La fièvre Flashcards
How much does temperature vary daily?
0.5C during the day according to the circadian rhythm
What is the normal body temperature?
36.8C ± 0.4C
Men: 36.7C
Women: 36.9C
What does temperature vary according to?
Moment in the day, sex, age, where temperature is taken, exercise, menstrual cycle, medication, digestion, certain diseases/illnesses
What is “nadir” and “pic” de température?
Nadir: 37.2C buccale (lowest at 6h00)
Pic: 37.7C buccale (highest at 16h00-18h00)
La température rectale est d’environ 0.6C (0.4-0.6C) supérieure à la température buccale
What temperature do you need to have to have a fever?
Donc la fièvre (buccale) est toute température supérieure à 37.2C tôt le matin ou supérieure à 37.7oC à tout moment durant la journée
Une température rectale supérieure à 37.8oC le matin ou 38.3C à tout moment dans la journée = fièvre
What are the two main corporal temperatures?
Centrale (core): viscera and muscles
Peripheral (shell): skin and sub-cutaneous tissue
Where can core temperature be measured?
Right atrium, esophagus, bladder, eardrum
- La membrane tympanique est perfusée par une artère tributaire de celle qui irrigue l’hypothalamus
- They used to think that rectal temperature was accurate but actually it is higher than core temperature
- Buccal is reliable but easily altered by food/drinks
What are the advantages of infrared thermometers?
- contact free —> minimize infection transmission
- easy to use and disinfect
- fast
What are some limitations of infrared thermometers?
- Technique used can alter the measurement
- Need to be < 1m away to take the temperature
- Need quite specific conditions to assure that reading isn’t messed with (no direct sun, no hats, weather, etc.)
What is a fever?
Elevation of corporal temperature due to a signal from the hypothalamus in response to the presence of pyrogens
Circadian rhythm is preserved
Responds to treatment with antipyretics
What is hyperthermia?
Elevation of corporal temperature NOT controlled by the hypothalamus (dépassement de la capacité du corps à perdre de la chaleur)
- Circadian rhythm no longer detectable
- Does not respond to antipyretics
- Ex: coup de chaleur, hyperthyroïdie, prise de substances ou d’agents pharmacologiques qui interfèrent avec la thermorégulation (hyperthermie maligne, syndrome neuroleptique malin, syndrome sérotoninergique)
What is hyperpyrexia?
Corporal temperature is very high… usually superior to 41.5C
- Usually caused by a severe infection or brain haemorrhage
- Can partially respond to antipyretics
What is thermoregulation?
The ensemble of mechanisms that allow an organism to maintain their ideal temperature to best perform necessary biochemical rxns
What is central temperature?
Balance between production de chaleur (thermogénèse) et la perte de chaleur (thermolyse)
What part of the brain controls corporal temperature?
Anterior hypothalamus (pre-optic region)
What are pyrogens?
Substances that can modify temperature regulation (hypothalamus) and cause fever
What are the two kinds of pyrogens?
- Exogen
- Cytokines (used to be called endogen)
What are “pyrogènes exogènes”?
Substances étrangères à l’organisme (pathogens)
- ex: bacteria, viruses, microbes, and their products
- for example, bacterial endotoxins (LPS) from GN bacteria —> bind to TLR on leukocytes which activate cytokine production —> fever
What are some examples of “pyrogènes exogènes”?
- La toxine TSST-1 du Staphylococcus aureus qui cause le syndrome du choc toxique
- Autres entérotoxines du Staphylococcus aureus
- Exotoxines du Streptococcus de groupe A
What are “cytokines pyrogènes”?
Small proteins that regulate immunity, inflammation, and erythropoiesis —> usually not detectable in healthy pts
Certain cytokines are pyrogenic and are produced by cells after the activation of TLR (monocytes, macrophages, neutrophiles, lymphocytes)
Cytokines —> synthesis of PGE2 in the hypothalamus
- en périphérie: c’est ce qui cause les myalgies et les arthralgies chez les personnes fébriles
What are some examples of “cytokines pyrogènes”?
- Interleukin-1 (IL-1)
- Interleukin-6 (IL-6)
- Tumor necrosis factor-alpha (TNF-⍺)
- Ciliary neurotropic factor (CNF)
- Interferon-gamma (IFN-ɣ)
What is the pathogenesis of fever? (2 ways)
two ways:
- exogenic pyrogen —> TLR on WBCs —> produce cytokines —> systemic circulation to epithelium of hypothalamus —> production of PGE2 —> increase temperature —> neurons in vasomotor center —> production and conservation of heat by different organs/muscles —> fever
- exogenic pyrogen —> direct action on TLR —> systemic circulation to epithelium of hypothalamus —> production of PGE2 —> increase temperature —> neurons in vasomotor center —> production and conservation of heat by different organs/muscles —> fever
Where else does the thermoregulation center send signals?
Cerebral cortex —> change positioning and behaviour to favour production/conservation of heat
Produce heat: contract muscles
Conserve heat: move to warmer area, more clothing, huddle together, change posture
What is the pathogenesis of lowering temperature?
exogenic pyrogens disappear —> cytokines no longer produced —> no more PGE2 —> thermoregulation center “sets” temp back to normal —> stop production of heat and increase processes that help you lose heat
How: Peripheral vasodilation —> inc. heat loss, sweating, taking off clothing, move to colder place, open window/AC
What is the “réponse de phase aiguë”?
Différents stimuli peuvent induire une réponse de phase aiguë qui a pour but d’optimiser les défenses de l’organisme en modulant l’inflammation et la réparation des tissus
- Infection, trauma, cancer, brûlure, infarctus, arthropathies microcristallines et autres atteintes inflammatoires, accouchement, exercice important
Stimulates hepatocytes to produce proteins (IL-6 = principal stimulator)
What are PCR and PSAa?
PCR: protéine-C réactive —> binds to necrotic/damaged cells to eliminate them
PSAa: protéine sérum-amyloïde A —> increases chemiotactism of phagocytes
Why are fevers so physically demanding?
Increase O2 consumption
Increase caloric and fluid needs (dehydration)
For each 1C of temperature increase above 37C:
- O2 consumption increases by 13%
- HR increases by 4.4 BPM
Can cause psychological stress —> dim. brain function in fragile/older pts
Much harder to handle in pts with chronic illnesses or older in age
Fevers put your body into a catabolic state… how?
Dim. in glucose availability
Anorexia and lethargy —> dim. in food intake Increase muscle catabolism due to certain cytokines
Weight loss
What are the clinical manifestations of fevers? (7+1)
- frissons/tremblements
- malaise
- faibless généralisée
- céphalées myalgies
- arthralgies
- perte d’appétit
- déshydration
In children —> febrile seizures (usually benign)
What is an FUO?
Fever of unknown origin —> term often used even if not FUO according to dx criteria
- Fever > 38.3C on multiple occasions, for longer than 3 weeks
- Uncertain dx after week of investigation in the hospital but has been modified recently due to reflect modern medicine:
- 3 visits to doctor or 3 days in hospital
What is a “fièvre factice”?
Produced by patient using various strategies
Must be considered in ddx
What questions do you ask a febrile pt? (4 main)
- Depuis combien de temps s’est installée la fièvre?
- La fièvre a été mesurée à combien et comment?
- Quand survient la fièvre?
- Est-ce un premier épisode?
What epidemiological questions do you ask fever pts? (8)
- Lieu de naissance Lieu où le patient habite
- Voyages récents ou passés
- Travail
- Loisirs
- Alimentation
- Exposition à des animaux
- Contacts infectieux adultes et enfants (en contact avec gens qui ont sx similaires à la votre)
- Expositions sexuelles
Approche du patient fébrile:
Investigations depending on clinical presentation
“Bilan septique” usually done when nothing obvious from initial questioning
What is a “bilan septique”?
Formule sanguine complète, hémocultures x2, culture urine, culture d’autres sites, RdRx des poumons
Why are fevers treated?
- make more comfortable
- diminish oxygen demand in pts with pre-existing CV or pulmonary conditions
- avoid mental deterioration in fragile or older patients
On essaie d’éviter les grands écarts de température qui sont inconfortables
- frissons et frilosité lorsque la température monte
- sudations profuses lorsque la température baisse
What the 3 main antipyrétiques that can treat fevers?
- Acetaminophen
- Aspirin and other anti-inflammatories
- Corticosteroids (not used as antipyrétiques but can diminish fever)
What are some secondary effects of antipyretics?
Acetaminophen: overdose —> hepatitis rx
AINS: epigastric pain, ulcers in upper GI tract
Aspirin: Reye’s syndrome in children and adolescents
- Associated with aspirin usage to treat viral infections
- Encephalopathy and deterioration of “bilan hépatique” (stéatose microvésiculaire)
What are some complications of fevers? (4 main ones)
Febrile seizures —> mostly b/w 6mths-5yrs… usually benign
Aggravation of CV/pulmonary disease
Development of organic brain syndrome
Hyperpyrexia (41.5C) —> cerebral lesions and cardiac arrhythmias
