Nervous system Nervous system

Central nervous system

Reduced functional tissue in the CNS is probably one of the factors that reduces the anaesthetic dose needed in older patients.

Old patients often have sluggish, impaired or absent reflex responses (e.g. pupillary light reflex) which may complicate monitoring during anaesthesia.

Loss of function of the special senses such as sight and hearing may lead to apprehension in strange environments (especially in cats), and sometimes sedation is needed to reduce preoperative stress which otherwise can significantly increase sympathetic simulation.

Geriatric animals have reduced ability to generate body temperature and are susceptible to develop hypothermia, particularly during prolonged surgery or the postoperative recovery period. In this context it is important to remember that core body temperature may differ from peripheral measurements, and the use of oesophageal thermometers or infra-red thermometers (applied in the aural canal) may be preferable to rectal temperature recording.

Peripheral nervous system

Supersensitivity of postsynaptic receptors may prolong the action of muscle relaxants.

Interpretation of the significance of poor reflex responses during anaesthesia is more difficult in older patients than in the young.