orthostatic hypotension vs. dehydration as causes of syncope

May 24, 2017
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I was hoping that someone could clarify these causes of syncope. I feel like I've learned on my medicine rotation that orthostatic hypotension and dehydration are actually different causes of syncope, even though many people use them interchangeably. My current understanding is that orthostatic hypotension is a physiologic impairment of the autonomic system such that the body cannot provide sufficient sympathetic tone to maintain adequate blood pressure when a patient moves from a supine or sitting position to a standing position. Syncope due to dehydration or hypovolemic technically should not be diagnosed as syncope due to orthostatic hypotension. Can someone confirm this?
Follow-up: If dehydration/hypovolemia is different from orthostatic hypotension, then does that mean that the tilt-table test should not be used to confirm dehydration syncope?
Thanks guys in advance!
 
Jun 24, 2017
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I would say dehydration, blood loss, and anemia are all common causes of orthostatic hypotension which could be diagnosed as syncope due to any one of the three prior causes or could be diagnosed as syncope due to orthostatic hypotension more in general


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Crayola227

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orthostatic hypotension is describing a consequence, a symptom, it is basically as you say, a decrease in blood pressure due to a change in position
it is NOT just caused by autonomic dysfunction

it can have different ultimate causes, such as autonomic dysfunction, blood loss, dehydration, etc
this would obviously make a difference in tx

ALSO

orthostatic hypotension, or any of its causes, may or may NOT lead to syncope

people may use orthostatic hypotension or dehydration interchangeably in discussing syncope because dehydration --> orthostatic hypotension --> syncope
essentially, that is how dehydration LEADS to syncope, by leading to a decrease in blood pressure 2/2 change in position

syncope itself describes a symptom, it can have different causes, some of which do NOT include orthostatic hypotension

I hope this helps you to think about orthostatic hypotension and syncope, they are not synonymous and they can have different proximal causes

all of that said, I would say that if you are discussing orthostatic hypotension NOT 2/2 something besides autonomic dysfunction, then essentially it is implied that is the cause, but as you point out, one would need to actually make that diagnosis by testing

also, you would only use the tilt table test to rule in or rule out autonomic dysfunction in orthostatic hypotension or syncope
typically before you get to tilt table you have already dealt with more obvious and easily treated potential causes such as dehydration

as you more precisely identify the cause of syncope, you start to use different terminology

AAFP articles on orthostatic hypotension
Orthostatic Hypotension - American Family Physician
Evaluation and Management of Orthostatic Hypotension - American Family Physician

SHORT ANSWER:
Actually, dehydration, blood loss, hypovolemia 2/2 any cause can be a cause of orthostatic hypotension
Once you have identified the cause of orthostatic hypotension, it would be silly to simply say orthostatic hypotension is the cause of syncope
In medicine, once you are able to describe something more precisely, you should
Orthostatic hypotension NOT secondary to causes besides autonomic dysfunction, usually implies that as the cause
In practice it would be silly to use tilt table to rule in or out dehydration syncope, one would just first treat any dehydration, if then the patient no longer has orthostatic hypotension, there is no need for the test, which is more expensive and time consuming than an IV bag or water, and more uncomfortable too
 
OP
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May 24, 2017
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Ok I see now. Thank you so much for your detailed response--it cleared up a lot of confusion!

New question: When presenting, would you say "50yo male pt p/w syncope found to be 2/2 anemia" or would you just say "50yo male pt p/w anemia"?
And would you say the former when presenting the patient for the first time, and then the latter when presenting him on the 2nd hospital day and so on?
 
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CherryRedDracul

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Ok I see now. Thank you so much for your detailed response--it cleared up a lot of confusion!

New question: When presenting, would you say "50yo male pt p/w syncope found to be 2/2 anemia" or would you just say "50yo male pt p/w anemia"?
And would you say the former when presenting the patient for the first time, and then the latter when presenting him on the 2nd hospital day and so on?
If the patient's initial presentation is syncope, I wouldn't immediately jump to attributing the syncope to anemia. Keep the differential broad. Present the case of syncope and then mention the pertinent history, physical exam, and diagnostic studies.

Then, during your assessment and plan, if you have reasonably strong suspicion that anemia is the cause, then you can mention it as the most likely cause and then decide if further workup is necessary to rule out other causes. On subsequent days, you can change your assessment as necessary based on new information you have gathered.
 
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