Barry C. Corke

Spinal anaesthesia for Caesarean section. The influence of hypotension on neonatal outcome.

The effect upon the neonate of a short period of maternal hypotension sustained during the initiation of spinal analgesia for Caesarean section was studied. Babies born to mothers with hypotension were significantly more acidotic than controls although acid‐base levels were still within normal limits. Neuro‐behavioural studies were found to be normal in both groups at 4 and 24 hours. It was concluded that a short period (<2 minutes) of hypotension was not harmful to the neonate.

Reflex apnea from laryngeal chemo-stimulation in the sleeping premature newborn lamb.

Summary: The laryngeal chemoreflex was studied during quiet and REM sleep and wakefulness in premature newborn lambs. The response to reflex stimulation with a 5 sec-water infusion was evaluated during 30 sec, as % change in ventilation, heart rate and blood pressure. Apnea, hypertension and bradoardia were more pronounced during sleep than during walleffilhess, when arousal was not associated with the stimulation. The response was similar during quiet and REM sleep. Arousal, which occurred in 24 and 31% of the tests respectively, resulted in a response comparable to that seen during wakefulness. The respiratory drive was evaluated by measurement of the mean inspiratory flow and was found to be decreased during both sleep states when compared to wakefulness. We propose that during sleep in the newborn period there is a decreased ability to respond to asphyxia possibly due to a functional immaturity of the arterial chemoreceptors. This results in a low incidence of arousal and a delayed termination of the pronounced poststimulus apnea resulting from laryngeal chemoreflex stimulation.Speculation: In the newborn lamb, quiet and REM sleep have been shown to be more vulnerable states than wakefulness to reflex apnea elicited by laryngeal chemoreflex stimulation with water, probably as a reflection of decreased respiratory drive and a failure to arouse. It is possible that reflex apnea during sleep triggered by a variety of mechanisms may play a role in the pathogenesis of Sudden Infant Death Syndrome (SIDS).

Prevention of fetal movement during invasive procedures with pancuronium bromide

The use of fetal intramuscular pancuronium (0.5 mg) to temporarily arrest fetal movement during antenatal intervention in six instances is reported. Successful arrest of movement without adverse side effects was observed. The use of this technique eliminates the need for the excessive and potentially dangerous maternal sedation currently used to minimize fetal movement.

The influence of 2-chloroprocaine on the subsequent analgesic potency of bupivacaine

Isolated rat sciatic nerves were used to study the interaction between 2-chloroprocaine (2-CP) and bupivacaine (BP). Five nerves studied as controls were treated with 5 × 10–4 m BP and the amplitude of the compound action potential (CAP) evoked by suprathreshold stimulation was measured. This concentration of BP completely blocked nerve conduction; but, following washout with normal Krebs–Ringer solution, the CAP amplitude recovered to 50% of initial values in 50 (±4) min with a rate of recovery of 1.7 (±0.6) %/min. In another series of experiments, five nerves were blocked first with 5 × 10–4 m 2-CP, allowed to fully recover, and then were blocked with BP under the same conditions as the controls. Under these conditions, the half time for the recovery of CAP amplitude following BP was shortened to 25 (±5) min, with a rate of recovery of 2.8 (±0.3) %/min. When five nerves were exposed to a 5 × 10–4 m solution of a 2-CP metabolite, 4-amino-2-chlorobenzoic acid, no nerve blockade was produced. When these nerves subsequently were blocked with BP, recovery to 50% of initial values occurred in 22 (±5) min, with a rate of recovery of 2.0 (±0.2) %/min. Although pretreatment with either 2-CP or 4-amino-2-chlorobenzoic acid significantly shortened the duration of BP-induced nerve blockade, neither drug had a significant effect on the rate of recovery once the CAP amplitude returned to measurable values.These results suggest that the metabolite of 2-CP, 4-amino-2-chlorobenzoic acid, remains in the nerve following recovery from neural blockade and interferes with the subsequent action of BP upon this nerve.

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.

The effect of human amniotic fluid on the isolated perfused rat heart

To test the hypothesis that amniotic fluid directly affects cardiac function, isolated rat hearts were perfused with varying concentrations of centrifuged and filtered human amniotic fluid. The most consistent change seen was a dose-dependent decrease in coronary flow rate. With 10% concentrations, a wide spectrum of changes was seen in both a positive and a negative direction for left ventricular pressure and change in pressure with respect to time, which were closely correlated with the degree of decrease in coronary flow rate. If amniotic fluid has a direct role in depressing cardiac function in amniotic fluid embolism, it may act by decreasing coronary flow rather than by directly suppressing myocardial activity.

1691 APNEA FROM LARYNGEAL CHEMOREFLEX (LCR) STIMULATION DURING SLEEP IN THE NEWBORN LAMB

In order to evaluate the effects of different activity states (AS): wakefulness (W), Rapid Eye Movement (REM), and Quiet Sleep (QS), on the recovery from LCR induced apnea, we studied 4 premature newborn lambs chronically instrumented with tracheostomy, EEG and EOG leads for 1 to 5 weeks. During each AS, the LCR was stimulated with water for 5 s. The response was evaluated as the % decrease in ventilation from the baseline period for 30 s after the onset of stimulation (ΔV). ΔV was greater during REM (85.9±17.8)+and QS (82.4±17.3) than during W (55.9±21.5)*, but there was no difference between REM and QS. Following arousal, which occured in 1/4 of the tests during sleep, the response was markedly reduced (ΔV=53.7±28.6). However, one lamb needed frequent resuscitation after stimulation during either REM or QS. Respiratory drive for each AS was evaluated during the baseline period by measuring mean inspiratory flow (Tidal Volume/Inspiratory Time: Vt/Ti), assuming no variations in lung resistance among different AS. Vt/Ti was lower during either QS (55.7±19.7) or REM (50.4±14.5) as compared to W (70.5±33.5)*.During both REM and QS, if arousal does not occur, the newborn lamb is more vulnerable to LCR stimulation induced apnea which can be fatal. A more sustained apnea during sleep may be related to a decreased respiratory drive and/or a decreased sensitivity to hypoxemia. It is postulated that, although the importance of such reflex apnea in the human infant is unknown, the impaired recovery observed during sleep may reproduce the sequence of events occuring in SIDS.

Epidural Anesthesia for the Woman in Labor

During the last decade, regional anesthetic techniques have become widely used in obstetrics. Local infiltration and pudendal block are probably employed most frequently, but lumbar epidural block has become a major form of pain relief during childbirth. At the Boston Hospital for Women, 50 to 60 percent of our vaginal deliveries and 30 to 40 percent of our cesarean births are performed with an epidural block. Epidural anesthesia is produced by injecting a local anesthetic into the space between the periosteum of the spinal canal (covered posteriorly by the ligamentum flavum) and the dural sac. The epidural space extends from the foramen magnum to the sacral hiatus and contains variable quantities of fat, lymphatics, and blood vessels. The epidural veins become markedly dilated during pregnancy, thereby reducing the volume of the epidural space. Thus, effective dosages fluctuate per spinal segment. Epidural anesthesia is effective because it delays the conduction of nerve impulses that transmit pain in the area served by that segment. The dural cuff is thought to be the major site of penetration and action of the local anesthetic. It is known, however, that some drugs permeate