Medical Care for a Patient With Hypothermia
Introduction
Hypothermia is a medical condition that develops when body temperature falls below 35 °C (1). In hypothermia, the body loses heat faster than it can produce it. Normal body temperature is approximately 37 °C.
As body temperature falls, the normal function of the cardiovascular, respiratory, nervous, and other organ systems becomes impaired. If timely assistance is not provided and the patient is not rewarmed, progressive failure of these organ systems may develop and ultimately result in death. Hypothermia refers to generalized cooling of the body, whereas frostbite is the effect of cold on specific parts of the body rather than the entire organism. Hypothermia most commonly develops in low environmental temperatures or following exposure to cold water. Consequently, cases of hypothermia occur most frequently during winter. The primary goal of treatment is to rewarm the affected person to a normal body temperature.
Symptoms
Table 1. Symptoms of Hypothermia According to Body Temperature
| Body Temperature | Stage | Most Common Symptoms |
|---|---|---|
| 37 °C | Normal body temperature | |
| 32–35 °C | Mild hypothermia | Shivering, goosebumps, bluish skin, confusion, speech and memory disturbances, tachypnea, tachycardia, increased diuresis |
| 28–32 °C | Moderate hypothermia | Shivering stops, severe drowsiness, lethargy, hallucinations, hypoventilation, arrhythmias, bradycardia, paradoxical undressing |
| Below 28 °C | Severe hypothermia | Rigidity, loss of consciousness, coma, respiratory arrest, cardiac arrest, oliguria |
A person with hypothermia is often unaware of the symptoms because most develop gradually and may go unnoticed. In addition, hypothermia of the brain impairs cognitive function, causing the person to become less critical of their own condition and increasing the likelihood of risky behavior (Table 1) (1–2).
Causes
Environmental Conditions
The most common situations in which hypothermia may develop include:
- wearing insufficiently warm clothing;
- remaining in cold weather for too long;
- being unable to change out of wet clothing or move to a warm, dry location;
- falling into cold water;
- living in an inadequately heated home.
Hypothermia most commonly results from increased convection during exposure to cold air or conduction during immersion in cold water (Table 2) (3–4).
Table 2. Physical Mechanisms of Heat Loss
| Mechanism | Explanation |
|---|---|
| Radiation / thermal radiation | Energy emitted by the body. Most heat is lost through exposed body surfaces. This mechanism largely depends on the ratio of body surface area to body mass: the greater the ratio, the faster the relative rate of heat loss. |
| Direct contact / conduction | During direct contact with a very cold surface, such as cold water or cold ground, heat is transferred to the colder object. During heat conduction, heat transfer depends on the temperature difference between the surfaces, the area of contact, and the thermal conductivity of the contacting material. |
| Convection | Heat is transferred through airflow; for example, wind removes body heat by displacing the thin layer of warm air above the skin. Through convection, a large amount of heat can be lost or, conversely, supplied even across a relatively small surface area. |
| Evaporation | Loss of water and heat through sweating and respiration. These physiological mechanisms are particularly important in hospitalized patients. On average, approximately 400 ml of warm, humidified air is exhaled per day. In tachypnea, this amount may increase 2–3-fold. |
Physiological Mechanisms
Body temperature reflects the balance between heat production and heat loss. Heat is produced in all cells of the body, with metabolically highly active cardiac and hepatic cells generating the greatest thermal potential. However, skeletal muscles are responsible for the largest proportion of total heat produced by the body because, although they are metabolically less active, they constitute a much greater mass. Most heat is lost through the skin and lungs, and the amount of heat lost varies considerably depending on sweating, body temperature, and respiratory rate (5).
Maintaining a constant body temperature is one of the fundamental elements of homeostasis. Various autoregulatory mechanisms are involved in temperature control, most of which are involuntary. Neural pathways and reflex circuits converge in the hypothalamus. When the body loses heat, several physiological mechanisms are activated in the hypothalamus to increase heat conservation and production (2, 6):
- heat conservation: peripheral vasoconstriction and behavioral changes. The sympathetic nervous system is activated and adrenaline is released, centralizing circulation and directing warm blood through shunts that bypass the skin. Behavioral changes include seeking a warmer environment or shelter and avoiding moisture;
- heat production: sympathetic nervous system activity increases, and involuntary shivering of skeletal muscles occurs, generating heat.
Risk Factors
Under certain conditions, hypothermia develops more rapidly than under normal circumstances (7):
- Conditions associated with increased heat loss. Examples include burns, severe psoriasis, dermatitis, newborns, and iatrogenic causes such as infusion of blood or other cold fluids and induced cooling.
- Conditions associated with impaired heat production. Examples include very old or very young age. The body's ability to regulate temperature and perceive cold decreases with age. Children lose heat more rapidly than adults and, while playing, may ignore the cold or inadequately assess weather conditions and therefore fail to dress appropriately. Other causes of impaired heat production include exhaustion, severe malnutrition, and neuromuscular diseases.
- Multifactorial causes:
- Drugs and toxins. For example, alcohol, certain antidepressants, antipsychotics, narcotic analgesics, anesthetics, vasodilators, and sedatives.
- Metabolic and endocrine disorders. Hypothyroidism, hypoadrenalism, hypopituitarism, hypoglycemia, diabetic ketoacidosis, lactic acidosis, and Wernicke encephalopathy.
- Neurological disorders. Central nervous system trauma, tumors, cerebral infarctions, Parkinson’s disease, and multiple sclerosis.
- Mental disorders. People with mental disorders, dementia, or other conditions that impair thinking and perception may dress inappropriately and are also more likely to become lost.
- Sepsis. More common among older and cachectic patients.
- Shock.
- Trauma. …
Continued in Internistas, No. 1, 2019
Alvita Vickienė
Vilnius University Faculty of Medicine
