A study of carbon dioxide tensions during halothane anaesthesia using the Magill circuit.

In thirteen patients capillary blood samples were obtained for measurement of pH and Pcoa immediately after the induction dose of thiopentone, after 45 minutes of 2 per cent halothane breathed spontaneously (with nitrous oxide and oxygen), and 30 minutes postoperatively. A very variable rise in Pco2 was observed which did not correlate well with changes in pulse rate, blood pressure, respiratory frequency, respiratory minute volume, or with the age of the patient. A single measurement of respiratory minute volume with a Wright respirometer was of no value in indicating which patients had the greatest carbon dioxide retention. The return of Pco, to normal values in the postoperative period was found to be rapid and, for practical purposes, complete in 30 minutes.