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Cushing's Triad - Not A Good Trifecta

*Disclaimer* -- this is NOT to be confused with the endocrine disorder Cushing's Syndrome (too much Cortisol). This is also NOT to be confused with Beck's Triad or the Trauma Triad.

Like the title suggests, a trifecta, is a grouping of THREE'S which is usually quite desirable -- for instance: when gambling on horses. However, Cushing's triad is a grouping of THREE symptoms that are present in the setting of an acute head injury/insult, where the odds are usually stacked against you. Increased intracranial pressures (ICP) helps to activate this reflex and it can stem from both medical or traumatic causes.

Source: Medicosis Perfectionalis

The clinical findings and the WHY behind their presence (also happens in THREE stages):

Hypertension - this is done in an attempt to restore blood flow to the ischemic brain tissues. Vasoconstriction happens early which reduces the ability for blood to flow. Simple algebra is at play here. CPP= MAP - ICP. In this stage ICP is overpowering the MAP, so to increase cerebral perfusion our BP has to also rise.

Keep in mind the pulse pressure (SBP-DBP) will continue to widen as the systolic number will generally outpace the diastolic number drastically in its rate of change.

Bradycardia - the cranial vault is composed of fused bone. It can't flex or move and its only got so much real estate for THREE things: brain/blood/CSF (see Fig 1). If you have an increase in one component, by default you have to have a decrease in another. As the brain continues to be ischemic, it continues to swell. This causes the parasympathetic nervous system to be activated in this second stage, but it also causes the brainstem to stretch and become distorted. The vagus nerve (CN X) is also beginning to fall victim here.

Figure 1: Monro-Kellie Doctrine (notice our theme of three's again)

Some say a 4th component should be added to the doctrine arguing that the calvaria (skull) may adjust slightly.

Irregular Breathing patterns - things are now getting more bleak, due to the increased pressure on the respiratory and cardiac control centers. The brain itself is beginning to herniate through the foramen magnum in this third and likely final stage.

This can progress to the point of apnea and subsequent death.

In addition to these findings - don't forget the pupils (their appearance and response to light -- you guessed it cranial nerve THREE -- are the window to the CNS, as this triad progresses, look for the pupils to become unequal as additional cranial nerves are affected negatively. Hyperventilation (slightly lowering ETCO2 levels) is up for debate here as a prophylactic therapy. It may give you more room in the cranial vault (d/t vasconscrition) but it comes at a cost of cerebral blood flow. It you proceed down this road - be controlled about the approach and titrate that ETCO2 to around 35 mmHg.

Whether it's a massive stroke or a fall from a great height. Cushing reflex is most usually an irreversible condition with a terminal prognosis for the patient. Initial emergency treatments aim to lower the ICP rapidly and include: elevation of the patient’s head 30 to 45 degrees, mannitol and/or furosemide, which act as an osmotic diuretic, induced hyperventilation, steroids, or cerebrospinal fluid drainage.

June 5, 2023

Author: Joshua Ishmael, MBA, MLS(ASCP)CM, NRP

Pass with PASS, LLC.

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