NBME 23 Hypovolemic shock (NBME Answers)

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Retired NBME 23 Answers

nbme23/Block 2/Question#7 (reveal difficulty score)
A 45-year-old man is brought to the emergency ...
Hypovolemic shock 🔍 / 📺 / 🌳 / 📖
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submitted by ∗sympathetikey(1600)

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Mad at myself for changing my answer.

Faulty logic made me wonder if hitting your head would caused increased ICP so, like a cushing ulcer, you would get increased Vagus nerve activity and maybe bradycardia + hypotension. But I guess the RAAS system would have counteracted that and caused vasoconstriction over 24 hours, so Hypovolemic shock is definitely the best choice.

Always should go with the obvious answer :)

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seagull I had the idea that this was a neurogenic shock and increasing intracranial pressure could affect the vagus too. I think the question really wants us to go that direction. +17

uslme123 The Cushing reflex leads to bradycardia! +7

purdude Wait I'm confused. I thought hypovolemic shock leads to an increased SVR? +2

littletreetrunk apparently, there's a thing called sympathetic escape that can happen after a while (i.e. he's been out for 24 hours): Accumulation of tissue metabolic vasodilator substances impairs sympathetic-mediated vasoconstriction, which leads to loss of vascular tone, progressive hypotension and organ hypoperfusion. +1

littletreetrunk also also if he hit his head he could have loss of sympathetic outflow from a hypoxic medulla which could lead to vasodilation, which further reduces arterial pressure, but this was a hard one for me lol. I also put increased ICP wah. +1

catch-22 Any lack of sympathetic outflow/increased vagal outflow should reduce HR, not increase it. Further, you would expect brainstem signs if there was hypoxia to the brainstem. For example, if you had damage to the solitary nucleus, you wouldn't be able to regulate your HR in response to reduced BP. Since this patient has reduced BP and increased HR, this indicates that the primary disturbance is likely the reduced BP. He's also been in a desert for 24+ hours so. +5

charcot_bouchard In a patient who develops hypotension following high-energy trauma, neurogenic shock is a diagnosis of exclusion that is made after hypovolemic and obstructive cardiogenic shock have been ruled out! Plus Absent Bradycardia rules it out +2

Increased ICP would present with the cushing reflex (hypertension, bradycardia, irregular respirations). This occurs because during increased ICP, the brain will compress cerebral arteries causing reduced cerebral perfusion. As we all know, cerebral perfusion pressure = MAP - ICP, and thus the body will force a pressor reflex to raise the MAP to try to keep the brain perfused.

Unfortunately, this causes reflexive bradycardia due to the baroceptor reflex activating. The irregular respirations are because the brainstem is compressed.

Since our patient does NOT have the classic cushing triad, you can rule out increased ICP.

+17/- drzed(333)

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submitted by ∗yex(128)

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Hmmm. Well my mind has blown off because what hit my mind was dehydration since he was in the desert. As soon as my mind started to wander about all of the other options that could make sense... I just clicked and moved!

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charcot_bouchard Smart boi +5

usmlecharserssss hiking in sahara desert SMH +4

cbreland Simple = smart +

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submitted by ∗diabetes(31)

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bleeding + pressure down +pulse up equal hypovolemic shock

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submitted by ∗nwinkelmann(366)

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I found this about raised ICP: "Presentation of raised intracranial pressure = headache, papilledema, nausea/vomiting, worse in the morning as ICP raises during the night as a consequence of recombency, a rise in PCO2 during sleep caused by respiratory depression, and probably a decrease in CSF absorption, pupillary dilation, ptosis, imapired gaze, respiratory irregularity, AMS, and changes in BP, HR, and respiratory pattern are usually late signs of raised ICP and related to brainstem distortion or ischemia."

https://jnnp.bmj.com/content/73/suppl_1/i23

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submitted by ∗hello(429)

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What's the echymoses supposed to be a clue about? Does this patient have DIC? Does DIC always cause hypovolemic shock?

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drdoom Disseminated intravascular coagulation (DIC) is a syndromic definition. (See tangent.) It does not “always” lead to shock but shock is definitely a possible sequela (since, by definition, DIC = “systemic thrombotic process”; anything systemic should get you a little worried), and so a patient with DIC should be monitored closely! +

yesa I think they add to the hypovolemia picture; he is dehydrated AND bleeding into his tissues because of contusions --> decreased intravascular volume.... +

From https://meshb.nlm.nih.gov/record/ui?ui=D004211:

Disseminated intravascular coagulation. A disorder characterized by procoagulant substances entering the general circulation causing a systemic thrombotic process. The activation of the clotting mechanism may arise from any of a number of disorders. A majority of the patients manifest skin lesions, sometimes leading to PURPURA FULMINANS.

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