Size matters when you're sick

A nice example of a difference between elective anaesthesia and critical care practice when it comes to airway management is the selection of appropriate tracheal tube size when intubating, which is highlighted in a recent Anaesthesia article.
In recent years progressively smaller tubes have been used in anaesthesia in pursuit of decreased tracheal injury, sore throat, and hoarseness and increased ease of placement.
Patients likely to remain intubated for some time due to critical illness, however, may benefit from larger diameter tubes for the following reasons:

  • Accumulation of biofilm debris, which increases with duration of intubation – this can significantly decrease the luminal internal diameter, but is less likely to be significant with larger tubes.
  • Work of breathing during weaning: spontaneous breathing trials prior to extubation require patients to breathe through tracheal tubes. Volunteer studies have demonstrated that work of breathing increases as tube diameter decreases.
  • Bronchoscopes and suction catheters: the standard adult ICU fibreoptic bronchoscope has a diameter of 5.7 mm with a 2-mm suction channel to enable adequate suction, which limits the tracheal tube to those larger than 7.5–8.0 mm, and even with an 8.0-mm tube, the bronchoscope occupies more than 50% of the tube diameter, which can lead to ventilation issues during bronchoscopy.

The authors conclude by recommending:

‘If admission to ICU is contemplated then the time-honoured ‘8.0 for females, 9.0 for males’ is a reasonable rule of thumb, unless circumstances dictate otherwise, e.g. in difficult airways or particularly small patients.’

Size matters: choosing the right tracheal tube
Anaesthesia. 2012 Aug;67(8):815-9

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