Correlation of tracheal size with body mass index – Retrospective computerised tomographic evaluation

Introduction: A question often asked in the anaesthetic room is 'What size endotracheal tube (ETT) should be used for this patient?' In the recent past, it has become common for anaesthesiologists to use ETTs 1–2 mm smaller than the expected tracheal size. However, it is difficult to gauge the appropriate size of ETT in obese patients. Aim: This study aimed to establish the baseline dimensions of the normal adult trachea and determine whether body mass index (BMI) affects cervical tracheal size. Patients and Methods: A total of 179 patients were included in the study. All imaging was performed on a 64-slice Lightspeed scanner (GE Healthcare) using collimation of 1.25 mm or 2.5 mm. Two axial levels were identified: the first tracheal ring and the most superior segment of the substernal trachea (i.e., the thoracic inlet). The diameter of the trachea in the anteroposterior (AP) and transverse (Trans) dimensions, as well as the cross-sectional area (using freehand region of interest tool) were measured at both the identified levels. The BMI was calculated from weight and height or taken directly from the clinical notes when available. To test the null hypothesis of no association between BMI and tracheal size, Pearson correlation coefficients along with 95% confidence interval were computed. Results: No trends or statistically significant associations were found between BMI and tracheal size on computerised tomography using AP, transverse and cross-sectional area measurements. Conclusion: Our study suggests that there is no link between BMI and tracheal size.