A noninvasive postoperative clinical score to identify patients at risk for postoperative pulmonary complications: the Air-Test Score

Abstract

Background: Postoperative pulmonary complications (PPCs) negatively affect morbidity, healthcare costs and postsurgical survival. Preoperative and intraoperative peripheral oxyhemoglobin saturation (SpO2) levels are independent risk factors for postoperative pulmonary complications (PPCs). The air-test assesses the value of SpO2 while breathing room-air. We aimed at building a clinical score that includes the air-test for predicting the risk for PPCs.

Methods: This is a development and validation study in patients -randomly divided into two cohorts- from a large randomized clinical trial (iPROVE) that enrolled 964 intermediate-to-high risk patients scheduled for abdominal surgery. Arterial oxygenation was assessed on room-air in the preoperative period (preoperative air-test) and 3h after admission to the postoperative care unit (postoperative air-test). The air-test was defined as positive or negative if SpO2 was ≤96% or >96%, respectively. Positive air-tests were stratified into weak (93-96%) or strong (<93%). The primary outcome was a composite of moderate-to-severe PPCs during the first seven postoperative days.

Results: A total of 902 patients were included in the final analysis (542 in the development cohort and 360 in the validation cohort). Regression analysis identified five independent risk factors for PPC: age, type of surgery, pre- and postoperative air-test, and atelectasis. The area under the receiver operating characteristic curve (AUC) was 0.79 (95% CI: 0.75-0.82) when including these five independent predictors. We built a simplified score termed "air-test score" by using only the pre- and postoperative SpO2, resulting in an AUC of 0.72 (95% CI: 0.67-0.76) for the derivation and 0.72 (95% CI: 0.66-0.78) for the validation cohort, respectively. The air-test score stratified patients into four levels of risk, with PPCs ranging from <15% to >75%.

Conclusions: The simple, non-invasive and inexpensive bedside air-test score, evaluating pre- and postoperatively SpO2 measured on room-air, helps to predict the risk for PPCs.