Effect of dexmedetomidine vs. acepromazine-methadone premedication on limb to lung circulation time in dogs

The study compared limb-to-lung circulation times (CT) in dogs under general anaesthesia after premedication with dexmedetomidine (DEX) or acepromazine-methadone (ACE-M). Healthy male and female dogs (n=20) were randomly assigned to receive acepromazine 0.04mg/kg and methadone 0.2mg/kg intramuscularly (IM), or DEX 0.01mg/kg IM. Anesthesia was induced with propofol and maintained with isoflurane at similar concentration in both groups. Mechanical ventilation was started immediately (20breaths/min; inspiratory to expiratory ratio 1:2) and tidal volume was adjusted to achieve an end-tidal CO2 concentration (PE'CO2) of between 3.9 and 5.3kPa. Ten minutes later arterial blood gas was analyzed and baseline data recorded for 3 minutes. A single dose of sodium bicarbonate 0,5mEq/kg was administered intravenously over 10 s starting with inspiration. Limb-to-lung CT was defined as the time interval between the start of bicarbonate injection and the recording of the highest PE'CO2. Following bicarbonate administration, PE'CO2 increased, and then rapidly decreased to baseline in both groups. CT was shorter in the ACE-M group (20±2.3 vs. 27±5.1s). Bodyweight was higher in the ACE-M group (30.6±3.9 vs. 23.3±6.8kg). Mean arterial blood pressure was higher in the DEX group (92±9 vs. 73±7mmHg) but premedication with DEX significantly prolonged CT compared to premedication with ACE-M.