RESUMO
Most anaesthetics inhibit baroreflex function which might explain why arterial hypotension ensues and why pressure is poorly maintained when blood loss occurs during general anesthesia. Although neuroleptanalgesia is characterized by stable blood pressure, baroreflex function has not attracted much attention during this type of anesthesia. It seemed therefore worthwhile to study this aspect of drug action for agents used with neuroleptanalgesia. The experiments were carried out on dogs under N2O analgesia (N2O/O2 3:1). For defined stimulation of the carotid baroreceptors the neck region of the dog was tightened into a pressure chamber. Application of sub- and above-atmospheric pressure within the chamber (+/- 100 mm Hg) resulted in a reflex decrease or increase in aortic blood pressure. Pressure response curves relating transmural carotid sinus and aortic pressure were derived and evaluated in respect to position and slope during the action of etomidate (0.3-1.2), fentanyl (0.04-0.08), and droperidol (0.5-1 mg/kg b.w.). Blood pressure fell slightly by a maximum of 12, 14 and 16 mm Hg, respectively, resulting in a corresponding shift in the pressure response curves without much change in the slope function i.e. reflex sensitivity. Maximum reflex sensitivity expressed as open loop gain was reduced slightly from -2 to -1. Thus, baroreflex function is hardly impaired during neuroleptanalgesia, i.e. the organism maintains the ability reflexly to stabilize its arterial blood pressure. This could explain why blood pressure is stable during neuroleptanalgesia.
