Early Warning for Desaturation by Oxygen Reserve Index

This is an observational study of the routine clinical practice with no specific additional interventions required. The investigators enrolled the ASA physical status I to III patients scheduled for elective surgery with planned arterial catheter placement before induction. ORi and standard monitors were placed. The patients were preoxygenated and received anesthesia induction as routine clinical practice. Intubation was done by video-laryngoscope. The endotracheal tube was not connected to the breathing circuit to avoid apneic oxygenation. Ventilation was resumed when SpO2 fell to 90%. ORi and SpO2 were recorded every ten seconds.