Frequency of hyperoxaemia during and after major surgery.

The oxygen concentration (FiO) and arterial oxygen tension (PaO) delivered in patients undergoing major surgery is poorly understood. We aimed to assess current practice with regard to the delivered FiO and the resulting PaO in patients undergoing major surgery. We performed a retrospective cohort study in a tertiary hospital. Data were collected prospectively as part of a larger randomised controlled trial but were analysed retrospectively. Patients were included if receiving controlled mandatory ventilation and arterial line monitoring. Anaesthetists determined the FiO and the oxygenation saturation (SpO) targets. An arterial blood gas (ABG) was obtained 15-20 minutes after induction of anaesthesia, immediately before the emergence phase of anaesthesia and 15 minutes after arrival in the post-anaesthesia care unit (PACU). We defined hyperoxaemia as a PaO of >150 mmHg and included a further threshold of PaO >200 mmHg. We studied 373 patients. The median (interquartile range (IQR)) lowest intraoperative FiO and SpO values were 0.45 (IQR 0.4-0.5) and 97% (IQR 96-98%), respectively, with a median PaO on the first and second ABG of 237 mmHg (IQR 171-291 mmHg) and 189 mmHg (IQR 145-239 mmHg), respectively. In the PACU, the median lowest oxygen flow rate was 6 L/min (IQR 3-6 L/min), and the PaO was 158 mmHg (IQR 120-192 mmHg). Hyperoxaemia occurred in 82%, 73% and 54% of participants on the first and second intraoperative and postoperative ABGs respectively. A PaO of >200 mmHg occurred in 64%, 41% and 21% of these blood gases, respectively. In an Australian tertiary hospital, a liberal approach to FiO and PaO was most common and resulted in a high incidence of perioperative hyperoxaemia.