Abstract
Midazolam was administered intravenously to 8 bitches in a randomised, placebo-controlled clinical trial before propofol induction of surgical anaesthesia. Anaesthesia was maintained with isoflurane-in-oxygen during surgical endoscopic examination of the uterus and ovariohysterectomy. Clenbuterol was administered at the start of surgery to improve uterine muscle relaxation, and to facilitate endoscopic examination of the uterus. Ventilation was controlled. Induction of anaesthesia with propofol to obtain loss of the pedal reflex resulted in a statistically significant (P < 0.05) decrease in minute volume and arterial oxygen partial pressure in the midazolam group. Apnoea also occurred in 50% of dogs in the midazolam group. The dose for propofol in the midazolam group was 7.4 mg/kg compared to 9.5 mg/kg in the control. Minute volume was significantly (P < 0.05) higher in both groups during isoflurane maintenance, compared to the value after incremental propofol to obtain loss of the pedal reflex. Propofol induction resulted in a 25-26% reduction in the mean arterial blood pressure in both groups, and the administration of clenbuterol at the start of surgery resulted in a transient, but statistically significant (P < 0.05), decrease in mean arterial blood pressure in the midazolam group during isoflurane anaesthesia. It is concluded that intravenous midazolam premedication did not adversely affect cardiovascular function during propofol induction, but intra-operative clenbuterol during isoflurane maintenance of anaesthesia may result in transient hypotension. Midazolam premedication may increase adverse respiratory effects when administered before propofol induction of anaesthesia.
Highlights
It has been suggested that the intraoperative administration of clenbuterol may facilitate the endoscopic examination of the canine uterus for diagnostic purposes
The pressure was unchanged after the incremental dose of propofol; in the placebo group, the mean arterial pressure increased from 12.7 (2.0) to 16.4 (4.4) kPa during the same period (Fig. 1)
The duration of anaesthesia was 80.3 (8.2) and 82.8 (10.6) min for the midazolam and control groups respectively. The purpose of this investigation was to examine the effects of midazolam premedication on some cardiopulmonary variables after propofol induction, and in clenbuterol-treated dogs during surgery and isoflurane maintenance of anaesthesia
Summary
It has been suggested that the intraoperative administration of clenbuterol may facilitate the endoscopic examination of the canine uterus for diagnostic purposes. Clenbuterol is a selective $2-adrenergic agonist that is administered to induce bronchial dilation and myometrial relaxation. Possible adverse effects that may occur are systemic hypotension and cardiac arrhythmias when used in conjunction with inhalation anaesthetic agents, and in particular in animals with pre-existing cardiac disease[13]. The use of this agent during anaesthesia is not recommended by the manufacturer, and its use during anaesthesia is listed as contra-indicated.
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