Objective: To observe the effect of neurally adjusted ventilatory assist (NAVA) on patient-ventilator synchrony in patients with acute respiratory distress syndrome (ARDS).
Methods: Eighteen patients with ARDS were enrolled in the study. Each patient underwent both an incremental pressure support ventilation (PSV) and NAVA run randomly in 4 steps. The PSV level was gradually increased 5 cm H2O (1 cm H2O = 0.098 kPa) every 5 min from 5 cm H2O until to 20 cm H2O. Incremental NAVA was individually set in steps of 0.2 - 1.0 cm H2O/microV every 5 min to determine the NAVA level predicted to give an airway pressure in each step equivalent to that of PSV. Parameters in patient-ventilator synchrony such as ventilation trigger, ventilation switching and ventilation maintenance were observed at the same time during PSV(PSV1-PSV4) and NAVA(NAVA1-NAVA4).
Results: (1) Ventilation trigger:(1) trigger delay: with progressive increases in PSV, the trigger delays increased significantly (P < 0.05). With increasing NAVA, the trigger delay did not increase significantly (P > 0.05) and each of them was shorter than that of PSV in each corresponding step (P < 0.05). (2) Ineffective trigger: At PSV1, the ineffective triggers accounted for 2. 3% of the neural respiratory rate (NRR), but the ineffective triggers added up to 22% in PSV4 significantly (P < 0.05). All neural efforts were triggered and there were not ineffective triggers at all level in NAVA. (2) Off cycle delay: the off cycle delays in PSV2 - PSV4 increased significantly when compared with PSV1 (P < 0.05). With increasing NAVA, the off cycle delays did not increase significantly (P > 0.05) and each of them was shorter than that of PSV in each corresponding step (P < 0.05). (3) Magnitude of assist [tidal volume (VT)]: The VT [(361 +/- 69) ml] in NAVA1 was equivalent to the VT[(361 +/- 121) ml] in PSV1(P > 0.05). The VT [(417 +/- 71) ml, (427 +/- 80) ml, respectively] in NAVA3-NAVA4 was significantly lower than the VT[(604 +/- 141) ml, (675 +/- 108) ml, respectively] in PSV3-PSV4 (P < 0.05). (4)Respiratory muscle loading: Increasing NAVA and PSV level reduced the magnitude of diaphragm electrical activity (EAdi) and the pressure-time products of esophagus (PTPes) (P < 0.05), but there was no significant difference in each corresponding step of PSV and NAVA(P > 0.05).
Conclusions: Compared with PSV, the ventilation cycle and the magnitude of assist in NAVA matched the patient's breathing pattern. NAVA improved patient-ventilator synchrony in patients with ARDS.