Neurally adjusted ventilatory assist feasibility during anaesthesia: A randomised crossover study of two anaesthetics in a large animal model.

BACKGROUND:Spontaneous breathing during mechanical ventilation improves gas exchange by redistribution of ventilation to dependent lung regions. Neurally adjusted ventilatory assist (NAVA) supports spontaneous breathing in proportion to the electrical activity of the diaphragm (EAdi). NAVA has never been used in the operating room and no studies have systematically addressed the influence of different anaesthetic drugs on EAdi. OBJECTIVES:The aim of this study was to test the feasibility of NAVA under sedation and anaesthesia with two commonly used anaesthetics, sevoflurane and propofol, with and without remifentanil, and to study their effects on EAdi and breathing mechanics. DESIGN:A crossover study with factorial design of NAVA during sedation and anaesthesia in pigs. SETTING:University basic science laboratory in Uppsala, Sweden, from March 2009 to February 2011. ANIMALS:Nine juvenile pigs were used for the experiment. INTERVENTIONS:The lungs were ventilated using NAVA while the animals were sedated and anaesthetised with continuous low-dose ketamine combined with sevoflurane and propofol, with and without remifentanil. MAIN OUTCOME MEASURES:During the last 5  min of each study period (total eight steps) EAdi, breathing pattern, blood gas analysis, neuromechanical efficiency (NME) and neuroventilatory efficiency (NVE) during NAVA were determined. RESULTS:EAdi was preserved and normoventilation was reached with both sevoflurane and propofol during sedation as well as anaesthesia. Tidal volume (Vt) was significantly lower with sevoflurane anaesthesia than with propofol. NME was significantly higher with sevoflurane than with propofol during anaesthesia with and without remifentanil. NVE was significantly higher with sevoflurane than with propofol during sedation and anaesthesia. CONCLUSION:NAVA is feasible during ketamine-propofol and ketamine-sevoflurane anaesthesia in pigs. Sevoflurane promotes lower Vt, and affects NME and NVE less than propofol. Our data warrant studies of NAVA in humans undergoing anaesthesia.