Endotracheal Intubation is a commonly performed procedure in the operating room to maintain the airway and respiration in patients receiving general anaesthesia. Endotracheal tubes are passed both through the oral route and nasal route depending on the type of surgery. Serious complications can occur from if the tube is too far inside and enters the mainstem bronchus, such as hypoxaemia caused by atelectasis formation in the unventilated lung and hyperinflation and barotrauma with development of a pneumothorax of the intubated lung. If the tube is too far out it there can be an accidental extubation. Hence, proper positioning of the endotracheal tube in relation to the carina is therefore clinically important. The recommended safe position of the tip of the endotracheal tube in the trachea is 2.5 to 4 cms.above the carina¹ .This positioning can however be checked and done only by using a flexible fiberscope in OT and is not practical in routine clinical  practice.

Other methods are available in clinical practice to check proper tube position .Institutions like the American Heart Association and the European Resuscitation Council and major textbooks on anaesthesia recommend bilateral auscultation of the chest to diagnose and prevent endobronchial intubation and this has been the conventional practice. Brunel et al, however, found that 60% of endobronchial intubations in patients in despite equal breath sounds on examination.² Other additional clinical tests to verify correct positioning have therefore become routine, including observation of symmetrical chest movements, palpation of symmetrical chest expansion, and use of the cm scale printed on the endotracheal tube. ^3,4

Recently a prospective blinded study published in BMJ was conducted to determine which bedside method of detecting inadvertent endobronchial intubation in adults has the highest sensitivity and specificity. The sensitivity and specificity for ruling out endobronchial intubation with auscultation alone was 65% and 93% respectively ,with observation was 43% and 90 % respectively and using depth of tube insertion was 88% and 98% respectively. Hence among the methods depth of insertion of tube was found to be most sensitive and specific. When all 3 methods were combined the sensitivity was 100% and the specificity was 95%.⁵ This study looked at only oral intubations and the optimal tube insertion depth was found be 20 cm in females and 22 cm in males (20/22 formula)

This study showed that auscultation alone is inadequate for assessment of proper position of endotracheal tube and that checking for symmetrical chest movements is of little use. The hierarchy of the methods used to assess the correct insertion depth should be changed and clinicians should rely more on depth insertion than on auscultation. The study showed that both experienced and inexperienced physicians wouldl benefit from using a 20/22 cm formula for depth of tube insertion while using oral tubes.

One of the limitations of the study was that it was done in a relatively smaller number of patients and also only in a western population .The depth of tube insertion may also depend on the length of the trachea and the distance from the nose /mouth upto the vocal cords which may be dependent on the height and weight of the patients .Hence the 20/22 cm formula for oral intubations may require modification for populations that have larger or smaller height.

There is not much literature available about the depth of insertion of the endotracheal tube while doing nasal intubations. An old study using nasal intubations ⁶ showed that at 26 cm in women and 28 cm in men, measured at the naris, resulted in adequate initial placement for most adult patients. However the numbers in this study were very small and the safe distance from the tip of the tube to the carina was considered as 2 cms which is an old recommendation and no longer accepted. This study was also done in western population.

We would like to do a prospective study in a large number of patients using the current recommendation for depth of insertion of endotracheal tube when passed orally (20/22 cms.) and nasally (26/28 cms) and see whether it can be applicable to Indian patient.

Our aim is to determine the correct depth of insertion of endotracheal tubes during nasal and oral intubation in the Indian population and determine whether there is any co-relation with the height, weight, sex and BMI of the patient. The gold standard for determining the exact position of the tube in the trachea in OT is by measuring it using a flexible fiberscope.