2014A12 Describe the alterations to the physiology of the nervous system in the older patient
 and outline the consequent effects on pain perception.

Pain

·   Unpleasant sensory and emotional experience associated with actual or potential tissue damage or is described in such terms

Ageing

·   Gradual time-dependent loss of cellular function and physiological reserve, resulting in death

Summary

·   ↓Nociceptive response to noxious stimuli

·   ↑Susceptible to analgesic toxicity

·   ↓Ability to communicate

·   Frequently undertreated

Changes

·   ↓Grey matter:

o ↓10,000 neurons per day from age 20

o Total 10% loss by age 80

·   ↓White matter (less affected)

·   ↓Neurotransmitters:

o ↓Serotonin and noradrenaline (+/-depression)

o ↓Dopamine in substantia nigra (+/-Parkinson’s disease)

o ↓Acetylcholine in hypothalamus (+/-senile dementia)

Effect on pain

·   ↓Cognition

·   ↓Communication of pain

·   ↓Reflex speed -> slower withdrawal from insult

·   ↓Activity of endogenous analgesic pathways

Disease

·   Dementia and delirium common

·   Inability to communicate

·   Pain perception preserved

Changes

·   Generally less affected

·   ↓Neurons

·   ↓Axons (myelinated and not)

·   ↓Synapses

·   ↓Neurotransmitters (substance P, CGRP)

Effect on pain

·   ↓Nociceptive afferents

·   ↓Sensitisation

·   ↓Speed of conduction

Disease

·   ↑Risk diabetes, +/- peripheral neuropathy -> ↓ pain e.g. toe amputation

Changes

·   ↓Cardiac β₁ adrenoceptors

·   ↓post-adrenoceptor signalling

·   (↑Circulating noradrenaline partly offsets above)

Effect on pain

·   ↓Autonomic response to pain

·   Risk of undertreatment intra-op

Drugs

·   β-blockers commonly prescribed -> attenuates HR response -> risk of undertreatment