Cushing reflex

The Cushing reflex, also known as the Cushing effect, Cushing reaction, or Cushing phenomenon, is a physiological response to increased intracranial pressure (ICP) in the brain. This reflex comprises three principal components: hypertension, bradycardia, and irregular or abnormal respirations.

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Discovery and Historical Context

This triad of responses was first described by the pioneering neurosurgeon, Harvey Cushing, in the early 20th century, hence the name 'Cushing reflex.' Cushing identified this phenomenon in the context of brain tumor patients who were experiencing increased intracranial pressure^[1].

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Physiological Mechanism

• The Cushing reflex is a physiological defense mechanism triggered by an increase in intracranial pressure. As the ICP rises, cerebral perfusion is compromised, leading to cerebral ischemia and subsequent hypoxia. This stimulates chemoreceptors, triggering a systemic vasoconstrictive response to raise systemic blood pressure and counteract the increased ICP to maintain cerebral perfusion.
• The systemic hypertension subsequently activates the baroreceptors in the carotid bodies and aortic arch, leading to a reflex bradycardia. Irregular or abnormal respirations (often described as Cheyne-Stokes respirations) are thought to result from direct brainstem compression or from the brain's response to hypoxia^[2].

Clinical Implications

• The Cushing reflex is a late sign of significantly elevated intracranial pressure and often indicates impending brain herniation, which can lead to irreversible damage and death if not immediately treated. Clinicians must be vigilant for signs of the Cushing reflex, such as high blood pressure, bradycardia, and abnormal respirations. Identifying these signs early can facilitate prompt intervention to reduce ICP, thereby preventing serious complications^[3].
• In a clinical context, treatments for elevated ICP can include administration of hyperosmolar therapy, sedation, hyperventilation, and in severe cases, neurosurgical interventions like decompressive craniectomy.

See also

• Intracranial pressure
• Harvey Cushing
• Hypertension
• Bradycardia
• Brain herniation
• Craniectomy

References

<references>

• |Cushing, H. (1901). Some experimental and clinical observations concerning states of increased intracranial tension. American Journal of the Medical Sciences, 124, 375-400.
• 2|Ropper, A.H., Samuels, M.A., & Klein, J.P. (2019). Adams and Victor's Principles of Neurology (11th ed.). McGraw Hill.
• 3|Chen, J., & Brodie, H. (2012). Cushing Reflex in Traumatic Brain Injury: A Protective Reflex? Current Neurovascular Research, 9(4), 231–235.

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