Adverse effects of maternally administered lidocaine on the asphyxiated preterm fetal lamb.

Lidocaine was infused at a constant rate of 0.1 mg.kg-1.min-1 for 180 min into 12 chronically prepared pregnant sheep while asphyxia, induced by partial umbilical cord occlusion, was maintained in the premature fetus (80% of gestation). In five similar preparations saline instead of lidocaine was infused into the mother for 180 min. Maternal and fetal arterial blood pressure, heart rate, pHa, PaCO2, and PaO2 were monitored, and fetal cardiac output and the distribution of blood flow to fetal organs were measured, using labeled microspheres, before and after asphyxia and again after maternal infusion of lidocaine or saline. Maternal and fetal arterial blood and maternal urine were obtained at intervals for determination of lidocaine concentrations and urinary drug clearance. At the end of infusion, these animals were killed and tissues dissected for determination of lidocaine concentrations and organ blood flow. Maternal and fetal lidocaine plasma concentrations at steady state were 2.32 +/- 0.12 and 1.23 +/- 0.17 microgram/ml, respectively, similar to those seen during human epidural anesthesia. Asphyxia resulted in a significant drop in fetal heart rate and increased blood flow to the brain, heart, and adrenals. Asphyxia and saline did not produce additional deterioration of the fetus, but asphyxia and lidocaine led to a significant increase in PaCO2 and decreases in pHa, mean arterial pressure, and blood flows to the brain, heart, and adrenals. It is concluded that the immature fetus loses its cardiovascular adaptation to asphyxia when exposed to clinically acceptable plasma concentrations of lidocaine obtained transplacentally from the mother.

Incidence of visceral pain during cesarean section: the effect of varying doses of spinal bupivacaine.

The safety of 0.5% hyperbaric bupivacaine, as well as the incidence and severity of visceral pain, were evaluated in 36 women undergoing elective cesarean section under spinal anesthesia who, randomly divided into two groups, received different dose ranges according to height, 7.5-10 mg in group A and 10-12.5 mg in group B. When sensory block to at least the fourth thoracic dermatome was established, surgery was begun and the occurrence and severity of visceral pain recorded (visual analog scale) by an observer unaware of patient data. The level of analgesia to pinprick was determined when and if there was onset of pain intraoperatively, and supplementary medication was administered as needed. Hypotension, the incidence of which was similar in both groups, was treated as necessary with ephedrine. No patients experienced pain until after delivery of the infant. Thereafter, moderate to severe pain, in association with peritoneal traction, occurred in 12 patients in group A (70.5%) but only in 6 patients in group B (31.6%). In patients experiencing moderate to severe pain, the mean time between induction of anesthesia and onset of pain was similar in both groups, as was the amount of systemic narcotic given. Total time for regression of sensory analgesia to L5 was longer in patients in group B (243.9 versus 195.4 min), and the incidence of complete motor blockade was greater in group B. Increasing the amount of 0.5% hyperbaric bupivacaine per spinal segment reduces the occurrence of moderate to severe visceral pain during elective cesarean section without jeopardizing mother or fetus.