Introduction
Post-operative mental dysfunction and confusion in aged
patients is a well recognized entity. Commonly known as
post-operative delirium and cognitive dysfunction (POCD),
these are important for any peri-operative physician dealing
with geriatric population. The incidence is more in older
patients with pre-existing impairment [1]. Impact of POCD is
grave. This can result in poor rehabilitation outcome and
increased hospital stay [2]. Incidence ranges from 15-50% with
˂5% for cataract surgery and as high as 60% after hip
replacement procedures [3].
Possible causes and aetiology
Even though the exact aetiology is not fully elucidated,
different mechanisms are being implicated, predominant being
imbalance between central nervous system cholinergic and
dopaminergic activity. It is proposed that a relative
underactivity of cholinergic system coupled with excessive
dopaminergic activity can precipitate POCD. This theory is
supported by the fact that delirium could be precipitated by
the use of anticholinergic or dopaminergic medications [4].
Inflammatory response to surgical stress is believed to play
an important role in the development of post-op delirium [5].
Evidence to this is found by the elevated levels of
inflammatory mediator chemokines during post-operative stage
in patients who become delirious after cardiac surgery [6]. It
is believed to happen as a result of leucocyte migration into
the central nervous system (CNS) [5]. In vitro studies have
shown that chemokines are capable of interrupting an intact
blood brain barrier [6]. Supporting the inflammatory
hypothesis is the fact that elevated levels of C - reactive
protein were found in patients who develop POCD following hip
surgery [5].
Many pre-operative and peri-operative factors or events have
been implicated as possible factors for the development of
POCD. Pre existing cognitive impairment is one proved factor
with strongest association for the development POCD [7]. Other
pre-operative risk factors include geriatric age group, visual
or hearing impairment, improperly treated pain,
alcohol/narcotic addiction [5]. Peri-operative contributory
factors include blood loss, multiple peri-operative
transfusions and post-operative haematocrit value of ˂ 30%.
Even though it is logical to conclude that
peri-operative events like hypotension or hypoxia may lead to
POCD, strong evidence to support the same are lacking [8].
Inouye attributed certain precipitating factors to POCD like
use of peri-operative physical restraints, bladder catheter
and fluid and electrolyte abnormalities [4]. There are at
present no guidelines regarding drugs to be avoided to
safeguard against POCD. But since POCD is proportional to the
number of medications the patient is prescribed, it is logical
to avoid poly pharmacy in the peri-operative settings. More
than three medications added 24-48 hours before the onset of
delirium is considered as a potent precipitating factor [4].
Earlier published data failed to associate any type of
anaesthesia as a definite risk factor [9]. But Rasmussen et al
in a recent randomised study showed a definite advantage of
regional anaesthesia in reducing the risk of early POCD [10].
Regional anaesthesia has shown a definite advantage in
reducing the incidence of POCD in the initial 3 months but not
beyond [10]. But even the early reduction in POCD assumes
significant in terms of immediate physical recovery and better
co-operation for post-operative care plan [5].
Prevention and treatment
Many authors have suggested certain risk reduction strategies
against POCD. This includes proper visual and hearing
equipments, attention to pre-operative pain, early
mobilisation and avoiding physical restraints [11,12]. It is
imperative to treat electrolyte imbalances and fluid deficit
as well as ensuring normal sleep-awake cycle and the presence
of family in the post-operative care plan. If we can entrust
competent caregivers and adequate support services,
undertaking the procedure as a day care procedure will go a
long way in reducing the incidence of POCD.
Haloperidol (0.5-1 mg) is a proved agent in cases of
pharmacological intervention [13]. Lorazepam is preferred in
cases of alcohol or benzodiazepine withdrawal [13]. Use of
haloperidol as a prophylactic agent has been shown to reduce
the severity of POCD but no change in the duration [13].
Literature also shows evidence of effective treatment with
cholinesterase inhibitors donepezil and gabapentine [14,15].
Summary
Development of POCD is a potential complication which can add
to the morbidity of geriatric patients. Chance of POCD
increases with advancing age. Some potential risk factors have
been identified and risk reduction strategies involve
identifying these potential agents and minimizing or
correcting them. There is limited evidence with respect to
pharmacological agents. Haloperidol is probably an agent being
used extensively. Agents like donepezil and gabapentine are
reported to be effective but yet to become popular.
References
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