Hypothermia describes a drop in body temperature that cannot be corrected by bodily heat production. There are multiple classifications for staging of hypothermia with the most comprehensive classification breaking the process into five stages. Using this classification, Stage I indicates mild hypothermia with body temperature in the range of 95 to 89.60 F. Stage II describes moderate hypothermia, ranging from 89.6 to 82.40 F. Stage III indicates severe hypothermia in the range of 82.4 to 75.20 F. Stages IV and V are not relevant to this case but describe patients who are apparently dead (stage IV, below 75.20 F with the need to rewarm to confirm death), or are deceased from irreversible hypothermia (stage V, below 590 F).
With mild hypothermia, symptoms are vague. Compared with temperatures above 950 F, shivering begins in earnest and becomes increasingly prominent as body temperature decreases. There is normal or near-normal level of consciousness. Autonomic symptoms are present (hypertension, tachypnea, tachycardia, peripheral vasoconstriction). During this stage, a cold-induced diuresis occurs with kidneys losing ability to concentrate urine. Later in the mild stage, there is impaired judgement, apathy, and ataxia.
With moderate hypothermia, there is significantly decreased level of consciousness. Shivering largely stops. At this point, people are no longer experiencing the discomfort of vigorous shivering and have moved into a calm, confused, apathetic state with amnesia, confusion, slurred speech, and loss of fine motor skills. Victims begin to paradoxically feel warm as a result of cold-induced dysfunction of the hypothalamus. That leads to undressing as they feel too warm and try to cool off. This classically described “paradoxical undressing” is a very common phenomenon, seen in up to 50% of cases of fatal hypothermia. There are diminished reflexes including gag reflex which correlates to the degree of sensory depression in these patients. Along with the loss of shivering, the previously elevated respiratory and heart rate become very low.
In severe hypothermia, there is frank coma, apnea, nonreactive pupils, pulmonary edema, and ventricular arrhythmias. It was in this severe stage that Mr. Maglies was found. This stage is characterized by unconsciousness. Physiologic systems falter and it may be difficult to detect vital signs though a patient is still alive. At this point, resuscitation is very possible, and even normally fatal arrhythmias may be reversed with body warming. Defibrillation often is not effective but may be effective after re-warming. Meanwhile, the brain and other critical organs remain relatively protected from ischemic damage due to decreased metabolic rate. For this reason, it is standard that resuscitation with advanced cardiac life support (ACLS) protocol should continue until a victim’s body temperature has been raised to 86-900 F unless there is an obvious fatal physical injury. People may survive even with fixed, dilated pupils and after hours of CPR.
The human body cools at different rates depending on the difference between ambient temperature and core body temperature with the body cooling more rapidly with a greater difference. Thus, the body temperature drops more rapidly at first and the rate of cooling gradually slows the colder the body temperature gets. At first, shivering can somewhat slow the process of cooling, but with loss of shivering as the core temperature drops below 900 F, there is more rapid cooling. Other factors that affect rapidity of cooling include age (elderly and very young patients cool faster), body habitus (thinner patients cool faster), clothing (patients with less insulating clothing cools faster), submersion in water (submersed patients cool much faster), as well as some medications or medical illnesses that impart varying effects.