Associations of a positive intra-operative air–test with postoperative pulmonary complications in general surgery patients

BACKGROUND: The air-test, which involves reducing the fraction of inspiratory oxygen (FiO 2 ) to 21% and monitoring pulse oximetry haemoglobin saturation (SpO 2 ), has previously been used to guide intra-operative ventilation strategies. However, it is unclear how often the air-test is positive (defined as an SpO 2 decrease below 97% during ventilation with an FiO 2 of 21%) in general surgery patients, and if a positive air-test is associated with the development of postoperative pulmonary complications (PPCs). OBJECTIVES: To assess the incidence of a positive air-test in general surgery patients, and to determine the association of a positive air-test with development and severity of PPCs. DESIGN: An observational study. SETTING: Single-centre study performed in the Amsterdam University Medical Centre, the Netherlands. PATIENTS: Adult patients undergoing intra-operative ventilation during general anaesthesia for general surgery. MAIN OUTCOME MEASURE: The primary endpoint is a previously used composite of PPCs. RESULTS: Out of 632 patients, 328 (52%) had a positive air-test. Patients with a positive air-test were older, had a higher BMI, were more often smokers and were more often diagnosed with chronic obstructive pulmonary disease. Patients with a positive air-test were ventilated with a higher PEEP and FiO 2 and they developed PPCs more often (18.6 vs. 12.5%; P = 0.038). The air-test had a sensitivity of 62% and a specificity of 50% for predicting PPCs. The PPV was 19% and the NPV was 88%. CONCLUSION: The intra-operative air-test is often positive in general surgery patients and is associated with a higher incidence of PPCs. Given the high NPV, the air-test is mainly useful in identifying patients at a low risk of PPCs. TRIAL REGISTRATION: NCT05345743.