ICU Hypothermia and Hyperthermia Review

Vocabulary-style flashcards covering the mechanisms, clinical signs, and complications of hypothermia, fever, and heatstroke in a clinical ICU setting.

Convection

A mechanism of heat loss where heat is carried away by a moving fluid, such as wind cooling the skin.

Conduction

The transfer of heat through direct touch, such as an ice pack placed on the skin.

Radiation

Heat loss where energy is sent out as waves, common on a cold night.

Evaporation

Heat loss occurring when liquid evaporates, such as through sweating.

A-delta fibers

Nerve fibers that relay cold signals from receptors to the central nervous system.

C fibers

Nerve fibers that relay warmth signals from receptors to the central nervous system.

Hypothermic Spiral

A condition occurring as core body temperature dips below 94^\text{\circ}F (34.4^\text{\circ}C), where thermoregulation is impaired, shivering ceases, and metabolic rate decreases.

J/Osborn wave

A specific electrocardiographic complication associated with hypothermia.

Afterdrop

A continued drop in core body temperature after rewarming begins, caused by the return of cold peripheral blood to the core and movement of warm core blood to the periphery.

Rewarming shock

A phenomenon characterized by significant vasodilation and metabolic burden during rapid rewarming that may overwhelm the circulatory system.

Hypothermia

Defined as a body temperature less than 99^\text{\circ}F (< 37^\text{\circ}C).

Primary hypothermia

Heat loss caused by environmental exposure despite normal heat production.

Secondary hypothermia

Altered heat production or loss resulting from a disease process, injury, or drug administration.

Hyperthermia

An increase in core body temperature beyond the expected physiologic normals.

Fever

An increase in the hypothalamic thermoregulatory set point, usually caused by pyrogens, allowing the body to still dissipate heat.

Pyrogens

Pathogenic or nonpathogenic molecules, such as bacteria, viruses, or sterile tissue necrosis, that have the ability to induce fever.

Endogenous pyrogens

Fever-producing cytokines, most importantly interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)-$\alpha$.

Heatstroke

Severe hyperthermia defined by a core body temperature > 104^\text{\circ}F (40^\text{\circ}C) along with CNS and organ dysfunction.

Panting

The main cooling method used by dogs to dissipate heat.

Exogenous pyrogens

External agents such as bacteria, bacterial products (lipopolysaccharide, endotoxin), fungi, viruses, rickettsiae, and protozoa that induce fever.

MODS

Multiple organ dysfunction syndrome, a critical risk for heatstroke patients resulting from SIRS, shock, DIC, and cytotoxicity.