British journal of anaesthesia
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We have evaluated a new method for measuring the oxygenated mixed venous PCO2 (PVCO2) in patients undergoing general anaesthesia. The lungs were inflated with a gas mixture containing 0% carbon dioxide and then 12% carbon dioxide and the expired gas was analysed both before and after a brief period of breath-holding. PVCO2 was estimated from the differences in carbon dioxide concentration before and after the apnoeic period. ⋯ The range of PaCO2 studied was 3.2--6.13 kPa. The relationship between mixed venous and arterial PCO2 was found to be PaCO2 = 0.87 PVCO2--0.44 (r = 0.91). We conclude that this method for measuring PVCO2 can be used during anaesthesia allowing PaCO2 to be estimated with considerable accuracy.