To the Editor:
In a very elegant bench-to-bedside investigation, Mietto et al.1 studied the secretion-induced cross-sectional area (CSA) reductions of tracheal tubes (TTs) in intensive care unit patients. Using ex vivo high-resolution computed tomography (CT) scans, extubated TTs showed a minimum CSA 25 ± 4% lower than new and nonused TTs; using in vivo standard clinical chest CT scans of selected patients, 6 of 20 intubated TTs showed measurable secretions with a CSA reduction of 24 ± 4% and an absolute reduction of 1.5 ± 0.4 mm in the anteroposterior diameter of TTs.
One main finding in the ex vivo CT scans was that CSA progressively decreased from oral to lung end of used TTs, suggesting that increases in the resistance to airflow that could result in higher ventilatory pressures and greater work of breathing are mainly caused by retained secretions at that end of TTs. However, TTs may bend and even “kink” in the part located in the neck and oral region, depending on the tube quality and the number of days it is in use, among other factors. Although this by itself could reduce the inner diameter of TTs, it will certainly increase the impact of secretions on resistance to airflow at this part of TTs. Because of design of the study, the in vivo CT scans did not allow Mietto et al. to review the extrathoracic part of TT, as neck and oral cavity were not included in the standard clinical chest CT scans.
I agree with the authors that the impact of retained secretions within the TT lumen is of greater clinical importance than often recognized and that CT scanning could be a useful tool for early detection of secretion-induced CSA reductions. But then we may need to deviate a little from the standard clinical chest CT scan by including the neck and oral cavity.
The author declares no competing interests.