Fever Flashcards
What is the difference between fever and hyperthermia?
Fever is regulated by the hypothalamus in response to pyrogens resulting in rise of core temperature to >=37.8 degrees
NOTE: Fever needs to be qualified in notes
Hyperthermia is not regulated by the hypothalamus and is an uncontrolled body temperature rise
What is hyperpyrexia?
Extraordinarily high fever >=41.5
Type of hyperthermia
What is the normal body temperature and how is this regulated during the day?
36.8 +/- 0.8
Heat generated by metabolically active cells and lost from conduction, convection, radiation and evaporation
Hypothalamus tightly regulates core temperature at thermal setpoint
What components of the brain are involved in neurological thermoregulation?
Rostral hypothalamus (pre-optic area)
Limbic system + brain stem
What is fever?
Elevation of core body temperature above the daily range for an individual i.e. not shell temperature
Abnormal temperature= 37.8 degrees
What causes hyperthermia?
Loss of thermoregulatory compensatory mechanisms due to:
-heat stroke syndromes
-metabolic diseases
(Thyrotoxic storm/phaeochromocytoma/DKA)
-pharmacological agents
(Atropine/certain anaesthetics/neuroleptic malignant syndrome/serotonin syndrome)
-neurological injury
(Brain haemorrhage/hypothalamic stroke/status epilepticus)
Hypothalamic set-point remains the same
How can atropine cause hyperthermia?
Inhibits sweat production meaning there is a loss of compensatory mechanisms to control body temperature
How could identify someone with neuroleptic malignant syndrome?
Recently started on anti-psychotics
Autonomic dysfunction
What can cause serotonin syndrome?
Cocaine NDMA Amphetamines TCAs SSRIs MAOI Lithium
How can you measure the core temperature? What are the potential problems with some of these routes?
Mouth
-can be affected by cold/warm drinks or foods
Rectum
- has large arterial supply so can be considered representative of core temp
- can give false low reading if patient in shock
Oesophagus
- close to core
- used in intensive care with hyperthermic
Tympanic membrane
-very reliable method
What are pyrogens? What are the 2 different causes?
Anything that causes a fever
Exogenous:
- outside of host
- microbes and their products
Endogenous:
-host-derived biologically active proteins = pyrogenic cytokines
What are the different exogenous pyrogens?
bacterial exotoxins
Eg TSST-1 toxin in Staph A + toxic shock syndrome
Eg Shiga toxin in shigella spp.
Bacterial endotoxins Eg Lipopolysaccharide (LPS) on gram -ve enterobacteriaceae
Viral infection i.e. influenza and RSV
Fungal elements
Are gram +ve or -ve more pyrogenic? Why?
Gram -ve due to LPS on cell wall acting as an exogenous pyrogen to drive pyrexia due to being bacterial endotoxins
What are the different endogenous pyrogens?
TLRs activation leads to production of pyrogenic cytokines such as IL-1, IL-6 and TNF
How is prostaglandin E2 involved in thermostat control?
Increased PGE2 in hypothalamic tissue and 3rd ventricle during a fever
Causes neurontransmission via cAMP (not NTM in own right)
What are the stages of developing a fever?
Infectious agent (i.e. bacterial endo/exotoxins or viral RNA) OR damaged tissue act as TLR-ligands for dendritic cells and macrophages
Pyrogenic cytokines produced which enter the systemic circulation
Reach endothelium reticulum which causes an increase in PGE2
PGE2 induces fever via cAMP neurotransmitter and vasomotor centre
What factors can affect the process of fever development?
Host genetic deficiencies
AI treatment i.e. Glucorticoids or Anti-IL-1 (anakinra) or Anti-TNF (infliximab)
Cytokine disease and non-infection fever
I.e lymphoma/leukaemia/systemic vasculitis
Brain injury
I.e. hypothalamic stroke/haemorrhage/status epilepticus
Use of anti-pyrexics
I.e. paracetamol/aspirin/NSAIDs
Why might a person on infliximab not present with the classic signs of fever?
acts as an anti-TNF which is the one of the major pyrogenic cytokines which drive the process of fever
Therefore can have infection without the presentation of a fever
What are the most common causes of fever in the returned traveller?
Pathogens endemic to other parts of the world i.e. malaria
Worldwide pathogens acquired by chance when travelling +/- added risk of drug-resistance i.e. primary EBV
What is the criteria for pyrexia of unknown origin?
Fever >= 37.8 on several occasions
Duration of fever >= 21 days
Uncertain diagnosis after 1 week of investigations in hospital
What are the 3 general classifications of PUO?
infections
Malginancies
Systemic rheumatic diseases
What conditions should you be worried about if a traveller returns with a fever?
Falciparum malaria
Leptospirosis
Viral haemorrhagic fevers (VHF)
What are the main areas which need to be assessed for risk of exposure with a returning traveller? Why is it important to ask about when the person travelled?
When and where they travelled
Activities whilst there i.e. animal or water contact, new sexual partner etc
Protection i.e. DEET
Immunity i.e. vaccination history or history of previous infection
It can be used to determine the possible incubation period which can indicate or exclude certain viruses
Eg. Falciparum malaria should have presented w/i 6 months
How might a person suffering from falciparum malaria present?
Impaired consciousness and seizures Renal impairement Hypoglycaemia Pulmonary oedema or ARDS Low Hb Spontaneous bleeding Shock Haemoglobinuria
How might a person with Middle East Respiratory syndrome present?
Severe respiratory infection
Symptoms of fever
Evidence of pulmonary parenchyma disease
History of contact with another known MERS-Cov infected person or been to area of high risk
