Triaging frostbite with Tc99 MDP

Objectives: 1. Review the pathophysiology of frostbite and staging classifications. 2. Illustrate utility of Tc99 MDP multiphase imaging in frostbite with correlation to gold standard angiographic imaging. 3. Report institutional (upper midwest level 1 trauma center) outcomes data from NM frostbite imaging implementation for triaging frostbite patients to amputation or tPA therapy. 4. Identify educational/caveat case examples and recommendations from institutional experience.

Background: Extreme cold exposure causes distal arterial vasoconstriction leading to ischemia. Early evaluation and treatment are critical to patient outcome. To minimize tissue damage, treatment should be initiated within 24 hours after exposure. Rapid rewarming using warm baths, early reperfusion with peripheral vasodilators, and heparin are historically mainstays for treatment. Angiography can be used to assess microvascular occlusion. Contiguous catheter-directed tPA has more recently been reported to improve tissue preservation and reduce amputation rates in stage 3/4 exposures. Angiography and tPA treatment is invasive with potential for life threatening bleeding risks. Often surgical management including amputation and deep debridements are necessary for stage 4 frostbite. However, the depth of injury and demarcation of vascularized tissue can be difficult to determine clinically especially in the early stages. Delineating the extent and depth of frostbite-induced tissue loss on clinical examination alone can be difficult, specifically with stage 2 or greater injury. Imaging can play a critical role in guiding appropriate nonsurgical and surgical care. Specifically, nuclear radiology multiphase bone scintigraphy provides a noninvasive prognostic evaluation demarcating viable perfused tissue from ischemic/infarcted tissue. Our institution identified a need for algorithmic imaging triaging of these patients for prompt clinical decisions and potential intervention.

Methods: 1. Implemented a modified 3 phase NM bone scan protocol, including early (day of presentation) and delayed (2-4 days after presentation) imaging with SPECT/CT. 2. All cases presenting during 2 winter seasons (partial 2019 and 2020) were reviewed for clinical correlate, outcomes data, and educational opportunity.

Results: Patient demographics, time to presentation, location of presentation, and duration of admission were reviewed. Staging distribution and results of NM early scans were assessed. In applicable cases, angiography, tPA, and/or amputation results were reviewed and correlated with the NM imaging. Pictoral educational review included in poster includes lessons and caveats identified in our NM imaging implementation (ie: timing of bandaging, marker use with imaging, and clinical imaging/evaluation of the extremities prior to imaging). Potential false negative results related to early rewarming were identified.

Conclusions: Imaging is proving itself critical in assessing frostbite injuries and guiding invasive and noninvasive care. While angiography is historically a gold standard, multiphase MDP imaging is readily available and a noninvasive modality which can aid prognostication.

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