Fever by Dr. Pandian M.

THIS PPT ONLY FIOR STUDY PURPOSE # MBBS#BDS#BPTH#ALLIED SCIENCES

1. Fever

2. Body Temperature Regulation
Thetemperaturewithinthedeeptissuesofthebody(core
temperature)isnormallymaintainedwithinarangeof
36.0°Cto37.5°C.
Withinthisrange,thereareindividualdifferencesand
diurnalvariations:
Internalcoretemperaturesreachtheirhighestpointin
lateafternoonandeveningandtheirlowestpointin
theearlymorninghours.
Bodytemperaturereflectsthedifferencebetweenheat
productionandheatloss.
Bodyheatisgeneratedinthetissuesofthebody,
transferredtotheskinsurfacebytheblood,andthen
releasedintotheenvironmentsurroundingthebody.

3. Body Temperature Regulation
Thethermoregulatorycenterisinthehypothalamusand
functionstomodifyheatproductionandheatlossesasa
meansofregulatingbodytemperature.
Thethermoregulatorycenterinthehypothalamus
regulatesthecorebodytemperature,notthesurface
temperature.
Thiscenterintegratesinputfromcoldandwarmthermal
receptorslocatedthroughoutthebodyandgenerates
outputresponsesthatconservebodyheatorincreaseits
dissipation=thermostaticsetpoint.
Whenbodytemperaturebeginstoriseabovethe
normalrange,heat-dissipatingbehaviorsareinitiated;
Whenthetemperaturefallsbelowthenormalrange,
heatproductionisincreased;
Acoretemperaturegreaterthan41°Corlessthan34°C
usuallyindicatesthatthebody’sabilitytothermoregulate
isimpaired.

4. Body Temperature Regulation -Heat
Gain
Mechanisminvolvedinregulation:
Vasoconstrictionofthesuperficialbloodvessels-confines
bloodflowtotheinnercoreofthebody;
Contractionofthepilomotormusclesthatsurroundthe
hairsontheskin-reducestheheatlosssurfaceoftheskin;
Assumptionofthehuddlepositionwiththeextremitiesheld
closetothebody-reducestheareaforheatloss;
Shivering-increasesheatproductionbythemuscles.Itis
initiatedbyimpulsesfromthehypothalamus;
Increasedproductionofepinephrine-increasestheheat
productionassociatedwithmetabolism;
Increasedproductionofthyroidhormone-isalong-term
mechanismthatincreasesmetabolismandheatproduction.

5. Body Temperature Regulation -Heat
Loss
Mechanisminvolvedinregulation:
Dilatationofthesuperficialbloodvessels-deliversblood
containingcoreheattotheperipherywhereitisdissipated
throughradiation,conduction,andconvection;
Therearenumerousarteriovenous(AV)shuntsundertheskin
surfacethatallowbloodtomovedirectlyfromthearterialto
thevenoussystem.
Whentheshuntsareopen,bodyheatisfreelydissipatedto
theskinandsurroundingenvironment;
Whentheshuntsareclosed,heatisretainedinthebody.
ThebloodflowintheAVshuntsiscontrolledalmost
exclusivelybythesympatheticnervoussysteminresponseto
changesincoretemperatureandenvironmentaltemperature
environment.
Sweating-increasesheatlossthroughevaporation.

6. Radiation
Radiationinvolvesthetransferofheatthroughtheair
oravacuum.
Heatfromthesuniscarriedbyradiation.Thehuman
bodyradiatesheatinalldirections.
Theabilitytodissipatebodyheatbyradiationdepends
onthetemperatureoftheenvironment.Environmental
temperaturemustbelessthanthatofthebodyfor
heatlosstooccur.

7. Conduction
Conductioninvolvesthedirecttransferofheatfrom
onemoleculetoanother.
Bloodcarries,orconducts,heatfromtheinnercoreof
thebodytotheskinsurface.
Theconductionofheattothebody’ssurfaceis
influencedbybloodvolume.
Inhotweather,thebodycompensatesby
increasingbloodvolumeasameansofdissipating
heat.
Exposuretocoldproducesacolddiuresisanda
reductioninbloodvolumeasameansof
controllingthetransferofheattothebody’s
surface.

8. Fever
Fever,orpyrexia,describesanelevationinbodytemperature
thatiscausedbyacytokine-inducedupwarddisplacementof
thesetpointofthehypothalamicthermoregulatorycenter.
Feversthatareregulatedbythehypothalamususuallydonot
riseabove41°C-safetymechanism.
Fevercanbecausedbyanumberofmicroorganismsand
substancesthatarecollectivelycalledpyrogens(manyproteins,
breakdownproductsofproteins,lipopolysaccharidetoxins
releasedfrombacterialcellmembranes,etc.).
Somepyrogenscanactdirectlyandimmediatelyonthe
hypothalamicthermoregulatorycentertoincreaseitsset
point.
Otherpyrogens,sometimescalledexogenouspyrogens,act
indirectlyandmayrequireseveralhourstoproducetheir
effect.

9. Causes of fever
Central type fever= neurogenic fever
Non –central type fever:
Infectious disorders
Noninfectious disorders:
Myocardial infarction
Pulmonary emboli
Neoplasms (e.g. malignant cells in leukemia,
Hodgkin’s disease produce pyrogens)
Trauma
Surgery

10. Neurogenic fever
Itusuallyiscausedbydamagetothehypothalamus
causedby:
centralnervoussystemtrauma;
intracerebralbleeding;
anincreaseinintracranialpressure
drugs(e.g.anesthetics)
Neurogenicfeversarecharacterizedbyahigh
temperaturethatisresistanttoantipyretictherapy
andisnotassociatedwithsweating.

11. Mechanisms of fever
(1)releaseofendogenouspyrogenfrominflammatory
cells;
(2)resettingofhypothalamusthermostaticsetpointto
ahigherlevel(prodrome);
(3)generationofhypothalamicmediatedresponses
thatraisebodytemperature(chill);
(4)developmentoffeverwithelevationofbodytonew
thermostaticsetpoint;
(5)productionoftemperatureloweringresponses
(flushanddefervescence)andreturnofbody
temperaturetoalowerlevel.

12. Mechanisms of fever
Exogenouspyrogensinducehostcells,suchasbloodleukocytes
andtissuemacrophages,toproducefever-producingmediators
calledendogenouspyrogens(e.g.,interleukin-1).
Theendogenouspyrogensmediateanumberofother
responses.Forexample,interleukin-1isaninflammatory
mediatorthatproducesothersignsofinflammation,suchas
leukocytosis,anorexia,andmalaise.
Thephagocytosisofbacteriaandbreakdownproductsof
bacteriathatarepresentinthebloodleadtothereleaseof
endogenouspyrogensintothecirculation.
Theendogenouspyrogensareincreasethesetpointofthe
hypothalamicthermoregulatorycenterthroughtheactionof
prostaglandinE2.
Inresponsetothesuddenincreaseinsetpoint,the
hypothalamusinitiatesheatproductionbehaviors(shiveringand
vasoconstriction)thatincreasethecorebodytemperaturetothe
newsetpoint,andfeverisestablished.

13. Mechanisms of fever

14. The effects of fever
Itenhanceimmunefunction;
Increasesmotilityandactivityofthewhitebloodcells;
Stimulatestheinterferonproductionandactivationof
Tcells;
Inhibitsgrowthofsomemicrobialagents:
Manyofthemicrobialagentsthatcauseinfection
growbestatnormalbodytemperatures,andtheir
growthisinhibitedbytemperaturesinthefeverrange
(therhinovirusesresponsibleforthecommoncoldare
culturedbestat33°C);
Dehydrationoccursbecauseofsweating.

15. The effects of fever
Metaboliceffects:
Increasedneedforoxygen;
Increasestheheartrate
Increasestherespirationrate
Increaseduseofbodyproteinsasanenergysource;
Duringfeverthebodyswitchesfromusingglucose(an
excellentmediumforbacterialgrowth)tometabolismbased
onproteinandfatbreakdown;
Withprolongedfever,thereisincreasedbreakdownof
endogenousfatstores;
Iffatbreakdownisrapid,metabolicacidosismayresult.

16. Types of fever
Intermittent
Temperaturereturnstonormalatleastonceevery24hours;
Itiscommonlyassociatedwithconditionssuchasgram-negative/
positivesepsis,abscesses,andacutebacterialendocarditis;
Remittent
Temperaturedoesnotreturntonormalandvariesafewdegreesin
eitherdirection;
Itisassociatedwithviralupperrespiratorytract,legionella,and
mycoplasmainfections;
Sustainedorcontinuous
Temperatureremainsabovenormalwithminimalvariations;
Itisseeninpersonswithdrugfever;
Relapsing
Thereisoneormoreepisodesoffever,eachaslongasseveraldays,
withoneormoredaysofnormaltemperaturebetweenepisodes;
Itmaybecausedbyavarietyofinfectiousdiseases,including
tuberculosis,fungalinfections,Lymedisease,andmalaria.

17. Manifestations of fever
Thereare4successivestages-notallpersonsproceedthroughthefour
stagesoffeverdevelopment:
1.Prodrome
nonspecificcomplaints,suchasmildheadacheandfatigue,
generalmalaise,andfleetingachesandpains;
2.Temperaturerises
generalizedshakingwithchillsandfeelingofbeingcold;
vasoconstrictionandpiloerectionusuallyprecedetheonsetof
shivering;
skinispale;
whentheshiveringhascausedthebodytemperaturetoreach
thenewsetpointofthetemperaturecontrolcenter,the
shiveringceases,andasensationofwarmthdevelops.
3.Flush
cutaneousvasodilationoccursandtheskinbecomeswarmand
flushed;
4.Defervescence
theinitiationofsweating.

18. Fever of unknown origin
Itisdefinedasatemperatureelevationof38.3°Cor
higherthatispresentfor3weeksorlonger.
Amongthecausesare:
malignancies(lymphomas,metastasestotheliver
andcentralnervoussystem);
infectionssuchashumanimmunodeficiencyvirus
ortuberculosis,orabscessedinfections;
drugfever;
cirrhosisoftheliver.

19. Principles of treatment
Becausefeverisadiseasesymptom,itsmanifestation
suggeststheneedfortreatmentoftheprimary
cause.
Actions:
modificationsoftheexternalenvironmentintended
toincreaseheattransferfromtheinternaltothe
externalenvironment;
supportofthehypermetabolicstatethat
accompaniesfever;
protectionofvulnerablebodyorgansandsystems;
treatmentoftheinfectionorconditioncausingthe
fever.

20. Antipyretic drugs
Antipyreticdrugs,suchasaspirinandacetaminophen,
oftenareusedtoalleviatethediscomfortsoffeverand
protectvulnerableorgans,suchasthebrain,from
extremeelevationsinbodytemperature.
Thesedrugsactbyresettingthehypothalamic
temperaturecontrolcentertoalowerlevel,
presumablybyblockingtheactivityofcyclooxygenase,
anenzymethatisrequiredfortheconversionof
arachidonicacidtoprostaglandinE2.

21. Fever in children
Themechanismsforcontrollingtemperaturearenotwell
developedintheinfant.
Ininfantsyoungerthan3months,amildelevationin
temperature(i.e.,rectaltemperatureof38°C)canindicate
seriousinfection.
Bothminorandlife-threateninginfectionsarecommonin
theinfantto3-yearagegroup.
Themostcommoncausesoffeverinchildrenareminor
ormoreseriousinfectionsoftherespiratorysystem,
urinarysystem,gastrointestinaltract,orcentralnervous
system.Occultbacteremiaandmeningitisalsooccurin
thisagegroupandshouldbeexcludedasdiagnoses.

22. Manifestations
Feverininfantsandchildrencanbeclassifiedaslow
riskorhighrisk,dependingontheprobabilityofthe
infectionprogressingtobacteremiaormeningitis.
Signsoftoxicity(andhighrisk)includelethargy,poor
feeding,hypoventilation,poortissueoxygenation,and
cyanosis.
Bloodandurinecultures,chestradiographs,and
lumbarpunctureusuallyaredoneinhigh-riskinfants
andchildrentodeterminethecauseoffever.
Febrileseizurescanoccurinsomechildren.

23. Fever in the elderly
Intheelderly,evenslightelevationsintemperaturemay
indicateseriousinfectionordisease.Thisisbecausethe
elderlyoftenhavealowerbaselinetemperature.
Normalbodytemperatureandthecircadianpatternof
temperaturevariationoftenarealteredintheelderly.
Theabsenceoffevermaydelaydiagnosis.
Unexplainedchangesinfunctionalcapacity,worseningof
mentalstatus,weaknessandfatigue,andweightlossare
signsofinfectionintheelderly.
Confusionanddeliriummayfollowmoderateelevations
intemperature.

24. Mechanisms
Disturbanceinsensingoftemperaturebythe
thermoregulatorycenterinthehypothalamus;
Alterationsinreleaseofendogenouspyrogens;
Thefailuretoelicitresponsessuchasvasoconstriction
ofskinvessels,increasedheatproduction,and
shiveringthatincreasebodytemperatureduringa
febrileresponse.
Becauseoftheincreasinglypooroxygenuptakebythe
aginglung,pulmonaryfunctionmayprovetobea
limitingfactorinthehypermetabolismthat
accompaniesfeverinolderpersons.
Confusion,incoordination,andagitationcommonly
reflectcerebralhypoxemia.