Objective:

The present study was performed to compare the effects of midazolam premedication, which is useful for its anti-anxiety and amnesic effects, with antihistamine hydroxyzine on cardiac sympathetic and parasympathetic activities using heart rate variability (HRV) at induction of anaesthesia.

Methods:

Eighty patients aged 40-60 years, with an American Society of Anaesthesiologists (ASA) physical status of I or II and undergoing general anaesthesia for neck and body surface surgery were randomised equally into midazolam and hydroxyzine groups. As a premedication, midazolam 0.06 mg kg−1 with atropine 0.5 mg (midazolam group) or hydroxyzine 1 mg kg−1 with atropine 0.5 mg (hydroxyzine group) were intramuscularly administered 15 min and 30 min before anaesthesia induction, respectively. Anaesthesia was induced with midazolam 0.1 mg kg−1 and thiopental 3 mg kg−1. Oro-tracheal intubation was facilitated with vecuronium 0.15 mg kg−1. Blood pressure, heart rate and HRV were measured at predetermined time points for 10 min after intubation.

Results:

Systolic blood pressure and heart rate significantly increased after intubation in both groups and the increase was greater in the hydroxyzine group. The high frequency (HF) component decreased significantly in both groups, and no difference was found between the two groups. The low frequency component/ HF ratio significantly increased in the hydroxyzine group but did not change in the midazolam group.

Conclusion:

Midazolam but not hydroxyzine premedication inhibited sympathetic activation at induction of anaesthesia.

Keywords: Premedication, anaesthesia induction, heart rate variability, midazolam, hydroxyzine