The Approach to Venous Thromboembolism

Author: Shivon Manchanda

Adapted from the lecture of Dr Kasia Gore

Unilateral Leg Swelling

When a patient complains of unilateral leg pain and swelling, we often get an ultrasound right away. Here at Rush, it’s often done in triage, and usually resulted by the time you see the patient. Why we do this makes sense – we have easy access and it is available 24 hours a day. Plus, the physical exam for the DVT is notoriously insensitive. But for those patients who you see who haven’t gotten one, you may want to hold off. Particularly if you are practicing out in the community. While the ultrasound does not have any medical risks to the patient, it is expensive and during busy days it can take a lot of time to get done.

So instead of instinctively ordering it, Dr. Gore reminds us that there isn’t just a Wells Score for PE, there’s one for DVT too, and we should use it. Once you calculate the score, you’ll have a better idea of the patients risk of DVT:

• If high risk: Get the ultrasound
  • Obviously if positive, consider treatment
  • If negative, check a d-dimer
  • IF the d-dimer is positive, then this is still concerning for a DVT
    • Have the patient come back in one week for a repeat US
• Medium risk: Get the high sensitivity d-dimer
  • If dimer positive, get the ultrasound
  • In this case if the ultrasound is negative, your suspicion is still low and you do not need to have them come back
• Low risk: Same rules as medium risk (use of moderate sensitivity d-dimer is allowed here)

The patient has a DVT, now what?

• ACEP’s level B recommendation is that you can start at NOAC as an alternative to LMWH/VKA
  • The NOAC we start is based off the patient’s insurance, because these things are crazy expensive
    • Here are some coupons you can give your patients:
      • Rivaroxaban
      • Apixaban (Rush Specific)
• Disposition:
  • ACEP level C – Home if low risk and can follow up
  • Consider other imaging if other symptoms like dyspnea
  • Admit if:
    • They can’t follow up or can’t get started on outpatient treatment
    • Have concomitant PE or other serious diseases
    • Are a major bleeding risk
    • Have what is described below

Proximal Symptoms

Most DVTs are proximal, and symptomatic or not, they will likely require anticoagulation. But if a patient comes in with severe pain and can’t ambulate, hopefully you won’t miss this:

• What’s going on here?
  • Phlegmasia alba dolens is due to a complete occlusion of the deep veins, but the superficial collaterals are still able to carry blood away. They just aren’t good at handling all the arterial blood coming in
  • Phlegmasia cerulea dolens occurs when the thrombosis extends through the superficial collaterals. This creates a bunch of edema and this together with the lack of venous outflow cause arterial inflow obstruction
    • This can lead to compartment syndrome
    • Eventually the ischemia will lead to venous gangrene in about 50% of these patients
• Make sure consult IR or vascular surgery ASAP, as they will require thrombolysis and/or thrombectomy
  • You can start unfractioned heparin right away, and it can be turned off when the above intervention is decided upon

TL;DR: Blue = bad

Pulmonary Embolism

• Like the approach to the DVT, you can use the Wells Score for PE to risk stratify. Consider the three-tier model and use it with the PERC. This applies to the high sensitivity d dimer assay. If using a moderately sensitive d dimer assay, consider using the two-tier model
  • If low risk (score < 4), use PERC (ACEP level B recommendation)
    • If you cannot rule out, get a d dimer
  • If intermediate risk (score 2-6) in the three-tier model, get a d-dimer
  • CT scan if high risk (score > 6)
  • For the two-tier model, > 4 is high risk, and 4 or less is low risk
• Remember you can use the age adjusted d dimer (ACEP Level B)
• Do remember that these rules do not apply to every patient, as certain populations were excluded in these studies. For example, patients with known thrombophilia
• Also, these rules apply once you’re considering PE, not just every chest pain or dyspneic patient

You found a PE, what now?

• What if its subsegmental?
  • Why is this different than any other PE? We aren’t even sure if they are PEs and treating them may have worse outcomes. It’s hard to say if they are the cause of the patient’s symptoms, and sometimes they are incidentally found
    • This being said, we do not have enough evidence to say NOT to treat at this time. You can however potentially discharge these patients on anticoagulation
• Consider their risk, use tools such as the PE Severity Index (PESI) or the Hestia Criteria
  • If low risk, they can be discharged home on anticoagulation
    • Make sure to keep follow up resources in mind!
  • Consider letting the inpatient team start anticoagulation if you are admitting and the patient is not symptomatic
• For cancer patients, use low molecular weight heparin instead of vitamin k antagonists as they have been shown to be superior
• Remember to keep in mind contraindications to anticoagulation
  • Active bleeding or severe bleeding diathesis
  • Major trauma or ICH
  • Recent or planned procedure with high bleeding risk
• How long should a patient be anticoagulated?
  • They are usually treated for 3 months and then reassessed. At that point an algorithm based on risk of bleeding, whether the initial clot was provoked or unprovoked, and a d-dimer is used to determine if they need additional anticoagulation
• If the d-dimer is positive but your CTPA is negative for PE, don’t forget to look for a DVT!

Special Cases

Known DVT, Subtherapeutic INR

And now they have chest pain, and you are worried about a PE

• You don’t need to look for a PE unless they are unstable
• Re-bridge them with heparin and admit

Pregnancy

Clinical suspicion for PE can be hard in pregnancy due to expected physiologic changes overlapping with clinical signs of PE.

Rush uses the UpToDate algorithm:

But there are other ways people approach suspected PE in pregnancy patients. I suggest looking into the YEARS algorithm.

Moreover, if a patient is low risk, Dr. Gore likes to get the d-dimer in the first trimester. While it is true that pregnancy raises the average d-dimer value, there is enough variation that you may be able to get away with not scanning the patient if the test is negative.

CT or V/Q?

• Generally, the V/Q has been the test of choice for pregnant patients with normal chest x-rays. CTPA is not as sensitive as it normally is during pregnancy. However, CT scans have the advantage of showing alternate pathologies
• CT scans give less radiation to the fetus, and more radiation to mom. The opposite is true for the V/Q scan

What about just the Q?

• There is some evidence that low dose perfusion only scanning (in the setting of a normal chest x-ray) is as good as CTPA and can decrease radiation to both mother and fetus. We aren’t doing low dose as far as I know, but due to covid we are currently doing perfusion only scans instead of V/Q scans, so this may be something to consider requesting

In general, if you are concerned about a PE, do not be afraid to get either scan just because of the radiation! If you get a chest x-ray, V/Q scan, and CTPA you would still get at most 1/100^th of the dose of radiation required to cause fetal anomalies.

What if they have a contraindication to anticoagulation?

• Consider the IVC filter
• It decreases PE risk but still increases long term DVT risk – which makes sense

You’re worried about PE, and they are hypotensive

• If unstable, bedside cardiac ultrasound can help find signs consistent with PE
• If not unstable, get the CTA
• Consider thrombolysis/thrombectomy:

Special, special case:

You are removing the IJ of a 50yo male, and when it is out, he develops increased work of breathing, tachypnea, and he becomes hypoxic. What’s going on?

• Consider the venous air embolism
  • It takes 3-5ml/kg of air to kill
  • This fills up the entire right ventricle and the pulmonary outflow tract and causes obstruction of blood flow
• Treatment:
  • Place them in left lateral decubitus position – this can get rid of the air lock causing obstruction
  • Give 100% O2 to eliminate nitrogen and reduce the volume of the embolus
  • Worst case, you may have to aspirate the air via the subxiphoid approach
• If the air embolism is arterial
  • It’s likely from trauma or paradoxical through an ASD/PFO
  • Lay them supine
  • They will need hyperbaric oxygen

References:

1. Anand SS, Wells PS, Hunt D, Brill-Edwards P, Cook D, Ginsberg JS. Does This Patient Have Deep Vein Thrombosis? JAMA. 1998;279(14):1094-1099. doi:10.1001/jama.279.14.1094
2. PERCs of the Wells Score. Taming the SRU. Accessed May 10, 2020. http://www.tamingthesru.com/blog/2019/5/4/percs-of-the-wells-score
3. Hutchinson BD, Navin P, Marom EM, Truong MT, Bruzzi JF. Overdiagnosis of Pulmonary Embolism by Pulmonary CT Angiography. AJR Am J Roentgenol. 2015;205(2):271‐277. doi:10.2214/AJR.14.13938
4. Carrier M, Righini M, Wells PS, et al. Subsegmental pulmonary embolism diagnosed by computed tomography: incidence and clinical implications. A systematic review and meta-analysis of the management outcome studies. J Thromb Haemost. 2010;8(8):1716‐1722. doi:10.1111/j.1538-7836.2010.03938.x
5. Sheen JJ, Haramati LB, Natenzon A, et al. Performance of Low-Dose Perfusion Scintigraphy and CT Pulmonary Angiography for Pulmonary Embolism in Pregnancy. Chest. 2018;153(1):152‐160. doi:10.1016/j.chest.2017.08.005
6. Toung TJ, Rossberg MI, Hutchins GM. Volume of air in a lethal venous air embolism [published correction appears in Anesthesiology 2001 Apr;94(4):723]. Anesthesiology. 2001;94(2):360‐361. doi:10.1097/00000542-200102000-00031