USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 74-year-old man is brought in by ambulance alone to the emergency department. He has a past history of mild vascular dementia. After examination, it is determined that he needs an emergent procedure. Which of the following is necessary to invoke implied consent in an emergent situation?
OK, let’s start with some basic brain anatomy. The brain has a few regions - the most obvious is the cerebrum, which is divided into two cerebral hemispheres, each of which is divided into four lobes: the frontal, parietal, temporal, and occipital lobe.
The frontal lobe controls movement, and our personalities, it also handles our ability to count and spell, and make decisions.
The parietal lobe processes sensory information, which lets us locate exactly where we are physically and guides movements in a three dimensional space.
Finally there’s the occipital lobe which is primarily responsible for processing visual information.
All the cells in the body need oxygen - and that’s particularly relevant for neurons, which can only function in aerobic conditions, meaning with constant supply of oxygen.
Neurons also don’t have long term energy stores, so they need a constant supply of glucose to keep working.
Once they reach the base of the brain, these arteries join to form a ring, called the circle of Willis, which then branches off into smaller and smaller arteries, the smallest being the perforating arteries, that eventually supply the entire brain with oxygen and glucose.
Vascular dementia develops in some individuals, when atherosclerosis starts to form in the arteries.
That’s when there’s a buildup of plaque that thickens and hardens the artery wall.
When this process affects the arteries supplying the brain, like the carotid arteries, it leads to a gradual decrease in blood flow to the brain - which is called chronic ischemia.
Sometimes, small parts of the plaques can break away and these bits can drift up towards the brain, and can then eventually block a smaller artery, completely stopping the blood supply to the part of the brain that’s supplied by that artery.
Other times, the tiny perforating arteries are affected by atherosclerosis and can get completely blocked off by plaque growing within them.
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- "Comparison of Different Diagnostic Criteria for Vascular Dementia (ADDTC, DSM-IV, ICD-10, NINDS-AIREN)" Stroke (1996)