We should hit this topic before the snow goes away and the spring flowers exchange cold injuries for allergies. (This is also inspired by a recent patient with frostbite who went to the burn ICU for treatment of his frostbite with . . .)
 
Cold injuries:
 
Types:
Frostnip: just a wee bit of being cold. Usually have paresthesias.

Chilblains: This is interesting because it is an inflammatory condition and not from direct tissue damage. The lesions are small, red, painful and itchy. It typically comes on after someone has been wet and cold, and it typically occurs above the freezing point.

Trench foot: defined by nerve damage caused by repetitive/prolonged exposure to cold and wet. This hurts a lot and can have hemorrhagic bullae. Trench foot was first noted in soldiers, but the homeless population is at a high risk.

Frost bite: tissue destruction from the cold itself (crystals form inside or outside of cells) or from inflammation during re-warming. The damage is multiplied if there are repetitive freeze-thaw cycles.
 
Grading of frostbite:
Grade 1: no cyanosis-->no amputation
Grade 2: Cyanosis that is just at the end of the finger or toe-->only soft tissue amputation and nail damage
Grade 3: Cyanosis that goes to the middle phalanx and the proximal phalanx-->predicts bone amputation
Grade 4: Cyanosis goes up to the wrist or mid foot-->bone amputation of the limb
 
There is another grading system that defines the damage by “degree." The take home from this system is that bigger blisters typically mean that the tissue has less damage-->smaller blisters are bad.
 
Treatment options: this is a mix of what to do in the field and in the hospital.

Imaging options: There are fancy scans (digital subtraction angiography; not the best name given the pathology) that can be done to see if tissue is viable and potentially treatable: these are only done in burn centers.  X-rays have no real utility.

Get them WARM as soon as you can, as long as you are sure they won't be getting cold again. Do this in warm water; and it is best if the water is circulating.

Don’t rub the skin,  which can cause the skin to slough off.

Get them DRY.

Re-warming tends to hurt: give pain meds.

Try find a way for the patient to not walk on frost bitten feet.

Don’t use hot water or open flames to re-warm. If the patient has nerve damage they can burn themselves without knowing it.

Once the tissue damage is done, you wait for the body to demarcate the area of dead tissue before surgeons will do a formal amputation. The demarcation will become apparent as a black line next to normal skin that shows where the viable tissue still lives. It can take months to finalize, so prepare your patients for an emotionally challenging waiting period.
 
. . . tPA
Yes this is an option if it looks like the patient may loose multiple digits or a limb.  There is a 24hr window for giving tPA and it is done in the a Burn ICU. They give the tPA into the artery (some studies are looking at using veins) proximal to the frostbite with a goal of re-establishing blood flow to the affected limb. The dose is low compared to what is used for stroke/MI/PE: 2-4 mg total for frost bite vs 50-100mg in the other settings.