Dexmedetomidine infusion without loading dose in surgical patients requiring mechanical ventilation: haemodynamic effects and efficacy.

We investigated the haemodynamic effects and the efficacy of a continuous infusion of dexmedetomidine without a loading dose in 50 patients having had cardiac surgery (n = 33), complex major surgery (n = 9) and multiple trauma (n = 8). The mean age was 60 (+/- 16) years, and the mean APACHE II score was 13 (+/- 5). Dexmedetomidine was commenced at an initial rate of 0.2 to 0.4 microg/kg/h (depending on whether anaesthetic or sedative agents had already been used) and rescue analgesia and sedation was administered with morphine and midazolam respectively. Propofol was used if additional sedation was needed. Sedation was targeted to a modified Motor Activity Assessment Score. Eighty percent of patients required no or "minimal" rescue therapy (< 10 mg midazolam/day and/or < 10 mg morphine/day and/or < 100 mg propofol/day). The cardiac surgery group needed the least rescue therapy. A statistically significant but clinically unimportant reduction in mean heart rate and mean systolic blood pressure was observed over the first six hours (P < 0.0001, and P = 0.009 respectively). The baseline heart rate of 85 (+/- 17) beats per minute (bpm), fell to a low of 78 (+/- 13) bpm at four hours and then remained stable throughout the infusion period. The systolic blood pressure fell from 125 (+/- 22) mmHg to a low of 112 (+/- 20) mmHg at 1.5 hours with minimal change afterwards. Dexmedetomidine was an effective sedative and analgesic in this group of complex surgical and trauma patients with pronounced benefit in the cardiac surgery group. Omitting the loading dose avoided undesirable haemodynamic effects without compromising sedation and analgesia.