Denitrogenation: comparison of three methods of preoxygenation

Preoxygenation is standard protocol before the onset of general anaesthesia. If we are able to find a way to increase efficiency and efficacy, it would save the anaesthetist both time and energy and reduce the rush to secure an airway. Aim of the study is to assess the clinical efficacy of different methods of pre oxygenation with gas monitoring using an advanced workstation. Primary objective: To compare the time taken and total number of breaths required to achieve EtO2 of 0.9 with delivery of fresh gas flow of 10L of oxygen between group A, group B and group C.

Group A: Conventional method, preoxygenation with tidal breaths for three minutes, with FiO2 of 1

Group B: Pre oxygenation with tidal breathing applying continuous positive airway pressure (CPAP) of 5 cm H2O

Group C: Pre oxygenation with tidal breaths following four room air vital capacity breaths in 30 seconds

Secondary objective: To assess the time taken for decline in EtO2 to 0.5 in group A, group B, group C

Inclusion Criteria: ASA I and II patients, Adults aged 18-59, Both gender, Patients undergoing elective surgery under any form of anaesthesia

Exclusion criteria: Anticipated difficult airway, Chronic smokers, Asthmatics, BMI >30kg/m2, Pregnant women, Cardiac/respiratory diseases, Patients who do not consent

General Electronics Avance CS2 work station with circle breathing system having a 2L capacity reservoir bag will be used.

Patients taking part in the study will be given anxiolytic Alprazolam 0.25mg HS. Prior to preoxygenation, baseline RR and EtO2 will be documented. Patients will be supine with a 20 degree head up position, transparent anaesthetic face mask held with air tight seal with FGF of 10L/min and FiO2 of 1.

During the denitrogenation process, the total time taken along with number of breaths will be recorded. Exhaled tidal volume, EtCo2, FiO2, and ETO2 will be recorded after each breath.

After this process, fresh gas flow will be switched to 100% air. Total time taken and number of breaths required to record a drop in ETO2 to 0.5 will be recorded.

Data will be analysed using SPSS 2021. Descriptive statistics will be reported using mean and SD for continuous variables and numbers and percentages for categorical variables