THERMOREGULATION

Thermoregulation

Ability to regulate body temperature near constant value; balances heat gain and heat loss; regulated by hypothalamus.

Normal body temp

36.2-37.6C (97.0-100F).

Normal core body temp

36.5-38.5C (97.7-101.3F).

Normothermia

State within normal temperature range.

Hypothermia

Body temp below normal.

Hyperthermia

Body temp above normal with unchanged set point.

Hyperpyrexia

Extremely high body temp.

Hypothalamus

Establishes 'set point'; regulates temp in negative feedback loop; neural and hormonal control.

Set point

Temperature range for optimal physiologic functioning.

Skin temp

Normally 0.5C (0.9F) lower than core temp.

Body heat produced by

Chemical reactions from metabolic activity, skeletal muscle contraction, chemical thermogenesis.

Chemical thermogenesis (nonshivering thermogenesis)

Due to release of epi and norepi; temporary increase in basal metabolic rate leading to increased body temp.

Heat conservation

Regulated through peripheral vasocontraction, skin and subcutaneous fat providing insulation, intentional actions (clothing, blankets, body positioning).

Heat loss

Due to radiation, conduction, convection, vasodilation, evaporation, reduced muscle activity, increased respiration.

Radiation

Release of heat through electromagnetic waves from skin.

Conduction

Release of heat through direct contact with surfaces.

Convection

Release of heat through air currents moving across body surface; accelerated by wet skin.

Evaporation

Release of heat through perspiration evaporating from skin surface; accounts for 600mL of water loss daily.

Peripheral vasodilation

Increased release of heat due to more blood coming to skin.

Reasons for Older Adults having difficulty for thermoregulation

Slower circulation, decreased vasoconstrictor responses, reduced thermoregulatory capacity of skin, reduced heat production, reduced shivering response, reduced perception of environmental temperature.

Fever

Immune response to pyrogens; hypothalamus maintains higher core temp.

Exogenous pyrogens

External fever-producing agents; bacterial endotoxins, viruses, antigen-antibody complexes.

Endogenous pyrogens

Internal fever-producing agents; interleukin-1, interleukin-6, tumor necrosis factor, interferon.

Mechanism that cause hyperthermia

Excessive heat production, inadequate ability to cool, hypothalamic regulator function.

Hyperthermia causes

Environmental, excessive physical exertion, genetic abnormalities, metabolic diseases, injury to hypothalamus, pharmacologic agents.

Mild hypothermia

34-36C (93.2-96.8F).

Moderate hypothermia

30-34C (86-93F).

Severe hypothermia

<30C (<86F).

Physiological factors of hypothermia

Excessive heat loss, insufficient production of heat, dysfunction of hypothalamic regulatory mechanism

Accidental hypothermia causes

Environmental exposure, complication of serious systemic disorders

Therapeutic hypothermia reason

Reduce metabolism and preserve tissue by preventing ischemia; counteract overstimulation of neuro cells by stabilizing calcium and glutamate release

Factors of consequences of variable body temperature

Extent of temperature change, duration of temperature variation

Elevated body temperature consequences

Excessive and prolonged sweating > sodium loss, dehydration > hypotension, tachycardia, decreased cardiac output > reduced profusion, coagulation within microcirculation > cardiovascular collapse, cerebral edema, CNS degeneration, renal necrosis

Hypothermia consequences

Shivering, vasoconstriction > intermittent reperfusion of peripheral tissues > reduced microcirculation perfusion, coagulation; vasoconstriction fails > vasodilation > false warming sensation

Risk factors for alterations in thermoregulation

Very young, very old, non-hispanic black male; impaired cognition, autoimmune conditions, burns, hypothalamic injury (TBI, stroke, brain neoplasm), infection, inflammation, long surgical procedure, metabolic conditions (hyperthyroidism, hypothyroidism), prematurity/preterm birth, protein calorie malnutrition, traumatic injury, malignant hyperthermia (genetic predisposition for surgical complication), recreational/occupational exposures

Assessment Monitoring vital signs

Temperature measurement, heart rate, respiratory rate, blood pressure

External warming devices

Warm blankets, administer warm oral fluids

Active core warming

Warm intravenous fluids, heated humidified oxygen, warm fluid lavage

Cooling measures

Cool water bath, cool intravenous fluids, cool fluid lavage, cooling blankets

Thermoregulation affects

Fluid and electrolytes, tissue integrity, perfusion, intracranial regulation

Thermoregulation affected by

Infection, nutrition, intracranial regulation

Clinical exemplars

Fever, hyperthermia, heat cramps, heat exhaustion, heatstroke, malignant hyperthermia, hypothermia, frostbite, therapeutic hypothermia

Malignant hyperthermia

Hypermetabolic disorder of skeletal muscle; triggered by anesthetic agents; leads to severe hyperthermia; mild to life-threatening

Heatstroke

Due to exposure to excessively high environmental temps; AMS, increased body temp, hot dry skin; severe may be fatal

Preterm/Newborn Hypothermia

Due to heat loss by radiation, evaporation, conduction; requires radiant warmer; swaddles, cap, skin-to-skin help

Environmental Exposure Hypothermia

Due to exposure to cold temps or immersion in cold water