Can you send home low probability vq scan patients?

[prolene60]

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I remember in school that low probability VQ scans were considered non-diagnostic. I had a patient today with low pretest probability and low probability VQ scan for PE. I thought we would have to do further work-up but my attending said that she could go home and likely no PE. I thought that there was still a big risk. Am I right or is he right?

 

[justaregularmed]

Could have done a l.e. doppler...has to come from somewhere.

 

[Tiger26]

I remember in school that low probability VQ scans were considered non-diagnostic. I had a patient today with low pretest probability and low probability VQ scan for PE. I thought we would have to do further work-up but my attending said that she could go home and likely no PE. I thought that there was still a big risk. Am I right or is he right?

.

 

[greatnt249]

I remember in school that low probability VQ scans were considered non-diagnostic. I had a patient today with low pretest probability and low probability VQ scan for PE. I thought we would have to do further work-up but my attending said that she could go home and likely no PE. I thought that there was still a big risk. Am I right or is he right?

I was always taught that you can't definitively diagnose PE with a V/Q scan (lots of things can cause mismatches), but if the patient has a negative/low-probability V/Q scan, then you can be pretty sure (like, high 90% probability) that the patient does not have a PE.

 

[WilcoWorld]

If you had a low pre-test probability and your VQ was low-prob then I think it's reasonable to discharge.

The lesson you're recalling from med school is that if you have a high pre-test probability a low-prob VQ result does not rule-out PE, because the negative predictive value of a low-prob VQ just isn't good enough.

 

[Cerberus]

If I had a low pre-test probability I'd probably skip the VQ Scan altogether and get a d-dimer. But to answer your question, what would be the point of even doing a VQ scan if a low probability result meant you still had a high risk for PE? I hate VQ scans personally. If you have a high pretest prob and a low prob scan, you still can't r/o PE, so what's the point of even ordering it? You might as well just treat or get a CT PE study if their kidneys can handle it.

 

[EctopicFetus]

If I had a low pre-test probability I'd probably skip the VQ Scan altogether and get a d-dimer. But to answer your question, what would be the point of even doing a VQ scan if a low probability result meant you still had a high risk for PE? I hate VQ scans personally. If you have a high pretest prob and a low prob scan, you still can't r/o PE, so what's the point of even ordering it? You might as well just treat or get a CT PE study if their kidneys can handle it.

So lets say their D-Dimer is barely up.. Allergy to iodine.. Doesnt meet perc with a pulse of 101...

For me v/q neg ----> dc home.

I would def Perc/D-dimer prior to VQ scanning.

 

[Cerberus]

So lets say their D-Dimer is barely up.. Allergy to iodine.. Doesnt meet perc with a pulse of 101...

For me v/q neg ----> dc home.

I would def Perc/D-dimer prior to VQ scanning.

Fair enough, and I'm not saying I never order V/Q scans, just that I dislike ordering them if I have any other option. I rarely get a "Low probability for PE" or "High probability for PE", it's usually "Intermediate probability for PE, correlate with history and physical and recommend CT angio chest PE protocol if indicated"

 

[pinipig523]

Low pretest and Low prob VQ = 4% shot at PE. I think that should be enough to send home.

 

[deleted109597]

So lets say their D-Dimer is barely up.. Allergy to iodine.. Doesnt meet perc with a pulse of 101...

For me v/q neg ----> dc home.

I would def Perc/D-dimer prior to VQ scanning.

I've never seen a negative V/Q.

Also, the problem with my patient population is that the vast majority of the can't CT crowd are going to be pointless V/Q anyway. None of them have a normal CXR, and most are morbidly obese.

 

[Arcan57]

I've never seen a negative V/Q.

Also, the problem with my patient population is that the vast majority of the can't CT crowd are going to be pointless V/Q anyway. None of them have a normal CXR, and most are morbidly obese.

Have you ever seen hard data on what percent of patients with abnormal CXRs have non-low prob V/Q scans? We're taught that a V/Q on a pt w/ an abnormal CXR is useless, but I've seen far more low-prob V/Q scans (usually ordered upstairs) on patients with abnl CXRs than intermediate prob. Unfortunately, my personal n is still in the high single digits so I don't know if it's a statistical fluke or one more example of a non-EBM lore being wrong.

 

[45408]

Could have done a l.e. doppler...has to come from somewhere.

You mean a duplex. The Doppler is the little machine that makes a wooshing noise when it's over a vessel. If you want to see the vessel, you use a duplex ultrasound in B-mode, and you can enable the Doppler function on a duplex ultrasound to see flow.

 

[jendc08]

What would even the point of getting a VQ scan if you can't use the result to make a decision? Of course low prob goes home. Otherwise why bother getting it?

 

[pinipig523]

What would even the point of getting a VQ scan if you can't use the result to make a decision? Of course low prob goes home. Otherwise why bother getting it?

Exactly.

 

[Groove]

1) PERC, d-dimer for low pre-test prob
2) CTA if dimer up or equivocal, if iodine allergy --> VQ, --> home if low prob and asymptomatic --> obs if something doesn't feel right or VS parameter that doesn't improve, etc..

Honestly, I kind of cringe with a VQ scan because they seem to always come back showing some sort of mismatch to where you can't completely r/o PE, which just makes admitting/obs that much easier.

I hate VQ scans... almost as much as I hate iodine allergies.

 

[logos]

Here if the only thing preventing a CT pulmonary angiogram is an "iodine" allergy or contrast allergy we give a prep consisting of a voodoo dose of solumedrol and benedryl and then CT 4 hours later.

 

[blackavar]

Here if the only thing preventing a CT pulmonary angiogram is an "iodine" allergy or contrast allergy we give a prep consisting of a voodoo dose of solumedrol and benedryl and then CT 4 hours later.

does that really work?

 

[WilcoWorld]

does that really work?

No, but it doesn't matter, because "iodine allergy" is a fictional condition.

 

[docB]

No, but it doesn't matter, because "iodine allergy" is a fictional condition.

Do you have data for this, particularly data from Rads? I have long suspected that you are right. I'd love to have something I could use to get these scans done.

For me I can't scan due to elevated creatinine much more than due to the "allergy."

 

[WilcoWorld]

Mr. docB,
From the EMedHome Clinical Pearl series (bonus - reference #3 is from the American College of Radiology):


Asking if patients are allergic to shellfish or iodine has no relevance to radiocontrast allergies. Iodine cannot be an allergen - it is found throughout our bodies in thyroid hormones and amino acids and is added to most salt used in the US. Both fish and shellfish contain iodine, but it is not the source of people's allergies. The major allergens in shellfish are muscle proteins, tropomyosins (1,2).
Reactions to IV contrast are anaphylactoid, not allergic and therefore not anaphylactic (3). These reactions are not caused by IgE and thus require no pre-exposure. Nearly all life-threatening reactions to IV contrast occur immediately or within the first 20 min after contrast media injection (1).
Although prior allergic reaction to seafood, shellfish, or iodine-containing solutions would create IgE sensitized to those allergens, this sensitized IgE would play no role in a reaction to IV contrast media, since the reaction to contrast is not IgE mediated. For the same reason, a patient who had an adverse event after contrast injection is unlikely to experience a similar or more severe reaction if given contrast again - non-immune-mediated means no immune system memory. (1,3-5).
The risk of reactions to contrast media in patients with seafood allergy is similarly elevated (about a 3-fold relative risk) for persons with allergy to egg, milk or chocolate, indicating that a general atopic disposition, rather than an iodine-specific reactivity, accounts for the increased incidence of reactions in this sub-group. Thus, reactions to contrast media should not be construed as an indication of an IgE antibody-mediated iodine allergy (1,4).
Do not delay emergent studies for steroid premedication. Only lengthy 12 hour premedication protocols have shown any effect on reaction rates, and this small benefit was manifested primarily by decreasing minor reactions. No steroid protocol has shown a statistically significant improvement in severe adverse reaction rates (1).
References:
(1) Schabelman E, et al. The Relationship of Radiocontrast, Iodine, and Seafood Allergies: A Medical Myth Exposed J Emerg Med 2009 Dec 31. [Epub ahead of print].
(2) Leung PS, et al. Seafood allergy: tropomyosins and beyond J Microbiol Immunol Infect 1999;32:143–154.
(3) American College of Radiology. Manual on contrast media. Reston, VA: American College of Radiology; 2008.
(4) American Academy of Allergy Asthma and Immunology. The risk of severe allergic reactions from the use of potassium iodide for radiation emergencies. Milwaukee, WI: American Academy of Allergy Asthma and Immunology; 2004.
(5) Mishkin MM. Contrast media safety: what do we know and how do we know it? Am J Cardiol 1990;66:34F–36F.

 

[gutonc]

Mr. docB,
From the EMedHome Clinical Pearl series (bonus - reference #3 is from the American College of Radiology):

That, my good sir, was beautiful. I'm going to make a pocket card out of it.

 

[docB]

Awesome. Thanks. I'm going to go bother my radiologist right now.

 

[DCGuava]

Here, if the only thing preventing a CT pulmonary angiogram is an "iodine" allergy or contrast allergy, we give a prep consisting of a voodoo dose of solumedrol and benedryl and then CT 4 hours later.

I'm adding this phrase to my vocabulary...it rules.

I found this when I went looking for further info; your version works well, and they are recommending a 2nd dose a few hours after the CT. I like the Benedryl idea -- even if it's not necessarily mediating the reaction, it's decreasing anxiety in the patient, because, hey! anaphylactoid reactions suck massively and a calmer patient will feel better. Yay!

I'm keeping all this info, my partner has an iodine 'allergy' and if I actually have to talk him into a contrast scan, the Benedryl will definitely come in handy.

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