hyperthermia/fever Flashcards
where is the thermoregulatory center located?
central nervous system in preoptic area of anterior hypothalamus
what is responsible for sensing the changes in ambient and core body temperatures (hint: these things relay information to the anterior hypothalamus via the CNS)
peripheral and central thermoreceptors
when ambient temperatures are normal, what is responsible for the body’s main source of heat?
muscles
definition of hyperthermia?
any elevation in core body temperature above accepted normal range
definition of fever?
hyperthermic animals in whom the set point in the AH has been reset to higher temperature
t/f: true fever is a normal response of the body to invasion or injury and is part of the acute phase response?
true
list other parts of the acute phase response besides fever
increased neutrophil numbers and phagocytosis
enhanced T and B lymphocyte activity
increased acute phase protein production by liver
increased fibroblast activity
increased sleep
what is responsible for initiating the acute phase response in fever? list some examples
exogenous pyrogens- infectious agents or their products, immune complex formation, tissue inflammation or necrosis, pharmacologic agents
what are the 4 different classifications of hyperthermia and give at least 1 example of each?
true fever- production of endogenous or exogenous pyrogens
inadequate heat dissipation- heat stroke, hyperpyrexic syndromes
exercise-induced hyperthermia- normal exercise, hypocalcemic tetany, seizures
pathologic or pharmacologic origin- lesions around anterior hypothalamus, maligant hyperthermia, hypermetabolic disorders, monoamine metabolism disturbances
what are the primary immune cells involved in endogenous pyrogen production?
macrophages
List the 11 endogenous pyrogens and their principal source
TNF-a (cachectin)-macrophages
TNF-b (lymphotoxin)- lymphocytes (T and B)
IL-1a- macrophages etc
IL-1b - macrophages, etc
IFNa- leukocytes, espec macrophages
IFNb- fibroblasts
IFNy- T lymphocytes
IL6- many cell types
macrophages inflammatory protein 1a- macrophages
macrophage inflammatory protein 1b- macrophages
IL8- macrophages
list examples of bacterial exogenous pyrogens
gram positive and gram negative bacteria
list examples of bacterial products that cause exogenous pyrogen production
LPS, streptococcal exotoxin, staph enterotoxin, staph proteins
fungi that cause pyrogen production?
fungal products, crypto polysaccharide, crypto proteins
nonmicrobial agents that can cause exogenous pyrogen release
soluble Ag-Ab complexes
bile acids
pharmacologic agents
tissue inflammation and necrosis
list the mechanisms for heat loss
radiation
conduction
convection
evaporation
describe radiation as a mechanism for heat loss
electromagnetic or heat exchange between objects in the environment
describe conduction as a mechanism for heat loss
between the body and environmental objects that are in direct contact with the skin, as determined by the relative temperatures and gradients
describe convection as a mechanism of heat loss
the movement of fluid, air, or water over the surface of the body
describe evaporation as a mechanism of heat loss
disruption of heat by the energy required to convert the material from a liquid to a gas, as with panting
Which of the following is not recommended for total body cooling of the heat stroke patient (in this chapter) ;) ? A- IVF therapy B- tepid water baths C- ice water bath D- placing fan near animals
C
Cooling should be discontinued in a heat stroke patient at what temp?
103 F
heat stroke is a result of what?
inadequate heat dissipation
hyperpyrexic syndrome is associated with what?
moderate to severe exercise and a hot/humid climate
list the cooling options for a hyperthermic patient
oxygen and IV fluid therapy
surface cooling techniques
internal cooling techniques
extracorporeal techniques (antipyretic drugs)
examples of surface cooling techniques?
clip fur
tepid water applied to skin/body
fan
ice packs over areas with large vessels (neck, axilla, inguinal)
examples of internal cooling techniques?
rectal admin of cool isotonic fluids
gastric lavage
open body cavity
peritoneal dialysis
examples of antipyretic drugs?
antiprostaglandins, dantrolene, dipyrone, aminoyrine, cox2 inhibitors, glucocorticoids, other NSAIDs
name 2 endocrine disorders that can cause increased metabolic rate, vasoconstriction resulting in excessive heat production, decreased ability to dissipate heat?
hyperthyroidism and pheochromocytoma
what is the mechanism of malignant hyperthermia?
disturbed calcium metabolism initiated by pharmacologic agents such as inhalation anesthetics (halothane) and muscle relaxants (succinylcholine) can cause myopathy and subsequent metabolic heat production
how may phenothiazines be effective in alleviating true fever?
depressing normal thermoregulation and causing peripheral vasodilation
list common causes of noninfectious fever in ICU patients
phlebitis, thrombophlebitis, post-operative inflammation, transfusion reactions, pancreatitis, hepatitis, cholecystitis, aspiration pneumonitis, ARDS, neoplasia
what is the suspected incidence of nosocomial infections in critically ill human patients?
3-31%
common sites for nosocomial infections in critically ill?
lungs (aspiration, VAP), bloodstream, catheters, incisions, urinary tract
what are the benefits of a fever?
decreases ability of bacteria to use iron, decreases ability of viruses to replicate, increased leukocyte function
detriments to having a fever?
increases tissue metabolism and O2 consumption; raises caloric and water requirements, supression in appetite center; may lead to DIC, arrhythmias, liver complications, GI signs
exertional heat stroke and malignant hyperthermia may lead to….
rhabdomyolysis, hyperK, hypoCa, myoglobinemia, myoglobinuria, increased CK
body temp >107 F may lead to what specific GI complications
epithelial desquamation, endotoxin absorption, bleeding
