ETT Size Selection

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

All current studies support the use of smaller ETTs for routine care, with size 6.0 to 6.5 for women being the most frequently recommended. Larger-sized ETTs are associated with subglottic tracheal stenosis (SGS), vocal cord dysfunction, recurrent laryngeal nerve damage, 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 causes 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 than 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 to the trachea and the recurrent laryngeal nerve (RLN) position in the tracheal-esophageal groove, the lateral wall is especially vulnerable to compression injuries.

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."

ETT Cuff Inflation

The majority of providers use an injection of air with a 10 cc syringe followed by manual palpation of the external balloon. This technique may fail to provide safe parameters for the patient. Many over-inflate, compromising tracheal perfusion. Many under-inflate, placing the patient at risk of micro-aspirations and pneumonia. Very few are in the acceptable range of 20-30 cm H₂O pressure.

Research: In a study to compare three different means of inflating the pilot balloon (the injection and palpation method, the minimum occlusive technique, and the set volume of air), Evans found NONE were within the appropriate range. Braz found high cuff pressure (>40 cm H₂O) in 90.6 % of patients, and Wujtewicz found a tendency toward over-inflation of endotracheal tube cuffs, with the problem more common in highly experienced anesthesiologists. He also found that over-inflation was more prevalent in 2009 than in 2002.

Other studies to support the need of a cuff manometer include:

“The mean intracuff pressure measured in the study group was 118.9 (SD= 54.3).” Koay.
“ This study revealed that the majority of cuff pressures exceeded safe pressure and required correction. Frequent measurement and adjustment of cuff pressure has been recommended, but this method requires a specific manometer.” Galinski.

There are no studies to support cuff inflation by any means other than a cuff manometer. Even as far back as 1979, Watson stated the need for a pressure gauge to take the “blindness” out of the art of anesthesia.

Injury to the patient can occur from an under- or over-inflated pilot balloon. A pressure less than 20 cm H2O places the patient at risk for micro-aspirations and ventilator-dependent pneumonia. Pressures greater than 30 can cause extreme injury to the trachea, as documented by Nordin. Excerpts of his findings:

“When the tube was placed in the trachea without inflation of the cuff it was quite clear that this was sufficient to cause minor superficial damage to the epithelial lamina. This damage only occurred over regions where a cartilage was situated. When the cuff was inflated, it resulted in an increase of the mucosal damage to the extent of the injury being directly related to the pressure in the cuff. A gradual increase in C-T (cuff tracheal) pressure led to progressive extension of the mucosal damage.”

“A C-T pressure of 20 mmHg for 1 to 2 h of intubation damaged the mucosa on top of the cartilages to such an extent that it was partly denuded almost down to the basement membrane.

“A C-T pressure of 50 mmHg for 2 h of intubation destroyed most of the epithelial cells on top of the cartilages. The basement membrane was partly denuded but seemed intact.

“At a C-T pressure of 100 mmHg for 1 h of intubation the whole part of the mucosa at cuff level was now damaged to some extent. Large areas of the basement membrane were denuded and in some areas it was completely absent, leaving the mucosal stroma visible. After 4 h of intubation the mucosa covering the cartilages were sometimes destroyed down to the cartilage itself, and bacteria were found, for the first time, to be invading the damaged mucosa.”

There is no research to support cuff pressure greater than 30 cm. If you believe your department can safely inflate the ETT cuff without a manometer, I urge you to test your theory with a pressure gauge. An example of pressures obtained without the use of a cuff manometer is displayed in the following graph. Note that the majority fall outside acceptable limits.

A discussion of time and tracheal injury must also be initiated. The “old” mindset is that damage can only occur with long-term intubations. This perspective must be changed. According to three separate authors, Dedo, Somri and Raynham, ischemic injury of the tracheal mucosa begins within 15 minutes with cuff pressures > 30 cm. Somri also states that tracheal mucosal blood flow is totally obstructed at 45 cm. According to Dedo, over-inflation for even a brief operation can lead to tracheal stenosis within 1 to 3 months. In conjunction with tracheal ischemia from high cuff pressures, decreased blood flow from hypovolemia, anemia, shock, and metabolic acidosis will cause even greater compromise.

Just as the nerves of the arms and legs are protected during surgery, we need to protect the nerves and blood supply of the trachea with the same care. It is essential to use smaller ETTs and check cuff pressure with each and every intubation. We need to bring new standards into the OR. The lives and well-being of our patients depend on it.

To conclude, we can no longer ignore these critical problems or the volume of supporting research before us. Our patients place their lives and safety in our hands. It is both an honor and a great responsibility, and we must take the initiative to adopt practices that validate this trust.

It is vital to adopt these new standards:

New Standard #1: Take cuff pressure measurements with every intubation.
New Standard #2: Standardize most female ETTs to size 6.0 and size 7.0/7.5 for men.

We do recognize that calling for new standards in this way is highly unconventional. However, no change has taken place in these routine ETT practices, even with the volume of research and papers that have been published on the topic

The following bibliography consists of studies that support our position. We urge you to read these articles carefully and then join us in the declaration of the need for these new standards.

To keep the focus on the problem and not the author, we are omitting our name but can be reached by email at [email protected]

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