Thermoregulation Flashcards
Thermoregulation
The process of maintaining the core body temperature at a nearly constant value
What does body temperature below 36 C or above 40 C cause
Disorientation
Body temperature above 42 C causes?
Convulsions and permanent cell damage
Normothermia
Normal body temperature 36.5-37.2
Hypothermia
Body temperature below 36.2
Hyperthermia
Body temperature above 37.6
Hyperpyrexia
Extremely high body temperature above 41.5
Fever
Elevation in body temperature due to a change in the hypothetical set point
Temporary resetting of the hypothalamic thermostat
Temperature regulation varies in response to :
Location Activity Environment Circadian Rhythm Gender
Heat production and conservation mechanisms
- Chemical reactions of metabolism
- Skeletal muscle contraction
- Chemical thermogenesis
- Vasoconstriction
- Shivering
- Voluntary mechanisms
Processes of heat transfer
Radiation
Convection
Conduction
Evaporation
Radiation
Objects warmer than environment lose heat as infrared radiation
Accounts for more than half of body’s heat loss
Conduction
Direct transfer of energy due to physical contact with cold object
Not very effective in gaining or losing heat
Convection
Heat loss to cooler air
Heat rises away from skin, cool air replaces it
Accounts for about 15% of body’s heat loss
Evaporation
Water changes from liquid to vapor as it evaporates
Absorbs energy and cools surface
Insensible perspiration from lungs and skins consistent
Accounts for about 20% of body’s heat loss
Sensible perspiration from sweat glands varies in rate
How is temperature regulation coordinated?
By the heat-loss centre and the heat gain centre
What pathways does the heat-loss centre use?
Parasympathetic pathways
Heat- gain centre uses which pathways
Sympathetic pathways
Populations at greatest risk for problems with thermoregulation are:
Very young persons
Very old persons
Poor persons
Persons living in very hot or cold climates
What damage can occur from hyperthermia
Nerve damage, coagulation of cell proteins and death
How can hyperthermia occur
Can be accidental, therapeutic or associated with stroke or head trauma
Thermoregulation Disorders - Hyperthermia
Fever
Heat stroke
Malignant Hyperthermia
Thermoregulation Disorders- Hypothermia
Frostbite
What happens when the Vasomotor centre is inhibited during hyperthermia?
Peripheral blood vessels dilate
Blood flows more to surface of the body
Increases heat loss by radiation and convection
What happens when the sweat glands are stimulated to increase secretions during hyperthermia?
Increases heat loss by evaporation
Limited capability in higher humidity environments
What happens when the respiratory system is stimulated during hyperthermia?
Increased respiratory depth and breathing more through mouth
Increased heat loss through evaporation from lungs
3 steps caused by hyperthermia
- Vasomotor center inhibited
- Sweat glands stimulated to increase secretions
- Respiratory centres stimulated
At what temperature does nerve damage produce convulsions in an adult?
41 degrees C
What temperature causes death
43 degrees C
What does fever activate?
Heat production and conservation measures to a new set point
What kind of pyrogens are associated with fever?
Exogenous and Endogenous
What is a central fever caused by
Trauma
What are the benefits of a fever?
Kills many micro-organisms
Decreases serum levels of iron, zinc and copper
Promotes lysosomal breakdown and auto destruction of cells
Increases lymphocytic transformation and phagocyte motility
Augments antiviral interferon production and phagocytosis
Pharmacotherapies for fever
Antipyretics
Acetaminophen
NSAIDS
What is the goal of pharmacotherapies used for fevers?
Lower body temperature, while treating the underlying cause of the infection
What is the drug of choice for treating fevers in children?
Acetaminophen
Action of Acetaminophen (Tylenol)
Inhibits synthesis of prostaglandins
Mild to moderate pain control
Antipyretic
Contraindications of Acetaminophen (Tylenol)
Known allergy Severe liver disease Genetic disease enzyme deficiency Chronic alcoholism Renal disease
Toxicity Symptoms of Acetaminophen (Tylenol)
Cyanosis Anemia Neutropenia CNS Stimualtion Delirium followed by vascular collapse Seizures Coma Death
Pharmacokinetics: Absorption of Acetaminophen (Tylenol)
Well absorbed after oral administration. Rectal absorption varies.
Pharmacokinetics: Distribution of Acetaminophen (Tylenol)
Widely distributed, crosses placenta and enters breast milk.
Pharmacokinetics: Metabolism of Acetaminophen (Tylenol)
By the liver, metabolites are excepted in the liver
Half life of Acetaminophen (Tylenol)
1-3 hours
Prostaglandins
Lipids that promote inflammation and are found in all tissues
Cyclooxygenase
Key enzymes in the biosynthesis of prostaglandins and have 2 forms
2 forms of cyclooxygenase
Cyclooxygenase-1
Cyclooxygenase-2
Cyclooxygenase-1 Location
Present in all tissues
Cyclooxygenase-1 Functions
Protects gastric mucosa, supports kidney function, promotes platelet aggregation
Cyclooxygenase-1 Inhibition by medications
Undesirable: increases risk for gastric bleeding and kidney failure
Cyclooxygenase-2 Location
Present at sites of tissue injury
Cyclooxygenase-2 Functions
Mediates inflammation
Sensitizes pain receptors
Mediates fever in the brain
Cyclooxygenase-2 Inhibition by medications
Desireable: results in suppression of inflammation
Misoprostol
A prostaglandin like substance that inhibits gastric acid secretions and stimulates the production of protective mucous
When is misoprostol usually used
used mostly when taking NSAIDS and glucocorticoids to prevent ulcers
What does misoprostol prevent
GI bleeds
What does a synthetic prostaglandin E1 analogue do?
inhibits gastric acid secretion and has a cytoprotective component
NSAIDS
A large and chemically diverse group of drugs that have: Analgesic activities Anti-inflammatory activities Antipyretic activities Aspirin-platelet inhibition
What are properties that all NSAIDS share?
Antipyretic properties
Analgesic properties
Anti-inflammatory properties
NSAIDS are used to relief
Mild to moderate headaches Myalgia Neuralgia Arthralgia Postoperative pain treatment of gout and hyperuricemia
NSAIDS help with pain that is associated with…
Arthritic disorders like rheumatoid arthritis, juvenile arthritis, ankylosing spondylitis, and osteoarthritis
NSAIDS mechanisms of action
Inhibit cyclooxygenase thus blocking inflammation
Blocking the chemical activity of the enzyme Cyclooxygenase
NSAIDS inhibit which pathways?
Leukotriene pathway, prostaglandin pathway or both
What is the drug of choice for mild to moderate pain, inflammation and fever
NSAIDS
Ibuprofen (Advil, Motrin) Action
Inhibits cyclooxygenase-1 and cyclooxygenase-2 thus decreases inflammation
Ibuprofen (Advil, Motrin) Dosage
Administered orally
200-400mg PO q6h
Ibuprofen (Advil, Motrin) uses
Mild to moderate pain in acute or chronic disorder
Ibuprofen (Advil, Motrin) Adverse effects
Headache
Dizziness
GI upset
Nephrotoxicity
NSAIDS Contraindications
Known drug allergy Conditions that place the patient at risk for bleeding Rhinitis Vitamin K deficiency Peptic ulcer disease
NSAIDS Adverse effects
Heartburn to severe GI bleeding Acute kidney injury Noncardiogenic pulmonary edema Altered hemostasis hepatotoxicity Skin eruption, sensitivity hearing Tinnitus, hearing loss
NSAIDS nursing considerations
Take with food or milk
Avoid alcohol
Assess for bleeding disorders/ GI bleed
Obtain baseline liver and renal function tests
Do not give to children
Consult with health care provider before taking herbal products
Use NSAIDS with care in which clients
Clients with alcoholism, CHF, Renal disease, hypertension, and fluid retention
How long does it take NSAIDS to reach optimal effects
1-3 weeks
Heatstroke
Potentially lethal result of an overstressed thermoregulatory centre
What temperatures can the brain not tolerate
40.5 degrees C and over
What happens when the body’s temperature exceeds 40 degrees C?
Regulatory centre stops functioning and the body’s heat loss mechanism fails
Cardiovascular and thermoregulatory centres may stop functioning
Causes of heatstroke
Exertion
Overexposure to heat
Impaired physiological mechanism for heat loss
Heatstroke Symptoms
High core temperature Absence of sweating Tachycardia Confusion Agitation Coma
Heatstroke Complications
Cerebral edema Degeneration of the CNS Swollen dendrites Renal tubular necrosis Hepatic failure Death
Heat Cramps
Severe spasmodic cramps in the abdomen and extremities
Following prolonged sweating and associated sodium loss
Who are heat cramps more common in
Individuals not accustomed to heat or those performing strenuous work in warm climates
Symptoms of heat cramps
Fever
Rapid pulse
Increased BP
Heat exhaustion
Result of prolonged high core temperatures
Profound vasodilation and profuse sweating
Manifestations of Heat Exhaustion
Dizziness Weakness Nausea Confusion Syncope
Malignant Hyperthermia
A potentially lethal hypermetabolic complication of a rare inherited muscle disorder that may be triggered by inhaled anaesthetics & depolarizing muscle relaxants.
What happens to the muscles in malignant hyperthermia
Muscle cells have an unregulated accumulation of calcium
Muscles contract and stiffen at the same time
Uncoordinated muscle contractions
Symptoms of Malignant hyperthermia
Absent reflexes
Fixed pupils
Apnea
Flat ECG
Risk factors for malignant hyperthermia
Genetic
History of heat stroke or hyperthermia after exercise
Muscle abnormalities that may be associated with malignant hyperthermia
Diagnosis Malignant hyperthermia
Genetic testing
Muscle biopsy
Expected duration of malignant hyperthermia
With timely treatment resolution of symptoms should occur within 12-24 hours
Clinical manifestations of Malignant hyperthermia
Altered calcium function in muscle cells with hyper metabolism Hyperthermia Uncoordinated muscle contractions Increased muscle work Increased oxygen consumption Raised level of lactic acid production Acidosis Rapid or painful muscles, especially in jaw Sweating Tachycardia Tachypnea Brown coloured urine Shock
Malignant hyperthermia treatment
Stop giving triggering medication Administer Dantrolene (Dantrium) Lower body temperature Administer oxygen Medicate to control heartbeat, BP and correct electrolyte imbalances
Use of Dantrolene (Dantrium)
Relaxes muscles and stops the increase in muscle metabolism
Given IV until stability is achieved, then continued PO for 3 days
Intervention strategies for hyperthermia
Remove excess clothing and blankets Provide external cool packs Provide a cooling blanket Hydrate with cool fluids Lavage with cool fluids Administer antipyretic drug therapy
Hypothermia
When body temperature falls below acceptable levels
How does the body prevent Hypothermia
heat-loss centre is inhibited and heat gain centre is activated
Steps of heat gain centre
- Stimulate vasometer centre
- Shivering thermogenesis
- Nonshivering thermogenesis
Stimulation of gasometer centre does what
Constricts peripheral blood vessels, reducing heat loss by radiation, convection and conduction
Shivering thermogenesis does what
Activates brief contractions of skeletal muscles
Nonshivering thermogenesis is stimulated how
Hormonally
Thyroid hormones and epinephrine increases metabolic activity of all tissues
Hypothermia produces
Ice crystals, which form inside the cells, causing them to rupture and die
Tissue hypothermia
Slows the rate of cellular metabolism
Increases blood viscosity and slows blood through the microcirculation
Facilitates blood coagulation and stimulates vasoconstriction
Hypothermia Response Mechanisms
Peripheral vasoconstriction
Intermittent repurfusion of extremities
shivering
Stupor
Peripheral Vasoconstriction
Shunts blood away from cooler skin to core to decrease heat loss and produces peripheral tissue ischemia
Intermittent reperfusion of extremities (Lewis Phenomenon)
Helps preserve peripheral oxygenation until core temps drop dramatically
Shivering
Induced by the hypothalamic centre
Thinking becomes sluggish
Coordination is depressed
Stupor
Heart & respiratory rate decline Cardiac output diminishes Metabolic rate falls Acidosis Eventually V fib & asystole occur at 30 degrees C
Therapeutic Hypothermia
Used to slow metabolism and preserve ischemic tissue during surgery or limb re-implantation
May lead to ventricular fibrillation and cardiac arrest
Accidental Hypothermia
Commonly the result of sudden immersion in cold water or prolonged exposure to cold
Hypothermia Risk factors
Hypothyroidism Hypopitutarism Malnutrition Parkinson's Disease Rheumatoid arthritis Chronic increased vasodilation Failure of thermoregulatory control resulting from cerebral injury, ketoacidosis, uremia, sepsis, and drug overdose
Hypothermia treatment
Reversible with rewarming
Hypothermic Injuries
Frost nip
Chilblains
Frostbite
Flash freeze
Frostnip
Mild and completely reversible injury characterized by skin pallor and numbness
Chilblains
More serious than frosting; violaceous skin colour with plaques or nodules, pain, and pruritus, but no ice crystal formation; chronic vasculitis can develop and is usually located on the face, anterior lower leg, hands, and feet
Frostbite
Tissues freeze and form ice crystals at temperature less than -2 degrees C progresses from distal to proximal and potentially reversible
Flash Freeze
Rapid cooling with intracellelular ice crystals associated with contact with cold metals or volatile liquids
What happens to frozen skin?
Becomes white or yellowish, has a waxy texture
What parts of the body does frostbite commonly affect
Fingers, toes, ears, nose and cheeks
First degree frost bite
Partial skin freezing
Second degree Frost bite
Full thickness skin freezing
Third degree Frost bite
Full thickness & subcutaneous freezing
Fourth degree frost bite
Deep tissue freezing
Intervention strategies for hypothermia
Remove person from cold
Provide external warming measures
Provide internal warming measures
Safety tip for core warming
Core rewarming must be done slowly to minimize the risk for dysthymias. Cardiac monitoring is required when the patient is recovering from severe hypothermia.
CNS trauma leads to…
Central fever
Inflammation, increased ICP, inter cranial bleeding
Does not induce sweating
Resistant to antipyretic therapy
Central fever
Sustained noninfectious fever Appears with or without bradycardia Caused by major body trauma Does not induce sweating Resistant to antipyretic therapy
