Cushing's response (also known as the Cushing reflex) is a physiological nervous system response to acute increases in intracranial pressure (ICP). It's essentially the brain's attempt to restore blood flow when it's being squeezed. This response manifests as the Cushing triad, a set of three vital sign changes.
The Cushing Triad: The Hallmark of Cushing's Response
The Cushing triad is characterized by:
- Widened Pulse Pressure: This means an elevated systolic blood pressure and a decreased diastolic blood pressure, resulting in a larger difference between the two numbers. For example, a blood pressure of 180/70 mmHg displays a widened pulse pressure.
- Bradycardia: A decreased heart rate, typically below 60 beats per minute in adults.
- Irregular Respirations: Changes in breathing patterns, which can include slow, irregular, or gasping respirations.
The Physiology Behind the Response
Increased ICP can compress arteries supplying the brain. This reduction in blood flow is sensed by the vasomotor center in the brainstem. The vasomotor center then triggers a sympathetic nervous system response, causing systemic vasoconstriction (narrowing of blood vessels throughout the body). This vasoconstriction aims to increase blood pressure to overcome the increased ICP and maintain cerebral perfusion.
The increased blood pressure triggers a baroreceptor response, which, in turn, stimulates the vagus nerve, leading to bradycardia. The irregular respirations are a result of direct pressure on the brainstem, which controls breathing.
Clinical Significance
The Cushing reflex is a late and often ominous sign of significantly elevated ICP. It indicates impending brain herniation (the displacement of brain tissue) and requires immediate medical intervention. Healthcare professionals should recognize these signs quickly and act to reduce ICP through measures like:
- Osmotic therapy: Administering medications like mannitol to draw fluid out of the brain.
- Hyperventilation: Temporarily reducing carbon dioxide levels to cause vasoconstriction and decrease cerebral blood volume.
- Surgical intervention: In some cases, surgery may be necessary to relieve pressure on the brain.
Why is it Important to Recognize?
Prompt recognition of Cushing's response is crucial, as it signifies a life-threatening condition. Failing to recognize and treat it can lead to permanent brain damage or death. It serves as a critical indicator that the brain's compensatory mechanisms are failing and that urgent action is required to alleviate the pressure.
