Background

Diaphragm dysfunction and its effects on outcomes of ventilator weaning have been evaluated in mixed critical care populations using diaphragm thickening fraction (the ratio of the difference between ultrasound diaphragm thickness at end-inspiration and end-expiration to diaphragm thickness at end-expiration) or neuroventilatory efficiency (the ratio of tidal volume and peak electrical activity of the diaphragm). Such data are not available in bilateral-lung transplant recipients. The authors hypothesized that (1) diaphragm dysfunction, as defined by a diaphragm thickening fraction less than 29%, is more likely to occur in difficult weaning; (2) diaphragm thickening fraction and neuroventilatory efficiency predict weaning outcome; and (3) duration of mechanical ventilation before the first spontaneous breathing trial is associated with diaphragm dysfunction.

Methods

Adult bilateral-lung transplant patients admitted to the intensive care unit were screened at the time of the first spontaneous breathing trial (pressure-support of 5 cm H2O and 0 positive end-expiratory pressure). At the fifth minute, diaphragm thickening fraction and neuroventilatory efficiency were measured during three respiratory cycles. Weaning was classified as simple, difficult, or prolonged (successful extubation at the first spontaneous breathing trial, within three or after three spontaneous breathing trials, 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 diaphragm thickening fraction (24 [20 to 29] vs. 39 [35 to 45]%) and neuroventilatory efficiency (34 [26 to 45] vs. 55 [43 to 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 to 0.99) for diaphragm thickening fraction and 0.85 (95% CI, 0.71 to 0.95) for neuroventilatory efficiency. The duration of ventilation demonstrated a linear inverse correlation with both diaphragm thickening fraction and neuroventilatory efficiency.

Conclusions

Diaphragm dysfunction is common after bilateral-lung transplantation and associated with difficult weaning. In such patients, average values for diaphragm thickening fraction and neuroventilatory efficiency 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.

Editor’s Perspective
What We Already Know about This Topic
  • The role of the diaphragm in influencing success of ventilator weaning in critically ill patients is receiving increasing attention

  • Quantitative assessment of its function is challenging, but parameters such as thickening fraction (assessed by ultrasound) and neuroventilatory efficiency (assessed using peak electrical activity via an esophageal catheter) have been reported on in mixed critical care populations

  • Their role in patients undergoing bilateral-lung transplantation has not been previously reported

What This Article Tells Us That Is New
  • In 44 patients, the authors categorized ventilator weaning as simple, difficult, or prolonged based on extubation relative to spontaneous breathing trial success rates

  • Diaphrag thickening fraction and neuroventilatory efficiency were assessed during the first spontaneous breathing trial

  • Diaphragm dysfunction (defined by thickening fraction less than 29%) was detected in 32% of all subjects and was present in 78% of subjects with difficult weaning

  • Quantitative indices of thickening and neurovascular efficiency were reduced in this subgroup and were inversely associated with duration of ventilation

  • Both indices showed similar predictive ability for determining weaning success

You do not currently have access to this content.