Fever Flashcards
hyperthermia
body overheats due to undesirable heat retention or overproduction of heat
caused by heat stroke, excitement, seizures, tremors, tetanus, adverse drug reactions, exercise
fever
exogenous or endogenous pyrogens stimulate the release of endogenous pyrogens by macrophages (IL-1, 6, TNF-a)
non-specific, adaptive/protective response
hyperthermia vs fever
hyperthermia: normal hypothalamic set point - tries to maintain normal temperature
fever: alters the hypothalamic set point
humoral mechanism of fever
endogenous pyrogens activate the arachidonic acid pathway in microglia –> increase PGE2 –> raises hypothalamic set point –> active generation and retention of heat
neuronal mechanism of fever
C5a stimulates PGE2 production in the liver –> signals hypothalamus via neuronal pathway using vagus nerve –> active generation and retention of heat
what are the ways that the body increases heat in both humoral and neuronal mechanisms
vasoconstriction
shivering
non-shivering thermogenesis
drug fever
increased body temperature due to drug induced alterations in muscle activity OR sensitivity of hypothalamic neurons to changes in body temperature
malignant hyperthermia syndrome
occurs in DOGS
autosomal dominant mutation of the ryanodine (RYR-1) receptor
causes excess intracellular Ca release in myocytes in presence of anesthetic agents
serotonin syndrome
medications can alter serotonin levels –> neuromuscular and hypothalamic effects
tramadol, antidepressants, antinausea
opioids induced fever
occurs in CATS
opioids interfere with hypothalamus causing unpredictable hyperthermia
excitement, excessive sedation, staring, hyperthermia
factors affecting fever
- age extremes
- renal failure
- immunosuppression
- anti-inflammatories
can fevers become maladapative
yes - only protective within a certain range
too high or prolonged - can be maladaptive
persistent fever
above normal temperature throughout the day
does not vary by more than 2F
remittent fever
above normal temperature throughout the day
varies by more than 2F (swings)
intermittent/relapsing fever
normothermic with periods of high fever
occurs with specific diseases (ex. borrelia)
low grade fever
<104F
indicates CHRONIC disease
high grade fever
> or = 104F
hyperpyrexia
> 106.7F
causes of fever - dogs
- immune mediated
- neoplasia (older)
- infectious (younger)
causes of fever - cats
almost always infectious
rare to have immune mediated
fever of unknown origin (FUO)
fever characterized by either:
1. 3 outpatient visits
2. 3 days in hospital without finding a cause of fever
3. one week of investigation without finding a cause
if unable to find a cause - consider immune mediated and neoplasia
localization of fever
- history
- PE - including eyes, skin, rectal, and musculoskeletal
- labs - CBC, chem, UA, aerobic urine culture, US
- imaging - thoracic and abdominal radiographs, AUS
- advanced labs - arthrocentesis, LN aspirates, blood cultures, serology, CSF
