Diaphragm muscle thinning in subjects receiving mechanical ventilation and its effect on extubation

BACKGROUND: Diaphragm muscle weakness and atrophy are consequences of prolonged mechanical ventilation. Our purpose was to determine whether thickness of the diaphragm (TDI) changes over time after intubation and whether the degree of change affects clinical outcome. METHODS: For this prospective, longitudinal observational study, we identified subjects who required mechanical ventilation and measured their TDI by ultrasonography. TDI was measured at baseline and repeated 72 h later and then weekly until the subject was either liberated from mechanical ventilation, was referred for tracheostomy, or died. The analysis was designed to determine whether baseline TDI and change in TDI affect extubation outcome. RESULTS: Of the 57 subjects who underwent both diaphragm measurements at 72 h, 16 died, 33 were extubated, and 8 underwent tracheostomy. Only 14 subjects received mechanical ventilation for 1 week, and 2 subjects received mechanical ventilation for 2 and 3 weeks. Females had significantly thinner baseline TDI (P =.008). At 72 h, TDI had decreased in 84% of subjects. We found no significant association between the rate of thinning and sex (P =.68), diagnosis of COPD (P =.36), current smoking (P =.85), or pleural effusion (P =.83). Lower baseline TDI was associated with higher likelihood of extubation: 12.5% higher for every 0.01-cm decrease in TDI (hazard ratio 0.875, 95% CI 0.80–0.96, P =.003). For every 0.01-cm decrease in TDI at 72 h, the likelihood of extubation increased by 17% (hazard ratio 0.83, 95% CI 0.70–0.99, P =.041). CONCLUSIONS: Although most of the subjects showed evidence of diaphragm thinning, we were unable to find a correlation with outcome of extubation failure. In fact, the thinner the diaphragm at baseline and the greater the extent of diaphragm thinning at 72 h, the greater the likelihood of extubation. Thickening ratio or other measurement may be a more reliable indicator of diaphragm dysfunction and should be explored.