Pre-intubation oxygenation is a recommended procedure general anaesthesia where 100% oxygen is delivered with a goal to increase the safe apneoa time( the delay until oxygen saturation falls to 90%). Achieving this target is dependent on the efficacy of pre oxygenation which can further vary based on the fio2, duration of pre oxygenation and alveolar ventilation. as fio2 is the fraction of o2 among the total gas, any other gas administered with 100% fio2 in the alveolar content will likely impact pre oxygenation. the study aims to quantify this.

also addition of inhalational agents during pre intubation oxygenation and ventilation in everyday practice helps in maintaining the depth of anaesthesia. further, undesirable hemodynamic effects associated with pre oxygenation like a decrease in heart rate and increase in blood pressure and systemic vascular resistance with hyperoxia which are countered by use of inhalational agents. the weightage of such advantages against possible impact on oxygenation target has to be evaluated.

All eligible patients will be told about the study. base line vitals like hr,bp,rr,spo2 are noted down. patients are induced with fentanyl 2 mcg/kg and propofol 2 mg/kg and pre intubation oxygenation is done with fresh gas flow fixed at 8l/min.group A will recieve 1% sevoflurane, group B will recieve 1% isoflurane and group C will get no inhalational agents. Parameters like fio2,feo2,spo2, etco2,hr,bp, minute ventilation, airway pressures and time to reach feo2 of 85% and 90% are noted down and compared. we expect that the addition of inhalational anaesthetic will affect pre intubation oxygenation negatively, but the hemodynamics will not be affected much.