Preliminary investigation into a new method of assessing the quality of anaesthesia: the cardiovascular response to a measured noxious stimulus.

It is suggested that the autonomic response to noxious stimulation may be measured during anaesthesia. The response may be marked despite considerable depression of cortical activity as measured by the cerebral function monitor. Preliminary results suggest that large doses of narcotic analgesics reduce the autonomic response to noxious stimulation and this may be used as a test to compare the potency and duration of action of narcotic drugs during anaesthesia. It is possible that the measurement of beat-to-beat variation in heart rate may be used to monitor autonomic nervous system activity and, indirectly, the degree of stress during surgery, provided that the efferent limb of the reflex arc remains intact. With the aid of the cerebral function monitor and with an index of reflex response to noxious stimulation it should be possible to monitor the effect of anaesthesia on the central nervous system more precisely.