What causes anesthesia-induced delirium?

Mechanisms of Anesthesia-Induced Delirium

Anesthesia-induced delirium is primarily caused by multiple etiologies including persistent drug effects, unmasked pre-existing vulnerabilities (such as dementia, alcohol use, or previous delirium), and the physiological stress response to surgery. 1

Definition and Incidence

Postoperative delirium is defined as a cognitive disturbance that:

• Occurs in hospital up to 1 week post-procedure or until discharge 1
• Meets DSM-5 diagnostic criteria for delirium 1
• Has a reported incidence of 15-53% in older individuals after surgery 1
• Occurs in 70-87% of elderly patients in intensive care 1

Causative Mechanisms

Anesthetic Agent Effects

• Volatile anesthetics increase the risk of delirium 1.8-fold compared to total intravenous anesthesia, with risk increasing to 6.2-fold in patients 87 years or older 2
• General anesthesia is associated with more frequent cognitive impairment in the immediate postoperative period compared to regional anesthesia techniques 3
• Persistent drug effects from anesthetic agents directly contribute to postoperative delirium by disrupting normal neurotransmission 1

Patient-Related Risk Factors

• Pre-existing cognitive impairment increases delirium risk 2.53-fold compared to cognitively normal patients 4
• Lower education levels are associated with higher delirium risk (OR 3.40 for those with <12 vs ≥16 years of schooling) 4
• Advanced age is consistently associated with increased risk of postoperative delirium 1, 2
• Cardiovascular disease is a significant risk factor for developing delirium regardless of anesthesia type 3

Surgical Factors

• Unplanned surgery increases delirium risk 3.0-fold 2
• Major surgery with its associated inflammatory response and stress contributes to delirium development 1, 5

Prevention Strategies Based on Mechanism

• Regional anesthesia when feasible may reduce cognitive impairment compared to general anesthesia 3, 6
• Combined epidural-general anesthesia reduces delirium incidence (1.8% vs 5.0%) compared to general anesthesia alone 5
• Total intravenous anesthesia may be preferable to volatile anesthetics, especially in elderly patients 2

Long-Term Implications

• Patients who experience postoperative delirium are 3 times more likely to be subsequently diagnosed with mild cognitive impairment or dementia 4
• This suggests that delirium may either unmask pre-existing cognitive vulnerability or contribute to long-term cognitive decline 4

Clinical Pitfalls and Caveats

• Emergence delirium vs. postoperative delirium: These are distinct entities but can be confused; a lucid interval between them is not required for diagnosis but should be documented when present 1
• Hypotension risk: While combined epidural-general anesthesia reduces delirium, it increases risk of intraoperative hypotension (49% vs 33%) and vasopressor requirements 5
• Underdiagnosis: Delirium detection varies dramatically based on assessment method (3% by chart review vs 53% using daily mental status testing) 1