Last Sunday, the SLR Wilderness Medicine group met for our second outdoor trip this year: snow-shoeing and cross country skiing in Fahnestock State Park, NY.  In the spirit of winter sports, we did a quick review about frostbite.  As a bonus, we learned how to build an emergency snow shelter.  

On one of the snow shoe trails

Cross country skiing around a lake

Here is a recap from Dr. Havryliuk on frostbite:

Pathophysiology:

-Pre-freeze: Tissue cooling with vasoconstriction and ischemia; paresthesias; no ice crystals. 

-Freeze-thaw: Ice crystal formation intra/extra cellularly, protein and lipid derangement, electrolyte shifts, cellular dehydration and cell death. Thawing process may lead to ischemia-reperfusion injury and inflammatory response.

-Vascular stasis: Vessels may fluctuate between constriction and dilation; blood may leak or coagulate.

-Late ischemic: Progressive tissue ischemia and infarction from cascade of events.

Classification:

-Frostnip: Distinct from frostbite but may precede it; frostnip is a superficial non-freezing cold injury associated with intense vasoconstriction on exposed skin, usually cheeks, ears, or nose; ice crystals, appearing as frost, form on the surface of the skin.

 -First-degree frostbite: Presents with numbness and erythema; a white or yellow firm, slightly raised plaque develops in the area of injury; no gross tissue infarction occurs; there may be slight epidermal sloughing and mild edema.

-Second-degree frostbite: Injury results in superficial skin vesiculation; a clear or milky fluid is present in the blisters, surrounded by erythema and edema.

 -Third-degree frostbite: Creates deeper hemorrhagic blisters, indicating that the injury has extended into the reticular dermis and beneath the dermal vascular plexus.

-Fourth-degree frostbite: Injury extends completely through the dermis and involves the comparatively avascular subcutaneous tissues, with necrosis extending into muscle and to the level of bone.

Simplified classification scheme:

-Superficial: No or minimal anticipated tissue loss, corresponding to 1st- and 2nd-degree injury

-Deep: Deeper injury and anticipated tissue loss, corresponding to 3rd- and 4th-degree injury

Diagnostic studies:

Use angiography and technecium 99 bone scan to evaluate and follow extent of injury

Treatment:

-Active rewarming in water bath at 38C with added antiseptic solution

-Treat moderate/severe hypothermia first (warm to 35C)

-IVF

-Ibuprofen (at least 400mg BID)

-Aloe vera: for superficial frostbite

-Dress and immobilize: avoid ambulation

-Blister care: aspiration prn, in general don’t touch hemorrhagic blisters

-Oxygen: if hypoxic or above 4000m

-Tetanus booster

-TPA: best if given intra-arterially within 24h, convince your vascular surgeons (references in the guidelines)

-Iloprost (prostacyclin analogue): not available in the US, some evidence from European studies

-Consider IV vasodilators (nitro) and heparin

-After 24h:

     -Hydrotherapy

     -Sympathectomy: long-term option for pain, paresthesias, hyperhidrosis

     -Amputation: usually 6-12 weeks out after well demarcated

The type of shelter we built was a quinzee.  This is somewhat labor intensive.  It's best for a group of 6-8 people who all have small shovels with them (you had to expect the possibility of needing an emergency shelter before heading outdoors).  Essentially you build a big mound of snow and then clear out the center.  Placing bags at the center of the mound makes the process a lot easier by occupying volume.  This shelter can protect you from the wind and precipitation and help you make it through the night.  It can take a few hours to make, especially if there are not many people helping out, so don't wait until the last minute to start if you actually need a snow shelter.

First, clear out space for the shelter.

Place packs in the center.  We only had one bag here, but more bags would have made the process easier.  The more packs you use, the less snow you need to shovel.

Start shoveling snow onto the pack.

As snow is added, it needs to be compacted.

Keep shoveling.

And keep packing the snow as tight as possible.

The mound is getting bigger.  Note the use of an avalanche probe here to help estimate the desired height.  Later on, when snow is being scooped out of the pile to create shelter space, the probe can be used to help achieve the right thickness of the walls.

Compacting the snow is really important.

Dinner break.  Everything was home made by one of our attendings who lives near the park.  Black beans, vegan chili, skillet corn bread, mashed yucca, meat, and plenty of good drinks.  It was delicious.

Once the desired size is attained (ours was quite small), start to shovel out an entrance hole from one of the sides (ideally the downhill side).

Keep digging through until you find the bag(s) at the bottom of the mound.

As you get deeper into the mound, it may be hard to fit the whole shovel inside.  If the shovel's handle is detachable, it will probably be easier to take it off at this point.

Pull out the bag.

And keep digging.

View of digging from the inside.  

Inside of our shelter.  

We ended up being able to fit 4 people inside of our snow shelter at once.