Abstract
BACKGROUND: Failure to wean from invasive mechanical ventilation is multifactorial, with diaphragmatic dysfunction a significant contributing factor. Diaphragmatic function can be easily and non-invasively assessed by ultrasound. However, it remains unknown how ultrasound measurements of diaphragm function are affected by changes in apparent work of breathing. METHODS: In patients undergoing weaning from mechanical ventilation, we evaluated diaphragmatic ultrasound measurements [diaphragmatic excursion (Dex), diaphragmatic thickening fraction (Tfdi)] simultaneously with manometric indices of breathing effort and load [esophageal pressure swings (ΔPes), transdiaphragmatic pressure swings (ΔPdi), and the pressure-time product of esophageal pressure (PTPes)]. These assessments were performed during two distinct phases; during an unassisted spontaneous breathing trial (phase SBT) and during an inspiratory resistive loading with 30 cmH(2)O/L/s (phase IRL), applied during the same SBT. Our primary aim was to evaluate the relationship between diaphragmatic ultrasound and breathing effort using the method of repeated measures correlation. RESULTS: Forty-nine patients were enrolled. Dex correlated with ΔPes (r = 0.5, p < 0.001), ΔPdi (r = 0.55, p = < 0.001) and PTPes (r = 0.32, p = 0.031). Tfdi did not correlate with ΔPes (r = 0.27, p = 0.052), ΔPdi (r = 0.2, p = 0.235) and PTPes (r = 0.24, p = 0.110). Dex and Tfdi increased during IRL compared to SBT [1.44(0.89-1.96) vs. 1.05(0.7-1.59), p = 0.002], [0.55(± 0.32) vs 0.46(± 0.2), p = 0.019] as did Pes, Pdi and PTPes [(11.87 (7.86, 18.32) vs. 6.8 (4.6-10.23), p < 0.001), (10.89 (± 6.42) vs. 7.94 (± 3.81), p < 0.001), and (181.10 (108.34, 311.7) vs. 97.52 (55.96-179.87), p < 0.001), respectively]. CONCLUSION: In critical care patients spontaneously breathing under resistive load, diaphragmatic excursion had a weak to moderate correlation with indices of breathing effort and differed between weaning success and failure.