Frequency of hyperoxaemia during and after major surgery

The oxygen concentration (FiO 2 ) and arterial oxygen tension (PaO 2 ) delivered in patients undergoing major surgery is poorly understood. We aimed to assess current practice with regard to the delivered FiO 2 and the resulting PaO 2 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 2 and the oxygenation saturation (SpO 2 ) 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 2 of >150 mmHg and included a further threshold of PaO 2 >200 mmHg. We studied 373 patients. The median (interquartile range (IQR)) lowest intraoperative FiO 2 and SpO 2 values were 0.45 (IQR 0.4–0.5) and 97% (IQR 96–98%), respectively, with a median PaO 2 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 2 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 2 of >200 mmHg occurred in 64%, 41% and 21% of these blood gases, respectively. In an Australian tertiary hospital, a liberal approach to FiO 2 and PaO 2 was most common and resulted in a high incidence of perioperative hyperoxaemia.