Surface electromyograms of extradiaphragmatic inspiratory muscles provides a simple, reliable and non-invasive indicator of respiratory muscle loading/unloading in mechanically ventilated patients. Because this EMG activity is strongly correlated to the intensity of dyspnea, it could be used as a surrogate of respiratory sensations in mechanically ventilated patients, and might, therefore, provide a monitoring tool in patients in whom detection and quantification of dyspnea is complex if not impossible.

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IntroductionThe objective was to compare the impact of three assistance levels of different modes of mechanical ventilation; neurally adjusted ventilatory assist (NAVA), proportional assist ventilation (PAV), and pressure support ventilation (PSV) on major features of patient-ventilator interaction.MethodsPSV, NAVA, and PAV were set to obtain a tidal volume (VT) of 6 to 8 ml/kg (PSV100, NAVA100, and PAV100) in 16 intubated patients. Assistance was further decreased by 50% (PSV50, NAVA50, and PAV50) and then increased by 50% (PSV150, NAVA150, and PAV150) with all modes. The three modes were randomly applied. Airway flow and pressure, electrical activity of the diaphragm (EAdi), and blood gases were measured. VT, peak EAdi, coefficient of variation of VT and EAdi, and the prevalence of the main patient-ventilator asynchronies were calculated.ResultsPAV and NAVA prevented the increase of VT with high levels of assistance (median 7.4 (interquartile range (IQR) 5.7 to 10.1) ml/kg and 7.4 (IQR, 5.9 to 10.5) ml/kg with PAV150 and NAVA150 versus 10.9 (IQR, 8.9 to 12.0) ml/kg with PSV150, P <0.05). EAdi was higher with PAV than with PSV at level100 and level150. The coefficient of variation of VT was higher with NAVA and PAV (19 (IQR, 14 to 31)% and 21 (IQR 16 to 29)% with NAVA100 and PAV100 versus 13 (IQR 11 to 18)% with PSV100, P <0.05). The prevalence of ineffective triggering was lower with PAV and NAVA than with PSV (P <0.05), but the prevalence of double triggering was higher with NAVA than with PAV and PSV (P <0.05).ConclusionsPAV and NAVA both prevent overdistention, improve neuromechanical coupling, restore the variability of the breathing pattern, and decrease patient-ventilator asynchrony in fairly similar ways compared with PSV. Further studies are needed to evaluate the possible clinical benefits of NAVA and PAV on clinical outcomes.Trial registrationClinicaltrials.gov NCT02056093. Registered 18 December 2013.Electronic supplementary materialThe online version of this article (doi:10.1186/s13054-015-0763-6) contains supplementary material, which is available to authorized users.