, due to its low lipid solubility produces numerous side effects when injected into the epidural space; most notably delayed respiratory depression (2). Fentanyl, a highly lipid soluble narcotic agonist, has a more rapid onset of action and a significantly lower incidence of side effects than those of morphine. In a dose-response study in patients after cesarean delivery, 50 pg of epidural fentanyl was found to provide maximal analgesia with minimal incidence of side effects (3). The effect of varying the volume of injectate on the onset, duration, and incidence of side effects produced by 50 pg of fentanyl has not been reported. This standard dose of fentanyl diluted in larger volumes could increase the surface area of drug exposure and thus augment the number of opioid receptors affected. Conversely, diluting the opioid in greater volume may reduce the concentration gradient between the central nervous system and epidural space and thereby decrease both the rapidity of onset and duration of analgesia. Fentanyl is being given epidurally in several different dilutions. To determine the most effective diluent volume, a double-blind, randomized study was undertaken with varying volumes of normal saIine solution to dilute a single 50 pg dose of epidural fentanyl.

Comparison of the maternal and neonatal effects of halothane, enflurane, and isoflurane for cesarean delivery.

: The maternal and neonatal effects of 50% O2-50% N2O alone and 50% O2-50% N2O combined with 0.5% halothane, 1.0% enflurane, or 0.75% isoflurane were studied in 42 healthy parturients undergoing general anesthesia for elective primary or repeat cesarean delivery at term. All patients received thiopental and succinylcholine for induction and were intubated and ventilated with a tidal volume of 10 ml/kg at a rate of 10 breaths/min. Two of 12 (17%) patients given O2-N2O alone had recall; none who received a potent inhalation agent had any recall. Blood loss was similar in all four groups. There were no significant differences between groups in induction-to-delivery and uterine incision-to-delivery intervals, the frequency of Apgar scores less than 7 at 1 and 5 min, maternal and fetal blood-gas tensions, acid-base balance, lactate values, and early neonatal neurobehavioral scores at 2-4 h. It is concluded that analgesic concentrations of halothane, enflurane, and isoflurane can be safely added to 50% O2-50% N2O to prevent maternal awareness during general anesthesia for cesarean delivery while maintaining normal maternal and neonatal conditions.

Epidural butorphanol-bupivacaine for analgesia during labor and delivery.

A double-blind, randomized, dose-response study of a combination of 0.25% bupivacaine combined with 0, 1, 2, or 3 mg of butorphanol was studied in 40 laboring parturients. The optimal dose of butorphanol combined with 8.5 to 10 ml 0.25% bupivacaine was 2 mg; with 2 mg, the duration of analgesia was significantly greater and the time to onset of analgesia significantly shorter than when no butorphanol was added, and the amount of bupivacaine could be reduced 50%. Adverse fetal effects were not observed except that of a low amplitude sinusoidal fetal heart rate pattern with doses of 3 mg butorphanol. All neonatal observations were normal. It is concluded that epidural butorphanol can be a useful and safe adjunct to bupivacaine used for epidural analgesia during labor.

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

: Acid-base status and Apgar scores were evaluated in 10 rigidly controlled insulin-dependent diabetic mothers and 10 healthy nondiabetic control women having spinal anesthesia for cesarean section. Dextrose-free intravenous solutions were used for volume expansion before induction of anesthesia, and hypotension was prevented in all cases by prompt treatment with ephedrine. There were no significant differences in the acid-base values between the diabetic and nondiabetic mothers and the infants of the diabetic and control group. Apgar scores were also similar in the two groups. If maternal diabetes is well controlled, if dextrose-containing solutions are not used for maternal intravascular volume expansion before delivery, and if maternal hypotension is avoided, spinal anesthesia can be used safely for diabetic mothers having cesarean section.

The Effect of Epidural Sufentanil on Shivering and Body Temperature in the Parturient

Temperature regulation is primarily controlled by the thermoregulating centers in the hypothalamus (1). Thermoreceptors in the skin and spinal cord provide afferent signals to the thalamus and hypothalamus. In addition, central thermoreceptors are sensitive to local core temperature. Stimulation of receptors in the anterior hypothalamus initiates anti-increase (in temperature) responses (vasodilation, sweating), whereas stimulation of the posterior hypothalamic receptors initiates the anti-decrease responses of vasoconstriction, epinephrine release, and shivering (2). Narcotics alter body temperature in animals (3). Possible mechanisms for this include centrally mediated alteration of thermogenesis (4) and peripheral effects altering the distribution of and rate of change of body heat (5). We have observed in a preliminary report a decrease in body temperature and a reduction in shivering in postpartum patients who received epidural sufentanil after epidural lidocaine anesthesia for cesarean delivery (6). To determine the effect of different doses of epidural sufentanil on body temperature, we undertook a randomized double blind study in patients undergoing cesarean delivery.

Comparison of the Maternal and Neonatal Effects of Halothane, Enflurane, and Isoflurane for Cesarean Delivery

The maternal and neonatal effects of 50% O2-50% N2O alone and 50% O2-50% N2O combined with 0.5% halothane, 1.0% enflurane, or 0.75% isoflurane were studied in 42 healthy parturients undergoing general anesthesia for elective primary or repeat cesarean delivery at term. All patients received thiopental and succinylcholine for induction and were intubated and ventilated with a tidal volume of 10 ml/kg at a rate of 10 breaths/min. Two of 12 (17%) patients given O2-N2O alone had recall; none who received a potent inhalation agent had any recall. Blood loss was similar in all four groups. There were no significant differences between groups in induction-to-delivery and uterine incision-to-delivery intervals, the frequency of Apgar scores <7 at 1 and 5 min, maternal and fetal blood-gas tensions, acid-base balance, lactate values, and early neonatal neurobehavioral scores at 2–4 h. It is concluded that analgesic concentrations of halothane, enflurane, and isoflurane can be safely added to 50% O2-50% N2O to prevent maternal awareness during general anesthesia for cesarean delivery while maintaining normal maternal and neonatal conditions.