 Welcome to emergency medicine video. This is hypothermia part one. It is winter. The paramedics array in a patient who has been lying outside in the snow for a few hours. How should we manage a patient like him? In this segment, we will talk about the causes and effects of hypothermia. What is normal temperature? In normal physiological state, a body functions the best between 36.5 to 37.5 Celsius. Anything colder than 35 degrees Celsius or 95 degrees Fahrenheit is defined as hypothermia. You can have hypothermia on the whole body or sometimes only part of the body is affected. How might someone become hypothermic? Well, if you imagine the body like a house and you're trying to keep the heat in, it's either that the heating element or the furnace is not working well. Causing decreased heat production? The heat is escaping from the house. Or the thermal stat for the furnace is not set properly. Let's talk about each. First, decreased heat production. There are three main causes. First, not enough fuel, such as poor nutrition or hypoglycemia. The furnace itself being very slow from hypothyroidism or adrenal insufficiency, causing very inefficient heat production. Or the furnace could be not working at all. Due to advanced age and comorbidity leading to impaired shivering. Next, for increased heat loss, it can be done through immersion in cold fluids, exposure to a cold surrounding. Heat loss will be even more if the patient is vasodilated. That can be caused from alcohol, sepsis or toxins. Heat loss will also be increased if the skin is broken down from burn or dermatitis. In the hospital setting, we can cause hypothermia by giving lots of cold fluids. Third, impaired thermal stat or impaired thermal regulation. In the body, it can be either central or peripheral. The central causes include metabolic causes such as cirrhosis, uremia. It can also include things like stroke or MS in the central nervous system. Peripheral causes include spinal cord injury and peripheral neuropathy. These all causes the body to have impaired thermal regulation. What happens with hypothermia? The effects are mainly in the heart and the brain. As you can imagine, these are worse as you get to a lower temperature. Myotypothermia is defined as 32 to 35 Celsius. The heart rate goes up. Hyperventilation occurs. Neurologically, there are changes in speech, judgment, gait, fine motor skills and gross motor skills. The muscles start to shiver. This is mild hypothermia. As we get to moderate hypothermia, the core body temperature has dropped to between 28 to 32. The heart now starts to slow down. Cardiac output decreases. Erythmias now start to occur such as atrial fibrillation or heart blocks. In terms of the brain, the patient will have decreased level of consciousness and ataxia. Shivering now stops. Severe hypothermia occurs under 28 degrees Celsius. The heart rate is even slower. The patient might have ventricular fibrillation or even a systole. Neurologically, the patient would be completely unresponsive. What about if only part of the body is exposed to the cold? Frostbite can happen when cold injury damages to mostly extremities. The patient will start to lose sensation. On examination, they will have poor capillary refill. The skin might be red, edematous, with blisters, or if worse, purple and aquatic. In summary, we discuss the causes of hypothermia and the effects on the body. In part 2 and 3, we will discuss the emergency department approach of the hypothermic patient.