medic8m

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My patient had a sudden increase in shortness of breath. Lung sounds are clear with just some diminished bases. Oxygen saturation is 96% on 2liters N/C. CXR just shows old infiltrates (no change). Vitals are stable. Sinus Rhythm. He is 7 days post-op for CABx2. ABG: pO2=68% pCO2=32, pH=7.5 What should I do??

I guess I shouldnt be posting threads on SDN
 

medic8m

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Baylor class of 2008? Its closer to a HIPPA violation than you think - Im at the Texas Med Center right sitting next to a Baylor resident.

Yes, the patient is on their way to nuclear medicine right now for their VQ scan.
 
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Kalel

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Originally posted by medic8m
Baylor class of 2008? Its closer to a HIPPA violation than you think - Im at the Texas Med Center right sitting next to a Baylor resident.

Yes, the patient is on their way to nuclear medicine right now for their VQ scan.

VQ scans will probably not give you a definitive diagnosis, particularly in a patient with "old infiltrates" and what sounds like pulmonary edema. Given your patient's respiratory alkalosis though (which occurs sometimes with PE's as patients hyperventilate) and post-op course, I do agree that PE should definitely be considered. You should probably get a high-res CT of the chest with contrast to check for PE in your patient if the VQ scan is unequivacol (which I suspect that it will be). Also, I don't think that it's a HIPAA violation unless identifying personal information about the patient or the patient's name is released. I wouldn't advise posting what medical center you are posting from though, to better protect patient confidentiality just in case.
 

Seaglass

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Yeah, there is no way this could be a HIPAA violation as absolutely no patient identifiers have been given - not even the hospital the patient is at!

CT that cat and anticoagulate them unless you have a good reason not to.


the "C"
 

Seaglass

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Also CT will be more helpful identifying alternate pathology.

Does the patient still have chest tubes in? Your other most likely differential is going to be PT.

Casey
 

medic8m

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yeah, I know it isnt a HIPPA violation.

VQ scan showed low perfusion AND low ventilation on the left side, so low probability for PE. Usually these microemboli are bilateral anyway, I think. I just thought the blood gases and d-dimer were pointing that way. Anticoag therapy is used with caution here d/t his myoledysplasia and bloody thoaracentesis from yesterday (i didnt mention these). He will probably need some type of chest tube for the recurring pumonary effusion which this seems to be.

Anyway, i was just bored at work and wanted to post an semi-interesting case. Not quite as interesting as the psychotic man you tried to shoot me with his water pitcher yesterday though.

(yes pO2 is generally reported in mmHg I guess I should proof-read my posts)
 

Kalel

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Originally posted by swandive
how about a D-Dimer? Cheap and quick

D-dimer should not be used to r/o patients who have a high probability of having a PE (like in-patients) because it loses it's sensitivity with the high pre-test probability.
 

Seaglass

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besides which this pt is guaranteed to have an elevated d-dimer due to his post-op status. Kalel hit the nail on the head - d-dimer is for ruling out low prob pts. AND the d-dimer studies were done with quantitative serum assays, not the qualitative latex-agglutination assays most hospitals use.

In this pt. angio or CT are still indicated.

C
 

medic8m

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Very true cg1155, I work on a CV surgery floor and I think every D-Dimer I've seen here is "positive". Someone once told me what you just posted but many physicians continue to order this test in this situation. This particular patient is now being evaluated for a chest tube at the recomendation of pulmonology for the recurring left pleural effussion.
 

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Originally posted by medic8m
Very true cg1155, I work on a CV surgery floor and I think every D-Dimer I've seen here is "positive". Someone once told me what you just posted but many physicians continue to order this test in this situation. This particular patient is now being evaluated for a chest tube at the recomendation of pulmonology for the recurring left pleural effussion.


They keep ordering it because if it happens to come back negative it essentially rules out the dx of PE.
 

Kalel

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Originally posted by johnd
They keep ordering it because if it happens to come back negative it essentially rules out the dx of PE.

That's not true. D-dimers can be "negative" in ~10% of PE's. That's why it loses it's validity in the setting of having a high pre-test probability. Also because as previous posters have mentioned, the very low specificity makes an elevated number meaningless as well.
 

johnd

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In this study which is cited on UptoDate the negative predictive value for negative D-Dimer was 99% regardless of pretest probability.

However, I know that the negative predictive value is not this high in all studies and that it improves with low pre test probability.

***********************************************
Usefulness of D-dimer, blood gas, and respiratory rate measurements for excluding pulmonary embolism.

Egermayer P, Town GI, Turner JG, Heaton DC, Mee AL, Beard ME.

Canterbury Respiratory Research Group, Christchurch School of Medicine, New Zealand.

BACKGROUND: A study was undertaken to assess the usefulness of the SimpliRED D-dimer test, arterial oxygen tension, and respiratory rate measurement for excluding pulmonary embolism (PE) and venous thromboembolism (VTE). METHODS: Lung scans were performed in 517 consecutive medical inpatients with suspected acute PE over a one year period. Predetermined end points for objectively diagnosed PE in order of precedence were (1) a post mortem diagnosis, (2) a positive pulmonary angiogram, (3) a high probability ventilation perfusion lung scan when the pretest probability was also high, and (4) the unanimous opinion of an adjudication committee. Deep vein thrombosis (DVT) was diagnosed by standard ultrasound and venography. RESULTS: A total of 40 cases of PE and 37 cases of DVT were objectively diagnosed. The predictive value of a negative SimpliRED test for excluding objectively diagnosed PE was 0.99 (error rate 2/249), that of PaO2 of > or = 80 mm Hg (10.7 kPa) was 0.97 (error rate 5/160), and that of a respiratory rate of < or = 20/min was 0.95 (error rate 14/308). The best combination of findings for excluding PE was a negative SimpliRED test and PaO2 > or = 80 mm Hg, which gave a predictive value of 1.0 (error rate 0/93). The predictive value of a negative SimpliRED test for excluding VTE was 0.98 (error rate 5/249). CONCLUSIONS: All three of these observations are helpful in excluding PE. When any two parameters were normal, PE was very unlikely. In patients with a negative SimpliRED test and PaO2 of > or = 80 mm Hg a lung scan is usually unnecessary. Application of this approach for triage in the preliminary assessment of suspected PE could lead to a reduced rate of false positive diagnoses and considerable resource savings.
 

Seaglass

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The point is that in this patient population (high risk) an elevated d-dimer is almost guaranteed and a negative d-dimer is useless.

So....a positive result tells younothing and a negative result tells you nothing. It is useless. There is no redeeming value to just knowing what it is. It is a waste of money to order a d-dimer in this patient and it is certainly not indicated.

Casey
 
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