Notes from Hugh Seaton (1992)
Morbidity after elective surgery 5% in those over 65, < 1% in
younger patients.
Mortality in emergency surgery approximately 10%.
1. CARDIOVASCULAR SYSTEM
Increase in cardiac volume due to increase in SVR causing
LVH
Myocardium and conducting system fibrose, valves calcify, coronary
arteries reduce calibre, elasticity and atherosclerose.
Other vessels undergo similar changes -> reduced compliance.
Cardiac output decreases by up to 40% - reduced EF/SV and HR.
Maximal HR in stress reduced.
Circulation time increased
Increase in blood pressure - particularly systolic
Reduced cardiac reserve
Associated reduced autonomic responsiveness -> decompensation.
\ treat hypertension, arrhythmia, hypokalaemia, CCF, angina
preoperatively and avoid elective surgery in the 3-6/12 post AMI.
2. RESPIRATORY SYSTEM
Decreased thoracic expansion
Diminished lung elasticity
Reduced alveolar surface area
Weakened respiratory muscles -> small airway closure
Decreased vital capacity
Increased FRC
Increased RV
Reduced MBC, TLC.
Decreased response to hypercapnoea and hypoxia.
PaO2 falls by 0.5 mmHg per annum after 20 years of age.
P(A-a)O2 gradient increases to 20 mmHg by the age of 70, due to V/Q
mismatching, decreased alveolar area and permeability.
Respiratory complications are a frequent cause of death:
- infections more in males
- protective upper airway reflexes decreased -> aspiration
- postoperative respiratory failure
Evaluate respiratory function preoperatively wrt planned
procedure:
- expiratory volumes and ABGs at least
- anticipate need for respiratory support
3. CENTRAL NERVOUS SYSTEM
(i) Anatomical
(a) Progressive functional and structural changes:
- weight of brain by age 80 is 1150g - decreased cortical
neurons,
- loss of myelin, reduction in synapses and fibres,
(ii) Physiological
(a) Decreased rate of turnover of neurotransmitters causing:
- behavioural changes
- memory problems
- confusion
(b) Muscle and neuromuscular function deteriorate:
Fewer motor units and each axon innervates fewer muscle fibres
-> may lead to denervation and atrophy.
Decreased analgesic and anaesthetic requirement.
Decreased MAC by about 25% by 80 years.
Increased sensitivity to NM relaxants.
Most frequent diseases are CVS insufficiency, Parkinson's [[Delta]],
neuropathies.
* confusion and neuropathy may contraindicate regional techniques
Transient psychological and EEG abnormalities after GA.
L-Dopa may predispose to arrhythmias, hypotension and chest rigidity.
4. RENAL AND HEPATIC SYSTEMS
RBF reduced to 40-50% of young adult's by age 65.
GFR, renal concentration and acidification decreased.
Reduced number of glomeruli, tubular atrophy or hypertrophy
Susceptible to:
* circulatory overload
* dehydration
* electrolyte imbalance
* reduced excretion of polar drugs: gallamine, procainamide,
pancuronium, chlorpropamide, digoxin, antimicrobials, cimetidine,
lithium.
Decreased CO leads to reduced hepatic blood flow.
Reduced clearance of lipid soluble/non-polar drugs.
Reduced microsomal enzyme activity.
Longer t1/2 and prolonged duration of action of many drugs.
More risk from hepatotoxins
Hypoxia, hypotension more deleterious
5. METABOLISM AND THE ENDOCRINE SYSTEM
BMR reduced by 1% per annum after 30 years.
Muscle tissue decreases, fatty increases -> hypothermia.
Most frequent endocrine problem is diabetes, related to slow insulin
response to hyperglycaemia.
Preoperative control to avoid hypoglycaemia, hyperosmolar and
ketosis.
6. MUSCULOSKELETAL SYSTEM AND SKIN
Osteoporosis and arthritis common in elderly men and
women.
Skin trauma, ischaemia and nerve compression more common \ mobilise
gently.
Neutral position (esp head to avoid vertebral artery
compression).
Pad pressure points.
Care with heating mattresses to avoid burns.
Mask fit poor due to bone resorption and edentulous - use airway.