Frosbite

Frostbite arises when tissues become frozen by the direct action of cold during exposure to temperatures below 0°C or below 10°C in cases of violent winds.

It is the complication that is the most dreaded by mountaineers, lost hikers, travellers to cold climates and homeless people.

1 - PATHOPHYSIOLOGY

Four phases of frostbite follow one another or may occur together between cooling and rewarming, i.e.:

1/ The first cooling phase before freezing leads to vasoconstriction and ischemia but without the formation of ice crystals. Neuronal cooling and inadequate blood circulation result in hyperesthesia or paresthesia

2/ The second freezing-thawing phase, during which ice crystals form within the cells (rapid cooling) or outside the cells (slow cooling), results in protein and lipid disturbances, leakage of electrolytes from cells and intracellular dehydration leading to cell lysis.

Thawing gives rise to vasodilatation with attempted recirculation subsequent to ischemia, resulting in the production of an inflammatory response.

3/ The third phase is characterised by vascular stasis: periods of vessel dilatation cycle with times of constriction accompanied by blood leakage or intravascular coagulation.

4/ Later, during the fourth phase, progressive ischemia of the tissues is observed characterised by a cascade of events: inflammation caused by release of thromboxane A2, prostaglandins F2alpha, bradykinins and histamine; intermittent vasoconstriction of arterioles and venules; diffuse embolism of microvessels; formation of thrombi in larger vessels.

The initial cell damage caused by the ice crystals and post-thawing events are aggravated and become permanent in cases of re-exposure to cold.

2 - CLINICAL ASPECTS

Frostbite affects the hands and feet in 90% of cases.

Loss of sensitivity and pale, white skin is the first sign of frostbite.

The severity of frostbite can only be assessed after rewarming by immersion of extremities in a bowl of warm water (between 38 et 40°C) for at least an hour.

Stage 1 frostbite: characterised by numbness and erythema, the affected skin may develop firm, whitish patches. The deep tissues are not affected but superficial epidermal necrosis may sometimes be observed. Sensitivity returns to the skin and it resumes a pinkish coloration after rewarming.

Stage 2 frostbite: characterised by the formation of blisters filled with clear or milky fluid, surrounded by erythema and oedema. The loss of sensitivity persists, limited to the terminal phalanges of the toes or fingers which remain cyanotic.

Stage 3 frostbite: characterised by the formation of large blood-filled blisters resulting from damage to the reticular dermis and to the blood vessels of the deep dermis. The loss of sensitivity and cyanotic appearance of the skin persist above the distal phalanges but do not affect the rest of the hand or the forefoot.

Stage 4 frostbite: extension of the damage to the whole of the dermis and non-vascular subcutaneous tissues and muscles and bones. The loss of sensitivity and cyanosis spread to the hand or the forearm.

3 - TREATMENT

3.1 - PROPHYLAXIS

• Maintain peripheral blood circulation:

– remain hydrated by drinking enough warm, not too sweet drinks; eat before feeling the need to eat;

– keep your internal temperature stable by adequately protecting yourself against the cold;

– avoid treatments that decrease blood circulation as well as smoking and drugs, and avoid undertaking activities in extreme conditions if you suffer from a disease that causes hypoxemia;

– cover your entire body, including your head;

– avoid wearing jewellery, tight clothing (several pairs of socks) or shoes that are too small;

– in anticipation of a risky situation, take anti-aggregating doses of aspirin (75 à 250 mg) on a daily basis;

– use oxygen in conditions of hypoxia, above 7500 m altitude .

• Avoid inactivity and do exercises that keep the peripheral blood circulating by increasing the cold-induced peripheral dilatation threshold.

• Protect yourself from the cold:

– avoid temperatures below -15°C;

– wear clothing that provides adequate protection from humidity, wind (wind chill factor) and cold;

– avoid wetting your extremities, change out of wet clothes as soon as possible;

– use hand and foot warming systems;

– Avoid using emollients or fat as their use provides no protection but actually increases the risk of frostbit.

3.2 - CURATIVE CARE

In the field:

Rewarming is the treatment priority:

Remove the patient from the cold, avoid further injury, loosen the patient’s clothing and keep the patient hydrated. Remove all jewellery and other objects that may lead to constriction in the event of oedema.

In the field, sheltered from the cold, immerse the frozen extremities in a water bath maintained at 38/40°C for at least one hour. Add an antiseptic such as povidone-iodine or chlorhexidine. Alternatively, warm the frozen extremities by placing them in contact with the armpits or abdomen of another person.

Do not rub the frozen area with snow. Do not re-expose the patient to cold after rewarming.

With stage 1 frostbite, the patient may resume his/her activity; there is no risk of amputation. The patient must continue taking aspirin.

With stage 2 frostbite, the patient must stop his/her activity but emergency repatriation is not required. The injuries generally take a month to heal.

With stage 3 or 4 frostbite, emergency repatriation is required because of the risk of amputation.

Recent developments in satellite telephone and internet access make it possible to contact experts for guidance on how to manage the patient as soon as the accident occurs. In France, an emergency medical telephone number (0826148000) was set up for frostbite in 2006.

In the hospital setting

Patients should preferably be treated in a specialised department.

Treatment aims to rewarm the frozen extremities and then to put a stop to vasospasm, hyperviscosity and thrombosis and to prevent inflammation and infection.

The patient should be screened and treated for possible hypothermia, potential concomitant injuries or systemic complications.

On admission, affected areas must be rewarmed rapidly in warm water (37-39°C) to which an antiseptic has been added for 15 to 60 minutes.

Fight against hypovolemia by hydrating the patient either orally or by administering warmed saline solution intravenously in cases of digestive problems or disorders of consciousness.

Treat clear fluid-filled blisters (containing prostaglandins and thromboxanes) by piercing them and by applying compresses coated with Vaseline or with an aloe vera-based preparation every 6 hours (local anti-prostaglandin effect).

Do not burst the blood-filled blisters.

Affected limbs may need to be protected with a splint and raised (to prevent oedema).

Determine whether the patient has been vaccinated against tetanus.

Prevent pain by the administration of appropriate products.

Use of ibuprofen 400 mg every 12 hours is recommended in publications due to its anti-prostaglandin effect; aspirin 1 g per day has an anti-inflammatory effect but that is associated with a risk of prolonged blocking of certain prostacyclins which promote the healing of wounds.

If the patient initially presents with oedema and a decrease in the intrinsic protective properties of the skin against anti gram + cocci, administer penicillin or pristinamycin for 48 to 72 hours using a probabilistic approach. Administration of antibiotics should be adjusted as a function of laboratory results and how the patient recovers.

3.3 - ASSOCIATED MEDICAL TREATMENTS

• Vasodilators: nifedipine 1 capsule per day. Buflomedil was removed from the market in France in February 2011 and pentoxyfilline in November 2011.

Ilomedin, a prostacyclin analogue, administered at the dose of 0.5 to 2 ng/kg per minute, 6 hours per day for 8 days as soon as the patient starts receiving care significantly reduces the risk of amputation in patients with stage 3 or 4 frostbite.

In a French prospective, controlled and randomised study conducted in 2011, three protocols were compared in 47 patients with stage 3-4 frostbite, i.e. buflomedil + aspirin, aspirin + ilomedin, aspirin + ilomedine + thrombolysis using recombinant tissue plasminogen activator (rt PA). Amputation rates were 49%, 0% and 2%, respectively for the hands and 34%, 0% and 4%, respectively for the feet.

The use of thrombolytic therapy must therefore be considered on a case by case basis, only for stage 4 frostbite, in patients with no head injuries or medical contraindications and taking into account the time elapsed between rewarming and the provision of care.

• Whether hyperbaric oxygen treatment should be used depends on the authors but animal and human studies have shown that it could be beneficial. Further studies are required bearing in mind that treatment gives rise to few side effects and is inexpensive.

• Early surgical or chemical sympathectomy is no longer recommended since the use of vasodilators

3.4 - ASSESSMENT OF THE RISK OF AMPUTATION

A clinical assessment after rewarming combined with imaging using technetium 99 scintigraphy in the 3 days following admission to hospital and on D7 makes it possible to precisely evaluate the extent of amputation required which, generally, is only assessed after 3 weeks of care.

This approach makes it possible, in certain cases, to schedule early surgery with pedicle flaps and targeted amputations or amputation in two stages and especially, to reassure or psychologically prepare the patient for amputation of the decaying tissues in the 6 to 12 weeks after the frostbite.