Thermoregulation

Thermoregulation Overview

  • Developed by: Jill Ray; Reviewed by Laura Madden, PhD, RN, CCRN-K

Lesson Outcomes

  1. Explain the physiologic processes involved in homeostatic regulation of temperature.

  2. Compare and contrast factors that increase or decrease body temperature.

  3. Demonstrate knowledge of proper temperature assessment.

  4. Implement health promotion interventions for preventing hypothermia and heat-related illness.

  5. Discuss priorities of care for clients with hyperthermia, fever, and hypothermia.

Introduction to Thermoregulation

  • Thermoregulation is an aspect of homeostasis that balances heat gain and heat loss.

  • Primary function: maintain stable core body temperature.

  • Controlled by the hypothalamus.

  • Body temperature measures the difference between heat produced and heat lost to the environment (in degrees).

  • Heat is generated by metabolic processes in core tissues, transferred to skin surface by circulating blood, and dissipated to the environment.

Body Temperature

  • Core Body Temperature Locations:

    • Intracranial

    • Intrathoracic

    • Intra-abdominal

  • Core temperatures are higher than surface temperatures and maintained within a fairly constant range by the thermoregulatory center in the hypothalamus.

  • Core temperature is the most reliable assessment of temperature.

Factors Affecting Body Temperature

  • Key factors that influence temperature:

    • Circadian rhythms

    • Age and biological sex

    • Physical activity

    • State of health

    • Environmental temperature

    • Time of day (low early in the morning/highest between 1600 - 2000)

Proper Temperature Assessment

  • Importance of accurate assessment techniques for determining body temperature.

  • Various methods of assessment to be covered in detail.

Key Terminology

  • Hyperthermia: Elevated body temperature due to excessive heat (over 37.6°C).

  • Fever: A complex physiological response that indicates illness.

  • Hypothermia: Abnormally low body temperature due to excessive heat loss or inadequate heat production.

Age-Related Variations in Normal Vital Signs (Table 25-1)

  • Newborn (C): 35.9-36.9 (F): 96.7-98.5

  • Infants (C): 37.1-38.1 (F): 98.7-100.5

  • Toddler (C): 37.1-38.1 (F): 98.7-100.5

  • Child (C): 36.8-37.8 (F): 98.2-100

  • Preteen (C): 35.8-37.5 (F): 96.4-99.5

  • Teen (C): 35.8-37.5 (F): 96.4-99.5

  • Adult (C): 35.8-37.5 (F): 96.4-99.5

  • Aged Adult (C): 35.8-36.8 (F): 96.4-98.3

Scope of Thermoregulation Ranges

  • Hyperpyrexia: >41°C (>106°F) Medical emergency

  • Hyperthermia: >40°C (>104°F) Extremely high

  • Mild Hyperthermia: 38.1 - 38.4°C (100.6 – 101.1°F)

  • Normothermia: 35.9° - 38°C (96.7°F – 100.4°F)

  • Mild Hypothermia: 34°C – 36°C (93.2°F – 96.8°F)

  • Moderate Hypothermia: 30°C - 34°C (86°F – 93°F) Extremely low

  • Severe Hypothermia: <30°C (<86°F) Medical emergency

Recommended Method of Temperature Measurements by Age

  • Under 3 months: Rectal

  • 3-6 months: Temporal

  • 6 months-3 years: Oral, Tympanic

  • 4 years-teens: Oral, Tympanic

  • Adults: Oral, Tympanic

  • Older adults: Oral, Tympanic

Heat Production

  • Heat is continually produced through:

    • Metabolic activity.

    • Ingestion and metabolism of food.

    • Basal metabolic rate (at rest).

    • Physical activity and shivering.

    • Hormonal activity (epinephrine, norepinephrine, thyroid hormone).

Heat Loss

  • Heat loss occurs mainly through skin.

  • Controlled by sympathetic nervous system:

    • Opens or closes arteriovenous connections to regulate heat retention and dissipation.

Mechanisms of Heat Loss

  • Radiation: Heat loss without direct contact (e.g., cold air).

  • Convection: Heat loss through air movement (e.g., fan).

  • Evaporation: Heat lost through sweating.

  • Conduction: Heat transferred through direct contact (e.g., ice pack).

Hypothalamic Regulation of Temperature

  • Decreased temperature:

    • Blood vessels constrict, sweat glands become less active, skeletal muscles contract (shivering).

  • Increased temperature:

    • Blood vessels dilate, sweat glands become more active.

Fever vs Hyperthermia

  • Fever is a controlled rise in body temperature as part of the immune response, often in response to infection.

  • Most fevers are self-limiting and not harmful unless excessively high (>40°C or 104°F).

  • Symptoms associated with fever include:

    • Loss of appetite

    • Headaches

    • Thirst

    • Muscle aches

Hyperthermia and Heat-Related Illnesses

  • Heat exhaustion and heat stroke are conditions arising from excessive heat affecting the body:

    • Heat exhaustion: Low fluid volume, symptoms include dizziness and low blood pressure.

    • Heat stroke: Medical emergency with severe symptoms like dry skin, confusion, and risk of organ failure.

Nursing Interventions for Temperature Management

  • Hyperthermia Interventions:

    • Identify underlying cause, remove excess clothing, provide hydration, consider antipyretics.

  • Hypothermia Interventions:

    • Remove patient from cold, apply heat slowly, administer warm IV fluids.

  • Frostbite Management: Rapid rewarming with controlled immersion in warm water and evaluation of symptoms.

Age-related Differences in Thermoregulation

  • Infants and older adults are particularly vulnerable to temperature extremes:

    • Infants have underdeveloped temperature regulation capacity and a high surface area to body mass ratio.

    • Older adults exhibit diminished febrile response and reduced thermoregulatory mechanisms.

Environmental and Individual Risk Factors for Thermoregulation Issues

  • Environmental extremes significantly affect at-risk populations, especially:

    • Infants, older adults, low-income groups.

  • Individual risk factors include:

    • Impaired cognition, comorbidities, substance abuse, and specific genetic predispositions such as malignant hyperthermia.

Nursing Assessment for Thermoregulation

  • Historical analysis of body temperature, health history, and environmental exposures are essential in assessing a patient's thermoregulatory status.

  • Vital signs, particularly temperature and blood pressure, must be monitored to determine the intervention needs and effectiveness.