Environmental emergencies comprise a wide variety of patient presentations, from straightforward heat and cold exposure to toxic envenomation and exposure to allergens and noxious plants. This article focuses on assessment of patients with heat and cold exposures.
It is a hot day with temperatures over 100° 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°-100oF (36°–38oC) through ambient temperature extremes as varied as 68°-130oF (20°–55oC).
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 98.6oF (37oC), 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 98.6oF (37oC) and increases rapidly as temperature increases. At less than 98.6oF (37oC), 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:
- Radiation occurs when an organism loses heat to the atmosphere without actually touching any object. Most heat loss through radiation occurs through the neck and head. When ambient temperature is greater than body temperature, heat dissipation through radiation alone is impossible.
- Convection results from body heat radiating into the surrounding air, warming it. This warmer air rises and is replaced by colder air. Water is one of the most effective mechanisms for heat loss.
- Conduction results from loss of body heat through direct contact with colder objects in the environment.
- Respiration dissipates heat by exhaling warm air from the lungs and inhaling colder ambient air. The amount of heat loss is dependent upon both rate and depth of respiration.
- Evaporation results in heat loss by evaporation of perspiration or wet skin. In high-humidity environments, high moisture content of air may severely curtail or prevent evaporative heat loss.
Assessment starts with obtaining an accurate measurement of the patient’s core temperature. Methods vary from thermal sensing of the tympanic membrane or temporal artery to temperature-sensing skin strips; the most reliable and accurate means is still the rectal thermometer. Temperature sensing strips are highly inaccurate.
During transport to the trauma center, the paramedic infused two liters of Ringer’s lactate solution without appreciable improvement in the patient’s level of consciousness or vital signs.
When the body can no longer shed heat effectively and the temperature rises above the body’s set point, hyperthermia occurs. Fever is an increase in the body’s temperature set point resulting from the body’s inflammatory response to pathogens. In this lesson, we will limit our discussion to hyperthermia from environmental causes. Heat emergencies are classified by skin signs, symptoms and core temperature:
- Heat exhaustion is characterized by moist skin that feels cool or normal. At this stage, the body is still able to dissipate heat through radiation and perspiration. Loss of electrolytes through sweat is the main cause of symptoms, and the patient may complain of thirst. He may experience weakness, dizziness, nausea and vomiting, and cramps of the muscles in the abdomen or legs resulting from loss of electrolytes, particularly potassium, in perspiration.
- Heat stroke is a life-threatening condition that occurs when the body cannot dissipate heat and core temperature rises above 105oF (40.5oC). Sustained temperatures above 105oF (40.5oC) can result in seizures, brain damage, organ failure and eventually death. Heat stroke is usually characterized by hot skin, which may or may not be dry, tachycardia and neurological changes such as confusion, disorientation and poor coordination. Seizures, coma and death can rapidly follow unless aggressive cooling measures are taken.
Basic treatment steps for heat-related emergencies begin with removing the patient from the hot environment, removing clothing and maximizing passive cooling through radiation and evaporative heat loss. Moving the patient to a cool environment, and, if nausea is not present, encouraging the patient to rehydrate with a cool, electrolyte-containing solution such as a sports drink is usually sufficient.
In heat stroke, far more aggressive cooling measures are necessary. Wrap the patient in moist sheets and blow cool air over them to maximize convective and evaporative heat loss. Ice packs to the groin, axillae, head and neck may be useful.
Just as with heat-related emergencies, children and the elderly are at greatest risk of hypothermia due to their less efficient thermoregulatory capacity. Children have larger body surface-area-to-mass ratio, compounding heat loss through the skin, while elderly patients often have less subcutaneous fat for insulation or may be taking medications that inhibit the body’s ability to withstand temperature extremes. Alcohol ingestion increases risk of cold-related emergencies.
When the body’s thermoregulatory mechanisms can no longer produce enough heat to overcome passive heat loss, hypothermia (<95oF or 35oC) occurs. Unlike frostbite, which is localized, hypothermia affects all organ systems and tissues. Classification of hypothermia is based upon core temperature:
- Mild hypothermia (90°-95oF or 32°-35oC) presents with the typical fight-or-flight response as the body releases epinephrine and norepinephrine to increase basal metabolic rate, and thus heat. Shivering, tachypnea, tachycardia, hypertension and peripheral vasoconstriction may all be present.
- Moderate hypothermia (82°-90oF or 28°-32oC) presents with more violent shivering, confusion begins, and fine motor skills deteriorate. Skin will be cold, and lips, ears and nailbeds may appear cyanotic.
- Severe hypothermia (68°-82oF or 20°-28oC) presents with increasing neurological impairment, beginning with sluggish thinking, difficulty speaking and amnesia, and progressing to stupor and coma. Fine motor skills are absent or severely impaired, and motor coordination begins to deteriorate. Heart rate and breathing slow dramatically, although tachydysrhythmias such as atrial fibrillation are not uncommon. Clinical death may occur, although due to the slowed cellular activity, full neurological recovery may still be possible even after prolonged resuscitation attempts.
- Profound hypothermia (<68oF or 20oC) invariably presents with clinical death, although resuscitation may still be possible. Asystole or slow PEA are usually the presenting rhythms.
Treatment for hypothermia in the field consists of moving the patient to a warm environment, removing wet or cold clothing, and beginning passive rewarming with blankets. Active peripheral rewarming with hot packs is discouraged due to risk of burns and the phenomenon known as afterdrop, in which cold blood from the extremities returns to the core, further cooling vital organs.
Core rewarming is generally only necessary in severe hypothermia and consists of warmed IV fluids, and possibly gastric and rectal lavage with warmed fluids.
During transfer of care to the emergency department, the paramedic jostled the patient while transferring him to the ED bed, and the patient immediately clenched his teeth and arched his back in what appeared to be a seizure. The cardiac monitor, however, revealed ventricular fibrillation, and the patient was defibrillated twice without success before being moved to a resuscitation room.
Later, the paramedic was approached by the ED physician, who asked if he cared to make a guess as to his patient’s core temperature.
“No,” the paramedic replied, “but I have a feeling it’s not good since you’re asking me that question.”
“82 degrees,” the physician confirmed. “Sometimes when you hear hoof beats, it IS a zebra.”
Management of environmental emergencies is usually straightforward, but as the scenario demonstrates, assessment can sometimes be complicated by tunnel vision and comorbid factors. This scenario really happened. The patient did indeed have a GI bleed, but his main problem was hypothermia. The paramedic never considered the possibility of severe hypothermia and his treatment definitely made the patient worse.
Assess your patients carefully, and assume nothing.
Steven “Kelly” Grayson, NREMT-P, CCEMT-P, is a critical care paramedic for Acadian Ambulance in Louisiana. He has spent the past 14 years as a field paramedic, critical care transport paramedic, field supervisor and educator. He is the author of the book En Route: A Paramedic’s Stories of Life, Death, and Everything In Between, and the popular blog A Day in the Life of An Ambulance Driver.
William E. (Gene) Gandy, JD, LP, has been a paramedic and EMS educator for over 30 years. He has implemented a two-year associate’s degree paramedic program for a community college, served as both a volunteer and paid paramedic, and practiced in both rural and
urban settings. He lives in Tucson, AZ.