Need for New Standards

Prevention of Subglottic Stenosis

As anesthesia providers, we have the privilege of providing care to patients during surgery, and with that privilege comes responsibility for their welfare. Because of this privilege and responsibility we would like to bring attention to routine adult endotracheal tube (ETT) practices in the OR that may place patients at unnecessary risk. These practices are:

#1: The blind inflation of pilot balloons, and

#2: The use of large-sized endotracheal tubes, especially for women.

High cuff pressure and large ETTs have both been implicated as causative factors of complications. From post-operative sore throat and hoarseness to catastrophic tracheal stenosis and recurrent laryngeal nerve (RLN) paralysis, these complications can have long-term negative sequel for our patients. As anesthesia providers, it is our duty to honor the Hippocratic oath of "first, do no harm" and adopt better practices.

New standards that need to be instituted include:

#1: Cuff pressure will be checked with each and every intubation, and

#2: Standardized tube sizes of endotracheal tubes in adults need to be decreased. Specifically, downsize to 6.0 ETT for most females and no larger than 7.5 for men.

Routine care will be described, followed by the supporting research for the proposed new standards. The articles and books cited should not be considered exhaustive of the research that supports these standards. It should also be known that there is no evidence found to support routine care as it is delivered today. Only the first author’s last name will be given followed by a full bibliography at the end.

<Arguments Against the Arguments in Support of Routine Care>

<References>

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

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 anaesthesiologists. He also found 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 then 20 cm H₂O places the patient at risk for micro-aspirations and ventilator-dependent pneumonia. Pressures greater than 30 can cause extreme injury of 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.

ETT Cuff Manometer

Over-inflated Cuff

This is a measurement of a cuff pressure from "routine practice", meaning without the use of a cuff manometer.

Since any pressure above 30 cm H2O pressure places the patient at risk of the catastrophic complications of ischemia, necrosis and ultimately, subglottic stenosis, it demonstrates why new safety standards are needed in anesthesia:

Check cuff pressure with a cuff manometer with each and every intubation and use the appropriate size ETT for the size of the patient's trachea.

Arguments

Arguments Against the Arguments in Support of Routine Anesthesia Practice

Arguments against the arguments in support of “routine anesthesia practice” (size 7 ETT for women and the injection and palpation technique of cuff inflation) and why they are wrong.

1.  Sub-glottic stenosis (SGS) only occurs with prolonged intubation.

FALSE: All research shows damage begins within 15 minutes of high cuff pressure.

2.  It is safe to use the injection and palpation technique to inflate the cuff.

FALSE: The palpation technique results in the majority of cuff pressures being too high and the risks of SGS, post-operative sore throats, post-operative hoarseness and recurrent laryngeal nerve damage.  The minimal occlusive technique can result in the majority of cuff pressures being too low and the risk of aspiration and pneumonia.  The potential life-long complications are too damaging to the patient if cuff pressure is not regulated by a manometer to safe limits.