Arterial oxygen saturation before intubation of the trachea. An assessment of oxygenation techniques

Arterial oxygenation in patients was measured with an ear oximeter to assess factors that were associated with hypoxaemia at the induction of anaesthesia. Twenty patients breathed air during the induction of anaesthesia with thiopentone and following neuromuscular blockade with suxamethonium. Mean SaO2 decreased from 95.7% before induction to 85.5% 1 min after induction. The SaO2 at 1 min was less in those patients whose weight was more than expected (SaO2 80.5%), than in those patients whose weight was as expected or less than expected (SaO2 88.8%). Other factors such as haemoglobin concentration, FEV1, FVC, age, or smoking habits, were not related to the degree of arterial desaturation. To assess the efficacy of different methods of oxygen administration, four groups of 10 patients, were given oxygen in different ways using a Magill anaesthetic system with a supply of 10 litre min-1. Measurements were made for up to 3 min after the induction of anaesthesia and maintenance of apnoea. Group I breathed normally from the system for 1 min before anaesthesia was induced. Group II were treated similarly, but the mask had a standardized "leak", a 9.5-mm diameter hole. Group III took three vital capacity breaths from the system before anaesthesia, and group IV breathed air before anaesthesia, but their lungs were given three maximal manual inflations after the induction of anaesthesia. Mean SaO2 values after 3 min apnoea were: 96.8% (group I), 93.6% (group II), and 98.0% (group III). In group IV, measurements were stopped at 2 min when mean SaO2 was 92.9%.(ABSTRACT TRUNCATED AT 250 WORDS)