DLT have 4 sizes, left and right sides. Guidance is required to obtain lung isolation without trauma or tube displacement. The pre-eminent formula using height and sex has few supporting data1. An alternative proposes using the smallest size for all patients2. We have audited the pre-eminent formula in clinical practice.
Methods: DLT were used in adults having elective thoracic surgery. Patients were intubated with a MallinckrodtTM (Coviden, Mansfield) DLT. Left tubes were used except for left lung resection. Tubes were allocated according to height: women ≤160 cm 35F, >160 cm 37F, men ≤170 cm 39F, >170 cm 41F. Distance markings on the tube at the teeth was noted. The bronchial cuff was identified by fibre-optic bronchoscopy (FOB) and moved if necessary to correct position. Distance mark at teeth was noted again. Tracheal and bronchial cuffs were inflated to 22 cmH2O. Volumes were measured with a 5 ml syringe. Ease of insertion, adequacy of ventilation, oxygenation, and intra-operative airway complications were recorded.
Results: 191 patients were studied: M 63% F 36%, median age 60, median BMI 26 kg.m−2. 188 (98%) patients were intubated with the tube as intended. One patient could not be intubated with a 41F DLT but was intubated using a 37F tube. In two patients smaller tubes were used by trainees as a first response to difficulty. 4 smaller tubes were chosen at variance to the instruction. A bougie was required in 10 patients, an exchange catheter in 1. DLT used were: 35F 25 (13%), 37F 47 (25%), 39F 27 (14%), 41F 92 (48%), L 157 (82%), R 34 (18%). 75% required to be advanced (21%) or withdrawn (53%) under FOB guidance. Median ultimate position was 29 (range 25-33) cm. Median cuff volumes were: bronchial: 1.6 (range 0.4-5.8) 90th percentile 2.6 ml, tracheal: 3.8 (range 1.2-8.0) 90th percentile 5.2 ml. 11 (6%) patients developed intra-operative hypoxaemia < 94% requiring intervention: the tube was moved during repositioning in 3 (1.6%).
Discussion: Successful position was obtained in 98% of cases. Complications associated with under-sized tubes2 were avoided. High quality imaging to obtain measurements3, were not required. Positioning DLT clinically without FOB4 may be incorrect in three quarters of patients. 90% of cuffs may be sealed by air 2.6 ml in the main bronchus and 5.2 ml in the trachea.