The Utility of Diaphragm Ultrasound in Reducing Time to Extubation.

PURPOSE: Prediction of optimal timing for extubation of mechanically ventilated patients is challenging. Ultrasound measures of diaphragm thickness or diaphragm dome excursion have been used to aid in predicting extubation success or failure. The aim of this study was to determine if incorporating results of diaphragm ultrasound into usual ICU care would shorten the time to extubation. METHODS: We performed a prospective, randomized, controlled study at three Brown University teaching hospitals. Included subjects underwent block randomization to either usual care (Control) or usual care enhanced with ultrasound measurements of the diaphragm (Intervention). The primary outcome was the time to extubation after ultrasound, and the secondary outcome was the total days on the ventilator. Only intensivists in the Intervention group would have the ultrasound information on the likelihood of successful extubation available to incorporate with traditional clinical and physiologic measures to determine the timing of extubation. RESULTS: A total of 32 subjects were studied; 15 were randomized into the Control group and 17 into the Intervention group. The time from ultrasound to extubation was significantly reduced in the Intervention group compared to the Control group in patients with a ∆tdi% ≥ 30% (4.8 ± 8.4 vs 35.0 ± 41.0 h, p = 0.04). The time from ultrasound to extubation was shorter in subjects with a normally functioning diaphragm (∆tdi% ≥ 30%) compared to those with diaphragm dysfunction (∆tdi% < 30%) (23.2 ± 35.2 vs 57.3 ± 52.0 h p = 0.046). When combining the Intervention and Control groups, a value of ∆tdi% ≥ 30% for extubation success at 24 h provided a sensitivity, specificity, PPV and NPV of 90.9%, 86.7%, 90.9%, and 86.7%, respectively. CONCLUSIONS: Diaphragm ultrasound evaluation of ∆tdi% aids in reducing time to extubation.

The Maximal Expiratory-to-Inspiratory Pressure Ratio and Supine Vital Capacity as Screening Tests for Diaphragm Dysfunction.

PURPOSE: The change in vital capacity from the seated to supine position (∆VC-supine) is used to screen for diaphragm dysfunction (DD), but some individuals are unable to tolerate the supine position. Since expiratory muscle function is often preserved in patients with isolated DD and inspiratory strength is reduced, the purpose of this study was to examine if the ratio of maximal expiratory pressure to maximal inspiratory pressure (MEP/MIP) may provide an alternative to ∆VC-supine when screening patients for DD. METHODS: We performed a cross-sectional analysis on 76 patients referred for evaluation of unexplained dyspnea and possible DD. MEP and MIP were measured in the seated position as well as the percent change in VC from the seated to supine position (∆VC-supine %). The presence of unilateral diaphragm paralysis (UDP), bilateral diaphragm paralysis (BDP), or normal diaphragm function (N) was confirmed by ultrasound. RESULTS: Of the 76 patients, 23 had N, 40 had UDP, and 13 had BDP. MEP/MIP was significantly greater for UDP compared to N (2.1(1.2-5.7) and 1.5(0.7-2.2), respectively) (median and interquartile range) and for BDP compared to UDP (4.3(2.3-7.5) and 2.1(1.2-5.7), respectively) (p < 0.001). The area (AUC) under the receiver-operating characteristic curve for MEP/MIP between N and UDP was 0.84 (95% confidence interval (CI) 0.74-0.94) and between UDP and BDP was 0.90 (95% CI 0.80-0.99). MEP/MIP had a strong monotonic relationship with ∆VC-supine % (Spearman's ρ = 0.68, p < 0.001). CONCLUSIONS: The MEP/MIP ratio provides a method with comparable sensitivity and specificity to ∆VC-supine % that can be used to screen patients with suspected isolated phrenic neuropathy and alleviates the need for measuring supine pulmonary function.