Electromagnetic stimulation of the phrenic nerve of intubated patients with obesity

Summary Background Noninvasive electromagnetic phrenic nerve stimulation generates diaphragmatic contractions, inducing tidal volumes above 3 ml/kg ideal body weight in both anesthetized, pulmonary healthy patients and critically ill patients. This intervention has the potential to mitigate critical illness-associated diaphragm weakness. In obese patients (15–20% of critically ill admissions) altered respiratory mechanics and anatomical changes could impair stimulation effectiveness. We aimed to assess the feasibility of noninvasive electromagnetic phrenic nerve stimulation to generate diaphragm contractions that produce tidal volumes above 3 ml/kg ideal body weight as a possible preventive or therapeutic option for critical illness-associated diaphragm weakness in obese anesthetized patients. Methods This single-center proof-of-concept study included five obese patients scheduled for elective surgery under general anesthesia and endotracheal intubation. After induction of anesthesia, patients received anterior bilateral phrenic nerve noninvasive electromagnetic stimulation at 30%, 40% and 50% intensity. The primary endpoint was the tidal volume of 10 consecutive stimulations per patient. Results The median age of the five anesthetized patients was 36 (interquartile range, IQR 22–45) years and their mean body mass index was 41.2 (IQR 36.8–49.1) kg/m 2 . Median tidal volumes increased linearly ( p < 0.001) from 0 to 1.61 (IQR 1.30–2.37) and 3.71 (IQR 3.38–4.15) ml/kg ideal body weight with 30%, 40%, and 50% stimulation intensity, respectively. At 50%, the stimulation generated tidal volumes above 3 ml/kg ideal body weight in 98% of breaths. Conclusion Bilateral noninvasive phrenic nerve stimulation generates tidal volumes above 3 ml/kg ideal body weight in pulmonary healthy, non-critically ill anesthetized obese patients.