118 - Pyrexia Flashcards
What is the febrile response?
Complex physiological response pyrogen mediated
- involves cytokines, acute phase reactants, endocrine and behavioural changes
What are the 4 phases of a fever?
1st) Prodromal: Non specific complaints, general malaise, aching
2nd) Chill: sensation of cold, shaking, vasoconstriction, piloerection. temp is actually increasing
3rd) Flush: Cutaneous dilation, skin warm and flushed
4th) Defevescence: Initiated by sweating
What are the 4 different patterns a fever can occur in?
Intermittent - returns to normal every 24hrs
Remittent - doesn’t return to normal
Sustained/continuous - Temp remains high
Recurring/relapsing - Episodes of fever lasting a few days with a day normal inbetween
How does HR and metabolic rate change with increased temperature?
1 degree temp increase, 15 beats/min increase HR
1 degree increase - 13% increase in metabolic rate
What alternative causes of a high temperature are there?
Hyperthermia
Malignant hyperthermia
Drug fever
Neuroleptic malignant hyperthermia
What do most cases of PUO (pyrexia of unknown origin) end up beign diagnosed as?
30% infection
20% malignancy
20% misc. (IBD, liver disease, drug reaction)
15% connective tissue disorder
What is defined as PUO?
Consistently high temp above 38.3 for 3 weeks of illness, with no diagnoses after 3 days as an inpatient or 3 outpatient consultations.
How is best to manage a fever?
Actively search cause
Reassure
Lightly clothed, cool, aid heat exchange
Don’t actively try to cool unless anti-pyretics given
Don’t give anti-pyretics just to reduce the temp!
Why is it sometimes viewed as a bad idea to treat fever with anti-pyretics?
Impairs natural immune response
May miss signs of serious infection
Doesn’t reduce febrile convulsions
Paracetamol may reduce antibody response
What ways are there to measure core temperature?
Rectal prove
Tympanic - in the ear
What ways are there to measure shell temperature?
Oral - 0.4 degrees lower than core
Axilla
- influenced by skin blood flow and environment, but non invasive and easy
What initiates fever?
Presentation of exogenous or endogenous pyrogens
Describe how fever is initiated and propagated
Pyrogens
- stimulates release of pyrogenic cytokines (IL-1, IL6, TNFalpha, Interferon)
- cytokine-receptor interactions occur at pre-optic region of hypothalmus
- Prostaglandin E2 released
- Modifies thermosensitive neurones
- Thermostatic set point changed
What prostaglandin modifies thermosensitive neurones in initiating fever?
E2
Which are pyrogenic cytokines?
Il-1, IL-6, TNF alpha, Interferon