Approach Considerations
Laboratory studies of tissue samples, blister fluid, or blood ordinarily do not provide any useful, clinically relevant information in isolated frostbite. Concurrent hypothermia, prolonged exposure with systemic physiologic changes, and previous medical illnesses may exist, however, and laboratory studies in these cases may be helpful.
Imaging studies early in the diagnosis and treatment of frostbite may help determine the extent of the frostbite injury and any associated trauma, such as fractures. They may also assist in predicting prognosis. Because transitory vascular instability lasts 2-3 weeks after the frostbite injury, no imaging technique (eg, thermography, angiography, plethysmography, radioisotope bone scanning) reliably predicts tissue demarcation during the initial frostbite presentation.
Laboratory Studies
Frostbite is a clinical diagnosis. Although laboratory studies are not important in the initial diagnosis and management of frostbite, they may be helpful in identifying delayed systemic complications, such as wound infection with sepsis or complications of underlying hypothermia.
Baseline laboratory studies to consider include complete blood count (CBC), electrolytes, blood urea nitrogen (BUN), creatine, glucose level, and liver function tests. Urinalysis may be used to detect evidence of myoglobinuria. Obtain Gram stains and cultures from suspected frostbite wound infections.
Radiography and Angiography
Radiography often demonstrates soft-tissue edema but does not distinguish viable from nonviable tissue. Plain radiographs are not useful except to screen for trauma-related fractures or dislocations. They may assist in the diagnosis of long-term complications, such as osteomyelitis.
Angiography often shows slowing of blood flow to the distal vasculature, but this too does not correlate well with eventual tissue loss. When a vasodilator is added, this technique can more accurately predict the final pattern of ischemia that will be observed after 2-3 weeks of observation. In centers using thrombolytics to manage frostbite injuries, angiography is used to identify appropriate patients. Unlike technetium-99m scintigraphy, angiography does not visualize the microcirculation soon after injury.
Scintigraphy and Bone Scans
Technetium-99m (99mTc) scintigraphy is sensitive and specific for tissue injury. Some authors recommend using it early in the management of frostbite (48 hours after injury) to aid in directing earlier debridement of nonviable soft tissue. This allows nonviable tissue to be visualized earlier than by clinical examination and thus presumably shortens patient hospitalization. [38, 39] In addition, scintigraphy is useful in assessing the response of damaged tissue to therapy. In some centers, 99mTc scanning is used to identify appropriate patients for treatment with thrombolytics.
Similarly, bone scans, particularly triple-phase bone scans, may help to delineate nonviable bone but should be reserved until microscopic tissue damage has had time to present itself clinically, generally 2-3 weeks post injury. [18]
Histologic Findings
The presence of a greater number of intracellular ice crystals compared to extracellular ice crystals suggests a rapid cooling of the skin.
The time frame of frostbite injury is as follows:
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First hour - Endothelial leakage
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First 6 hours - Erythrocyte extravasation
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Within 6-24 hours - Leukocyte migration and vasculitis
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Within 1-2 weeks - Medial degeneration, loss of intracellular attachments, and vacuolization of keratinocytes
Imaging Studies
Magnetic resonance imaging (MRI), when combined with physical findings, may also be helpful in the early determination of margins of tissue viability. However, experience with this application of MRI is limited.
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Frostbite of the foot. Photo courtesy of Kevin P. Kilgore, MD, Department of Emergency Medicine, Regions Hospital.
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Frostbite of the ear. Photo courtesy of Kevin P. Kilgore, MD, Department of Emergency Medicine, Regions Hospital.
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Frostbite of the hand.
