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Less than 50 years ago, surgery was considered hazardous
for patients 50 years or older. In 1955, Bedford
published a retrospective review of 1,194 elderly
patients (50 years or older) who had surgery under
general anesthesia during a five-year period.1
He found cognitive impairment in 10 percent of patients
and concluded that the effects were related to anesthetic
agents and hypotension and recommended that “operations
on elderly patients should be confined to unequivocally
necessary cases.”
Today the fastest growing segment of the United
States population includes people 65 or older, and
it is estimated that more than half of these individuals
will require some form of surgery in their lifetime.2
Improvements in surgical techniques, anesthesia
and intensive care units have made surgery in these
elderly patients possible. Despite improved operative
outcomes in the elderly, a significant proportion
of these patients experience postoperative cognitive
impairment.3-7
The most common forms of postoperative cognitive
impairment are delirium and postoperative cognitive
dysfunction (POCD). The socioeconomic implications
of postoperative cognitive decline are unknown,
but abrupt declines in cognitive function in elderly
individuals living in the community often lead to
a loss of independence, withdrawal from society
and death.8
Postoperative delirium is common in patients after
surgery with the overall incidence for all age groups
estimated to range from 5 percent to 10 percent
and for the elderly from 10 percent to 15 percent.6
The rate of delirium in the elderly varies with
the type of surgery and is reported to be 1 percent
to 3 percent following cataract surgery, 10 percent
following general surgery, 28 percent to 61 percent
following major orthopedic surgery (e.g., joint
replacement, fracture) and as high as 47 percent
after cardiac surgery.6
Delirium is characterized by fluctuating levels
of consciousness, a disturbed sleep-wake cycle and
altered psychomotor activity. Delirious patients
often exhibit disorders of cognitive function, thinking,
perception and memory. The etiologic factors associated
with this disorder include advanced age, polypharmacy,
cerebral damage, surgery and anesthesia, hypoxia,
sepsis, sensory deprivation or overload, electrolyte
disturbances, pain and endocrine or metabolic disorders.
Delirium is a very costly disorder, and Medicare
expenditures associated with the diagnosis and treatment
of this problem exceed $4 billion per year (1994
dollars).7
POCD has recently been demonstrated in 20 percent
to 60 percent of patients following coronary artery
bypass (CAB) surgery and 10 percent to 16 percent
of elderly patients following major, noncardiac
surgery.3-5
POCD is defined as a “deterioration of intellectual
function presenting as impaired memory or concentration.”9
The clinical features of this disorder range from
mild forgetfulness to permanent cognitive impairment
resulting in a loss of independence. POCD is considered
a mild neurocognitive disorder, and the diagnosis
can only be made if the cognitive decline can be
corroborated by the results of neuropsychological
testing (presurgical and postsurgical). In addition
testing must demonstrate that the individual has
a new onset of cognitive deficits in at least two
areas of cognitive functioning lasting two weeks
after surgery or longer.9
| “An emerging
concept in neuropsychology and clinical geropsychology
espouses a ‘functional cliff’ hypothesis
of cognitive decline and dementia in later adulthood.
…” |
While it is now accepted that POCD is a real entity,
little is known about the etiology of POCD and the
risk factors for this problem in the aging population.
It is likely that the etiology of POCD in the elderly
patient is multifactorial. Potential risk factors
for the development of this problem include the preoperative
cognitive status of the patient, intraoperative events
related to the surgery itself and anesthetic agents.
The preoperative cognitive state of the patient may
be linked to the development of postoperative cognitive
function. An emerging concept in neuropsychology and
clinical geropsychology espouses a “functional
cliff” hypothesis of cognitive decline and dementia
in later adulthood. This hypothesis is essentially
a threshold model that argues that, with increasing
age and normal cognitive declines, individuals move
closer and closer to a level that might be considered
“impaired” or “demented.”
As this threshold is approached, individuals enter
a high-risk phase that might be considered “preclinical
dementia.”10
For individuals in this preclinical state, research
suggests that the sudden onset of even mild neurological
trauma such as surgery may be a sufficient proximal
cause to move people over the clinical threshold and
into the range of functioning that might be classified
as “impaired.”
Systemic and cerebral emboli can occur during surgical
procedures and may represent a possible mechanism
for postoperative cognitive decline. One possible
explanation for POCD after CAB is that embolic material
is released during crossclamping of an aorta affected
by atherosclerosis and that this embolic material
enters the cerebral vessels during surgery, resulting
in occlusion of both large and small vessels.3
The incidence of postoperative neurocognitive deficits
has been shown to correlate with the number of microemboli
detected during the CAB grafting procedure.3
| “Exposure
to anesthetic agents has been suggested as a
possible cause of POCD in elderly patients.” |
Microemboli also are common during orthopedic surgery
and may be responsible for the cognitive decline seen
after this type of surgery.
Exposure to anesthetic agents has been suggested as
a possible cause of POCD in elderly patients. Anesthetic
agents affecting the release of central nervous system
neurotransmitters such as acetylcholine, dopamine
and noradrenaline could potentially impair memory,
especially in elderly patients. There are no definitive
conclusions on the effects of anesthesia on learning
and memory.
There is wide variation in the reported incidence
of POCD in the literature. Much of this variation
is due to methodological differences between the studies
such as the use of varying test batteries, inadequate
statistical power, the lack of adequate control subjects
in the studies and the lack of a standard criteria
for diagnosing POCD.9
Rasmussen et al.9
demonstrated that the incidence of POCD in a group
of 176 volunteers could vary between 0 percent and
40 percent if 10 different commonly used criteria
for POCD were utilized.
Long-term follow-up of patients with POCD is needed
to provide insight into the financial and emotional
burden of this problem and the impact of this problem
on the patient, the patient’s family and society
at large. Future research should identify which neuropsychological
tests are best for the diagnosis of the problem and
which of the varying criteria for POCD is associated
with functional impairment. Additional research also
is needed to gain an understanding of the etiology
of POCD and to develop interventions to minimize or
prevent this serious complication.
References:
1. Bedford PD. Adverse cerebral effects of anaesthesia
on old people. Lancet. 1955; 2:857-861.
2. Weintraub HD, Kekoler LJ. Demographics of Aging.
In: McLeskey CH, ed. Geriatric Anesthesiology.
Baltimore: Lippincott Williams & Wilkins. 1997:3-11.
3. Newman MF, Kirchner JL, Phillips-Bute B, et al.
Longitudinal assessment of neurocognitive function
after coronary-artery bypass surgery. N Engl
J Med. 2001; 344:395-402.
4. Moller JT, Cluitmans P, Rasmussen LS, et al.
Long-term postoperative cognitive dysfunction in
the elderly, ISPOCD 1 Study. Lancet. 1998;
351:857-861.
5. Price CC, Garvan CW, Monk TG. Neurocognitive
performance in older adults with postoperative cognitive
dysfunction. Anesthesiology. 2003; 99:A50.
6. Parikh SS, Chung F. Postoperative delirium in
the elderly. Anesth Analg. 1995; 80:1223-1232.
7. Bekker AY, Weeks EJ. Cognitive function after
anaesthesia in the elderly. Best Practice &
Research Clinical Anaesthesiology. 2003;
17:259-272.
8. Bosworth HB, Schaie KW. Survival effects in cognitive
function, cognitive style, and sociodemographic
variables in the Seattle Longitudinal Study. Exp
Aging Res. 1999; 25:121-139.
9. Rasmussen LS, Larssen K, Houx P, et al. The assessment
of postoperative cognitive function. Acta Anaesth.
2001; 45:275-289.
10. Greiner PA, Snowdon DA, Schmitt FA. The loss
of independence in activities of daily living: The
role of normal cognitive function in elderly nuns.
Am J Public Health. 1996; 86:62-66.
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Terri G. Monk, M.D., is Professor of Anesthesiology,
Duke University Medical Center, Durham, North
Carolina. She is President-Elect of the Society
for the Advancement of Geriatric Anesthesia. |
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