Twenty-four-hour neurally adjusted ventilatory assist and volume cycled ventilation have similar effects on respiratory neuromuscular function in a porcine model of fecal peritonitis

Introduction

Sepsis and muscle inactivity may lead to neuromuscular dysfunction. Neurally adjusted ventilatory assist (NAVA) converts diaphragm electrical activity (EAdi) into airway pressure (Paw) and preserves respiratory muscle activity [1]. We hypothesised that respiratory neuromuscular function would be better preserved with NAVA compared with volume cycled ventilation (VCV) in early sepsis.

Methods

Twenty-eight pigs (40.0 (37.6; 41.8) kg; median (quartiles)) were randomized (n = 7 per group) to fecal peritonitis or nonseptic controls ventilated for 24 hours with either NAVA or VCV (nonparalyzed, Vt 6 to 8 ml/kg, rate adjusted to suppress EAdi). Fluids and norepinephrine (NE) were used based on protocols to keep mean arterial pressure (MAP) >50 mmHg. Before sepsis and after 24 hours, transcutaneous supramaximal stimulations of the cervical phrenic nerve (tPNS) and expiratory occlusion manoeuvres (eOM) were performed. Latency and amplitude of diaphragm compound muscle activity potentials (CMAP) were measured during tPNS; maximal deflections of Paw (ΔPaw), esophageal (ΔPes), and transdiaphragm (ΔPdi) pressures were measured during repetitive tPNS (40 Hz, 100 stimuli) and eOM.

Results

Hemodynamic parameters were not different among groups before sepsis and remained stable in controls. MAP did not change in septic NAVA but decreased in septic VCV animals from 91 (74; 95) mmHg before sepsis to 58 (57; 68) mmHg at 24 hours (P < 0.001, MANOVA t-g interaction). The heart rate increased (P < 0.001) and stroke volume decreased (P = 0.034) in both septic groups. Fluid balance was not different among septic groups. Three septic NAVA and six septic VCV animals received NE. CMAP latency and amplitude, as well as ΔPaw, ΔPes, and ΔPdi were not different among all groups during repetitive tPNS and eOM before sepsis and after 24 hours (P = NS).

Conclusions

Respiratory neuromuscular function is not affected by the mode of ventilation during the first 24 hours of abdominal sepsis. Early effects of sepsis on neuromuscular function are not reflected in respiratory muscle strength. NAVA may reduce the need for hemodynamic support in early sepsis.