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.

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What

An examination of fresh autopsy specimens of Caucasian larynxes aged from newborn to 126 months, to assess airway anatomy and relation of Microcuff endotracheal tubes to laryngeal structures.

How

2-part assessment.

Firstly, examination and measurement of autopsy larynxes with measurement of AP and transverse diameter of the cricoid outlet, interarytenoid diameter, cricothyroid membrane and distance from vocal cords to cricoid outlet.

Secondly, the relationship between anatomical structures and the Microcuff tube was assessed with the larynx intubated with the black mark at the vocal cords as per the manufacturer’s instructions.

Findings

The calibrated internal diameter of the cricoid outlet varied between 3.1-6.0mm in infants (0-10 months), 5.7-7.0mm in toddlers (17-34 months) and 6.5-10.5mm in those 42-126 months.

The vocal cord to cricoid outlet distance was 9.1-13.17 mm in infants, 11.55 to 15.17 mm in toddlers and 13.19-18.34 mm in children.

The AP diameter of the proximal trachea was always smaller than the transverse diameter.

The cricoid outlet is circular.    The cricothyroid membrane is short and minimally distensible.

When intubated with the black mark on the Microcuff tube at the vocal cords:

• 77% (95% CI 58-90) of intubated specimens had the proximal cuff within the cricoid outlet.
• 23% had the cuff close to the cricoid outlet.

Discussion

When intubated, using the black line at the vocal cords, the proximal cuff was within or in close proximity to the narrow cricoid outlet the majority of the time. This may cause pressure necrosis. There is concern the cuff-free vocal cord – cricoid outlet distance is too short with the Microcuff tube.

Using this data, the optimal cuff-free distance would be 13.5mm for a 3.0 Microcuff, 15mm for a 3.5 & 16-19mm for larger sizes.

Manufacturers should further evaluate cuff location and length in relation to the vocal cord safe insertion markings.

Comments

There is an attached well worded editorial which surmises the cuffed vs. uncuffed tube debate. It makes the point that while there is room for improvement in cuff position/design there is not a convincing argument to change our current practice with regard to the routine use of cuffed tubes.

It may be worth placing your Microcuff tube slightly deeper in smaller infants to ensure the cuff is clear from the cricoid outlet.  Especially if longer term ventilation is planned.

Reviewed by James Houghton