Age and the Solubility of Volatile Anesthetics in Ovine Tissues

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Abstract
To determine the effect of age on the solubility of volatile anesthetics in tissues, we measured the blood/gas and tissue/gas partition coefficients of isoflurane, enflurane, halothane, and methoxyflurane in vitro at 37°C in newborn lambs and postpartum adult sheep. The tissue specimens examined were brain, heart, liver, kidney, muscle, and fat. Hematocrit and serum concentrations of albumin, globulin, cholesterol, and triglycerides were measured. The blood/gas partition coefficients, hematocrit, and the serum concentrations of albumin, globulin, cholesterol, and triglycerides in the newborn lambs did not differ from those in the adult sheep. The tissue/blood partition coefficients [the ratio of (tissue/gas)/(blood/gas)l in newborn lambs were 28% [mean value for the four anesthetics] less than those in the adults. The tissue/blood partition coefficients for enflurane and methoxyflurane in newborn tissues were significantly less (P < 0.05) than those for halothane and isoflurane. We conclude that the blood/gas partition coefficients in sheep do not change significantly with age, that the tissue/blood partition coefficients in sheep increase with age, and that the time required for equilibration of volatile anesthetics (particularly enflurane and methoxyflurane) in newborn tissues is probably less than in adult sheep.