Re-warming Strategies in Hypothermia
All patients with hypothermia have to be re-warmed, but how to re-warm is very important part of treatment of hypothermia. The decision to re-warm actively or passively is very important in the outcome of the treatment. Active re-warming can be active external re-warming and active core re-warming.
Passive re-warming of hypothermia patient is done in a warm environment by covering (with blanket) and insulating the patient. The head of the patient also should be covered leaving only the face open. Body temperature increase of 0.5° C to 2.0°C per hour is satisfactory and aimed for. For passive re-warming to be successful the patient should have adequate store of glycogen to produce enough heat (calorie) and for this reason passive re-warming is successful in previously health patients, who get hypothermia accidentally.
In many cases of hypothermia passive re-warming may not be successful in treating severe hypothermia and may require active re-warming. The situation where active re-warming is required are cardiovascular instability, hormone insufficiency, very young or very old patient, any accompanying CNS problem, if core temperature is below 32°C called poikilothermia, or if hypothermia is due to some disease. Active re-warming is done by air heating blankets (best method), hot packs, radiant heat etc.
In severe cases of hypothermia the patient may have to be given active core re-warming like re-warming by heating and delivering fluid or blood with a countercurrent in-line heat exchanger (the best and fast method), heated humidified oxygen (40°–45°C) via mask (it eliminates respiratory heat loss and adds 1°–2°C to the overall re-warming), normal saline or ringer lactate should be heated to 40°–42°C (but the quantity of heat provided is significant only during massive volume resuscitation) and infused, heated irrigation of the gastrointestinal tract or bladder (minimal effect due to small surface area), peritoneal dialysis at 40°–45°C and standard hemodialysis (very good and successful). All the above mentioned techniques are reserved in patients with cardiac arrest and used in combination with all available active re-warming techniques. In general these techniques are not required.
Warnings: Application of direct heat to the extremities should be avoided in chronic hypothermia, because it may cause dilatation of blood vessels in the periphery and precipitate core temperature called “afterdrop” which is a response characterized by a continual decline in the core temperature after removal of the patient from the cold. To avoid afterdrop heat should be applied to the trunk of the body. Electric blankets also should be avoided because vasoconstricted skin burns easily. Monitoring a hypothermia patient in a heated tub is extremely difficult and should be avoided.