Insertion depth of left-sided double-lumen endobroncheal tube: A new predictive formula

Background: In the field of thoracic anesthesia, it is well-established practice that the insertion depth of left-sided double-lumen tube (LDLT) is achieved after checking its position via fiberoptic bronchoscopy (FOB). Several studies have shown positive correlation between body height (BH) and the optimal insertion depth of a LDLT. Each of these studies has developed a formula for proper insertion depth of the LDLT. In this study, we prospectively studied our patients whose tracheas were intubated correctly with LDLT using FOB confirmation and examined the optimal insertion depth of LDLT aiming at finding a formula suitable for our patients. Methods: After obtaining the institutional review board approval of College of Medicine Research Centre, King Saud University, we recruited 41 adult patients who underwent thoracic surgery with one-lung ventilation (OLV). The study included patients whose procedure required placement of a LDLT. The optimal insertion depth of the LDLT was confirmed using FOB. The following variables were recorded, the patient's sex, age, BH, and the final correct insertion depth of the LDLT (cm) measured from the corner of the mouth. The results of LDLT insertion depth in our study were compared to another published five studies. Statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) version 22 software (SPSS Inc., Chicago, IL, USA). Results: Positive correlation was found between BH (cm) and insertion depth of LDLT (cm) since r = 0.744 (P < 0.05). Also, positive correlation was found between the LDLT size (Fr) and insertion depth of LDLT (cm) since r = 0.792 (P < 0.05) where r is Pearson's correlation coefficient. By fit curve (Curve Estimation), we were able to get the predicted equation for our cases as follow: the insertion depth of LDLT (cm) = 0.249 x (BH)(0.916) with significant correlation to the other five formulae (P < 0.05). Conclusion: In the present study we have obtained a novel formula to predict the insertion depth of LDLT. Currently we are conducting a verification study on a larger sample size to attest its validity. However at this stage and till the results are released we cannot judge on it. We believe time will tell about the validity of our formula for our patients.