To determine the effects of tracheostomy on respiratory mechanics and work of breathing (WOB).Design: A before-and-after trial of 20 patients undergoing tracheostomy for repeated extubation failure.Setting: Surgical intensive care unit at a university teaching hospital and a level I trauma center.Patients: A consecutive sample of 20 patients who met extubation criteria (PaO 2 , Ͼ55 mm Hg; pH Ͼ7.30; and respiratory rate, Ͻ30/min on room air continuous positive airway pressure after 20 minutes) but failed extubation on 2 occasions were eligible for the study.Interventions: Respiratory mechanics, lung volumes, and WOB were measured before and after tracheostomy.Main Outcome Measures: Patients in whom extubation fails often progress to unassisted ventilation after tracheostomy. The study hypothesis was that tracheostomy would result in improved pulmonary function through changes in respiratory mechanics.Results: Data are given as means ± SDs. After tracheostomy, WOB per liter of ventilation (0.97 ± 0.32 vs 0.81 ± 0.46 J/L; PϽ.09), WOB per minute (8.9 ± 2.9 vs 6.6 ± 1.4 J/min; PϽ.04), and airway resistance (9.4 ± 4.1 vs 6.3 ± 4.5 cm H 2 O/L per second; PϽ.07) were reduced compared with breathing via an endotracheal tube. These findings, however, do not fully explain the ability of patients to be liberated from mechanical ventilation after tracheostomy. In 4 patients who were extubated before tracheostomy, WOB was significantly greater during extubation than when breathing through an endotracheal or tracheostomy tube (1.2 ± 0.19 vs 0.81 ± 0.24 vs 0.77 ± 0.22 J/L).
Conclusions:We believe that the rigid nature of the tra-cheostomytuberepresentsreducedimposedWOBcompared with the longer, thermoliable endotracheal tube. The clinical significance of this effect is small, although as respiratory rate increases, the effects are magnified. In patients in whom extubation failed, WOB may be elevated because of incompletecontroloftheupperairway.Futurestudiesshould evaluate the cause of increased WOB after extubation.
Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.
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