Ultrasound-guided Transcutaneous Phrenic Nerve Stimulation in Critically Ill Patients: A New Method to Evaluate Diaphragmatic Function

Background: Diaphragm dysfunction is common in intensive care unit and associated with weaning failure and mortality. The diagnosis gold standard is the transdiaphragmatic or tracheal pressure induced by magnetic phrenic nerve stimulation. However, the equipment is not commonly available and requires specific technical skills. This study aimed to evaluate ultrasound-guided transcutaneous phrenic nerve stimulation for daily bedside assessment of diaphragm function by targeted electrical phrenic nerve stimulation. Methods: This randomized crossover study compared a new method of ultrasound-guided transcutaneous electrical phrenic nerve stimulation (SONOTEPS) using a peripheral nerve stimulator, with magnetic phrenic nerve stimulation. Intensive care unit adult patients under mechanical ventilation with a Richmond Agitation–Sedation Scale score of −4 or −5 were included. Each patient received the two methods of stimulation, in a randomized order. The primary outcome was the tracheal pressure induced by stimulation. Results: This study analyzed 232 measures of tracheal pressure from 116 patients, of whom 77 presented diaphragm dysfunction (tracheal pressure less than 11 cm H 2 O) and 50 presented severe diaphragm dysfunction (tracheal pressure less than 8 cm H 2 O). The Passing–Bablok regression showed no significant differences (intercept A of −0.03 [95% CI, −0.83 to 0.52] and slope B of 0.98 [95% CI, 0.90 to 1.05]) between the SONOTEPS method and magnetic stimulation, which were positively correlated ( R ² = 0.639). The mean bias was −1.08 (95% CI, 5.02 to −7.18) cm H 2 O. The receiver operating curves showed an excellent performance for the diagnosis of diaphragm dysfunction and severe diaphragm dysfunction with areas under the curve of 0.90 (95% CI, 0.83 to 0.97) and 0.88 (95% CI, 0.82 to 0.95), respectively. This performance was not significantly affected by the body mass index or the presence of a neck catheter. Conclusions: The SONOTEPS method is a simple and accurate tool for bedside assessment of diaphragm function with ultrasound-guided transcutaneous phrenic nerve stimulation in sedated patients with no or minimal spontaneous respiratory activity.