Diaphragm Dysfunction Predicts Weaning Outcome after Bilateral Lung Transplant

Abstract

Background Diaphragm dysfunction and its effects on outcomes of ventilator weaning have been evaluated in mixed critical care populations using diaphragm thickening fraction (TFdi; the ratio of the difference between ultrasound diaphragm thickness at end-inspiration and end-expiration to diaphragm thickness at end-expiration) or neuro-ventilatory efficiency (NVE; the ratio of tidal volume and peak electrical activity of the diaphragm). Such data are not available in bilateral-lung transplant recipients. We hypothesized that: i) diaphragm dysfunction, as defined by a TFdi<29%, is more likely to occur in difficult weaning; ii) TFdi and NVE predict weaning outcome; iii) and duration of mechanical ventilation before the first spontaneous breathing trial (SBT) is associated with diaphragm dysfunction. Methods Adult bilateral-lung transplant patients admitted to our ICU were screened at the time of the first SBT (pressure-support of 5cmH2O and zero positive end-expiratory pressure). At the fifth minute, TFdi and NVE were measured over three respiratory cycles. Weaning was classified as simple, difficult or prolonged (successful extubation at the first SBT, within three or after three SBTs, respectively). Results Forty-four subjects were enrolled. Diaphragm dysfunction occurred in 14 subjects (32%); all of whom had difficult weaning (78% of the subgroup of 18 patients experiencing difficult weaning). Both TFdi (24[20-29] vs 39[35-45]%) and NVE (34[26-45] vs 55[43-62]ml/µV) were lower in difficult weaning (both p<0.001). The areas under the receiver operator curve predicting difficult weaning were 0.88 [95%CI 0.73-0.99] for TFdi, and 0.85 [95%CI 0.71-0.95] for NVE. Duration of ventilation demonstrated a linear inverse correlation with both TFdi and NVE. Conclusions Diaphragm dysfunction is common following bilateral-lung transplantation and associated with difficult weaning. In such patients, average values for TFdi and NVE were reduced compared to patients with simple weaning. Both parameters showed similar accuracy for predicting success of ventilator weaning, demonstrating an inverse relationship with duration of ventilation.

Clarifying the Role of Diaphragm Ultrasound Imaging in the Discontinuation of Mechanical Ventilation

“…Indeed, some measurements in medicine such as the Pao 2 /fractional inspired oxygen tension ratio or the oxygen saturation measured by pulse oximetry/fractional inspired oxygen tension ratio can be physiologically flawed, 11 and yet they may provide useful information on clinical outcomes. 12 the case of Boscolo et al, 2 should we conclude that the results of their study give us license to abort a spontaneous breathing trial in a lung transplant recipient if diaphragm thickening is less than 29% shortly after the start of the trial? No, for the very reasons cogently put forth by the investigators.…”

“…If the latter is the case, would we then feel confident enough to prolong mechanical ventilation or proceed with a tracheostomy in a patient who consistently displays decreased diaphragm thickening during the first few minutes of a series of spontaneous breathing trials? These are tough questions raised by the findings of Boscolo et al 2 that we must be ready to answer if we want to clarify, once and for all, the role of diaphragm ultrasound imaging in weaning and extubation.…”

“…1 Early identification of patients at risk of failure to wean, and the mechanisms thereof, remain unresolved challenges. In the current issue of Anesthesiology, Boscolo et al 2 try to address this important gap in our knowledge. Specifically, they describe the relationship between diaphragm dysfunction, assessed by means of diaphragm ultrasonography, and weaning outcome in this specific population.…”

“…6 Measurements of diaphragm thickening also do not provide accurate quantification of the pressure output of the diaphragm. For example, Poulard et al 7 The unreliability of diaphragm thickening as a surrogate of diaphragm pressure output is further underscored by the observation of Boscolo et al 2 (and of other investigators 8 ) that diaphragm thickening in patients who fail a spontaneous breathing trial is smaller than the diaphragm thickening of patients who succeed in it. This finding is at odds with the common observation that in mixed populations of mechanically ventilated patients, tidal changes in transdiaphragmatic pressure during spontaneous breathing trials are not smaller (and can be bigger) in weaning failures than in weaning successes.…”

“…Where does this leave us? The carefully executed study of Boscolo et al 2 builds upon a growing body of evidence possibly hinting at an association between weaning outcome and diaphragm thickening. 8 The moment has come to prospectively test the accuracy of diaphragm thickening in predicting weaning outcome.…”