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 American Society of Anesthesiologists (ASA) physical status I to III patients scheduled for elective surgery with planned arterial catheter placement before induction. Patients were positioned supine on the operating room table. Standard monitors and the ORi sensor were placed. The patients were preoxygenated with a facemask (flow rate of 8 to 10 liters/minute) for 3 minutes with spontaneous ventilation. Propofol (2-2.5 mg/kg), fentanyl (2-3 mcg/kg) and rocuronium (0.6-0.9 mg/kg) were administrated to achieve anesthesia induction during following 3 minutes. The patient was keeping ventilated manually by the anesthesiologist during the induction phase and intubated under direct visualization with a video-assisted laryngoscope at 6 minutes. The endotracheal tube was not connected to the breathing circuit to avoid apneic oxygenation. The patients remained apneic. Ventilation was resumed when SpO2 fell to 90%. ORi and SpO2 were recorded every ten seconds. Arterial blood is sampled every minute, from preoxygenation to resumed ventilation, to observe blood oxygen concentration changes.

Inclusion criteria

• Male and female patients aged 18 to 80 years with ASA physical status I to III scheduled for elective surgery with planned arterial catheter placement before induction of general anesthesia.

Exclusion criteria

• Age <18 years
• Inability to give primary consent
• Pregnancy
• History of chronic obstructive pulmonary disease (COPD)
• History of asthma
• Suspected difficult intubation
• Preoperative hemoglobin less than 10 mg/dl.