A low-dose remifentanil infusion is well tolerated for sedation in mechanically ventilated, critically-ill patients

Purpose: To study the analgesic and sedative effects of remifentanil in critically-ill patients. Methods: Remifentanil infusion was started at 0.02,mug(.)kg(-1.)min(-1) in ten mechanically ventilated critically-ill patients, and the infusion rate was increased to 0.05, 0,10, 0.15, 0.20, and 0.25 mug(.)kg(-1.)min(-1) every 30 min. Basally and 25 min after each increase we measured: the Ramsey sedation score (RSS) and the respiratory response subscore of comfort scale (CSRR); the bispectral index (BIS) before and after lightly touching tracheal mucosa; heart rate and systemic arterial pressure; respiratory variables; plasma epinephrine and norepinephrine levels. Results: Infusion rates up to 0.05 mug(.)kg(-1.)min(-1) were effective against agitation and achieved a good degree of adaption to the respirator in all patients (RSS 2 or more and CSRR 3 or less); BIS decreased significantly; respiratory and circulatory variables were unaffected; mean plasma epinephrine levels decreased. At infusion rates higher than 0.05 mug(.)kg(-1.)min(-1) RSS but not BIS decreased further and patient arousability caused by noxious stimuli was not prevented; respiratory drive suppression occurred at the infusion rates higher than 0.05 mug(.)kg(-1.)min(-1) in four patients; bradycardia and arterial hypotension was observed in three patients; plasma epinephrine levels decreased significantly, while norepinephrine was unaffected; severe itching was experienced by one patient. Conclusions: Low doses of remifentanil (up to 0.05 mug(.)kg(-1.)min(-1)) can be useful in critically-ill patients in order to achieve calm and sedation. Higher doses can inhibit respiratory drive and require controlled mechanical ventilation.