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In our opinion the recommendation [1] for choosing a larger size of tracheal tube for patients anticipated to require admission to ICU is not applicable to all patients.

Farrow et al. mentioned the Hagen-Poiseuille equation and the work of breathing which is increased in smaller diameter tubes. However, the pressure is also directly related to the length of the tube. In patients likely to be ventilator-dependent for a prolonged period of time, tracheostomies are usually inserted; these are shorter and hence decrease the work of breathing, reduce dead space and resistance and facilitate suctioning and bronchoscopy.

More importantly, studies have shown a clear association between the size of the tracheostomy or tracheal tube and long-term debilitating complications such as subglottic stenosis. A recent multicentre study in the USA [2], including 1175 patients, demonstrated that 22.7% of those whose tracheas were intubated with a tracheal tube larger than 7.5 ;mm developed airway stenosis, compared with 3.3% of those with a tube size ≤7.5 mm. This study also demonstrated that obese patients are more likely to receive a larger sized tracheal tube compared with non-obese patients, in order to overcome the work of breathing which is believed to be less with a larger tube (to overcome reduced chest wall compliance). Also, individuals requiring intubation for longer than a week are 2.5 (95% CI 0.8-7.9) times more likely to develop airway stenosis than if intubation is for under a week.

From our National Centre for Airway Reconstruction database of 600 patients, 312 were diagnosed with subglottic stenosis related to tracheal intubation/prolonged ventilation on ICU. Seventy per cent of these were managed with endoscopic surgical procedures and on average underwent three operations to cure them of symptoms. A third of these required an open surgical procedure followed by 2-3 postoperative microlaryngoscopies +/‒ laser treatments. Thus these patients not only have a prolonged period of debilitating illness before they are diagnosed, but also have to undergo multiple surgical interventions before they can lead a normal life. Hence the size of tube does matter and in our opinion, a default size of 8 or 9 mm should not be advised for ICU patients.

Lastly, the tube size selection is best correlated with the height, and not sex, of the patient, so 8 mm tubes for women and 9-10 mm for men are only likely to result in an increase in the incidence of these complications.

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