RESULTS: Forty one patients were enrolled in the study (21 males, mean age 68.9 years, and mean duration of MV 4.9 days). The most common diagnosis was septic shock. Ten patients had failure of removal from MV. There was no significant difference between patients that were successfully removed from MV and those who failed with respect to clinical characteristics, rapid shallow breathing index, MV duration, and absolute values for diaphragm thickness fraction, excursion and contraction velocity. During SBT and following extubation, diaphragm excursion (p<0.001) and velocity (p=0.006) were significantly reduced while lung aeration score was significantly worse (p=0.0001) in the patient group that failed removal of MV when compared to patients who were successfully extubated.