What are the causes of delirium in patients undergoing surgery and how can it be prevented with anesthesia?

Causes of Delirium in Surgical Patients and Prevention Through Anesthesia Management

Regional nerve blocks and lighter anesthesia depth should be used to prevent postoperative delirium in surgical patients, particularly those at high risk such as elderly patients. 1

Risk Factors for Postoperative Delirium

Identifying patients at high risk for delirium is crucial for implementing preventive strategies:

• Patient-specific factors: Advanced age, male sex, higher BMI, lower education level, smoking history, previous delirium episodes, institutionalization, comorbidities, and polypharmacy are independently associated with postoperative delirium (POD) 1
• Physiological factors: Elevated serum CRP levels (inflammation marker) increase delirium risk 1
• Surgical factors: Higher ASA status and longer duration of surgery/anesthesia are significant predictors 1

Anesthesia-Related Causes of Delirium

Several anesthesia-related factors contribute to postoperative delirium:

• Anesthesia depth: Deeper anesthesia (BIS values around 35) is associated with higher delirium rates compared to lighter anesthesia (BIS values around 50) 1, 2
• EEG burst suppression: Excessive anesthetic depth causing burst suppression patterns increases delirium risk 1
• Volatile anesthetics: Use of volatile anesthetics may increase delirium risk in elderly patients compared to total intravenous anesthesia (TIVA), particularly in those ≥75 years old 3
• Ketamine administration: Intraoperative ketamine does not reduce delirium risk and may increase hallucinations and nightmares 1
• Opioid administration route: Intravenous opioids are associated with higher delirium rates compared to oral opioids 1

Prevention Strategies Using Anesthesia Techniques

Anesthesia Depth Management

• Target lighter anesthesia: Maintain BIS values around 50 rather than deeper anesthesia (BIS around 35) to reduce delirium incidence (19% vs 28%) 1, 2
• Monitor anesthesia depth: Use processed EEG monitoring (such as BIS) in patients over 60 years to avoid excessive anesthetic depth and prevent hypotension 1
• Avoid volatile overdose: Closely monitor age-adjusted minimum alveolar concentration (MAC) to prevent side effects like hypotension 1

Regional and Neuraxial Techniques

• Regional nerve blocks: Implement regional blocks when appropriate, particularly in orthopedic surgery patients 1

  • Fascia iliaca blocks for hip fracture surgery can reduce delirium incidence (10.78% vs 23.8%), severity, and duration 1
  • Femoral nerve catheters for knee arthroplasty can lower delirium rates (25% vs 61%) 1

• Combined epidural-general anesthesia: Consider this approach for major thoracic and abdominal surgeries, which can reduce delirium incidence (1.8% vs 5.0%) 4

  • Caution: This approach increases risk of intraoperative hypotension (49% vs 33%) and vasopressor requirements 4

Pain Management Optimization

• Multimodal analgesia: Implement opioid-sparing techniques to minimize delirium risk 1
• Non-opioid analgesics: Use scheduled acetaminophen and NSAIDs when not contraindicated 1
• Avoid problematic opioids: Limit use of tramadol and meperidine, which have been linked to increased delirium risk 1
• Prefer oral over IV opioids: When opioids are necessary, oral administration is associated with lower delirium risk than intravenous routes 1

Implementation Considerations

• Preoperative risk assessment: Identify high-risk patients using factors such as age, comorbidities, and previous delirium history 1
• Anesthetic agent selection: No specific anesthetic agent is clearly superior for maintenance, but depth of anesthesia is critical 1
• Postoperative nausea and vomiting (PONV) prevention: Use multimodal prophylaxis to reduce PONV, which can contribute to delirium 1
• Temperature management: Prevent hypothermia, which can impair drug metabolism and increase delirium risk 1

Special Considerations for High-Risk Patients

• Elderly patients (≥60 years): Always use depth of anesthesia monitoring and target lighter anesthesia 1, 2
• Emergency surgery patients: Higher vigilance needed due to increased delirium risk from physiological derangements 1, 5
• Patients with history of delirium: Consider regional techniques when possible and minimize sedative medications 1, 5

By implementing these evidence-based strategies, particularly focusing on anesthesia depth management and regional techniques, the incidence of postoperative delirium can be significantly reduced, improving patient outcomes and quality of life.