Fever
Fever: Excerpt from The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter
Lyle J. Fagnan
Fever is a physiologic state in which the body temperature is elevated above the individual’s normal temperature. Patients and clinicians consider fever an important sign of illness.
Approach to the febrile patient.
The presence or absence of fever is frequently addressed in the patient interview and a measurement of temperature is one of the vital signs recorded as a part of the physical examination.
A. The mean oral temperature for healthy adults is 36.8°C ± 0.4°C (98.2°F ± 0.7°F) with a maximal high of 37.2°C (98.9°F) at 6 am and a maximal high of 37.7°C (99.9°F) at 4 pm. Rectal temperatures are 0.6°C (1.0°F) higher. Axillary temperatures are 0.55°C (1.0°F) less than oral readings. Helpful
centigrade–Fahrenheit conversions are 40.0°C = 104.0°F; 37.0°C = 98.6°F; and 35.0°C = 95.0°F.
B. Hyperpyrexia is when the oral temperature exceeds 41.1°C (106.0°F). This is a medical emergency.
C. A number of factors affect baseline values, including race, postprandial state, pregnancy, ovulation, physical activity, clothing, ambient temperature, and endocrine states.
History
A. Taking a detailed patient history is critical; include questions relating to travel, animal exposure, occupation, injuries or operations, household members or contacts who are ill, medications, past illnesses, and a complete review of systems.
B. Chills, malaise, myalgia, headache, and fever are common with infectious diseases.
C. The febrile pattern may be helpful in making a diagnosis. Antipyretics, antibiotics, and glucocorticoids affect the fever pattern. Specific patterns of fever are shown in Table 2.4.
Physical examination
A. The examination should include the skin, lymph nodes, eyes, nail beds, heart, lungs, abdomen, joints, nervous system, and genitourinary system, including rectal and bimanual pelvic examinations.
B. Infections will increase the pulse rate approximately 10 beats per minute for each 0.5°C (1.0°F) temperature increase.
C. When fever is present, the respiratory rate will frequently increase above the usual 12 to 14 breaths per minute.
D. Infections with Mycoplasma pneumonia, psittacosis, and typhoid fever are often associated with a relative bradycardia.
Testing.
In cases of a fever in which the cause is unclear, a number of diagnostic tests may be useful, depending on history and physical examination. These include:
A. Urinalysis with microscopic examination
B. Blood cultures, both aerobic and anaerobic
C. Blood tests: human immunodeficiency virus (HIV), rapid plasma reagent (RPR), antistreptolysin-O (ASO) titer, rheumatoid arthritis (RA) factor, antinuclear antibody (ANA), sedimentation rate, and serum enzymes and chemistries
D. Tuberculosis (TB) skin test
E. Spinal fluid examination
F. Diagnostic imaging: chest film, abdominal ultrasound, abdominal computed tomography (CT), bone scan
G. Biopsies: liver, bone marrow, lymph node, skin, muscle, temporal artery
Diagnostic assessment.
The approach to the febrile patient involves a number of considerations, including the patient’s age, clinical history, risk factors, community illness pattern, and physical presentation. In the family physician’s office, most febrile illnesses are the result of self-limited viral illnesses (e.g., upper respiratory infections). A number of cases of fever will be caused by bacterial infections (e.g., streptococcal pharyngitis or urinary tract infections). The challenge is to select those studies with the highest sensitivity and specificity to increase the probability of a correct diagnosis. When the diagnosis continues to be elusive, repeat the history and the physical examination. Special considerations in specific populations and certain types of fever include:
A. The elderly: 10% of elderly patients will fail to generate a febrile response with pneumonia (1). Fever in the elderly is more likely to indicate a bacterial infection than a fever in younger adults (2).
B. Fever of unknown origin (FUO). An FUO is characterized by the first three criteria listed below:
1. A temperature greater than 38.3°C (101.0°F) on several occasions
2. A duration of 3 weeks
3. Unclear cause after a full physical examination, routine blood tests, cultures, and chest x-ray studies
4. The cause of FUOs will be determined 90% of the time; it will often be a common illness that presents in an unusual manner.
5. Two leading causes of FUO are tuberculosis and infective endocarditis.
6. Other causes include hepatic or subphrenic abscess, neoplasm, and lymphomas such as Hodgkin’s disease.
C. Factitious fever. Factitious fever is a consideration in a patient with a complex emotional disorder. The absence of a normal diurnal pattern, pulse elevation, and diaphoresis may suggest a diagnosis of factitious fever.
D. Drug fever. Drugs are an important cause of noninfectious fever (3).
1. This is a diagnosis of exclusion and requires the fever to coincide with the prescribing of the drug and the resolution of the fever on discontinuing the medication.
2. Drug-associated fevers can be high and take several days to resolve.
3. Among the medications causing a fever are diphenylhydantoin, carbamazepine, histamine-2 (H2) blockers, methyldopa, allopurinol, sulfonamides, cephalosporins, and isoniazid.
E. Postoperative fever. The temporal relationship of the fever to the surgery may provide a clue to the primary source of the infection (4).
1. If fever duration is less than 48 hours, consider atelectasis of the lung.
2. If duration is more than 3 days, consider urinary tract infection or infected intravascular device.
3. If fever has been present more than 5 days, consider wound infection, intraabdominal abscess, or empyema.
F. Hyperthermia. A disruption of thermoregulation can result from excessive heat production, inadequate heat dissipation, or hypothalamus malfunction (5).
References
1. Harper C, Newton P. Clinical aspects of pneumonia in the elderly veterans. J Am Geriatr Soc 1989;37:867–872.
2. Mellors JW, Horwitz RI, Harvey MR, et al. A simple index to identify occult bacterial infection in adults with unexplained fever. Arch Intern Med 1987;147:666–671.
3. Mackowiak PA, ed. Fever: basic mechanisms and management. New York: Raven Press, 1991:239.
4. Mackowiak PA, ed. Fever: basic mechanisms and management. New York: Raven Press, 1991:245.
5. Simon HB. Hyperthermia. N Engl J Med 1993;329(7):483–487.
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Book Source Details
- Book Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter
- Author(s): Robert B. Taylor (editor)
- Year of Publication: 2000
- Copyright Details: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter, Copyright © 2000 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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