The Predictive Value of Diaphragm Muscle Ultrasound for Ventilator Weaning Outcomes after Spinal Cord Injury: A Retrospective Case Series

Abstract

Objectives Neuromuscular respiratory failure after spinal cord injury (SCI) can lead to dependence on a ventilator. Ventilator-free breathing after SCI is associated with improved morbidity, mortality, and quality of life. We investigated the use of diaphragm muscle ultrasound to predict ventilator weaning outcomes after spinal cord injury. Methods This is a retrospective case series conducted at a university-affiliated freestanding acute rehabilitation hospital. We identified patients with cervical spinal cord injury who had a tracheostomy and were dependent on an invasive mechanical ventilator at the time of admission to the rehabilitation unit. A diaphragm muscle ultrasound was performed, which included measurements of the thickness of the diaphragm and a calculation of the thickening ratio (TR), a marker of diaphragm contractility. The primary outcome measure was the need for mechanical ventilation at time of discharge from acute inpatient rehabilitation. Results Of the 21 patients enrolled, 11 (52%) were able to wean successfully (partially or fully) from the ventilator. Of the ultrasound measurements that were taken, the TR was the optimal predictor for ventilator weaning outcomes. A threshold of TR≥1.2 as the maximum hemidiaphragm measurement had a sensitivity of 1.0 and specificity of 0.90 for predicting ventilator weaning. Conclusion Normal diaphragm contractility (TR ≥1.2) as determined by diaphragm muscle ultrasound is a strong positive predictor for successful ventilator weaning in patients with cervical spinal cord injury. Diaphragm ultrasound can guide clinical practice by assisting in prognosticating the ability to wean from a ventilator after cervical SCI.