Oxygen Reserve Index Predicts Hypoxemia During One-Lung Ventilation: An Observational Diagnostic Study

Abstract

Objective: To determine the accuracy of the Oxygen Reserve Index (ORi) to predict hypoxemia during one-lung ventilation (OLV).

Design: An observational diagnostic test study.

Setting: A tertiary care teaching hospital.

Participants: Forty consecutive patients scheduled for thoracic surgery with OLV.

Measurements and main results: Patients were ventilated with tidal volumes of 8 mL/kg ideal body weight during two-sided ventilation and 6 mL/kg during OLV, and with fraction of inspired oxygen (F_IO₂) of 60%. ORi was measured continuously. Sensitivity, specificity, positive and negative predictive values, likelihood ratios, and accuracy were calculated for ORi = 0 in different phases of anesthesia. Hypoxemia during OLV was defined as SpO₂ < 90%. Hypoxemia owing to malpositioning of the double lumen tube was an exclusion criterion. ORi = 0 five minutes after tracheal intubation in the supine position showed a sensitivity of 63.6% (confidence interval [CI] 95% 31.6-87.6), specificity of 93.1% (95% CI 75.8-98.8), and an accuracy of 85.0% (95% CI 69.5-93.8). The rate of hypoxemia was 27.5% (95% CI 15.14-44.14).

Conclusions: An ORi value equal to zero, 5 minutes after the onset of mechanical ventilation in the supine position, predicts the development of hypoxemia during OLV. These findings may be helpful to adjust F_IO₂ individually in patients undergoing OLV and to avoid unnecessary high concentrations of oxygen.

Keywords: hypoxemia; one-lung ventilation; oxygen reserve index.