Using remifentanil in mechanically ventilated rats to provide continuous analgosedation

Remifentanil is a potent synthetic opioid with sedative effects. Intravenous remifentanil provides deep sedation and analgesia in laboratory animals during experimental procedures. We hypothesized that remifentanil would provide effective analgosedation during assisted mechanical ventilation without affecting respiratory mechanics in rats. Five male Sprague-Dawley rats (weight, 400 to 450 g) were assigned to receive assisted mechanical ventilation with continuous positive airway pressure for 5 h. Remifentanil (0.4 μg/kg/min IV) was delivered for the duration of ventilation. There were no differences between baseline, 1 h, and 5 h of ventilation in the mean arterial pressure, cardiac output, heart rate, and body temperature of all rats. Similarly, no differences were observed in the tidal volume, respiratory rate and minute ventilation, and gas exchange was equal in all rats at all time points. Frequent assessment of sedation by toe pinch documented loss of the pedal withdrawal reflex in all rats. We conclude that continuous remifentanil infusion provides sufficient analgosedation for mechanically ventilated rats without compromising hemodynamics, respiratory function, or gas exchange.