The use of paralysants precludes the use of simple criteria such as the strength of the corneal blink reflex, the character of the breathing and the flexor withdrawal reflex on pinching the paw or achilles tendon.
The variables recommended to be monitored include both autonomic and CNS indicators. Monitoring must be continuous or, if intermittent, frequent.
Autonomic indicators: heart rate, blood pressure, pupil size: together with the effects on these of mild noxious stimuli.
CNS indicators: the EEG
The investigator is responsible for ensuring that the monitoring procedure is meaningful at all times.
For example, hypocapnia may synchronize the EEG without causing anaesthesia, atropine dissociates the EEG waveform and behaviour in normal alert cats and will interfere with some autonomic indicators, ketamine may have atropine-like effects on the EEG.
It cannot be assumed that nitrous oxide alone is an adequate anaesthetic. It should be supplemented with another agent: the proportion may be adjusted for the individual animal on the information from the monitoring.