Cushing's triad

Cushing's triad is a set of three primary signs that often indicate an increase in intracranial pressure (ICP). This medical condition is named after Harvey Cushing, a pioneering American neurosurgeon who first described the triad. Cushing's triad is significant in the field of neurology and critical care medicine as it helps in the early detection of life-threatening conditions such as brain hemorrhage, brain tumor, and traumatic brain injury.

Components of Cushing's Triad

Cushing's triad consists of the following three physiological responses:

1. Bradycardia: This is a slower than normal heart rate. It is a counterintuitive response to increased ICP, as one might expect the body to increase heart rate to improve brain perfusion. However, the increased pressure actually triggers a reflex bradycardia.
2. Hypertension: Elevated blood pressure is observed as the body attempts to maintain adequate cerebral perfusion pressure (CPP) in the face of increased ICP. The widening pulse pressure (difference between systolic and diastolic blood pressure) is particularly characteristic.
3. Respiratory irregularity: This can range from irregular breathing patterns to periods of apnea. The change in respiration is due to the pressure on the brainstem, which houses the respiratory centers.

Pathophysiology

The underlying mechanism of Cushing's triad involves the body's attempt to maintain cerebral perfusion in the context of rising intracranial pressure. The Monro-Kellie doctrine posits that the cranial compartment is incompressible, and the volume inside the skull is a fixed sum of brain tissue, blood, and cerebrospinal fluid. An increase in any one of these components must be compensated by a decrease in the volume of the others. When this compensation reaches its limit, ICP rises sharply, leading to the symptoms observed in Cushing's triad.

The increased ICP stimulates baroreceptors in the carotid arteries and aorta, which in turn signal the vagus nerve to reduce heart rate, causing bradycardia. Hypertension occurs as a compensatory mechanism to ensure adequate blood flow to the brain, mediated by the body's autonomic response to increase systemic blood pressure. Respiratory irregularities are due to direct pressure on the respiratory centers in the brainstem or indirectly through the Cushing reflex, a defensive mechanism of the central nervous system to maintain cerebral perfusion.

Clinical Significance

Cushing's triad is a late sign of increased intracranial pressure and is often considered a pre-terminal event. Its presence indicates a need for immediate medical intervention to reduce ICP and prevent further brain injury or death. Treatment options may include mannitol, hyperventilation to reduce CO2 levels and thus cerebral blood flow, surgical intervention to remove the cause of increased pressure, or the insertion of a ventricular drain to relieve pressure.

Diagnosis

The diagnosis of conditions leading to Cushing's triad involves clinical assessment and imaging studies such as CT scan or MRI of the brain to identify the cause of increased ICP. Continuous monitoring of intracranial pressure may also be employed in critical care settings.

See Also

• Intracranial pressure
• Brain herniation
• Cerebral perfusion pressure
• Harvey Cushing