Efficacy of height-based formula to predict insertion depth of left-sided double lumen tube: A prospective observational study.

The insertion depth of the left-sided double-lumen tube needs careful positioning and bronchoscopic confirmation. Several formulae based on body height have been used for estimating the optimal insertion depth of a left-sided double-lumen tube. We conducted this prospective study to test the hypothesis that our earlier developed height-based formula (0.25 × body height) could predict the accurate insertion depth of a left-sided double-lumen tube. After obtaining ethical approval, 66 patients who underwent thoracic surgery were included. A left-sided double-lumen tube was advanced blindly to the predicted depth of insertion calculated using our formula. The optimal position of the left-sided double-lumen tube was confirmed using a fibreoptic bronchoscope. The primary outcome was the percentage of tubes placed in the optimal position without the need for further adjustments. The secondary outcomes included the need for bronchoscopic adjustments and the final correct insertion depth of the left-sided double-lumen tube. The formula resulted in an optimum position of the left-sided double-lumen tube without further adjustments in 45 patients (70%) (95% confidence interval 58%-80%). The left-sided double-lumen tube was withdrawn or advanced in 18.2% and 12.1%, respectively, to achieve the optimal insertion depth. We found that our formula provided satisfactory positioning in about 70% of patients and that in the remaining patients, the adjustments required to achieve satisfactory positioning under fibreoptic bronchoscope guidance were minimal. Nevertheless, as it is not possible to predict which patients will have a satisfactory tube position, bronchoscopic confirmation for the final positioning is still required.