The aim of the study was to compare the effect of
halothane anaesthesia on sympathetic nerve discharge in mechanically normoventilated and spontaneously breathing rats. Renal sympathetic nerve activity (rSNA), mean arterial pressure (MAP) and heart rate (HR) were measured in the conscious state and at the inspiratory
halothane concentrations of 0.6%, 1.2% and 2.4% in one mechanically normoventilated and one spontaneously breathing group, while a third group was subjected to controlled
hypoventilation at 1.2%
halothane concentration.
Halothane in blood was determined in two separate groups at 1.2%. In an additional group of spontaneously breathing rats, PaCO2 was analysed during consciousness and the
halothane concentrations of 1.2% and 2.4%. There was a pronounced decrease in rSNA, MAP and HR at all levels of anaesthesia in the mechanically ventilated rats. However, rSNA, HR and MAP were significantly higher in the spontaneously breathing rats at increasing levels of
halothane anaesthesia. Controlled
hypoventilation at 1.2%
halothane increased the variables significantly. In spontaneously breathing animals, PaCO2 increased significantly during the
halothane exposure. The concentration of
halothane in blood was significantly higher in the spontaneously breathing rats. Thus, the
halothane-induced
respiratory depression in the spontaneously breathing rats preserved rSNA during
halothane anaesthesia, possibly via CO2-mediated chemoreceptor stimulation.