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We assessed the effects of varying doses of remifentanil on respiratory drive and timing in patients receiving Pressure Support Ventilation (PSV) and Neurally Adjusted Ventilatory Assist (NAVA). Four incrementing remifentanil doses were randomly administered to thirteen intubated patients (0.03, 0.05, 0.08, and 0.1μg·Kg⁻¹·min⁻1) during both PSV and NAVA. We measured the patient's (Ti/Ttot_neu) and ventilator (Ti/Ttot_mec) duty cycle, the Electrical Activity of the Diaphragm (EAdi), the inspiratory (Delay_trinsp) and expiratory (Delay_trexp) trigger delays and the Asynchrony Index (AI).

Increasing doses of remifentanil did not modify EAdi, regardless the ventilatory mode. In comparison to baseline, remifentanil infusion >0.05μg/Kg⁻¹/min⁻¹ produced a significant reduction of Ti/Ttot_neu and Ti/Ttot_mec, by prolonging the expiratory time. Delay_trinsp and Delay_trexp were significantly shorter in NAVA, respect to PSV. AI was …