The only constant in medicine is change. A corollary is that whatever you think you know as truth will turn out to be completely wrong in 10 years. The curious thing though, is that if you live long enough, say another 10 years, the new truth turns out to be completely wrong and the original truth is well, the truth again! When I (Myron) was a kid growing up in Brooklyn, my mother of blessed memory, was absolutely sure that sunshine, milk, beef and of course, frozen vegetables were essential for good health (and the “American way”). Might as well as have asked for my casket’s measurements. This idea of what you think is right turning out to be wrong and then right again is best depicted in Woody Allen’s movie Sleeper which portrays the misadventures of the owner of a health food store, Woody Allen, “who is cryogenically frozen in 1973 after a botched medical procedure and is then defrosted 200 years later in an ineptly led police state”. From the movie:
“Dr. Melik: This morning for breakfast he (Woody Allen) requested something called "wheat germ, organic honey and tiger's milk."
Dr. Aragon: [chuckling] Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.
Dr. Melik: You mean there was no deep fat? No steak or cream pies or... hot fudge?
Dr. Aragon: Those were thought to be unhealthy... precisely the opposite of what we now know to be true.
Dr. Melik: Incredible”.
In today’s PAAD we will be reviewing an article and editorial on the dimensions of the pediatric airway and endotracheal tubes. So just when you thought the cuffed vs uncuffed tube debate was long dead some new insights may change your minds. It’s also highly appropriate to post this PAAD this during Ron Litman’s birthday week…the pediatric airway was an area of great interest to him…indeed,Ron and I (Lynne) thought we had this all figured out years ago. 1,2
Myron Yaster MD and Lynne Maxwell, MD
Original article
Isa M, Holzki J, Hagemeier A, Rothschild MA, Coté CJ. Anatomical In Vitro Investigations of the Pediatric Larynx: A Call for Manufacturer Redesign of Tracheal Tube Cuff Location and Perhaps a Call to Reconsider the Use of Uncuffed Tracheal Tubes. Anesth Analg 2021 Oct 1;133(4):894-902.PMID: 33901057
Editorial
Peyton J, Foglia E, Lee GS. Pediatric Airway Anatomy and Tracheal Tubes: It Is Not All About the Cuff. Anesth Analg. 2021 Oct 1;133(4):891-893. PMID: 34524987
Using fresh fixative-free pediatric cadavers, Isa et al. carefully measured laryngeal and tracheal specimens and found that:
1. The cricoid ring (“outlet”) is circular, non-distensible, and the narrowest part of the airway.
2. The thick black line on the Microcuff™ endotracheal tube which is designed to be placed at the vocal cords and thereby assist in proper tube placement will actually misplace the cuff of the tube within or close to the distal edge of the cricoid ring most of the time.
3. Because of its position, inflating the cuff within the cricoid ring may cause mucosal pressure necrosis
4. Because of points 1-3 above Isa et al. urge the redesign of cuff placement and vocal cord (black line) guide on the Microcuff™ tube AND recommend the use of uncuffed tubes in small children. This should result in an adequate seal at the level of the circular non-distensible cricoid ring.
5. The rigid circular conformation of the cricoid ring confirms that the previously described funnel shape of the pediatric airway is incorrect.
6. “The cricothyroid membrane (CTM) is small, minimally distensible, and cephalad confirming the potential difficulty for surgical cricothyrotomy in neonates and toddlers and the importance of choosing appropriately sized cannulas for trans-CTM access to the trachea”.
The Isa et al. study differs from prior cadaver investigations in that the specimens were fresh and fixative- free. The authors argue that the dimensions they found are more representative of those present in living children than CT or MRI obtained images in living, spontaneously breathing children1 because dimensions obtained in those studies were not correlated with phase of respiration.
When we were young guppies, uncuffed endotracheal tubes were mandatory in children < 6-8 years of age…cuffed tubes were not allowed because of the risk of tracheal damage when the high pressure low volume cuff was inflated in the cricoid ring. The Microcuff™ tube was a game changer because it was a high volume low pressure cuff made of polyurethane and the cuff was physically located more distally on the tube (below the cricoid ring), which was enabled because of the elimination of the distal murphy eye.2 Prior to the development of the Microcuff™ tube design, cuffed tubes were used in younger children, with careful attention to avoid overinflation of the cuff through use of auscultation of the leak around the cuff (< 20 cm H2O). The many advantages of the cuffed tube included: easier ventilation in poorly compliant lungs, more accurate end tidal CO2 and anesthetic gas level measurements, use of lower fresh gas flows, less waste gas pollution in the OR, and the ability to intubate once rather than multiple times to find the right tube size. Ron Litman and I (Lynne) thought the debate was over. To be honest, we and the editorial writers still do. Cuff pressure injury is known to occur with the Microcuff™ but so too is injury from multiple tube changes. Obviously, the longer a tube stays in place, as occurs in the NICU and PICU, the greater the risk of injury.
Although not discussed in either the editorial or original article, there may be a relatively simple fix until there is a new tube design, namely measuring the cuff pressure. Several easy manometers to measure cuff pressure are available, and many of our European colleagues monitor cuff pressure continuously through a transducer and pressure cable with monitor display. There are also indicator (green/red) devices that can be built into the cuff pressure line to help guide the amount of air (and pressure) within the cuff.
Thus, friends take heart - uncuffed tubes may be BACK but probably not for more than 10 years….although we agree with the editorial’s conclusion that in the absence of evidence of cuff-related injury, the results of this cadaver study do not justify a change in clinical practice at this time.
Myron Yaster MD and Lynne Maxwell MD
References
1. Litman RS, Weissend EE, Shibata D, Westesson PL: Developmental changes of laryngeal dimensions in unparalyzed, sedated children. Anesthesiology 2003; 98: 41-45
2. Litman RS, Maxwell LG: Cuffed versus uncuffed endotracheal tubes in pediatric anesthesia: the debate should finally end. Anesthesiology 2013; 118: 500-1
PS: the good news is that for purposes of the Board exam the narrowest part of the trachea is still the cricoid ring! MY