Usefullness of oxygen reserve index as an early warning for desaturation during rapid sequence induction : a cross sectional study

Prolonged hypoxemia can produce tissue injury and serious peri operative complications including dysrhythmias, brain injury or death. Prior to utilisation of pulse oximetry , hypoxemia was the leading cause of anaesthesia associated peri operative mortality worldwide.Assessment of patient’s oxygenation to detect desaturation early facilitates intervention that prevent complication of prolonged hypoxemia. Arterial blood gas provides a definitive measurement of oxygenation status but is limited by its intermittent and invasive nature Pulse oximetry is non invasive and provides efficient monitoring , so it is often used in lieu of ABG analysis . Pulse oximetry oxygen saturation is determined by measuring the absorption of two emitted light wavelengths and calculating the proportion of oxyhemoglobin to deoxyhemoglobin. The SPO2 to PaO2 relationship is linear at lower PaO2 , but plateaus quickly at PaO2 >80mmhg, above which SpO2 will be 98-100% regardless PaO2 , consequently providing limited information regarding a patient’s PaO2 in the hyperoxic range. Conversely ,SpO2 decreases rapidly as PaO2 falls below 80mmhg and can fail to provide early detection of impending critical hypoxemia . An infrared transmission pulse oximetry technology that utilises >_ 7 additional wavelengths of light transmission can determine a value called the oxygen reserve index. Oxygen reserve index is reported on a unit less scale from 0 ( minimal reserve ) to 1 (high reserve) and correlates to PaO2 values in the mildly hyperoxic range between approximately 100 and 200mmhg. Oxygen reserve index is not a direct measure of PaO2 and there is wide variation in supra normal PaO2 values after oxygen reserve index values plateau. Oxygen reserve index has been shown to provide a clinically useful advanced warning of arterial haemoglobin desaturation in paediatric patients, during one lung ventilation, and during rapid sequence induction. The ability of oxygen reserve index to detect changes in arterial oxygenation within the mildly hyperoxic range could provide additional time to respond .

Aim: to find out the utility of oxygen reserve index in the early detection of impending desaturation and prevention of hyperoxia during preoxygenation.

Objective:

Primary objective:to find out whether oxygen reserve index detects impending desaturation before noticeable changes in SpO2 occurs

Secondary objective: to find out the utility of oxygen reserve index as a guide to preoxygenation for avoiding hyperoxia

Materials and method: cross sectional study

Sample size:97