Effect of Halothane on Regional Cerebral Blood Flow and Cerebral Metabolic Oxygen Consumption in the Fetal Lamb In Utero

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Abstract
The effects of halothane on maternal and fetal hemodynamics, distribution of fetal cardiac output, regional cerebral blood flow, and fetal cerebral oxygen consumption were studied in the ewe (N = 9) using radionuclide-labeled microspheres. An adjustable uterine artery occluder was used to produce a controlled state of fetal asphyxia. Measurements were taken during three periods of study: 1) control, 2) asphyxia, and 3) asphyxia plus 15 min of 1% maternal halothane. The fetal cardiovascular response to asphyxia was acidosis, hypoxia, hypertension, bradycardia, and preservation of vital organ blood flows. There was a significant drop in maternal blood pressure when halothane was administered but uterine blood flow was maintained, 308 ml ± min−1 during asphyxia versus 275 ml ± min−1 with halothane. Fetal blood pressure during asphyxia plus halothane (54 mmHg) was significantly lower than that during asphyxia alone (59 mmHg), while heart rate was significantly higher: 172 beats per minute (bpm) versus 125 bpm (P < 0.05). Despite these changes, the administration of halothane during asphyxia did not produce a reduction in vital organ flows. Cerebral blood flow was maintained: 357 ± 37 ml ± 100 g−1 • min−1 during asphyxia alone and 344 ± 26 ml ± 100 g−1 min−1 after halothane administration (P = NS, mean ± SEM). Cerebral oxygen delivery also was maintained: 8.3 ± 0.8 ml ± 100 g−1 during asphyxia alone versus 9.7 ± 1.5 ml ± 100 g−1 • min−1 after halothane, compared with 11.2 ± 1.1 ml ± 100 g−1 • min−1 during the control period. Cerebral oxidative metabolism (CMRO2) decreased significantly from 4.1 ± 0.6 ml ± 100 g−1 • min−1 during control to 2.8 ± 0.4 ml ± 100 g−1 • min−1 during asphyxia alone, but no further significant change occured after halothane (2.0 ± 0.3 ml ± 100 g−1 • min−1). Fetal myocardial blood flow was maintained: 625 ± 93 ml ± 100 g−1 ml−1 during asphyxia alone versus 529 ± 79 ml ± 100 g−1 • min−1 after halothane administration. The authors conclude that the addition of 1% maternal halothane in the briefly asphyxiated fetal lamb does not abolish the protective reflexes of increased coronary and cerebral blood flow and decreased CMRO2.