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.