British journal of anaesthesia
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We have investigated 296 inpatients in a single-blind observer study to determine the incidence, degree and duration of hypoxaemia during anaesthesia. The clinical recognition of hypoxaemia, period of time until recognition and risk factors were studied. Oxygen saturation (Spo2) was monitored continuously with a pulse oximeter (Ohmeda, model 3700). ⋯ After intervention a mean time delay of 57 s was recorded until Spo2 exceeded 90%. Utilizing a stepwise multiple logistic regression analysis, we found that risk factors associated with a greater incidence of hypoxaemia were patient age (P less than 0.005) and anaesthetic technique (P less than 0.00001). We conclude that hypoxaemic episodes in our operating rooms are common during anaesthesia and suggest preoxygenation in all patients in addition to administration of supplementary oxygen during arousal from anaesthesia and during transfer to the recovery room.
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We have studied the effects of anaesthesia on atelectasis formation and gas exchange in 45 patients of both sexes, smokers and nonsmokers, aged 23-69 yr. None of the patients showed clinical signs of pulmonary disease, and preoperative spirometry was normal. In the awake patient, partial pressure of arterial oxygen (PaO2) decreased with increasing age (P less than 0.001) and the alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) increased with age (P less than 0.001). ⋯ Atelectasis and shunt did not increase significantly with age, whereas log SD Q and perfusion of regions with low VA/Q ratios did (r = 0.55, P less than 0.001 and r = 0.35, P less than 0.05, respectively). Awake, the major determinant of PaO2 was perfusion of regions of low VA/Q ratios, which increased with age. During anaesthesia shunt influenced PaO2 most, low VA/Q being a secondary factor which, however, was increasingly important with increasing age, thus explaining the well-known age-dependent deterioration of arterial oxygenation during anaesthesia.