Environmental emergencies comprise a wide variety of patient presentations. This article focuses on assessment of patients with heat and cold exposures.
It is a hot day with temperatures over 100°F when Medic Six is dispatched to an unconscious 54-year-old who had been working outside in the heat, came inside complaining of weakness and nausea, vomited blood and passed out. His mother removed his clothing, cleaned him with a wet washcloth, and wrestled him onto the bed in front of the air conditioner. She says his only medical problems are hypertension, a “stomach ulcer” and drinking too much.
On the mattress near the patient’s head is a small puddle of coffee ground emesis, with a larger puddle on the carpet. He is unconscious, with pale, cold skin and cyanotic fingertips.
Vital signs are:
- Heart rate 64 and regular, with faint and thready distal pulses
- Respirations 12 per minute, non-labored
- BP 70/44
- SpO2–unable to detect
- ECG sinus rhythm at 64.
The crew begins rapid transport. En route, the paramedic places a 14-gauge IV catheter in the left antecubital fossa, bolusing with Ringer’s lactate solution and administering oxygen via non-rebreather mask.
When ambient temperatures and physical exertion combine to overwhelm the body’s thermoregulatory mechanisms, a heat or cold emergency occurs. Often the process is exacerbated by the use of depressant or stimulant drugs, but when the body can no longer maintain a stable temperature, rapid intervention is necessary.
Human beings, like all mammals, are homeothermic, meaning they can maintain a fairly constant internal body temperature of 98°–100°F (36°–38°C) through ambient temperature extremes as varied as 68°–130°F (20°–55°C).
Thermoregulation is accomplished via a combination of passive and active mechanisms. The hypothalamus, a small, almond-sized section of tissue lying just above the brain stem, is responsible for, among other functions, coordinating and controlling the body’s active thermoregulatory mechanisms. A portion of the hypothalamus, the pituitary gland, known as the body’s “master gland,” serves to bridge the body’s nervous and endocrine systems.
The body constantly generates heat as a product of normal metabolic processes, and the hypothalamus regulates this heat at a set point of roughly 98.6°F (37°C), although normal temperatures may vary a degree either way. Deviations from the body’s “set temperature” are detected by sensors within the hypothalamus and trigger a cascade of active physiologic mechanisms designed to maximize thermoregulation through the body’s two primary means of shedding heat: the lungs and skin. These mechanisms include:
- Sweating. Sweating begins at almost precisely 98.6°F (37°C) and increases rapidly as temperature increases. At less than 98.6°F (37°C), sweating ceases.
- Peripheral vasoconstriction/vasodilation. Since blood carries heat, dilating surface blood vessels results in increased blood flow, bringing blood to the skin, where heat can be rapidly dissipated through radiation. Conversely, surface blood vessels constrict to preserve body heat.
- Shivering. Shivering generates more heat when the hypothalamus senses that heat loss exceeds heat production.
- Secretion of hormones and neurotransmitters. Epinephrine and norepinephrine increase the basal metabolic rate, increasing heat production.
Thermoregulatory mechanisms are designed to maximize the efficiency of passive heat transfer between the body and the environment. The ways the body can lose heat to the environment include: