Although age itself is not a disease, advanced age can be a predictor for increased risk of certain disease conditions. Additionally,
as our patients age, normal changes occur in their physiology that can change their responses to anesthesia and analgesic
medications as well as potentially put them at higher risk of peri-anesthetic complications. A patient is considered geriatric
when they have reached 65 to 75% of the expected life span for that particular breed. In general larger breed dogs can be
classified as geriatric after 6 to 8 years of age and small breed dogs and cats after 10 to 12 years of age.
Physiologic changes in geriatric patients
Geriatric patients can have age related changes in their cardiovascular, respiratory, hepatic, renal, and nervous systems.
With identification of these changes, an anesthetic plan can be formulated to provide the best possible outcomes.
The cardiovascular system can be greatly impacted with age related changes. Cardiac output, blood volume, and the ability
of the vascular system to quickly adapt in the face of stressors are reduced and vagal tone, myocardium fibrosis, and thickening
of vessel walls is increased. This results in a reduction in cardiac reserves and the ability to increase stroke volume and
vessel flexibility, and an increase in the chances for arrhythmias.
Age related changes to the lungs are common and can be seen as increased fibrosis on thoracic radiographs. Lung elasticity,
muscle strength, chest wall compliance, and elastic recoil are all reduced. Respiratory rate, tidal volume, oxygen uptake,
and protective airway reflexes are also reduced. Similar to the cardiovascular system, these changes result in decreased
reserves and put patients at risk for respiratory compromise and decreased gas exchange.
With a decreased functional mass and blood flow, common in aged patients, the hepatic system has a decreased ability for metabolism
and elimination of drugs. Additionally, there may be a decrease in glycogen reserves, particularly in very thin patients,
and thus be at risk for hypoglycemia. Clotting factors and blood proteins production may also be present putting the patient
at risk for excessive surgical bleeding, decreased oncotic pressure, and decreased drug binding in the plasma.
At patient age, there is a decrease in function mass of the kidneys (loss of nephrons), this is expecially problematic in
cats who are born with less nephrons than dogs. Additionally, there is decreases renal blood flow and glomerular filtration
rate as cardiac output is decreases. With these changes, there is a decreases ability to regulate electrolyte and fluid balance.
These patients are less tolerant of dehydration, anesthesia induced hypotention, and the ability to excrete some drugs.
Elderly patients may have decreased brain mass due to degeneration of neurons, myelin sheaths, and have a decreased production
of neurotransmitters. Their ability to have an appropriate neuro-endocrine response to stress can also be greatly diminished.
There may be an enhanced effect of anesthetic and analgesic drugs and these patients may show greater anxiety and higher susceptibility
to cardiovascular depression as their sympathetic nervous system may be less functional.
Formulating an anesthetic plan
Prior to any anesthesia of geriatric patients, a through physical examination should be performed. Specific targets of an
examination should include the cardiovascular and respiratory systems. A cursory neurologic examination can also be performed
taking into account any signs of central nervous system disease. A complete blood count, serum chemistry and electrolyte
analysis, and urinalysis should be performed. These tests will help to identify any dysfunction in specific organ systems
so that corrections can be made if possible and anesthetic drugs can be tailored to that patient. Fluid and electrolyte imbalances
should be corrected. Patients with renal disease can be admitted the day prior to anesthesia and be administered intravenous
crystalloid fluids for dieresis to reduce nitrogenous wastes.
Analgesic and anesthetic drugs should be chosen that will have minimal impact on the cardiovascular and respiratory systems.
Drug dosages can be reduced in geriatric patients to compensate for decreased metabolism and smaller volumes of distributions.
Opioids are often chosen because of their minimal impact to the cardiovascular system. Benzodiazepines can be used as premedications
or co-induction agents as their effects on the cardiovascular system and respiratory systems are nearly nonexistent at clinical
doses. Propofol can be used as an induction agent as it provides smooth inductions and recoveries and is metabolized by various
organ systems so that if one is dysfunctional, others can increase the amount they metabolize. Maintenance is performed with
isoflurane or sevoflurane but inhalant sparing techniques such as concurrent opioid infusions can be done to minimize the
inhalant impact on the cardiovascular system. Vigilant patient monitoring should be performed for early identification of
potential problems such as hypotension and bradycardia. A quiet, warm recovery area should also be provided to help reduce
emergence delirium and additional stress. With proper planning and an understanding of the disorders occurring in a specific
geriatric patient, anesthesia can be provided ensuring the best possible outcome.