Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is a new, objectively measurable decline in memory, executive function, attention or processing speed that persists for weeks to months after surgery. It is distinct from delirium, which is acute and fluctuating. Current terminology separates delayed neurocognitive recovery (up to 30 days) from postoperative neurocognitive disorder (30 days to 12 months).

Epidemiology. After major noncardiac surgery in older adults, about 25% to 40% show decline at 1 week and about 10% to 15% at 3 months. After cardiac surgery, rates are higher at discharge and 10% to 30% persist at 3 to 6 months. Figures vary with the testing method.

Risk factors. Increasing age, low educational attainment, preexisting cognitive impairment, frailty, depression, alcohol misuse, cerebrovascular disease, major or prolonged surgery, postoperative delirium, infection, pain, sleep disruption and polypharmacy with anticholinergics, benzodiazepines or opioids. The effect of anaesthetic depth and intraoperative hypotension is uncertain.

Prognosis. Most patients improve over 3 months. Persistent decline is linked to prolonged recovery, loss of work and independence, and later dementia.

Pathophysiology.

Surgical trauma releases interleukin-1 beta, interleukin-6 and tumour necrosis factor alpha. These disrupt the blood brain barrier and activate microglia in the hippocampus.

Cerebral hypoperfusion, microemboli (especially in cardiac surgery), cholinergic deficiency and interaction with amyloid and tau pathology in vulnerable brains contribute.

Patient or family report of forgetfulness, slowed thinking, poor concentration, difficulty with complex tasks or multitasking, delayed return to work, and mood or sleep change. Consciousness and attention are normal, and onset is gradual over days to weeks.

Red flags.

• Fluctuating attention or altered consciousness (delirium).
• Focal deficit, new headache or seizure (stroke, subdural haematoma).
• Rapid progressive decline.
• Fever or meningism.

Formal diagnosis needs a preoperative baseline and repeat testing after surgery. The usual criterion is a fall of 1 unit of population spread or more (or a composite z-score of 1.96 or more) in at least two domains of a neuropsychological battery.

In practice, screen with the Montreal Cognitive Assessment (under 26 of 30 is abnormal) or Mini-Cog, and exclude delirium with the Confusion Assessment Method or 4AT.

Investigations. Sodium, glucose, calcium, urea, creatinine, liver tests, thyroid function, vitamin B12, full blood count, oxygen saturation, drug review and brain imaging if focal signs, trauma or anticoagulation. Screen for depression and obstructive sleep apnoea.

Differential diagnosis.

• Delirium, including hypoactive delirium.
• Depression.
• Medication effect from benzodiazepines, anticholinergics or opioids.
• Metabolic disorder.
• Stroke or subdural haematoma.
• Hypoxia.
• Early dementia unmasked by surgery.

There is no proven drug treatment. Management is prevention and support.

Prevention.

• Screen cognition preoperatively in adults over 65 and document it.
• Stop or avoid benzodiazepines, anticholinergics and pethidine.
• Keep mean arterial pressure within 20% of baseline and at 65 mmHg or more.
• Use processed EEG to avoid excessive anaesthetic depth.
• Maintain oxygenation, normocapnia, glucose control, haemoglobin and hydration.
• Use regional techniques and multimodal opioid sparing analgesia where possible.
• Support sleep, early mobilisation, glasses, hearing aids and orientation cues.
• Treat infection and pain promptly.

Analgesia.

• Paracetamol: 1 g orally or IV every 6 hours (over 50 kg) for 3 to 5 days as needed; maximum 4 g in 24 hours; use 2 to 3 g daily if under 50 kg, malnourished, chronic alcohol use or hepatic impairment; check liver enzymes when high doses continue beyond 3 days.

After discharge. Reassure that most recover. Repeat cognitive testing at about 3 months.

Referral and escalation. Refer to a memory clinic or geriatrician if decline persists beyond 3 months, if function is affected, or if dementia is suspected. Urgent imaging and neurology review for focal signs.