Sunday, February 09, 2014

Funnel or tapered shaped pediatric airway - where does this concept come from?

Pediatric airway, especially for those 2 years of age, has often been described as a funnel-shaped with its narrowest part at the level of the cricoid cartilage (in contrast with the cylindrical adult larynx).

But where does this concept originate from?

Ríos Medina et al (2012) in a review article (click here to download in pdf) stated that it was way back in 1951 when Eckenhoff wrote about the anatomical considerations of the pediatric larynx and their implications for anesthesia.

However, Eckenhoff's article was in turn based on descriptions made half a century before by Bayeux, who reported the findings from anatomic dissections in 15 bodies of children between 4 months and 14 years of age, together with their corresponding plaster models. In that article, Eckenhoff describes the cricoid cartilage as a rigid structure that cannot be distended in order to pass the ETT, and describes how its parts come together to form a ring around the larynx. Eckenhoff actually clearly states the danger of extrapolating such cadaver findings to live human beings. Unfortunately a number of anesthesiology textbooks picked up on these anatomical descriptions of the pediatric airway since then.

In 2003, Litman et al., in a study using MRI on 99 children under 14 years of age showed that the narrowest portion was identified at the cross-sectional diameter of the vocal cords.

Dalal et al. (2009), in another study using video bronchoscopy on 128 children under 13 years of age seems to confirm Litman's findings. Although the approaches are different, the glottis is identified as the narrowest portion and the larynx as being more cylindrical than rather than traditionally taughted to be tapered. Nonetheless, Litman observes that, although his results show that the narrowest portion of the pediatric airway is at the glottis entrance, functionally the cricoid cartilage is a rigid structure that cannot be distended, and it is still the site of the greatest risk for injury.

Although this new concept is probably still evolving,  the clinical implication is that cuffed ET tubes can be used safely just as with uncuffed tubes.

1 comment:

Unknown said...

Great info... Will share, it so deserves too!!!

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