Partial pressure of oxygen level at admission as a predictor of postoperative pneumonia after hip fracture surgery in a geriatric population: a retrospective cohort study

Objective To identify whether the partial pressure of oxygen in arterial blood (PaO2) level at admission is an independent risk factor as a prognostic biomarker to predict postoperative pneumonia (POP) in the geriatric population who have undergone hip fracture surgical repair at our hospital. Design A retrospective cohort study. Setting This is a retrospective chart review of POP after hip fracture surgery in China. Participants In training cohort, patients aged >= 65 years who had hip fracture surgery between 1 January 2018 and 30 November 2019. In the validation cohort, a series of patients who underwent hip fracture surgery between 1 January 2020 and 28 February 2020. Interventions Receiver operating characteristic (ROC) analysis was used to obtain the area under the ROC curve (AUC) and cut-off values of PaO2 to predict POP. A binomial logistic regression model was used to identify potential risk factors for POP by analysing demographic distribution factors, laboratory results, preoperative comorbidities and surgical factors. Then the regression model was validated using an independent cohort. Results In the training cohort, ROC curves were generated to compare the predictive performance of PaO2 for the occurrence of POP, and the area under the receiver operating characteristic curve (AUC) was 0.653 (95% CI 0.577 to 0.729, p<0.0001), with sensitivity and specificity values of 60.0% and 63.8%, respectively. The cut-off value of the PaO2 for POP was 72.5 mm Hg. Binary logistic regression analysis revealed that hypoxaemia (PaO2 <72.5 mm Hg) at hospital admission (OR=3.000, 95% CI 1.629 to 5.528; p<0.0001) was independent risk factors associated with POP after hip fracture surgery. In the validation cohort, PaO2 had a predictive effect for POP (AUC 0.71, 95% CI 0.541 to 0.891). Conclusions The current study revealed that the PaO2 level at hospital admission is a simple and widely available biomarker predictor of POP after hip fracture surgery in elderly patients.