Porth's Essentials of Pathophysiology, 4e

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Cell and Tissue Function

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parents or caregivers are deemed reliable. Older chil- dren with fever without source also may be treated on an outpatient basis.

Fever in Children Fever occurs frequently in infants and young children (i.e., ages 1 day to 3 years) and is a common reason for visits to the clinic or emergency department. 42,43 The dif- ferential diagnosis of fever is broad and includes both infectious and noninfectious causes, with the majority of febrile children having an underlying infection. The most common causes are minor or more serious infec- tions of the respiratory system, gastrointestinal tract, urinary tract, or central nervous system. The epidemiol- ogy of serious bacterial disease has changed dramatically with the introduction of the Haemophilus influenzae and Streptococcus pneumoniae vaccines in developed countries. H. influenzae type b has been nearly elimi- nated and the incidence of pneumococcal disease has declined substantially. Febrile children who are younger than 1 year of age and females between 1 and 2 years of age should be considered at risk for a urinary tract infec- tion (see Chapter 24). While most children have identifiable causes for their fevers, many have fevers without localizing signs or symptoms. These fevers, which are usually of rapid onset and present for less than a week, are commonly referred to as fever without source . The American College of Emergency Physicians has developed clinical guidelines for use in the treatment of previously healthy infants and children ages 1 day to 3 years with fever without a source. The guidelines define fever in this age group as a rectal temperature of at least 38°C (100.4°F). The reli- ability of other methods of temperature measurements (e.g., axillary, ear) is lower and must be considered when making decisions about the seriousness of the fever. 43 The approach to the young child who has fever with- out a source varies depending on the age of the child (neonate [0 to 28 days], young infant [1 to 3 months], and older infants and toddlers [3 to 36 months]). 44 All have decreased immunologic function and are more com- monly infected with virulent organisms. Neonates are at particularly high risk for serious bacterial infections that can cause bacteremia or meningitis. Also, neonates and young infants demonstrate limited signs of infection, often making it difficult to distinguish between seri- ous bacterial infections that require immediate medical attention and other causes of an elevated temperature. Fever without source in children younger than age 3 months requires careful history and physical exami- nation. 42 The temperature-lowering response to anti- pyretic medications does not change the likelihood of a child having a serious bacterial infection and should not be used as an indicator of infection severity. 45 Neonates with signs of toxicity (and high risk) including leth- argy, poor feeding, hypoventilation, poor tissue oxy- genation, and cyanosis usually require hospitalization and treatment with antibiotics. Diagnostic tests such as white blood cell count, blood and urine cultures, chest radiographs, and lumbar puncture usually are done to determine the cause of fever. Infants with fever who are considered to be at low risk for bacterial infections often are managed on an outpatient basis provided the

Fever in the Elderly In the elderly, even slight elevations in temperature may indicate serious infection, most often caused by bacteria, or disease. This is because the elderly often have a lower baseline temperature (36.4°C [97.6°F] in one study) than younger persons, and although their temperature increases during an infection, it may fail to reach a level that is equated with significant fever. 45,46 Therefore, it has been recommended that the definition of fever in the elderly be expanded to include an elevation of tempera- ture of at least 1.1°C (2°F) above baseline values. The absence of fever may delay diagnosis and initia- tion of antimicrobial treatment. Unexplained changes in functional capacity, worsening of mental status, weak- ness and fatigue, and weight loss are signs of infection in the elderly and should be viewed as possible signs of infection and sepsis when fever is absent. A thorough history and physical examination are critically impor- tant. 47 The probable mechanisms for the blunted fever response include a disturbance in sensing of tempera- ture by the thermoregulatory center in the hypothala- mus, alterations in release of endogenous pyrogens, and the failure to elicit responses such as vasoconstriction of skin vessels, increased heat production, and shiver- ing that increase body temperature during a febrile response. Another factor that may delay recognition of fever in the elderly is the method of temperature measurement. Oral temperature remains the most commonly used method, but research suggests that rectal and tympanic membrane methods are more effective in detecting fever in the elderly. 47 This is because conditions such as mouth breathing, tongue tremors, and agitation often make it dif- ficult to obtain accurate oral temperatures in the elderly. ■■ The systemic manifestations of inflammation include the effects of the acute-phase response, such as fever and lethargy; increased erythrocyte sedimentation rate (ESR), levels of C-reactive protein (CRP), other acute-phase proteins, and white blood cells; and enlargement of the lymph nodes that drain the affected area. In severe bacterial infections (sepsis), large quantities of microorganisms in the blood result in the production and release of enormous quantities of inflammatory cytokines and development of what is referred to as the systemic inflammatory response syndrome. SUMMARY CONCEPTS