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Hypothermia is defined as a drop in body core temperature below 35°C. Peripheral thermometers are of limited utility in hypothermia – they can be inaccurate and vary by as much as 2°C – but their readings can provide paramedics and EMRs with valuable data in respect to trends. Because core temperature probes (either rectal or esophageal) are generally unavailable in a out-of-hospital setting, recognition of the different stages of hypothermia is more important than an understanding of the exact boundaries.
General hypothermia management consists of removing the patient from the cold environment, ensuring the patient is dry, and to prevent further heat loss. Paramedics and EMRs/FRs should handle patients gently and attempt to keep them supine whenever possible.
Although patient presentations can vary widely, the signs and symptoms of hypothermia can be divided into three categories:
Warning: Hypothermia is a significant contributor to mortality in trauma
In general, patients should be treated in a step-wise manner, beginning with less aggressive rewarming techniques. “Passive rewarming,” through the use of blankets around the body and the head, coupled with “active rewarming” using heated IV solutions, offers an effective initial strategy for most patients who are perfusing effectively.
While environmental exposure may trigger an assessment for hypothermia, paramedics and EMRs/FRs are cautioned that other groups of patients may be at risk for developing hypothermia in atypical environments. Clinical problems that produce an altered level of consciousness can eventually result in hypothermia, including (but not limited to) behavioural or psychiatric problems, prolonged seizures, alcohol or drug intoxication, strokes and cerebrovascular accidents, and diabetic or other metabolic emergencies. Elderly or frail individuals who are “found down” in their homes are at significant risk for developing hypothermia. Paramedics and EMRs/FRs must perform comprehensive assessments, and treat identified conditions concurrently with the hypothermia.
Depending on the degree of thermogenesis from shivering, the rewarming rate for patients may be anywhere from 0.5°C to 2°C per hour. The addition of active rewarming measures, using insulated or wrapped heat packs applied to the torso (groin, sides of chest, back of neck, small of back, and axillae) will significantly improve comfort and may lessen thermal stress.
Do not attempt to rewarm frozen or frostbitten limbs.
Hypotension can result from decreased cardiac output. Fluid shifts into the extracellular space are common, producing dehydration. Vascular access is indicated in hypothermia with warmed saline (between 37°C and 42°C) as the fluid of choice, if available. In the out-of-hospital environment, it can be difficult to warm or measure the temperature of fluids; paramedics are cautioned that “room temperature” fluids will significantly worsen hypothermia.
Hypothermic patients have significantly reduced metabolic demands and have dramatic reductions in heart and respiratory rates. A range of 30 to 45 seconds should be taken to accurately assess spontaneous respiration and pulse rates. Afterdrop, a phenomenon where cold blood from the extremities returns to the core, can occur producing an additional drop in core temperature.
Electrocardiogram findings in hypothermia can include J or Osborn waves (positive deflections following the QRS complex), most prominently in V2 through V5. The height of the wave is roughly proportional to the degree of hypothermia, though these are non-specific and may be due to other clinical phenomena.