Study of early warning for desaturation provided by Oxygen Reserve Index in obese patients

Acute hemoglobin desaturation can reflect rapidly decreasing PaO(2). Pulse oximetry saturation (SpO(2)) facilitates hypoxia detection but may not significantly decrease until PaO(2) < 80 mmHg. The Oxygen Reserve Index (ORI) is a unitless index that correlates with moderately hyperoxic PaO(2). This study evaluated whether ORI provides added arterial desaturation warning in obese patients. This IRB approved, prospective, observational study obtained written informed consent from Obese (body mass index (BMI) kg m(−2); 30 < BMI < 40) and Normal BMI (19 < BMI < 25) adult patients scheduled for elective surgery requiring general endotracheal anesthesia. Standard monitors and an ORI sensor were placed. Patient’s lungs were pre-oxygenated with 100% FiO(2). After ORI plateaued, general anesthesia was induced, and endotracheal intubation accomplished using a videolaryngoscope. Patients remained apneic until SpO(2)reached 94%. ORI and SpO(2) were recorded continuously. Added warning time was defined as the difference between the time to SpO(2) 94% from ORI alarm start or from SpO(2) 97%. Data are reported as median; 95% confidence interval. Complete data were collected in 36 Obese and 36 Normal BMI patients. ORI warning time was always longer than SpO(2) warning time. Added warning time provided by ORI was 46.5 (36.0–59.0) seconds in Obese and 87.0 (77.0–109.0) seconds in Normal BMI patients, and was shorter in Obese than Normal BMI patients difference 54.0 (38.0–74.0) seconds (p < 0.0001). ORI provided what was felt to be clinically significant added warning time of arterial desaturation compared to SpO(2). This added time might allow earlier calls for help, assistance from other providers, or modifications of airway management. Trial registration ClinicalTrials.gov NCT03021551.