Yung-Fong Sung, M.D.
Professor, Anesthesiology, Emory University School of Medicine
Chief of Anesthesiology, Emory Clinic Ambulatory Surgery Center
yung-fong_sung@emory.org
In the 1950s, it was very unlikely that one would live to be
more than 100 years old, or even 90. At that time, 35 was considered
middle age. However, less than half a century later the age
group of 85 and above is the fastest growing population in the
United States. Thanks to advances in medical science (prevention,
early diagnosis and treatment), Americans are living longer
than they ever have before.
While people are living longer, there are also more diseases
and other disorders in the aging population. Thus, geriatric
medicine is rapidly developing as more studies of the aged are
being done. Concomitant existing disease cannot be ignored when
preparing the geriatric patient for anesthesia and surgery.
This article will concentrate on diseases and other disorders
of the geriatric population.
The cause of aging is unknown, but genetic and environmental
factors play important roles.
GENERAL CHANGE DURING AGING
Externally, one's hair turns gray and the skin begins to wrinkle.
Internally or physiologically, aging means that atrophic changes
affect many organs as well as decrease the function of many
systems due to a slowing of the metabolism. The aging process
decreases the volume of body fluids and increases fatty tissue.
These changes, coupled with a frequently sedentary lifestyle,
predisposes the elderly to obesity. However, the very old tend
to lose weight, perhaps due to a decrease in appetite occasionally
bordering on anorexia.
Environment and life style affect the body concomitantly with
advancing age and disease. Education and socioeconomic status
and character traits are particularly important because they
can be modified and may potentially alter the aging or disease
process. Lifestyle habits such as exercise, diet, cigarette
smoking and alcohol use also affect the aging process
CENTRAL NERVOUS SYSTEM (CNS) DISORDERS
The aging process often causes brain atrophic changes. There
are substantial age-related declines in brain function, i.e.,
decrease in norepinephrine and dopamine synthesis. The righting
reflexes and Stage 4 sleep also decrease. Some neurons gradually
die in the brain; however, others will grow to compensate for
the age-related deaths of their neighbors, similar to what happens
in hippocampus. There are also age-related neurological and
psychiatric disorders.
1. Neurologic Disorders
Neurological symptoms in the elderly are common, such as
impairment of memory, decreased cognitive or intellectual
functions, deterioration of mobility (e.g., change in gait),
altered sleep pattern, decreased sensory input, (visual, acoustic,
taste, smell, etc.), and autonomic nerve system imbalance.
2. Psychiatric Disorders
The symptoms are often depression, dementia, confusion, catatonia
and delirium. The CNS diseases in the elderly are often Parkinson's
disease, depression, dementia and delirium.
AUTONOMIC NERVOUS SYSTEM DISORDERS
The autonomic nervous system serves as a vigilant guardian
for homeostasis of the human body. In other words, the autonomic
nervous system is capable of maintaining a constant internal
environment in spite of external challenges. However, since
the homeostatic mechanisms slow and weaken during advancing
age, changes are reflected in the alterations of sympathetic
and parasympathetic responsiveness, i.e., decreased sensitivity
of baroreceptor and change in thermoregulation.
Consequently, orthostatic hypotension and syncope are common
problems for the elderly and are only worsened by disease, especially
diabetic autonomic dysfunction.
Thermoregulation is affected by autonomic impairment, as well
as changes to the skin and blood vessels. Thermoregulation is
further impaired by many chronic medications. The overall effects
of these conditions include inadequate heat production and conservation,
increased heat loss and reduced heat tolerance. The elderly,
especially the poor elderly, may lack resources for environmental
control (adequate heating/cooling systems, clothing, mobility,
etc.), which is vital to temperature control.
As a consequence, the elderly are vulnerable to heat stroke
and hypothermia and die in disproportionate numbers every year.
EYE AND EAR DISORDERS
Eye Disorders - Physiological changes of presbyopia
and lens opacification subsequently cause decreased accommodation
and increased susceptibility to glare. These physiological changes
often result in decreased visual acuity as well as blindness.
Ear Disorders - For the ear, the physiological change
is decreased high frequency acuity, making it difficult to discriminate
words if noise is present in the background. Consequently, there
is deafness and a decrease in acoustic acuity.
CARDIOVASCULAR SYSTEM DISORDERS
Physiological change in the aging individual produces decreased
arterial compliance (decreased elasticity) and increases in
systolic blood pressure, subsequently causing left ventricle
hypertrophic (LVH). It also results in decreased beta-adrenergic
receptor responsiveness as well as decreased baroreceptor sensitivity.
There is also a decrease in SA node automaticity.
Diseases include hypertension, coronary disease, congestive
heart failure as well as heart block or arrhythmia.
RESPIRATORY SYSTEM DISORDERS
Physiologically, aging also affects the respiratory system
with decreases in responsiveness to hypercapnia, and often with
hypoxia due to decreased carotid and aortic body sensitivities.
There is an increase in chest wall rigidity, chest wall compliance
and muscle strength. Also, as the airway from the nose to the
terminal bronchi become more narrow or stiff, there is a decrease
in the exchange of gas. The lung parenchyma contains three important
gas exchange structures: 1) alveolar, the gas exchange airways
distal to the terminal bronchioles, 2) capillary bed and 3)
the interstitial structure of the lung (elastic recoil). Under
normal situations, the distal airways maintain patent by the
elastic recoil forces of the surrounding lung parenchyma. The
forces that hold intraparenchymal airways (small airways) open
will therefore decrease as the aging lung loses its elastic
recoil due to thickening of parenchyma. The thickening of parenchyma
will also decrease gas exchange between the alveolar and capillary
bed. There is ventilation perfusion mismatching and decreased
arterial oxygen.
The respiratory system is also affected by environmental changes,
including smoke, dust, air pollution, etc. Respiratory diseases
include emphysema, dyspnea, and hypoxia.
GASTROINTESTINAL SYSTEM DISORDERS
The gastrointestinal system in the elderly is often characterized
by decreased hepatic function, gastric acidity and absorption
of certain foods and substances, such as calcium. There is also
a decrease in colon mobility and motility, as well as in anal/rectal
function.
Subsequently, the elderly may have hepatic cirrhosis, constipation,
fecal impaction, fecal incontinence, osteoporosis or vitamin
B12 deficiency due to poor absorption.
RENAL DISORDERS
As one gets older, the kidneys change morphology due to atrophic
change of the parenchyma and sclerotic change of the vasculature.
The result is profound functional changes: decreased renal plasma
flow, decreased glomerular filtration rate and decreased ability
for urinary concentration or dilution. These changes delay responses
to electrolytes fluid restriction or overload.
In the final stages, renal changes cause increased serum creatinine,
blood urea nitrogen, renal failure and increased or decreased
electrolyte retention.
GENITOURINARY SYSTEM DISORDERS
In the female there are atrophic changes of the vaginal and
urethral mucosa. In the male, prostate enlargement often causes
urinary tract incontinence or retention, which can lead to urinary
infection.
ENDOCRINE SYSTEM DISORDERS
In elderly individuals, the activity of the endocrine system
also decreases, causing impaired glucose hemostasis, decreased
thyroxine clearance or production, decreased production of renin,
aldosterone and testosterone, decreased vitamin D absorption
and activation and increased plasma concentration of antidiuretic
hormone.
So, the consequences of all of these changes include the development
of diabetes mellitus, thyroid dysfunction, decreased sodium
retention, increased potassium absorption, impotence and osteoporosis,
which causes bone fractures.
HEMATOLOGICAL AND IMMUNE SYSTEM DISORDERS
Bone marrow production is decreased in the elderly, as is T-cell
function. There is an increase in autoantibodies. In such cases,
the combination of a poor dietary intake and poor vitamin absorption
often causes the development of anemia and autoimmune disease.
MUSCULAR SKELETAL SYSTEM DISORDERS
Decreased muscle mass, bone density and lubrication of the
joints causes stiffness of the joints, osteoporosis, frequent
fractures of the hip and bone/joint functional impairment.
CANCER AND AGING
Age is the most significant risk factor for cancer. Two-thirds
of all cancer cases occur in the population aged 65 years or
older. Thus, the probability of a person developing cancer is
age-dependent: 1:58 men, and 1:52 women for age 0-39; but 1:11
men, and 1:13 women from age 40-59; and 1:3 men, and 1:4 women
for the age range of 60-79 years.
DRUG METABOLISM DISORDERS
Drug metabolism often relates to the organ system functions
and their reserve. Because of the decreased CNS, hepatic, renal,
gastric and lung function and decreased cardiovascular reserve,
as well as decreased lean body mass, decreased body fluid volume
and increased fatty tissue, the elderly often metabolize drugs
differently from the younger age group. In general, drug metabolism
may be significantly reduced due to the failing function of
the systems previously mentioned. Due to the increase in fatty
tissue, the decrease in total body water, the distribution of
the medication either from oral, intravenous or intramuscular
routes and increases in volume of drug distribution, the elderly
often have a change in uptake, and thus reduced clearance. Decrease
in the metabolism and excretion is also due to decreased hepatic
and renal functions. The elderly group should be treated differently
when prescribing medication, and more attention should be paid
in particular to drug interaction. Further study definitely
needs to be done for drug metabolism in the aged group so that
drugs can be prescribed intelligently to avoid adverse reactions.
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