Blood solubility of isoflurane measured by a multiple gas phase equilibration technique

Using a multiple gas phase equilibration technique, we determined the solubility of isoflurane in arterial blood at 37 degrees C obtained from patients anaesthetized with isoflurane. Goodness of fit of individual sets of data to a predicted decline of isoflurane concentration in successive equilibrated gas phases and reproducibility of results indicate that the analytical technique was acceptably accurate. In blood samples taken from twenty-three patients undergoing minor surgical procedures, the blood/gas partition coefficient of isoflurane was 1.20 +/- 0.08 (mean +/- S.D.). Individual values were not detectably related to absolute tension of isoflurane, preoperative haemoglobin concentration nor patient age. In samples taken from twenty neurosurgical patients, the blood/gas partition coefficient was slightly less, 1.14 +/- 0.09 (p less than 0.05), a difference we attribute to the effect of previously infused mannitol. In vitro, blood solubility of isoflurane was decreased by haemodilution with normal saline, mannitol 20 per cent or plasma, was increased by hypothermia (30 degrees C) and was decreased by hyperthermia (40 degrees C). We conclude that the solubility of isoflurane in human blood is approximately half that of halothane.