4. Ageing Flashcards
Physiological Changes with Increasing Age
progressive and global decline in physiological function
is measurable after about the fourth decade of life,
more rapid deterioration occurs when patients reach their seventies.
CNS
- there is progressive structural change with cerebral atrophy
(the weight of the brain decreases by more than 10%), - a decrease in neurotransmitter concentrations,
- diminished cerebral blood flow and a fall in oxygen consumption.
- MAC decreases with age both for general and for local anaesthesia.
- It declines by about 5% per decade after the age of 40 years,
and if this curve is extrapolated, it reaches zero at the age of 137. - Basal metabolic rate is said to decline by 1% per year after the age of 30 years.
- There may be some increase in receptor sensitivity, for example to benzodiazepines,
while the effect of opioids may be enhanced because of decreased protein binding.
Autonomic nervous system
- There is a gradual functional decline as evinced by orthostatic hypotension
owing to impairment of baroreceptor function. - This occurs in 25% of subjects older than 65 years.
- Temperature control is impaired,
and heat generation is reduced by the decline in BMR. - The frail and elderly may also have less subcutaneous fat for insulation.
- The autonomic changes have been described as ‘physiological beta blockade’.
Cardiovascular system:
there is gradual functional decline;
- cardiac output decreases (by 20% at age 60),
with decreases in heart rate, stroke volume and myocardial contractility. - A decline in receptor numbers means
that there is decreased sensitivity to inotropes. - The risk of pulmonary thromboembolism is increased,
both because of age itself, and .
because of the nature of the surgery for which elderly patients may
present, particularly orthopaedic fractures and intra-abdominal procedures. - Anaemia is common and a preoperative haematocrit of
less than 24% is associated with worse outcomes
Respiratory system
*There is a progressive decline with age.
The closing volume matches functional residual capacity (FRC)
in the upright position at around the age of 65 years
but encroaches on FRC by age 44 if supine.
Increased V/Q mismatch leads to a widening of the
alveolar–arterial oxygen gradient (A–aDO2),
there is decreased sensitivity to hypoxia and hypercapnia,
and there is a decrease in lung compliance.
The airway:
elderly patients are more likely to be edentulous,
with mandibles that are osteoporotic. .
Oropharyngeal muscle tone is lax, and cervical spondylosis and osteoarthritis
are common problems.
Gastrointestinal system
elderly subjects have slower gastric emptying,
parietal cell function is impaired and hiatus hernia
gastro-oesophageal reflux are more common.
Renal system:
Renal blood flow diminishes and glomerular filtration rate
is decreased by 30–45% in the elderly.
Renal concentrating function is diminished,
fluid handling is impaired and preoperative dehydration is more likely.
Drugs
: hepatic and renal function decline with a decrease in the clearance of drugs,
protein binding is reduced and receptor sensitivity alters.
It is increased for CNS depressants,
but decreased for inotropes and for β-adrenoceptor blockers.
The response to α-agonists is similar to that seen in younger patients.
Factors of Particular Relevance to Anaesthesia
Coexisting disease is common:
the list is potentially very long
includes ischaemic heart disease,
hypertension,
chronic airways disease,
cerebrovascular disease,
osteoarthritis,
diabetes mellitus,
dementia (which has an incidence of 20% in those aged over 80 years),
Parkinson’s Disease,
physical frailty,
malnutrition,
polypharmacy
sensory impairment
Surgical mortality is high
Surgical mortality is high:
about 15% of the population of the UK is aged over 65,
and the population is continuing to age.
This is a group in whom surgery is more common,
and in whom mortality rates are higher.
In the 1999 National Confidential Enquiry into Perioperative Deaths (NCEPOD) report,
which looked at the extremes of age,
75% of reported deaths were more than 70 years,
and the overall mortality rate was 10%
Regional anaesthesia
neurological and physiological impairments seen
with increasing age, regional and neuraxial techniques are an appropriate alternative,
assuming that the advantages are not negated by excessive sedation.
Hypotension is a
potential problem with neuraxial blocks and is associated with a poorer outcome in
surgery such as fixation of femoral neck fracture
pressure do vary, but it is prudent not to let the intraoperative
mean arterial pressure fall by more than 20% of baseline
Fluid administration as
a means of countering hypotension is rarely effective without concurrent administration
of a vasopressor and risks circulatory overload. Apart from replacement
for surgical losses, it is recommended that fluid infusion should not usually exceed
8–10 ml kg–1
Summary of anaesthetic considerations
there is a high probability of coexisting disease,
an increased regurgitation risk (but not enough to mandate rapid sequence
induction),
an increased sensitivity to effects of hypnotic and opiate drugs,
greater difficulty in maintaining perioperative oxygenation,
skin fragility and high susceptibility to pressure effects of prolonged immobility,
reduced temperature control,
an increased likelihood of POCD
and thromboembolic events.
Clinical Frailty SCore
