Effect of halothane on cardiac acceleration response to somatic nerve stimulation in dogs

In six dogs, the authors investigated the effect of halothane on cardiac acceleration response to the electrical stimulation of a cutaneous nerve. It was found that increasing the concentration of halothane was associated with a proportional depression of the cardiac acceleration response to somatic nerve stimulation (y--99.8 - 44.3x; y--delta HR, x--halothane end-tidal concentration). Relationship of the response to end-tidal anesthetic concentration was characterized by a strong correlation (r= -0.93, P less than 0.0001). Complete abolition of the increase in heart rate in response to somatic nerve stimulation was observed at a halothane end-tidal concentration of 2.2 vol% (extrapolation). It is suggested that suppression of heart rate increase to noxious stimulation may be used as a graded index of the depth of anesthesia for halothane.