A new method for measurement of anaesthetic partial pressure in blood.

We have developed a simple, reliable method for rapid analysis of the partial pressure of volatile anaesthetic agents, based on a two-stage, head-space analysis. It is designed to solve the problems associated with reduced solubility of modern anaesthetics. After equilibration and analysis of a 2-ml sample of blood at 37 degrees C, 1 ml is transferred to another vial for a second equilibration. This ensures that there is no vapour in the headspace before the second equilibration. Measurements were performed on human blood samples equilibrated with 1% sevoflurane, 2.5% isoflurane or 3% desflurane in a tonometer. The mean error in the sample measurements was -2.3% of the tonometer reading and the 95% confidence interval for an individual measurement was +/- 8.5%. Blood samples may be stored overnight without any significant change in the results.