Canadian Journal of Anesthesia, Vol 11, 313-317, Copyright © 1964 by Canadian Anesthesiologists' Society

Some Observations on the Use of the Nunn Blood Gas Predictor

¹ Department of Anaesthesia, University of Alberta Hospital, Edmonton, Alberta

In 1962 Nunn described a predictor for arterial pCO₂ and pH This was in the form of a slide rule and its function was based on the patient's weight, sex, metabolic rate, and ventilation A clinical investigation of 40 healthy patients undergoing extrathoracic surgery was performed The anaesthetic technique consisted of thiopentone, nitrous oxide, methoxyflurance, relaxant, 4nd artificial ventilation After one hour predicted values of pCO₂ and pH were compared with those measured from arterial blood samples The predicted pCO₂ was always lower than the measured value, and the difference increased with the degree of hyperventilation It was found that to maintain a pCO₂ of 35–45 mm Hg ventilation had to be increased to 105–130 per cent of thje value predicted necessary to maintain a pCO₂ of 40 mm Hg These finding were considered to be mainly due to an increase in physiological dead space, and an increased in carbon dioxide production during methoxyflurane anaesthesia