[Avoiding hypoxemia during anesthesia]

The incidence of unexpected hypoxaemia during general anaesthesia was studied in 230 healthy patients undergoing a peripheral surgical procedure. Measurements of arterial oxygen and carbon dioxide tension (paO2 and paCO2) were performed under rigorously controlled conditions in regard to the age of the patients, their smoking habits, course and type of the anaesthetic and surgery, body position, inspiratory fraction of oxygen (FiO2), expiratory fraction of carbon dioxide (FECO2), respiratory minute volume and inspiratory to expiratory time ratio. 10% of the patients receiving FiO2 of 0.33 and 3.3% of those receiving 0.40 were found to have a paO2 below 80 mm Hg. 25% respect. 0% of older (greater than 60) and 6.7% respect. 4.4% of younger patients (less than 60 years) receiving FiO2 of 0.33 respect. 0.40 were hypoxemic (paO2 less than 80 mm Hg). These figures were compared with the results of an inquiry of practicing anaesthesiologists (in USA, West Germany and Switzerland) and their opinions about the safe FiO2 and paO2 limits. Most of the respondents use under the described conditions of this study an FiO2 of 0.33. At the same time 96% of them expect a paO2 over 80 mm Hg. On the basis of 10% incidence of hypoxaemic values among the patients studied it was concluded that FiO2 of 0.33 can not be considered as safe: increasing FiO2 to 0.40 helps to decrease the incidence of unexpected hypoxaemia especially in the patients over 40 years old.