Changes in the work of breathing induced by tracheotomy in ventilator-dependent patients

Abstract

Tracheotomy is widely performed on ventilator-dependent patients, but its effects on respiratory mechanics have not been studied. We measured the work of breathing (WOB) in eight patients before and after tracheotomy during breathing at three identical levels of pressure support (PS): baseline level (PS-B), PS + 5 cm H2O (PS+5), and PS - 5 cm H2O (PS-5). After the procedure, we also compared the resistive work induced by the patients' endotracheal tubes (ETTs) and by a new tracheotomy cannula in an in vitro bench study. A significant reduction in the WOB was observed after tracheotomy for PS-B (from 0.9 +/- 0.4 to 0.4 +/- 0.2 J/L, p < 0.05), and for PS-5 (1.4 +/- 0.6 to 0.6 +/- 0.3 J/L, p < 0.05), with a near-significant reduction for PS+5 (0.5 +/- 0.5 to 0.2 +/- 0.1 J/L, p = 0.05). A significant reduction was also observed in the pressure-time index of the respiratory muscles (181 +/- 92 to 80 +/- 56 cm H2O. s/min for PS-B, p < 0.05). Resistive and elastic work computed from transpulmonary pressure measurements decreased significantly at PS-B and PS-5. A significant reduction in occlusion pressure and intrinsic positive end-expiratory pressure (PEEP) was also observed for all conditions, with no significant change in breathing pattern. Three patients had ineffective breathing efforts before tracheotomy, and all had improved synchrony with the ventilator after the procedure. In vitro measurements made with ETTs removed from the patients, with new ETTs, and with the tracheotomy cannula showed that the cannula reduced the resistive work induced by the artificial airway. Part of these results was explained by a slight, subtle reduction of the inner diameter of used ETTs. We conclude that tracheotomy can substantially reduce the mechanical workload of ventilator-dependent patients.