Thermoregulation and pyrexia Flashcards
Pros and cons of shivering
Pros: Good short term way of raising body temperature to gain yourself a little extra time
Cons: Very metabolically expensive. So if you have pneumonia patient who already has low O2 levels, this can have adverse consequences
How is the skin blood flow vital for heat loss & conservation?
When hot: lots of blood rushes to the surface of our skin, resulting in heat loss
When cold: vasoconstriction of blood vessels diverts blood centrally, less goes to the skin and so we conserve heat
- ANS mediated (sympathetically)
Explain piloerection
Erector pili muscles, when stimulated, pull on the base of the hair root to get it to stand on end, creating a pocket of air between the hair and skin which acts as an insulator
- Sympathetically mediated
- Minimal efficacy
Neuroendocrine function of heat generation
Catecholamines increase general metabolic rate, contractility of muscles etc which generate heat as a byproduct
Thyroxine controls metabolic rate over a longer period. In normal states, it does not do much. In disease states (hyper/hypothyroidism), if a patient has hypothyroidism, they are at much higher risk of being admitted with hypothermia
- Always check thyroid levels in hypothermic patient to see if it is a contributing factor
Different means of heat loss
Conduction - 60%
Radiation - 25%
Evaporation - 15% (sweating)
What is hypothermia? Definition & temperature range Causes Clinical features Management
- Definition
- Core temperature of <35 degreesC
- Severe if <28 degreesC - Causes
- Hypothyroidism
- Behavioural (being in cold environment = most common cause)
- Dermatological - people with red skin conditions (psoriasis and eczema) and particularly when they get secondary infections, have very vasodilated skin and suffer greater heat loss - Clinical features
- Confusion
- Coma
- Cardiovascular relapse - susceptible to ventricular arrhythmias, but you have to warm the patient up before using a defibrillator. - Management
- Aluminium foil sheet
- ABC = airway, breathing (adequate breathing), circulation (normalised BP and HR)
- Controlled warming = you don’t want a 27 degreeC patient to be immediately heated up to 37 as it will cause cardiovascular instability, making them prone to arrhythmias and their BP will plummet, this is why we use a warming blanket or cardiopulmonary bypass machine in more severe cases
What is hyperthermia? Definition & temperature range Causes Clinical features Management
- Definition
- Temp of greater than 38 degreesC
- Life-threatening if >40 degreesC - Causes
- Exertional
- Situational
- Drugs
- Pyrexia - Clinical features
- Confusion
- Seizures
- Coma
- Cardiovascular collapse - Management
- Cooling the person down with cold spray & removing excess clothing
- Cold ice water bath
- Giving fluids
Explain the process of pyrexia
- Start with normal set point
- Suddenly get viraemia AKA cold
- Body reacts to this by making pyrogens which alter the hypothalamus’ set point value to a higher level
- The body now thinks it is colder than it wants to be, so it causes chills to increase temperature (vasoconstriction, epinephrine for metabolic components, piloerection and shivering)
- After a few hours, viraemia will stop and the hypothalamus is returned to normal set point value, whilst the body is still at 39. So you want to lose heat rapidly, this is done by sweating.
Causes of pyrexia
- Infection
- Blood transfusion / iatrogenic pyrogens
- Inflammation
- Malignancy - lots of cells dividing faster than normal, being metabolically active.
- Hypothalamic insults
Treatment of pyrexia
- Glucocorticoids/anti-inflammatory steroids will inhibit phospholipase A2 which normally breaks down phospholipids and catalyses the arachidonic acid pathway (prostaglandin - pyrogenic effect)
Most common pyrogens
Endotoxins which are lipopolysaccharides produced by G-ve bacteria such as E.coli