Principles of Neuroanaesthesia

Key principles:

• Preoperative assessment
  • Presentation
    • Neurological findings
      Pre-operative deficits.
    • Conscious state
  • Treatment
    • Steroids
      • Diabetes
      • Neutrophilia
    • Anticonvulsants
• Optimal operating conditions
  • Relaxed brain
    
    • Reduce global ICP
    • Reduce retraction pressure
      May reduce CVA risk under retractor.
  • Haemodynamic stability
• Cerebral protection
  • Maintain DO₂
  • Ischaemic protection
• Emergence
  • Haemodynamic stability
  • Rapid and predictable return of consciousness

Anaesthesia Considerations

• A
  • Remote airway and inaccessible
  • Avoidance of coughing
    • Remifentanil extubation
    • Laryngeal mask exchange
• B
  • CO₂ control
• C
  • Haemodynamic stability
    Most cases require precise haemodynamic control.
• D
  • Anaesthetic choice
    • Volatile impairs cerebral autoregulation in:
      • ↑ concentrations
        Always some vasodilation, but the effect is dose-dependent. Often ⩽1 MAC is acceptable.
        • Sevoflurane has the least effect on cerebral blood flow, and is the most suitable volatile agent
          Isoflurane and desflurane significantly worse.
      • Presence of hypercarbia
        Loss of CO₂ reactivity is a bad sign.
    • Nitrous oxide has several detrimental effects due to cerebral vasodilation
    • Propofol reduces ICP and ↑ CPP to a greater extent than sevoflurane
      TIVA desirable in any patient with severely raised ICP
  • Rapid emergence improves neurological assessment and early detection of complications

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References

1. Dinsmore J. Anaesthesia for elective neurosurgery. Br J Anaesth. 2007 Jul 1;99(1):68–74.