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submitted by brise(17),

so I was stuck on this because his BUN /creatinine ratio led me to think he had an intrinsic renal dysfunction. And a PGI2 inhibition would lead to a pre-renal azotemia, where the BUN/ creatinine ratio would be more than 20. I know that NSAIDs inhibit PGIS. But how are you supposed to cross out induction of distal tubular acidosis?

purdude  You can cross out Distal RTA because the urine pH is 5. In Distal RTA, urine pH becomes greater than 5.5 because a-IC cells can't secrete H+ +  

submitted by sympathetikey(258),

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 :)

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. +1  
uslme123  The Cushing reflex leads to bradycardia! +  
purdude  Wait I'm confused. I thought hypovolemic shock leads to an increased SVR? +1  
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. +  
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. +  
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. +  
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 +