ETT Size Selection

The majority of anesthesia providers use a size 7.0 for women and size 8.0 for men.

All current studies support using smaller ETTs for routine care with size 6.0 for women as most frequently recommended. Larger sized ETTs are associated with subglottic tracheal stenosis (SGS), vocal cord dysfunction, recurrent laryngeal nerve palsy, post-operative sore throats and hoarseness. Ranestad found the inner diameter of the female cricoid ring does not permit passage of a standard size (7 mm) tracheal tube in some women, and the small distance between the cricoarytenoid joints and standard size tubes cause pressure necrosis at the medial sites of the arytenoid cartilages.

Dedo describes the pathologic changes that occur to vocal cords from pressure necrosis:

 “… the mucosa and the perichondrium of the arytenoid cartilages can be necrosed by an endotracheal tube that is too large….As the body tries to heal the ulcers on the arytenoids and seal off and heal the underlying chondritis, granulation tissue forms on the medial surfaces of the arytenoids. This produces two possible results. Granulomas can occur on the arytenoids that may heal spontaneously or that may require repeated laser removals every few months via direct laryngoscopy until the arytenoids epithelialize and heal; or the granulomas can fuse and through scar formation cause the arytenoids to grow together. If the endotracheal tube pressure causes the necrosis to extend into the cricoarytenoid joints, they will become frozen, so that even if posterior commissure stenosis is repaired, the vocal cords will not be able to adduct (open) to provide and adequate airway.”

The anatomical differences may also help explain why SGS occurs in females at a rate that is two- to five-fold higher than in men. Studies of SGS and occurrence rate include: Zias: 75% women to 25% men. Mehta: 15 women to 3 men, McGaffrey: 50 women compared to 22 men. Poerker: more women then men. Ghadiali and Dedo also link ETT sizes and SGS. These studies make it clear that it is imperative to use smaller sized ETTs, especially in women.

Because of the location of the blood supply of the trachea and recurrent laryngeal nerve (RLN) position in the tracheal-esophageal groove, the lateral wall is especially vulnerable to compression injuries. The following diagram illustrates this anatomy:

 Trachea Anatomy: Tewfik MD, Medscape reference

Hoarseness, vocal cord palsy and mucosal ischemia could be the result of pressure on the lateral wall. Xu, Cros, Stout, Jaensson, Bradwein, Dedo, Otani, and Mendels have all linked this pressure to post-operative sore throat, hoarseness or recurrent nerve injury and paralysis, and subsequently support the use of smaller ETTs and cuff measurement.

Work of breathing (WOB) is frequently cited as the rationale for choosing larger size tubes. Fiastro disputed this in 1988 (well over two decades ago) with the conclusion, “…when adjusting for an endotracheal tube’s diameter and VT/TI (mean inspiratory flow) pressure support can be used to compensate for the added inspiratory work due to artificial airway resistance.” In 2004, Koh discussed WOB, concluding, “Positive pressure ventilation could be achieved with the use of small sizes of tracheal tubes.” Koh also stated, “There is evidence that glottis damage is less likely after both short- and long-term intubation when smaller sizes of tube are used."

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