Cushing’s Triad and Cushing’s Reflex

Cushing’s Triad is a clinical triad described with bradycardia, Systolic hypertension and irregular breathing. It is named after Harvey William’s Cushing, who actually demonstrated cushing’s reflex (again him) first. [jpg]

Cushing’s Reflex is the physiological phenomena, in which raised intracranial pressure leads to irregular breathing, bradycardia and systolic hypertension/ increased wide pulse pressure.  Cushing’s Reflex is also known as Cushing’s Effect, Cushing’s Reaction, Cushing’s Phenomenon and Cushing’s Law.

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So, what’s the difference between Cushing’s Triad and Cushing’s reflex?

Cushing’s Triad is a clinical finding, where all the three signs are found. Cushing’s Reflex is the physiological phenomena demonstrating effects of increased ICT that leads to Cushing’s Triad. Not necessarily a Cushing’s Triad may show up always with Cushing’s Reflex. But There should be very high level of suspicion when the above mentioned signs are present.

How does it happen: Mechanism of Cushing’s Reflex

Mechanism of action of cushing’s reflex is shown in the above flow chart schematically. However, it’s believed that complex multifactoial mechanisms may be involved that not as easy to understand. In brief, after head injury – intracranial tension raises. When ICT rises above Mean Arterial Pressure, cerebral ischaemia starts. At this point, mechanical pressure in the cranium stimulates both the sympathetic and parasympathetic nervous systems (Through Vagus) . Sympathetic stimulation leads to increase Blood Pressure and heart rate. Parasympathetics try to slow down the heart rate. In response to raised BP, aortic arch baroreceptors triggers para sympathetic nervous system. Thus the vagal tone cumulatively causes bradycardia.

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Irregular or difficulty in breathing is better explainable. Same mechanical pressure also effects brainstem functions. And we all know brainstem control’s involunary respiration, it leads to irregular respiration or apnoea.


Differential Diagnosis of Cushing’s Reflex

  • Anything that may cause raised ICT
  • Severe/Moderate head Injury
  • Cerebral Stroke
  • Neurosurgery
  • Transplant Rejection
  • Severe Autoimmune Responses
  • Very Low Cerebral Perfusion Pressure (CPP)

References: NCBI PMIDCurrent Opinion in Anaesthesiology

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