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CNS Ischemic Response Mechanisms tutorial

Nov 8, 2024

Lecture Notes: Central Nervous System Ischemic Response

Overview

  • Topic: Central Nervous System (CNS) Ischemic Response
  • Focus: Early and late phases of response to cranial insult (injury to the head)
  • Key Terms:
    • Cranial Insult: Injury causing bleeding and swelling in the skull.
    • Intracranial Pressure (ICP): Pressure inside the skull.
    • Cerebral Perfusion Pressure (CPP): Pressure ensuring blood flow to the brain, calculated as Mean Arterial Pressure (MAP) minus ICP.

Early Phase

Pathophysiology

  • Cranial Insult: Blow to the head causes bleeding (hemorrhage) and swelling (vasogenic edema).
  • Intracranial Pressure Increase: Due to hemorrhage and edema.
  • Compression of Cerebral Arteries: Leads to decreased CPP.

Body's Compensatory Mechanisms

  • CSF Shifting: Cerebral spinal fluid shifts to spinal cavity to reduce pressure (Monro-Kellie Hypothesis).
  • Vasodilation: Cerebral arteries dilate to increase blood flow as hypoxia (low oxygen) and hypercapnia (high CO2) occur.

Late Phase

Problems with Continued ICP Increase

  • Hypoxia and Hypercapnia: Persisting issues leading to neuronal stress.
  • Mean Arterial Pressure Increase: Attempt to improve CPP by increasing blood pressure.

Mechanisms to Increase Blood Pressure

  • Sympathetic Nervous System: Systemic vasoconstriction increases total peripheral resistance and MAP.

Cushing's Triad

  • Definition: Clinical signs indicating increased ICP.
  1. Increased Systolic Blood Pressure: Due to systemic vasoconstriction.
  2. Bradycardia (Low Heart Rate): Due to parasympathetic stimulation (via vagus nerve) in response to high BP.
  3. Cheyne-Stokes Respirations: Irregular breathing patterns indicating brain stem compression.

Clinical Implications

  • Respiration Monitoring: Count for 30 seconds to a minute to ensure accuracy due to irregular patterns.
  • Severe Outcomes: Unchecked pressure can lead to excitotoxicity, neuronal death, and potentially patient death.

Conclusion

  • The CNS ischemic response is a critical reaction to head injury, involving complex compensatory mechanisms.
  • Early intervention is crucial to prevent severe outcomes such as brain damage or death.

The lecture provides an understanding of the body's response mechanisms to increased intracranial pressure and highlights the importance of recognizing clinical signs like Cushing's Triad for timely intervention.

Full transcript