Neurally adjusted ventilatory assist in patients recovering spontaneous breathing after acute respiratory distress syndrome: physiological evaluation.

OBJECTIVE: Pressure-support ventilation is widely used during the weaning phase in patients with acute respiratory distress syndrome. The pressure-support level is adjusted to prevent ventilator-induced lung injury while limiting the patient's work of breathing. Neurally adjusted ventilatory assist is an assist mode that applies a positive pressure proportional to the integral of the electrical activity of the diaphragm. The objective was to assess the physiologic response to varying pressure-support ventilation and neurally adjusted ventilatory assist levels in selected acute respiratory distress syndrome patients and to evaluate the effect of neural triggering.

METHODS: We prospectively assessed 11 consecutive patients with acute respiratory distress syndrome attributable to pulmonary diseases. Pressure-support ventilation and neurally adjusted ventilatory assist were used in random order. Neurally adjusted ventilatory assist was used with a low electrical activity of the diaphragm trigger (neurally adjusted ventilatory assist-electrical activity of the diaphragm) and with a high electrical activity of the diaphragm trigger that led to rescue triggering by inspiratory flow (neurally adjusted ventilatory assist-inspiratory flow). With each ventilation modality, four levels of assistance (100%, 120%, 140%, and 160%) were used in random order. Statistical analysis was performed using analysis of variance for repeated measurements and mixed models.

MAIN RESULTS: Contrary to pressure-support ventilation, neurally adjusted ventilatory assist-electrical activity of the diaphragm and neurally adjusted ventilatory assist-inspiratory flow were associated with stable tidal volume levels despite increasing assistance. For the asynchrony index, an interaction was present between ventilation mode and assist level (p = .0076) because asynchrony index increased significantly with the pressure-support ventilation level (p = .004), but not with the neurally adjusted ventilatory assist-electrical activity of the diaphragm or neurally adjusted ventilatory assist-inspiratory flow level. The lowest asynchrony index was obtained with neurally adjusted ventilatory assist-electrical activity of the diaphragm.

CONCLUSION: Compared to pressure-support ventilation, neurally adjusted ventilatory assist in acute respiratory distress syndrome patients holds promise for limiting the risk of overassistance, preventing patient-ventilator asynchrony, and improving overall patient-ventilator interactions. Neural triggering (neurally adjusted ventilatory assist-electrical activity of the diaphragm) considerably decreased patient-ventilator asynchrony.