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Changes to Procedures for Identifying DVT in COVID-19 Patients Reduces Sonographer Exposure

Key findings

  • The COVID-19 pandemic has resulted in increased requests for ultrasound (US) testing for deep vein thrombosis (DVT), which puts vascular technologists at risk of exposure
  • Massachusetts General Hospital now recommends routine therapeutic anticoagulation for patients positive for COVID-19 without the need for confirmatory DVT US if the patient meets the criteria of this novel algorithm, unless the referring and imaging physicians agree US is needed to mitigate anticoagulation risk
  • Over a 4-week study period, implementation of the algorithm decreased the number of DVT US scans performed
  • Separately, the hospital's radiology department modified its protocols for performing US scans in COVID-19 patients, which decreased technologist time per examination
  • Even if a DVT US examination is negative in COVID-19 patients, therapeutic anticoagulation with D-dimer >4000 may be appropriate, given that microthrombi can form and cause significant end-organ damage

There is increasing evidence that hypercoagulability contributes significantly to morbidity and mortality of COVID-19 patients. In intubated patients, deep venous thrombosis (DVT) is difficult to identify because symptoms such as swelling or pain often cannot be ascertained. This led to a surge in orders for bedside vascular ultrasound (US) during the pandemic.

Conventional protocols for US venous studies require 40 to 70 minutes of direct contact between a patient and sonographer, presenting risks not fully mitigated by personal protective equipment. Moreover, COVID-19 can be spread throughout the hospital if technologists become asymptomatic carriers.

Researchers at Massachusetts General Hospital have created procedures meant to ensure US examinations for COVID-19 patients who will benefit while minimizing unnecessary exposure for vascular technologists. Anahita Dua, MBChB, MSc, MBA, assistant professor of Vascular Surgery and director of the Mass General Vascular Lab, and Matthew Eagleton, MD, chief of Vascular and Endovascular Surgery and co-director of the Fireman Vascular Center at Mass General; James Brink, MD, radiologist-in-chief, and Sandeep Hedgire, MD, clinical fellow of the Department of Radiology at Mass General; and colleagues report the results in the Journal of Vascular Surgery: Venous and Lymphatic Disorders.

Study Methods


Patient Population

At Mass General, both the vascular laboratory and the Radiology Department perform vascular US imaging to identify DVT. This prospective study included all 160 adult COVID-19 patients admitted between March 13 and April 16, 2020, for whom DVT US orders were sent to either department.

The Algorithm

Treating physicians were asked to forego ordering imaging and initiate therapeutic anticoagulation with low-molecular-weight heparin (LMWH) if DVT or pulmonary embolism was suspected because of:

  • Serum D-dimer >4000 ng/mL
  • Swelling and/or pain in extremity
  • Persistent unexplained fevers >101.5 °F
  • Increased oxygen requirements on ventilator settings or new-onset hypoxia
  • Late dead space fraction

There is an exception: If the patient had a contraindication to therapeutic anticoagulation or might not tolerate LMWH due to kidney disease, the vascular laboratory medical director (or cardiovascular or emergency radiology staff of the day) and the ordering physician were asked to discuss the benefit/risk ratio of US before proceeding, or defer US to a time when the patient would be less contagious.

The algorithm was implemented only by the vascular laboratory, halfway through the four-week study period.

Modified US Protocols

Meanwhile, the Radiology Department modified its US protocols for COVID-19 patients in an effort to decrease scanning time. The abbreviated protocols are listed in a table in the article. Most notably, calf veins were not included in scans of lower-extremity veins and the use of color/spectral Doppler US imaging was confined to proximal veins.

Results


Number of Scans

The vascular laboratory received 66 orders for US in COVID-19 patients: 41 before algorithm implementation and 25 afterward. Of those 25, 18 (72%) were canceled or deferred.

Sonographer Exposure Time

During the study period, the Radiology Department performed 97 DVT US examinations on COVID-19 patients, of which 53 were conventional and 44 were done according to the modified protocols. The examination time was 13 minutes versus 6 minutes (P < .001). There was no difference between groups in DVT or PE rates.

New Policies

The vascular laboratory at Mass General has now adopted the algorithm, and the Radiology Department continues to modify its US protocols for COVID-19 patients.

It's worth noting, though, that even if a DVT US examination is negative in these patients, full anticoagulation may be appropriate, given that microthrombi can form and cause significant end-organ damage.

72%
reduction in number of ultrasound scans ordered to detect deep vein thrombosis in COVID-19 patients after implementation of a novel algorithm

50%
reduction in technologist time per examination for deep vein thrombosis in COVID-19 patients after modification of ultrasound protocols

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