Stylet bend angles and tracheal tube passage using a straight-to-cuff shape

Objectives: Malleable stylets improve maneuverability and control during tube insertion, but after passage through the vocal cords the stiffened tracheal tube may impinge on the tracheal rings, preventing passage. The goal of this study was to assess insertion difficulty with styletted tubes of different bend angles. Methods: Tube passage was assessed with four different bend angles (25 degrees, 35 degrees, 45 degrees, and 60 degrees) using straight-to-cuff-shaped tubes. In two separate airway procedure classes, 16 operators in each class (32 total) placed randomly ordered styletted tubes of the different angles into eight cadavers (16 total). Operators subjectively graded the ease of tube passage as no resistance, some resistance, or impossible to advance. Results: No resistance was reported in 69.1% (177/256) at 25 degrees, in 63.7% (163/256) at 35 degrees, in 39.4% (101/256) at 45 degrees, and in 8.9% (22/256) at 60 degrees. Tube passage was impossible in 2.3% of insertions (6/256) at 25 degrees, in 3.5% (9/256) at 35 degrees, in 11.3% (29/256) at 45 degrees, and in 53.9% (138/256) at 60 degrees. The odds ratios of impossible tube passage for 35 degrees, 45 degrees, and 60 degrees vs. 25 degrees were 1.52 (95% confidence interval [CI] = 0.55 to 4.16), 5.32 (95% CI = 2.22 to 12.71), and 48.72 (95% CI = 21.35 to 111.03), respectively. Conclusions: Bend angles beyond 35 degrees with straight-to-cuff styletted tracheal tubes increase the risk of difficult and impossible tube passage into the trachea. The authors did not compare different stylet stopping points, stylets of different stiffness, or tracheal tubes with different tip designs, all variables that can affect tube passage.