How does POCD manifest?
What causes POCD?
References
Further reading
Post-operative cognitive decline, or dysfunction (POCD), is a recognized clinical phenomenon in which patients experience lasting cognitive impairment for some time following anesthesia.
Cognitive decline. Image Credit: pathdoc/Shutterstock.com
Typically, older patients are more likely to experience POCD, with around 40% over the age of 60 who are hospitalized for surgery experiencing POCD on discharge, and 10% three months later, though patients of any age can experience POCD.
Considering the aging population and the increasing number of surgeries the average person receives as they age, POCD is becoming an increasingly encountered problem, particularly with regards to patients reliably giving informed consent to further medical procedures while in a delirious state. This article will discuss the incidence and potential causes of POCD.
How does POCD manifest?
POCD has been recognized in patients following anesthetized surgery since the mid-19th century. The British Medical Journal published a paper titled “Insanity Following the Use of Anaesthetics in Operations” in 1887.
Memory and performance of intellectual tasks are most usually affected by POCD, in particular, the ability to learn and recall new information, comprehend and express language, and recognize emotions in others is degraded.
Visual perception and coordination, the ability to plan and make decisions, and the ability to maintain focus and attention are also influenced by POCD. Recognizing changes in these functions from pre- to post-surgery forms the basis of POCD diagnosis. Therefore, accurate diagnoses of POCD require both pre- and post-operative psychometric testing, which may express in a subtle and dynamic manner.
Typically, tests involving connecting a series of numbered or alphabetized shapes in ascending order, memorizing and recalling a number series, or tests of manual dexterity such as the grooved pegboard test, are employed during clinical neuropsychological examination.
Delirium following anesthetized surgery is relatively common and occurs in around 80% of patients in critical care. Hyperactive delirium is generally easily identified as the patient may be an active risk to themselves or others, though hypoactive delirium is likely significantly under-diagnosed as patients appear calm but upon examination display inattentiveness and disorientation.
POCD may manifest in specific manners that include but are not exclusive to delirium, and as discussed can last for significant periods of time following surgery. Monk et al. (2008) documented POCD in 36.6% of patients aged 18-39, 30.4% aged 40-59, and 41.4% of patients aged over 60 at discharge, though as discussed older patients tend to experience more intense and long-lasting effects.
The same study found that patients that had experienced POCD had a higher risk of death within one year than those that had not, normalized by condition, and an 8.5-year follow-up study by Steinmetx et al. (2009) found higher average mortality under the same conditions of 1.63.
Whether the higher mortality rate observed amongst those with POCD is related to the condition directly or a result of common underlying causes is as yet unclear, compounded by difficulties in separating the effect of one of numerous anesthetics, the type of surgery performed, and various comorbidities that may be present.
What causes POCD?
POCD occurs more frequently following extensive or repeated rounds of surgery, though the precise mechanism causing the dysfunction is yet to be made clear.
A history of alcohol abuse, even with recent abstinence, a clinical history of depression, and a low educational level are each additional risk factors in the development of POCD, and cardiac surgery in particular is known to lead to a higher incidence of POCD amongst elderly patients.
Indeed, those having undergone cardiac bypass procedures are known to encounter cognitive decline independent of the occurrence of POCD, according to some studies at the same ultimate rate whether surgery was performed or not.
Peripheral surgery activates inflammatory tumor necrosis factor-alpha signaling cascades that in turn cause the release of various inflammatory cytokines that may be involved in weakening the integrity of the blood-brain barrier towards macrophages, potentially allowing them to migrate into the hippocampus and cause memory impairment.
Interestingly, local anesthetic may cause POCD at almost or equal incidence rate as general anesthesia, and no evidence of long-term anesthetic neurotoxicity has emerged from twin studies, thus it is not necessarily thought that anesthesia itself is the cause of POCD.
Changes in brain structure have been observed in those with POCD indicating reduced thalamic and hippocampal volume and reduced cerebral blood flow, suggesting that neuronal death may be involved.
Pre-existing mental health or brain disorders also contribute heavily to the development of POCD, and where patients are found to have a silent brain ischemia during heart surgery they are around three times as likely to then develop POCD upon completion of the surgery, perhaps lending credence to the idea of inflammatory changes in the brain being the root cause.
However, the choice and intensity of anesthetic, as well as the occurrence of any hypoxia and organ ischemia during surgery, have also been found to play a role in the incidence of POCD developing.
It may be that POCD is the result of a number of confounding factors, and all that can be done is to best reduce risk where possible and weigh the benefits of surgery with the potential downsides of POCD developing, thus continued investigation of risk factors is underway.
References
Further Reading
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