To the Editor:
Dalal et al.1 described the cross-sectional area of the paralyzed glottis in children to be smaller than that at the level of the cricoid cartilage. Although this is not a surprising finding for pediatric airway endoscopists, we have concerns regarding the article's conclusions.
The authors compared an opening surrounded by a rigid (cricoid) structure with an opening surrounded by an actively movable and passively pliable one (vocal folds). The diameter of the pliable, paralyzed vocal folds, acting like a curtain, is irrelevant when passing a tube through both openings at intubation. This effect of the vocal folds can be observed endoscopically in every single intubation when the beveled tip of the endotracheal tube enters the larynx between the paralyzed vocal folds, pushing them gently aside, but obtaining a seal only in the caudal part of the cricoid ring, which has a circular shape.2–4 This means that the exit of the cricoid ring is functionally the narrowest part of the pediatric upper airway. This was also confirmed by Fayoux et al.5 in a postmortem study in premature infants from the 37th week of gestation until infancy within 6 hours after death without using fixatives, approximating observations in in vivo studies. Injuries of the pediatric larynx develop practically only within the cricoid ring and not within the glottic area as observed in large numbers of patients undergoing ear-nose-throat surgery.6
Declaring a pliable structure as the narrowest part of the pediatric upper airway, as stated by Dalal et al., will in our opinion inevitably lead to attempts to seal the upper airway with an endotracheal tube at this location, the vocal folds. This might in turn lead to otherwise avoidable damage to the larynx by using inadequate methods (perhaps a cuffed tube) for sealing the airway at this pliable location. This problem has been addressed in the editorial accompanying the article by Dalal et al.7 and in an article demonstrating severe airway injuries after the use of inadequate methods of sealing the upper airway.8
The time at which the infant larynx approaches adult anatomy is variably addressed in the literature. Eckel et al.2 found the infant larynx to reach almost the equivalence of the adult larynx in the fifth year of life, whereas Wheeler et al.4 described the cricoid and thyroid cartilage reaching adult proportions at the age of 10 to 12 years. However, according to Wheeler et al., many adults live with a slightly funnel shape of their larynx throughout their life, which makes it even more difficult to define the age when the pediatric larynx reaches adult proportions. Only further studies will help us understand fully the complicated structure of the pediatric larynx.
Josef F. Holzki, MD
Michael Laschat, MD
Christian Puder, MD
Children's Hospital Cologne
Cologne, Germany
[email protected]
REFERENCES
1. Dalal PG, Murray D, Messner AH, Feng A, McAllister J, Molter D. Pediatric laryngeal dimensions: an age-based analysis. Anesth Analg 2009;108:1475–9
2. Eckel HE, Koebke J, Sittel C, Sprinzl GM, Pototschnig C, Stennert E. Morphology of the human larynx during the first five years of life on whole organ serial sections. Ann Otol Rhinol Laryngol 1999;108:232–8
3. Holinger LD, Lusk RP, Green CG. Pediatric Laryngology and Bronchoesophagology. Philadelphia, PA: Lippincott-Raven, 1997:19–26
4. Wheeler M, Coté CJ, Todres ID. The pediatric airway. In: Coté CJ, Lerman J, Todres ID eds. A Practice of Anesthesia for Infants and Children. 4th ed. Philadelphia, PA: Saunders Elsevier, 2009:238–43
5. Fayoux P, Devisme L, Merrot O, Barciniak B. Determination of endotracheal tube size in a perinatal population. Anesthesiology 2006;104:954–60
6. Cotton RT. Management of subglottic stenosis. Otolaryngol Clin North Am 2000;33:111–30
7. Motoyama EK. The shape of the pediatric larynx: cylindrical or funnel shaped? Anesth Analg 2009;108:1379–81
8. Holzki J, Laschat M, Puder C. Stridor is not a scientifically valid outcome measure for assessing airway injury. Paediatr Anaesth 2009;19(suppl 1):180–97
