An Initial Investigation of Diaphragm Neurostimulation in Patients with Acute Respiratory Distress Syndrome

Abstract

Background Lung protective ventilation aims at limiting lung stress and strain. By reducing the amount of pressure transmitted by the ventilator into the lungs, diaphragm neurostimulation offers a promising approach to minimize ventilator induced lung injury. This study investigates the physiological effects of diaphragm neurostimulation in acute respiratory distress syndrome (ARDS) patients. The hypothesis was that diaphragm neurostimulation would improve oxygenation, would limit the distending pressures of the lungs and would improve cardiac output. Methods Patients with moderate ARDS were included after 48 hours of invasive mechanical ventilation (MV) and had a left subclavian catheter placed to deliver bilateral transvenous phrenic nerve stimulation. Two 60-minute volume-controlled MV (control) sessions were interspersed by two 60-minute diaphragm neurostimulation sessions delivered continually, in synchrony with the ventilator (MV+STIM). Gas exchange, lung mechanics, chest electrical impedance tomography and cardiac index were continuously monitored and compared across four sessions. The primary endpoint was the PaO2/FiO2 ratio at the end of each session and the secondary endpoints were lung mechanics and hemodynamics. Results Thirteen patients were enrolled but the catheter could not be inserted in one, leaving 12 patients for analysis. All sessions were conducted without interruption and well tolerated. The PaO2/FiO2 ratio did not change over the four sessions. Plateau pressure was 23 (20 – 31) cmH2O and 21 (17 – 25) cmH2O, driving pressure was 14 (12 – 18) cmH2O and 11 (10 – 13) cmH2O and end inspiratory transpulmonary pressure was 9 (5 – 11) cmH2O and 7 (4 – 11) cmH2O during MV alone and during MV+STIM session respectively. The dorsal/ventral ventilation surface ratio was 0.70 (0.54 – 0.91) when on MV and 1.20 (0.76 – 1.33) during the MV+STIM session. The cardiac index was 2.7 (2.3 – 3.5) L/min/m 2 on MV and 3.0 (2.4 – 3.9) L/min/m 2 on MV+STIM. Conclusion This proof-of-concept study showed the feasibility of short-term diaphragm neurostimulation in conjunction with mechanical ventilation in ARDS patients. Diaphragm neurostimulation was associated with positive effects on lung mechanics and on hemodynamics.