Canadian Journal of Anesthesia, Vol 30, 155-161, Copyright © 1983 by Canadian Anesthesiologists' Society

Blood Solubility of Isoflurane Measured by a Multiple Gas Phase Equilibration Technique

¹ Department of Anaesthesia, University Hospital and University of Western Ontario, London, Canada

Address Correspondence to: Dr. R.L. Knill, Department of Anaesthesia, University Hospital, P.O. Box 5339, Postal Station A, London, Ontario N6A 5A5.

Using a multiple gas phase equilibration technique, we determined the solubility of isoflurane in arterial blood at 37° 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 < 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° C) and was decreased by hyperthermia (40° C). We conclude that the solubility of isoflurane in human blood is approximately half that of halothane.

Key Words: SOLUBILITY: partition coefficients • ANAESTHETICS, VOLATILE: isoflurane