Fever Flashcards
Best approximation of core temp
RECTAL or esophageal
(oral and axillary are lower)
Normal core temperature range
35.6 to 38.5
Fever is an increase in core temperature due to a …
change of the hypothalamic setpoint
A fever is rarely over…
41.1
Hyperthermia is due to an…
overriding of the set point (temp can be >41.5) - elevation of body core temperature above normal range due to failure of thermoregulation (no change in hypothalamic set point)
Hyperpyrexia
Extreme high fever over 41.5 (rare)
How our body increases temperature
- Vasoconstriction
- Shivering
- Piloerection
- Increased thermogenesis in brown fat
- Behavioural changes (decreased physical activity)
How our body decreases temperature
- Vasodilation
- Insensible losses (evaporation)
- Sweating
- Behavioural changes (increased physical activity)
Causes of hyperthermia (4)
- Environmental heat and humidity
- Exertion
- Endocrine (thryotoxicosis i.e. too much thyroid hormone)
- Drugs (anesthetics)
Proteins that relay signals between cells
cytokines
Pathogenesis of fever
- Immune cells (macrophages, monocytes, neutrophils) have a type of PRR call TLR.
- TLRs bind PAMPs and DAMPs
- Activation of NF-kB
- NF-kB stimulates the production of pro-inflammatory cytokines
What are NOD receptors?
They are PRRs inside the cytoplasm of cells
What cytokines are secreted under the influence of NFkB?
- IL-1 beta
- TNF-alpha
- IFN-alpha and gamma
Secretion of IL1-beta, TNF-alpha, IFN-alpha and gamma triggers production of…
IL-6
IL-6 role in inflammaion and fever
- Acts directly on the liver to upregulate inflammatory molecules (CRP)
- Stimulates the vagus nerve peripherally. This nerve connects to the hypothalamus, and causes it to change its setpoint
3 cytokines that are increased in the serum during fever
IL-1, TNF-alpha, IL-6
Other than production of IL-6, TNF-a and IL-1 stimulate…
COX-2 which results in increased levels of prostaglandins, especially PGE2, which plays a key role in inducing fever
What accounts for the muscle aches and malaise which accompany fever?
PGE2 production peripherally
What is the role of PGE2 in fever?
It is the final mediator! (note that it is not involved in normal thermoregulation, only abnormal thermoregulation)
Neurologic damage from fever is only really a concern if…
the patient already has an underlying brain injury
