Impact of the Assisted Ventilation Mode on Diaphragm Efficiency in Critically Ill Patients (NAVA_PSV)

Impact of Pressure Support Ventilation (PSV) Versus Neurally Adjusted Ventilatory Assist (NAVA) Diaphragm Efficiency

This study evaluates the impact of the assisted mode of mechanical ventilation on diaphragm efficiency in mechanically ventilated critically ill patients. Participants will be randomized to the neurally adjusted ventilatory assist (NAVA) mode or to the pressure support ventilation (PSV) mode.

During mechanical ventilation the ventilator applies positive pressure to the respiratory system. Often in the acute phase of critical illness patients are ventilated in the control mode (CMV), where the patient is completely passive. This quickly (within 48 hours) has been shown to induce diaphragm atrophy and dysfunction (Levine et al New England Journal of Medicine, 200; 358:1327-35). To preserve diaphragm function, guidelines suggest to shift as soon as possible to the assisted mode (the ventilator applies positive pressure to assist spontaneous inspiratory effort). The synchrony between patient and ventilator is critical in this context. PSV is the classical assisted mode and applies a constant pressure whatever the patient effort. NAVA is a newer mode based on the diaphragm electrical activity (EAdi) measurement. It assist patient effort proportionally to the EAdi and hence to patient's effort. The investigator hypothesis is that NAVA would improve diaphragm efficiency more efficiently than PSV.

Diaphragm neuro-ventilatory efficiency (NVE) to convert the electrical diaphragm activity (EAdi) into volume. NVE is impaired by controlled mechanical ventilation (CMV) and the assisted mode should serve to restore it. All the studied patents were ventilated for more than 48 hours in CMV, a period shown to be sufficient to induce diaphragm atrophy and therefore depress NVE. NVE is measured by the ratio between tidal volume (VT) and the EAdi peak (NVEpeak) or by the ratio between VT and the are under the EAdi signal. EAdi is obtained by the EAdi catheter, a nasogastric catheter equipped with electrodes (Maquet Critical Care, Solna, Sweden). EAdi is measured in microVolt. The Servo i ventilator (Maquet Critical Care, Solna Sweden) is equipped with a module able to amplify and show on a screen the EAdi trace and the corresponding value. Both the Servo i ventilator and the EAdi catheter are approved for clinical use.

Diaphragm neuro-mechanical efficiency (NME) to convert the electrical diaphragm activity (EAdi) into negative pressure is impaired by controlled mechanical ventilation (CMV). The assisted mode should serve to restore it. All the studied patents are ventilated for more than 48 hours in CMV, a period shown to be sufficient to induce diaphragm atrophy and hence depress NME. NME is measured by simultaneously recording EAdi and airway opening pressure during an end-expiratory airway opening occlusion and expressed in centimeters of waters (cmH2O)/microVolt.

Inclusion Criteria: older than 18 years oro-tracheally or naso-tracheally intubate had been ventilated for acute respiratory failure in control mechanical ventilation for at least 72 hours consecutively candidate to assisted ventilation Hemodynamically stable without vasopressor or inotropes (excluding a dobutamine and dopamine infusion lower than 5 gamma/Kg/min and a 3 gamma /Kg/min, respectively normothermia Exclusion Criteria: Neurological or neuromuscular pathologies phrenic nerve dysfunction contraindications to the insertion of a nasogastric tube (for example recent upper gastrointestinal surgery, esophageal varices).

Di Mussi R, Spadaro S, Mirabella L, Volta CA, Serio G, Staffieri F, Dambrosio M, Cinnella G, Bruno F, Grasso S. Impact of prolonged assisted ventilation on diaphragmatic efficiency: NAVA versus PSV. Crit Care. 2016 Jan 5;20:1. doi: 10.1186/s13054-015-1178-0.