Patients with underlying medical problems such as diabetes, thyroid disease, cardiovascular disease, malnutrition, psychiatric disorders, and many other chronic medical conditions are also at risk. Neonates and infants are at special risk, as are the elderly. The physiology of hypothermia is fairly well understood. When the body perceives itself to be cold, a set of adaptive mechanisms takes over. Resting muscle tone increases, which generates heat.
Atrial arrhythmias develop, and pulse, respiration, and level of consciousness decrease.
Pupils become dilated. Voluntary movement ceases, cardiac output is less than half normal, and the risk of ventricular fibrillation is maximal. Palpable pulses may not be appreciable because of decreased cardiac output. The patient appears dead. Efforts should be directed toward minimizing further heat loss by using dry insulating blankets.