NSG 170 Thermoregulation

thermoregulation

balances heat production, heat loss to maintain body's temperature

1. Surface temperature fluctuates in response to environmental factors

B. Core temperature more reliable; relatively constant 37°C, or 98.6°F

afebrile

absence of a fever

basal metabolic rate (BMR)

the amount of energy expended by the body at rest

brown adipose tissue (BAT)

brown fat found in newborns that helps protect their organs from extreme temperature changes

chemical thermogenesis

the stimulation of heat production in th ebody through increased cellular metabolism

conduction

the process of heat transfer through physical contact of one surface with another surface

convection

the process of heat transfer through the fluid motion of air or water across the skin

evaporation

the process of converting water to a vapor

febrile

presence of a fever

fever

a protective immune response to foreign antigens within the body that causes an increase in the cellular metabolic rate that further increases the body's temperature

heat balance

the amount of heat produced by the body equals the amount of heat lost, and the individual's body temperature remains within the normal range

heat transfer

movement of heat from one place or object to another

hyperthermia

the body produces more heat than is lost

(fever) temperature over 38ºC (100.4ºF)

1. Heat exhaustion

2. Heat stroke

hypothermia

more heat is lost than is produced

core temperature below 36ºC (96.8ºF)

1. Excessive heat loss

2. Inadequate heat production to counteract heat loss

3. Impaired hypothalamic thermoregulation

malignant hyperthermia

a potentially fatal, inherited disorder that results from the body's reaction to inhalation of volatile anesthetic gases and succinylcholine

neutral thermal environment (NTE)

an incubator-environment temperature similar to that of a newborn's body temperature designed to minimize thermal body stress

normothermia

usual range of core body temperature

usual core body temperature range 36 and 38.5°C (96.8 and 101.3°F)

radiation

the process of heat transfer with no physical contact

heat balance - heat produced =

heat lost

factors affecting heat production

1. Basal metabolic rate (BMR)

2. Muscle activity

3. Thyroxine output

4. Epinephrine, norepinephrine, sympathetic stimulation/stress response

5. Fever

6. Heat transfer

types of heat transfer

a. Conduction transfer of heat from one molecule to a molecule of lower temperature

b. Convection dispersion of heat by air currents

c. Radiation transfer of heat from surface of one object to surface of another

d. Evaporation continuous evaporation of moisture from respiratory tract, mucosa of mouth, skin

regulatory system has 3 components

1. Sensors detect heat send signals to effector system to decrease heat production, increase heat loss

2. Sensors detect cold send signals to effector system to increase heat production, decrease heat loss

3. Hypothalamus controls core temperature

three physiologic responses to cold

i. Shivering increases heat production

ii. Sweating inhibited to decrease loss

iii. Vasoconstriction decreases heat loss

febrile

patient with fever

genetic considerations for thermoregulation

A. Hereditary periodic fever syndromes

B. Malignant hyperthermia

1. Two screening methods

a. Genetic testing

b. Muscle biopsy or caffeine halothane contracture test (CHCT)

factors that increase risk for hyperthermia

age, obesity, medications, unfamiliarity with the climate

collaborative efforts to reduce risk of hyperthermia

cooling stations, shade, unrestricted access to fluids

population at greatest risk for hypothermia

older adults

neonates

contributing factors of hypothermia

outdoor exposure, trauma, alcohol or drug abuse, endocrine disorders, neurologic or autonomic dysfunction, social isolation, economic status

interventions to support thermoregulation

A. Maintain thermoregulatory mechanisms—environmental changes

B. Elderly patients, young infants warmer environment

C. Adequate hydration important

D. Patient education

interventions for hyperthermia

A. Should alleviate injuries and begin cooling process

B. Emergency medical services (EMS) notification of suspected heat injury if outside the hospital

C. Monitor patient's airway, breathing, ventilation, circulation

D. Cool fluids, shade, air conditioning

E. Removal of clothing to facilitate cooling process

F. Icepacks to groin/armpits if symptoms severe

G. Pediatric patients with febrile seizure history precautions in place when temperature begins to rise

interventions for hypothermia

A. Immediate rewarming core to extremities slow process

B. Warm compresses/water bottles if severe

medications to reduce shivering while cooling for cooling patients with hyperthermia

benzodiazepines

five types of care for cooling patients with hyperthermia

1. Prehospital care EMS personnel immediate attention to airway, breathing and ventilation, and circulation (ABCs)

2. Emergency department care administer antipyretics

3. Inpatient care to designated care settings pediatric, geriatric

4. Admission to intensive care unit (ICU)

5. Outpatient and follow-up care

rewarming patients with hypothermia

A. Method depends on severity

B. Moderate to severe, older adults with mild active external rewarming

C. Active internal rewarming, core rewarming

D. Endovascular rewarming

E. Extreme cases extracorporeal blood rewarming

F. Localized injury water bath digits rewarmed no more than 30 minutes after core

G. Other therapies debridement or excision of damaged, dead, infected tissue; antibiotics; pain medications

thermoregulation in infants

A. Have brown adipose tissue (BAT), brown fat to help protect from extreme temperature changes

B. Newborns are homeothermic

C. Thermoregulation in the newborn closely related to rate of metabolism and oxygen consumption

D. Less subcutaneous fat than adults

E. Blood vessels closer to the skin

F. Flexed posture decreases surface area

G. Size and age affect establishing of neutral thermal environment (NTE)

H. Adversely affected by heat loss through conduction

I. Tympanic route fastest and most convenient for temperature assessment, axillary also used but not as accurate, rectal route least desirable

thermoregulation in children and adolescents

A. Until they reach puberty, children's temperatures are more variable than adults

B. Healthy child can handle temperature as high as 41ºC (105.8ºF) without difficulty

C. Tympanic route, oral route (age >3), rectal route

thermoregulation in pregnant women

A. Marked changes experienced throughout the gestational period protect fetus from hyperthermia

thermoregulation in older adults

A. Those over age 75 at risk for hypothermia

B. Inadequate diet, loss of subcutaneous fat, lack of activity, reduced thermoregulatory efficiency

C. Particularly sensitive to temperature extremes due to decreased thermoregulatory controls

D. Fever may not be exhibited as a sign of infection

E. Common fever sources—infection, noninfectious inflammatory disorders, cancer

constant fever

the body temperature fluctuates minimally but always remains above normal

endogenous pyrogens

interleukins, interferons, and tumor necrosis factor released by macrophages in response to an infection

febrile seizure

generalized seizures that usually occur in children as the result of rapid temperature that rises above a rectal reading of 39°C (102.2°F) in association with an acute illness without evidence of intracranial infection or other defined cause

fever of unknown origin

a temperature above 38.3°C (100.9°F) that occurs on several occasions within a short time span, lasts for more than 3 weeks, and does not have a definitive cause after 1 week of clinical investigation

fever phobia

caregivers' fear about the harmful effects of fever; typically include seizure, brain damage, and death

fever spike

temperature that fluctuates from normal to fever level rapidly, and then returns to normal within a few hours

1. Bacterial blood infections often cause fever spikes

heat exhaustion

elevated temperature that is a result of excessive heat exposure and dehydration

heat stroke

a more serious life-threatening form of heat exhaustion

intermittent fever

the body temperature alternates at regular intervals between periods of fever and periods of normal or subnormal temperatures

relapsing fever

short febrile periods of a few days are interspersed between periods of 1-2 days of normal temperature

remittent fever

a wide range of fluctuating temperatures (more than 2°C [5.3°F]) are experienced, all of which are above normal; occurs over a 24-hour period

types of fevers

1. Intermittent fever—alternates at regular intervals between periods of fever and periods of normal temperatures

2. Remittent fever—wide range of temperature fluctuations, all above normal

3. Relapsing fever—short febrile periods of a few days interspersed with periods of 1 to 2 days of normal temperature

4. Constant fever—little fluctuation, above-normal temperature

a. Typhoid fever

core temperature high

rate of heat loss increases resulting in decrease in temperature

core temperature low

rate of heat production increases resulting in increase in temperature

effects of fever

1. Effects of tissue destruction, pyrogenic substances, dehydration

2. Core body temperature reaches new set point after several hours

3. Usual heat production responses that elevate body temperature occur

4. At set point patient feels neither cold or hot, no chills

5. Very high temperatures damage parenchyma of cells throughout body

6. Brain destruction of neuronal cells irreversible

7. Liver, kidneys, other organs disrupt functioning, eventually cause death

response to infection

1. Macrophages release endogenous pyrogens

2. Pyrogens travel through circulatory system to hypothalamus trigger production of prostaglandins (raise body's thermoregulatory set point) cause fever to occur

3. Heat loss reduced body temperature is elevated to new temperature set point

4. Increases heart rate, metabolic need for oxygen, vasodilation

manifestations due to cause of fever

1. Flushing

2. Skin warm, hot to touch

3. Increased metabolic rate increased need for fluids, tachypnea, tachycardia

4. Fatigue

5. Malaise

6. Weakness

7. Decreased responsiveness

8. Difficulty concentrating

9. Skin rash

10. Poor appetite

11. Vomiting and/or diarrhea

12. Body aches

preferred antipyretics for children

acetaminophen

ibuprofen

antipyretics affect on fever

1. Antipyretics reduce fever inhibiting prostaglandin synthesis results in lowering body's temperature set point

aspirin associated with

reye syndrome

antibiotics administered for

infectious diseases

febrile seizures

1. Generalized seizures, usually in children

2. Result of rapid temperature rise above 39C (102.2F)

3. Associated with acute illness

4. No evidence of intracranial infection, other cause found

5. Seen in children from 6 months to 5 years

Hyperthermic exposure and maternal fever in the first trimester have been associated with

congenital birth defects

two major routes of heat loss

from the internal core to the body surface and from the external surface to the environment

induced hypothermia

A. Deliberate lowering of body temperature to decrease metabolic rate reducing body's need for oxygen

B. Variety of reasons

1. Reduce metabolic rates

2. Lower cellular demand for oxygen in tissues—particularly brain

3. Used to reduce neurologic damage

4. Following head trauma

5. Strokes

6. During cardiac surgery

C. Studies have focused on its use with in-hospital cardiac arrests

accidental hypothermia

A. Unintentional exposure to cold temperatures overwhelms body individual unable to move or shiver depletes energy stores

B. Described in stages based on symptoms stages I-IV

C. Frostbite

frostbite

1. Freezing injury to skin and underlying tissues

a. If limited skin, subcutaneous tissue involved

b. Increased exposure deeper structures freeze

c. Skin freezes at -5°C (23°F)

d. Most common on exposed or peripheral areas of body

i. Nose

ii. Ears

iii. Feet, hands

2. As tissue freezes

a. Ice crystals form increase intracellular sodium content

b. Small vessels initially vasoconstrict, then vasodilate become more permeable, cause cells, tissues to swell

c. Continued exposure vasoconstriction

i. Increased viscosity of blood infarction, necrosis of tissue

3. Superficial frostbite

a. Numbness, itching, prickling

b. Cyanotic, reddened, white

c. Deeper frostbite stiffness, paresthesias

4. Thawing of tissue

a. Skin white or yellow

b. Loses elasticity

c. Burning pain

d. Edema, blisters

e. Necrosis

f. Gangrene

risk factors for hypothermia

A. Exposure to cold environment

B. Immersion in cold water

C. Lack of adequate clothing, shelter, heat

D. Advanced age

E. Associated with near-drowning body heat lost more quickly in water

F. Other causes

1. Windy conditions

2. Trauma, especially spinal cord injury

3. Traumatic resuscitation

4. Sepsis

5. Alcohol ingestion

6. Certain medications

7. Skin wounds associated with burns

8. Immaturity of temperature regulatory system and ineffective thermoregulation

mild hypothermia clinical manifestations

A. Mild hypothermia (32-35C [90-95F])

1. Fatigue

2. Slurred speech

3. Poor coordination and clumsiness

4. Confusion and poor judgment

5. Inappropriate behavior

6. Shivering

7. Tachycardia and tachypnea

moderate hypothermia clinical manifestations

B. Moderate hypothermia (28-32C [82-90F])

1. Depressed mental status

2. No shivering

3. Depressed respirations

4. Slow pulse or irregular heartbeat

5. Low blood pressure

6. Pale or cyanotic color

7. Hallucinations

8. Coma

severe hypothermia clinical manifestations

C. Severe hypothermia (body temperature below 28C [82-90F])

1. Absence of respirations and pulse

2. Ventricular fibrillation

3. Dilated and unresponsive pupils

4. Coma

when rewarming from frostbite...

bedrest with affected body part elevated

severe hypothermia treatments

E. Severe hypothermia

1. Hemodialysis, peritoneal dialysis, colonic irrigation to increase core body temperature

2. Used when hypothermia is result of damage to hypothalamus, due to trauma, stroke

3. Damage may make return of thermoregulation physiologically impossible

Diagnostic Tests

A. Used to assess effects, for infection, coagulopathy, rhabdomyolysis

B. Serum electrolytes

C. Renal function

D. Serum glucose

E. CBC

F. Metabolic panel

G. Cardiac enzymes

H. Electrocardiogram

I. Arterial blood gases (ABGs)

J. Coagulation studies

K. Creatine kinase

Circulatory Management

A. Airway management, support of respiratory status

B. CPR may be required

C. Cardiac monitoring for arrhythmias

hypothermia in infants

A. Large body surface area in relation to mass

B. Limited insulating subcutaneous fat

1. Loses 4 times more heat than adult

2. After birth dried losses from radiation, convection

C. Thermal conduction

1. Marked difference between core and skin temperature

2. Responds to cool environment with peripheral vasoconstriction not entirely effective

D. Physiologic mechanisms that increase heat production thermogenesis

1. Increased metabolic rate

2. Muscular activity

3. Nonshivering thermogenesis (NST)

E. Shivering—rare in newborn

F. Shivering means metabolic rate already doubled

G. Muscular activity does little to produce heat

H. Increased basal metabolism increases oxygen consumption

I. Decreased environmental temperature of 2C from 33 to 31C doubles oxygen consumption

J. Keeping newborn warm promotes normal oxygen requirements chilling can cause signs of respiratory distress in newborn

nonshivering thermogenesis (NST)

a. Unique to newborns

b. Skin receptors perceive drop in environmental temperature transmit sensations to stimulate sympathetic nervous system

c. Uses brown adipose tissues (BAT)

Hypothermia in Older Adults

A. Increased risk because unable to maintain constant internal temperature

B. More sensitive to variations in environmental temperature decreased thermoregulatory control, loss of subcutaneous fat, environmental factors

C. Illness, central nervous system (CNS) disorder impair thermostatic function of hypothalamus

D. Extremely dangerous because of lack of physiologic reserves

E. Treatment similar to other age groups

physical assessment for hypothermia

1. Lowered body temperature below normal range

2. Cool skin

3. Cyanotic nail beds due to vasoconstriction

4. Pallor

5. Piloerection (goosebumps)

6. Shivering or no shivering

7. Slowed capillary refill

8. Tachycardia

9. Weak pulse