Prediction Value of Oxygenation Index as Predictor for Postoperative Pulmonary Complications in Urologic Surgery

Abstract

Introduction: It is believed that pressure/flow (P/F) ratio (arterial oxygen to inspired oxygen fraction) does not give the best expression of oxygenation status in mechanically ventilated patients. Therefore, a new oxygenation index (OI) where the mean airway pressure (MAP) is incorporated (PaO2/FiOxMAP) is showed as superior to P/F in expression of the lung oxygenation status. In this article we wanted to assess the prediction value of OI calculated during urological surgeries as a predictive marker for developing postoperative pulmonary complications (PPC).
 Material and methods: We evaluated all elective urologic patients operated in general endotracheal anesthesia, aged 18 to 65 years, without any known history of respiratory disease for the period from January till December 2017. We calculated the P/F ratio and the OI at three time points: after induction in general endotracheal anesthesia in the beginning of mechanical ventilation, 1 hour after induction in anesthesia, and at the end of the surgery before weaning the mechanical ventilation. The primary outcomes were PPC defined by European Society of Anesthesia. The second outcomes were: length of hospital stay, admission to intensive care unit (ICU) and mortality. 
 Results: A total of 240 patients who met the inclusion criteria were included in this evaluation and finally analyzed. PPC were diagnosed in 25% of patients and respectively 75% were without complications. Postoperative hospital stay was longer in PPC group no matter they were operated laparoscopically or with classic open surgery (PPC laparoscopy 4.9 ± 2.2 vs. non PPC laparoscopy 3.3 ± 1.7, PPC laparotomy 6.8 ± 5.2 vs. non PPC 5.6 ± 2.1 laparotomy). Ten patients were admitted to ICU, 8 from PPC group and 2 from non PPC group. In PPC group patients were admitted to ICU for mean 3.7 ± 2.4 days, and in non PPC group patients were hospitalized in ICU only for 2 days. All evaluated patients were discharged from the hospital and no mortality was observed in the 30 postoperative days.
 In the univariate and multivariate logistic regression analysis neither OI nor P/F were significantly associated with PPC.
 Conclusion: This study does not offer a conclusive answer to the prediction value of OI for PPC. It would be fruitful to pursue further research about predictive variables for pulmonary complications.