What Do We Know About Postoperative Cognitive Dysfunction?

Postoperative cognitive dysfunction (POCD) is a form of cognitive decline that involves a functional deterioration of activities of the nervous system, such as selective attention, vigilance, perception, learning, memory, executive function, verbal and language abilities, emotion, visuospatial and visuomotor skills. It occurs in the absence of cranial trauma or other brain injuries, and prevalence rates range from 36.6% in young adults to 42.4% in older adults, as a consequence of significant invasive procedures such as cardiac, noncardiac, and carotid surgeries that are lengthy and intensive.

Alzheimer’s disease (AD), the most common form of dementia, accounts for about two thirds of all cases of dementia globally. It is estimated that 41 million patients with dementia remain undiagnosed worldwide, and 25% of patients are diagnosed only when they are fully symptomatic. AD is a neurodegenerative disorder defined by neuropathologic changes, including beta-amyloid (Aβ) plaques composed of aggregated Aβ and neurofibrillary tangles containing aggregated tau proteins.

Patients with AD are unaware of their condition. Dementia, especially in its early stages, is often a hidden disease. Even when suspected, patients and families may believe that the symptoms are part of normal aging and may not report them to the doctor. In these patients, surgery may unmask subclinical dementia.

The complex correlation between POCD and AD has sparked debate following numerous anecdotal reports of how older adults undergoing surgical procedures may experience long-term cognitive decline with clinical characteristics such as those of patients with dementia. Despite advances in knowledge, it is still difficult to establish a priori how much surgery and anesthesia can increase the risk or accelerate the progression of a prodromal and asymptomatic AD condition (stages I-II) to clinically evident stage III AD. The current trend of an aging population poses a challenge for anesthesiology surgery because as the age of patients undergoing surgery increases, so does the likelihood of developing POCD.

Recent research in these fields has improved knowledge of the characteristics, epidemiology, risk factors, pathogenesis, and potential prevention strategies associated with POCD. It has improved the perspectives of future prevention and treatment.

Definition and Diagnostic Criteria

POCD, according to the cognitive impairment classification in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, is characterized by mild neurologic disturbance resulting from routine surgical procedures, excluding conditions such as deafness, dementia, or amnesia. The definition of POCD involves prolonged cognitive decline that can last for weeks, months, or even years. POCD may be confused with postoperative delirium, an acute and fluctuating disorder of consciousness that typically occurs within 3 days of surgery.

The diagnosis of POCD is based primarily on neurocognitive function scales. Widely used assessments include the Montreal Cognitive Assessment, the Wechsler Memory Scale, and the Mini–Mental State Examination.

Epidemiology

POCD is prevalent among patients undergoing cardiac or orthopedic surgery. In patients undergoing aortic-coronary bypass and cardiopulmonary bypass, 50%-70% develop POCD 1 week after surgery. In addition, 10%-30% experience long-term effects on cognitive function at 6 months after the procedure. In patients undergoing hip arthroplasty, 20%-50% exhibit POCD within 1 week of surgery, with 10%-14% still presenting it after 3 months.

Risk Factors

Age

POCD is typically observed in patients older than 65 years. However, after surgery, around 30% of younger patients and about 40% of older patients develop POCD at the time of hospital discharge. Specifically, 12.7% of older patients continue to have POCD 3 months after surgery, compared with 5% of younger patients.

Type of Surgery 

Hip and knee arthroplasty procedures entail a higher risk for POCD than general surgery. The same is true of cardiac surgery, especially aortic-coronary bypass and cardiopulmonary bypass.

Types of Anesthesia 

Initial assessments of postoperative cognitive function in cardiac surgery did not provide significant correlations between observed changes and the type of anesthesia because of the high number of confounding factors involved. A more recent meta-analysis of 28 randomized clinical trials concluded that the incidence of POCD is lower in surgeries using intravenous anesthesia with propofol than in those using inhalation anesthesia with isoflurane or sevoflurane.

Pain

Postoperative pain is a common issue, mainly resulting from substantial surgical trauma or potential wound infection. Patient-controlled postoperative analgesia independently increases the risk for POCD compared with oral postoperative analgesia. Meta-analyses indicate that persistent pain can lead to a decline in patients’ cognitive abilities, attention, memory, and information processing.

Evolving Scenarios

Current research on POCD has deepened our understanding of its pathogenesis, implicating factors such as central nervous system inflammation, neuronal apoptosis, synaptic plasticity damage, abnormal tau protein modification, chronic pain, and mitochondrial metabolic disorders. Several neuroprotective drugs are currently under study, but none have shown consistent benefits for the prevention and treatment of POCD. The available evidence on the subject does not unambiguously guide the practicing physician. But neither does it exclude the importance of a careful assessment of POCD risk factors and the cognitive status of an older patient before surgery to provide useful information to the patient, family, and doctors when deciding on appropriate and shared procedures. 

This story was translated from Univadis Italy, which is part of the Medscape professional network, using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.