Written by Clay Smith
There’s debate over the utility of orthostatic vital sign measurement (OVS) to detect orthostatic hypotension (OH) as a cause of syncope. Some consider OVS a complete waste of time. Yet, the 2017 AHA Guideline on syncope says, “A thorough history and physical examination, including orthostatic vital signs, is particularly important in older patients.”
Orthostatic hypotension (OH) is a drop in SBP of ≥20, DBP ≥10 after standing for at least 3 minutes. Orthostatic reflex tachycardia is a HR increase by ≥30 beats per minute.
Problems with OVS
The problem is, OH may or may not be symptomatic.
OH was present in >30% of patients over 70 years of age.
OH was noted in 25% of all-comers to the ED.
OH was found in 50% of nursing home residents.
A JAMA review found that OVS did not have diagnostic utility in determining dehydrated vs non-dehydrated patients but did reliably predict patients who had lost >630mL of blood.
Some quote a study stating that 44% of healthy adolescents had OH; however, this was not truly OH, as it only occurred 20 seconds after standing and all resolved within 60 seconds. See figure and discussion at the end.*
Does OH matter?
It may matter. An ED-based study found that OH was associated with an increased risk of hospitalization (51% vs 23%) and with mortality in patients >75 years old. So, it may not be benign. Or this may have simply been a confounder - older patients often have incidental OH and are also more likely to be admitted and have greater mortality.
What’s the real question?
The focus of this review was:
“to define the diagnostic utility of OVS as a test for orthostatic syncope, and
to determine whether OVS help diagnose or exclude life-threatening causes of syncope in ED patients.”
After performing a literature review, they concluded that OH was determined to be the cause of syncope in 12-24% of patients. OVS had poor accuracy as a diagnostic test to determine if OH was, in fact, the cause of syncope. There was a high risk of incorporation bias in the studies as well; once OH was identified, they stopped looking for other etiologies and assumed OH was the cause. With incorporation bias, the gold standard is also the test used to make the diagnosis (OVS in this case), which overestimates the diagnostic accuracy of that test. Remember, with >25% of all-comers to the ED having OH, “a substantial subset of patients with other causes of syncope, including cardiac causes, will have abnormal OVS.”
In answer to their key questions, I gleaned the following.
OVS had poor accuracy as a diagnostic test to determine if OH was the cause of syncope.
Since OH is so prevalent in the general ED population, especially among elderly patients, it is not very helpful in ruling out other life threatening causes of syncope and may lead to false reassurance and premature diagnostic closure.
Putting it into clinical context
Let’s think through two examples.
The best estimate is that 12-24% of patients with syncope have OH as the cause. So let’s assume the prevalence of the disease, orthostatic syncope, is in the middle, 18%.
The best negative likelihood ratio (NLR) estimates, based on two relatively low quality studies with high risk of bias, are 0.34 and 0.39. The best positive likelihood ratios (PLR) were 2.8 and 6.9.
We will split the difference and call the NLR 0.37 and PLR 4.9.
Now, consider a patient presenting with syncope. The pretest probability for orthostatic syncope is 18%; assume they do not have OH based on orthostatic VS, NLR 0.37; posttest probability = 7.5%. Can we say orthostatic hypotension as the cause of syncope has been ruled out? No.
Consider the positive scenario. The pretest probability for orthostatic syncope is 18%; assume they do have OH based on orthostatic VS, PLR 4.9; posttest probability = 52%. Can we say this patient definitely has OH as the cause of syncope? No.
Danger on both sides
There are two dangers with orthostatic vitals.
If negative for OH, the patient may still have volume loss, blood loss, or orthostatic syncope. Worse, the clinician may feel false assurance that these conditions have been ruled out.
On the other hand, if OH is present, the clinician may have premature closure, assume the cause of syncope is OH, not pursue other potentially lethal causes, and miss a critical diagnosis.
So…what to do?
So, what should we do with this information? Some, like Anand Swaminathan, advocate that orthostatic vitals should not be done at all. It’s hard to vigorously argue against that point of view. However, we have one guideline recommending OVS in all patients with syncope. So, we can’t just ignore orthostatics. Also, the cost is minimal and harm is nil. However, I agree with the authors, doing OVS in all syncope patients, as the guideline states, is overkill.
My take home points
A HR increase of >30 from supine to standing is helpful in detecting acute, large volume blood loss (>630mL). Source: JAMA
If a patient is unable to stand due to severe postural dizziness, this is helpful in determining large volume blood loss (>630mL). Source: JAMA
OVS are not helpful in diagnosing or determining the severity of other causes of volume depletion not related to blood loss. Source: JAMA
Normal OVS measurements do not rule out anything. Normal OVS should not be considered reassuring or factor into decision making about whether or not a patient is safe for discharge if there are other concerning clinical features. Source: JAMA
Abnormal OVS should be considered in clinical context. This does not conclusively rule in orthostatic hypotension as the cause of syncope. Further testing must still be carried out. Source: Letter in Ann of EM
Some patients really have orthostatic hypotension as the cause of syncope, and OVS help confirm this diagnosis. But this is usually suggested by recurrent postural syncope on history, and other causes of syncope still require investigation. Source: This review
Routine use of OVS in all syncope patients, as per the 2017 AHA guideline, is unhelpful and unnecessary. Source: This review
REBEL EM has a post that covers the diagnostic accuracy in detail. It is outstanding.
Anand Swaminathan stars in this Vimeo lecture. He makes a compelling case why OVS are not worth doing at all. However, the slide stating 44% of normal adolescents had OH is incorrect. The drop in SBP was at 20 seconds, but all resolved by 60 seconds.* The paper states, “All patients were normotensive within 1 minute of tilt.” So, this is not OH. That is actually normal.
emDOCs goes deep into syncope pearls and pitfalls.
The AHA syncope guideline in full text is here.
Do Orthostatic Vital Signs Have Utility in the Evaluation of Syncope? J Emerg Med. 2018 Dec;55(6):780-787. doi: 10.1016/j.jemermed.2018.09.011. Epub 2018 Oct 10.
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* Here is the key figure from the study in adolescents.