Serial Lung and Diaphragm Ultrasonography to Predict Successful Discontinuation of Mechanical Ventilation

Abstract

PURPOSE: This study seeks to evaluate the performance of serial bedside ultrasonography to assess lung aeration and diaphragmatic function during weaning from mechanical ventilation (MV). METHODS: Study subjects were patients in the medical intensive care unit who required endotracheal intubation with MV and who were under consideration for extubation. When the patient was ready for extubation as per standard clinical criteria, bedside ultrasonography was performed on three occasions: (1) on assist control mode with consistent ventilator triggering (2) following spontaneous breathing trial (SBT) for 30 minutes (CPAP 5cmH2O/PS 5cmH2O) (3) 4-24 hours after extubation. Ultrasonography was used to assess lung aeration pattern in 8 predefined thoracic regions, and to measure diaphragm thickness fraction (calculated as percentage from: thickness at end inspiration - thickness at end expiration / thickness at end expiration), diaphragm excursion, and diaphragm contraction velocity. Failure of weaning from mechanical ventilation was defined as either the need for non-invasive ventilation or re-intubation within 48 hours of extubation. The success of removal from mechanical ventilation was co-related with the above measurements using the Mann-Whitney test. 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. CONCLUSIONS: These results show a significant difference between groups with successful and failed extubation with regards to serial evolution of diaphragm function and lung aeration pattern on ultrasonography following removal from MV.