Fever DefinitionA fever is any body temperature elevation over 100 F (37.8 C).DescriptionA healthy persons body temperature flu!tuates bet"een #7 F (3$.1 C) and 100 F (37.8 C)% "ith the avera&e bein& #8.$ F (37 C). 'he body maintains stability "ithin this ran&eby balan!in& the heat produ!ed by the metabolism "ith the heat lost to the environment. 'he (thermostat( that !ontrols this pro!ess is lo!ated in the hypothalamus% a smallstru!ture lo!ated deep "ithin the brain. 'he nervous system !onstantly relays information about the bodys temperature to the thermostat% "hi!h in turn a!tivates different physi!alresponses desi&ned to !ool or "arm the body% dependin& on the !ir!umstan!es. 'hese responses in!lude) de!reasin& or in!reasin& the flo" of blood from the bodys !ore% "hereit is "armed% to the surfa!e% "here it is !ooled* slo"in& do"n or speedin& up the rate at "hi!h the body turns food into ener&y (metaboli! rate)* indu!in& shiverin&% "hi!h &eneratesheat throu&h mus!le !ontra!tion* and indu!in& s"eatin&% "hi!h !ools the body throu&h evaporation.A fever o!!urs "hen the thermostat resets at a hi&her temperature% primarily in response to an infe!tion. 'o rea!h the hi&her temperature% the body moves blood to the "armerinterior% in!reases the metaboli! rate% and indu!es shiverin&. 'he (!hills( that often a!!ompany a fever are !aused by the movement of blood to the bodys !ore% leavin& thesurfa!e and e+tremities !old. ,n!e the hi&her temperature is a!hieved% the shiverin& and !hills stop. -hen the infe!tion has been over!ome or dru&s su!h as aspirin oracetaminophen ('ylenol) have been ta.en% the thermostat resets to normal and the bodys !oolin& me!hanisms s"it!h on) the blood moves to the surfa!e and s"eatin& o!!urs.Fever is an important !omponent of the immune response% thou&h its role is not !ompletely understood. /hysi!ians believe that an elevated body temperature has several effe!ts.'he immune system !hemi!als that rea!t "ith the fever0indu!in& a&ent and tri&&er the resettin& of the thermostat also in!rease the produ!tion of !ells that fi&ht off the invadin&ba!teria or viruses. 1i&her temperatures also inhibit the &ro"th of some ba!teria% "hile at the same time speedin& up the !hemi!al rea!tions that help the bodys !ells repairthemselves. 2n addition% the in!reased heart rate that may a!!ompany the !han&es in blood !ir!ulation also speeds the arrival of "hite blood !ells to the sites of infe!tion.Causes and symptomsFevers are primarily !aused by viral or ba!terial infe!tions% su!h as pneumonia or influenza. 1o"ever% other !onditions !an indu!e a fever% in!ludin& aller&i! rea!tions*autoimmune diseases* trauma% su!h as brea.in& a bone* cancer* e+!essive e+posure to the sun* intense e+er!ise* hormonal imbalan!es* !ertain dru&s* and dama&e to thehypothalamus. -hen an infe!tion o!!urs% fever0indu!in& a&ents !alled pyro&ens are released% either by the bodys immune system or by the invadin& !ells themselves% thattri&&er the resettin& of the thermostat. 2n other !ir!umstan!es% the immune system may overrea!t (aller&i! rea!tions) or be!ome dama&ed (autoimmune diseases)% !ausin& theun!ontrolled release of pyro&ens. A stro.e or tumor !an dama&e the hypothalamus% !ausin& the bodys thermostat to malfun!tion. 3+!essive e+posure to the sun or intenselye+er!isin& in hot "eather !an result in heat stroke% a !ondition in "hi!h the bodys !oolin& me!hanisms fail. 4ali&nant hyperthermia is a rare% inherited !ondition in "hi!h a persondevelops a very hi&h fever "hen &iven !ertain anestheti!s or muscle relaxants in preparation for sur&ery.1o" lon& a fever lasts and ho" hi&h it may &o depends on several fa!tors% in!ludin& its !ause% the a&e of the patient% and his or her overall health. 4ost fevers !aused byinfe!tions are a!ute% appearin& suddenly and then dissipatin& as the immune system defeats the infe!tious a&ent. An infe!tious fever may also rise and fall throu&hout the day%rea!hin& its pee. in the late afternoon or early evenin&. A lo"0&rade fever that lasts for several "ee.s is asso!iated "ith autoimmune diseases su!h as lupus or "ith some!an!ers% parti!ularly leu.emia and lymphoma.DiagnosisA fever is usually dia&nosed usin& a thermometer. A variety of different thermometers are available% in!ludin& traditional &lass and mer!ury ones used for oral or re!taltemperature readin&s and more sophisti!ated ele!troni! ones that !an be inserted in the ear to 5ui!.ly re&ister the bodys temperature. For adults and older !hildren% temperaturereadin&s are usually ta.en orally. 6oun&er !hildren "ho !annot or "ill not hold a thermometer in their mouths !an have their temperature ta.en by pla!in& an oral thermometerunder their armpit. 2nfants &enerally have their temperature ta.en re!tally usin& a re!tal thermometer.As important as re&isterin& a patients temperature is determinin& the underlyin& !ause of the fever. 'he presen!e or absen!e of a!!ompanyin& symptoms% a patients medi!alhistory% and information about "hat he or she may have in&ested% any re!ent trips ta.en% or possible e+posures to illness help the physi!ian ma.e a dia&nosis. 7lood tests !anaid in identifyin& an infe!tious a&ent by dete!tin& the presen!e of antibodies a&ainst it or providin& samples for &ro"th of the or&anism in a !ulture. 7lood tests !an also providethe do!tor "ith "hite blood !ell !ounts. 8ltrasound tests% ma&neti! resonan!e ima&in& (492) tests% or !omputed tomo&raphy (C') s!ans may be ordered if the do!tor !annotreadily determine the !ause of a fever.Treatment/hysi!ians a&ree that the most effe!tive treatment for a fever is to address its underlyin& !ause% su!h as throu&h the administration of antibiotics. Also% be!ause a fever helpsthe immune system fi&ht infe!tion% it usually should be allo"ed to run its !ourse. :ru&s to lo"er fever (antipyreti!s) !an be &iven if a patient (parti!ularly a !hild) is un!omfortable.'hese in!lude aspirin% a!etaminophen ('ylenol)% and ibuprofin (Advil). Aspirin% ho"ever% should not be &iven to a !hild or adoles!ent "ith a fever sin!e this dru& has been lin.ed toan in!reased ris. of 9eyes syndrome. 7athin& a patient in !ool "ater !an also help alleviate a hi&h fever.A fever re5uires emer&en!y treatment under the follo"in& !ir!umstan!es) ne"born (three months or youn&er) "ith a fever over 100.; F (38 C) infant or !hild "ith a fever over 103 F (3#.< C) fever a!!ompanied by severe headache% ne!. stiffness% mental !onfusion% or severe s"ellin& of the throatA very hi&h fever in a small !hild !an tri&&er sei=ures (febrile sei=ures) and therefore should be treated immediately. A fever a!!ompanied by the above symptoms !an indi!atethe presen!e of a serious infe!tion% su!h as meningitis% and should be brou&ht to the immediate attention of a physi!ian.Prognosis4ost fevers !aused by infe!tion end as soon as the immune system rids the body of the patho&en and do not produ!e any lastin& effe!ts. 'he pro&nosis for fevers asso!iated"ith more !hroni! !onditions% su!h as autoimmune disease% depends upon the overall out!ome of the disorder.