During the induction of general anesthesia, the anesthesiologist needs to provide the oxygen supply to meet the patient's needs continuously. In the clinical scenario, the pulse oximeter is used as a standard to monitor hemoglobin oxygen saturation (SpO2) but is limited to assess the oxygenation status beyond the measurement of 100%. The Oxygen Reserve Index (ORi) is a dimensionless parameter between 0 and 1 that is related to real-time oxygenation reserve status. This study was designed to evaluate the duration of warning time for desaturation provided by different ORi alarm triggers during prolonged apnea in surgical patients. The primary endpoint was the duration of additional warning time provided by the ORi trigger. The secondary endpoint was the correlation of ORi and PaO2.
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.
Study Type
OBSERVATIONAL
Enrollment
25
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.
Department of Anesthesiology, Taipei Veterans General Hospital
Taipei, Taiwan
Additional warning time provided by ORi trigger
The ORi peak warning time was defined as the duration from ORi decreased by 0.05 from the plateau or peak values until SpO2 decreased to 90%. The ORi 0.55 warning time was defined as the duration from the ORi value was 0.55 to SpO2 90%. The SpO2 waring time was defined as the duration from SpO2 98% to 90%. The added warning time provided by ORi peak or ORi 0.55 was defined as the difference between ORi peak warning time, ORi 0.55 warning time, and SpO2 warning time. The investigators will check the duration of the additional warning time provided by the ORi trigger.
Time frame: From time of starting preoxygenation until the time of SpO2 90%, assessed up to 20 minutes
Correlation between ORi and PaO2
The Oxygen Reserve Index is a dimensionless parameter between 0 and 1 that is related to real-time oxygenation reserve status in the moderate hyperoxic range (PaO2 of about 100 to 200 mmHg). The investigators will check the correlation between ORi and PaO2 in our study.
Time frame: From time of starting preoxygenation until the time of SpO2 90%, assessed up to 20 minutes
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