Changes in respiratory mechanics after tracheostomy

Objective: To determine the effects of tracheostomy on respiratory mechanic s 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 ( PaO2, >55 mm Hg; pH >7.30; and respiratory rate, <30/min on room air contin uous positive airway pressure after 20 minutes) but failed extubation on 2 occasions were eligible for the study. Interventions: Respiratory mechanics, lung volumes, and WOE were measured b efore and after tracheostomy. Main Outcome Measures: Patients in whom extubation fails often progress to unassisted ventilation after tracheostomy. The study hypothesis tvas that t racheostomy would result in improved pulmonary function through changes in respiratory mechanics. Results: Data are given as means+/-SDs. After tracheostomy, WOE per liter o f ventilation (0.97 +/- 0.32 vs 0.81 +/- 0.46 J/L; P<.09), WOB per minute ( 8.9 +/- 2.9 vs 6.6 +/- 1.4 J/min; P<.04), and airway resistance (9.4+/-4.1 vs 6.1+/-4.5 cm H2O/L per second; P<.07) were reduced compared with breathi ng via an endotracheal tube. These findings, however, do not fully explain the ability of patients to be liberated from mechanical ventilation after t racheostomy. In 4 patients who were extubated before tracheostomy, WOB was significantly greater during extubation than when breathing through an endo tracheal 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 tracheostomy tube repr esents reduced imposed WOB compared with the longer, thermoliable endotrach eal tube. The clinical significance of this effect is small, although as re spiratory rate increases, the effects are magnified. In patients in whom ex tubation failed, WOB may be elevated because of incomplete control of the u pper airway. Future studies should evaluate the cause of increased WOB afte r extubation.