Humans adapt to cold be peripheral vasoconstriction which reduces heat loss and increases the metabolic rate which produces more heat. Shivering which involves muscular work occurs when there is abrupt demand to increase heat production. The core temperature will drop if there is failure to maintain thermal balance.
Freezing cold injury (Frost bite)
This is seen in persons exposed to temperatures below freezing point such as mountaineers, explorers, war casualties, or victims of natural disasters. There is freezing of extravascular fluid with formation of ice crystals in tissues leading to vascular damage, intravascular sludging and cellular death.
Management: General warming of the body to elevate core temperature should be under-taken before local warming of the affected limb. After restoration of the core temperature, the affected limb should be warmed in water at a temperature of 10 degrees to 15 degrees initially, progressively rising to 40 degrees and 42 degrees, the temperature of the water being raised every 5 or 10 minutes. Analgesics and antibiotics are given if indicated. Administration of low molecular weight dextran may help in relieving vascular sludging if given early in the disease. In severe cases, intra-arterial reserpine and sympathectomy help in controlling vasospasm. Impending gangrene can be aborted by exposure to hyperbaric oxygen. The condition can be prevented by covering the body with proper clothing, protection of the affected part, avoidance of local pressure, frequent changes of position and avoidance of smoking.
Non-freezing cold injury (trench foot, immersion foot)
Exposure to cold damp environment above freezing point for long periods leads to tissue ischemia. This is seen in warfare, persons marooned in floods, cases of shipwreck and other natural calamities. Initially, vasospasm occurs leading to vascular insufficiency. During the next phase hyperemia develops. Initially, the limb is cold, numb and pale. Movements may not be possible. Arterial pulses may be undetectable. The next stage is one of pain and erythema. The limbs are especially susceptible to trauma and infection leading on to gangrene and maceration. In many cases, permanent sequels like sensory motor defects may result.
management: The body is gradually warmed keeping the limb elevated, taking care to avoid overheating of the part. Analgesics and antibiotics should be given as indicated. Chilblains result from minor forms of cold injury and these manifests as red, tender, pruritis subcutaneous swellings. The condition is reversible if the environment is altered.