The study will be conducted at the Department of Anaesthesiology and Critical Care, VIMS Ballari. The patients will be selected for the study depending on the inclusion and exclusion criteria. The complete data will be collected from the patients in a specially designed Case Record Form (CRF) which includes history of illness and detailed clinical examination and relevant investigations. Before subjecting the patients for investigations and andanaesthesia, written/informed consent will be obtained from each patient and /or parents or legal guardian. All children will be appropriately premedicated the previous night and the day of surgery. Children will be kept Nil by mouth 6 hours for solids and 2 hours for clear water.

After having done preoperative anesthesia drill and taking the child in to the operating theatre (OT) all basic monitors (ECG, SPO2,NIBP, ETCO2,TEMP ) will be attached and the OT temperature will be maintained between 24-26 degree Celsius. 

General anaesthesia will be induced with inhalational or intravenous induction agent and maintained with inhalational agent in oxygen nitrous oxide mixture. Following complete muscle relaxation after administration of appropriate muscle relaxant, the first attempt of endotracheal intubation was done with uncuffed tube size calculated based on Height {( ID(mm = (Height in Cm /30) + 2)}. Following intubation correct placement will be confirmed by end  tidal carbon dioxide ( ETCO2) trace  and five point  auscultation. Once the tube is secured ,the  leak pressure will be measured by closing the pressure relief valve and auscultating over the larynx. The absence of considerable leak at an airway pressure between 10 -25 cms of water is considered as appropriate size. If there is leak at airway pressure lower than 10 cmsH2O , then the size is considered as too small and will be replaced with a tube Size 0.5 mm more than that used . Similarly if there is no leak at all, at airway pressure of 25cms of H2O or more, tube is considered as too large and will be replaced with 0.5mm smaller size. After having secured appropriate tube ventilation will be continued according to the requirements as per normal settings. 

The final (actual) tube size used will be correlated with the size predicted by ABF, HBF and WBF as follows :

Following extubation the children will be monitored  in PACU for sorethroat, harseness of voice, cough, aspiration stridor or any other complications. 

Design of study

The statistical package for social sciences ( SPSS ) version 26.0 will be used for statistical analysis. The quantitative variables will be expressed as mean with 95% confidence intervals (95% CI) and will be compared using paired â€˜t’ test. Data will be presented as mean ± SD ,number(%) as appropriate. Pearson correlation coefficient test for association of various parameters for selection of ETT and inter rater kappa static for strength of agreement. A p-value less than 0.05 was considered significant.