3.1 - Fever Flashcards
What is a fever?
- It is an elevation in core body temperature above the daily range of an individual
- Usually defined as a body temperature > 100 degrees F (37.8 C) orally
- Normal body temperature is low in the a.m. and high in the evening.
Define fever of unknown origin
Body temperature of 101 F (38.3 C) or above rectally for > 3 weeks without an apparent causes, despite workup for at least 1 week in patients without neutropenia or immunosuppression
Describe the pathophysiology associated with fever development
- Normal body temperature is controlled in the thermoregulatory center located in the anterior hypothalamus
- Infectious agents or microbial products, as well as, cytokines and other inflammatory processes, induce macrophages, endothelial cells and the reticuloendothelial system to produce and secrete pyrogenic cytokines into the circulation.
- These pyrogenic cytokines induce the synthesis of prostaglandin E2 (PGE2)
- Elevated levels of PGE2 in the hypothalamus trigger the raising of core body temperature.
- This activates neurons in the vasomotor center to begin vasoconstriction, which produces a noticeable cold sensation in the hands and feet.
- As blood is shunted away from the periphery to the internal organs, heat loss is decreased from the skin, the patient feels cold.
- In combination with this, thermogenesis in fat contributes to the increase in core body temperature.
- Thermogenesis in either the fat or muscle causes an uncoupling of proteins, which release adenosine triphosphate (ATP) and heat.
- This combination of heat conservation and thermogenesis accounts for fever.
What are pyrogens?
The term pyrogens describes any substance that causes fever and can be exogenous or endogenous. Endogenous pyrogens belong to a class of proteins called cytokines.
What are common causes of fevers?
A. Infection:
- Bacterial
- Viral
- Rickettsia
- Fungal
- Parasitic
- Chlamydia
B. Autoimmune/collagen vascular disease/vasculitis
C. Central nervous system (CNS) disease
D. Malignancy
E. Cardiovascular disease
F. GI disease
G. Drug/medication induced
H. Familial Mediterranean fever
I. Tissue damage
J. Hematoma
K. Factitious Fever
L. Heatstroke
M. Malignant hyperthermia secondary to inhalation anesthetics and succinylcholine
N. Malignant neuroleptic syndrome
O. Exercise
P. Microcrystalline arthritis
Q. Surgery
R. Blood products (reaction)
S. Endocrinopathies
What is the diagnostic approach to adults with fever?
1. Take a good history and note any of the following:
- Localizing symptoms
- Fever and chills
- Sweats/night sweats
- Weight loss
- Arthralgias and myalgias
- Use of medications and onset of symptoms
- Co-morbidities – DM, HTN, CAD, COPD, Malignancy, Renal failure, Sickle cell trait/disease, Immunosuppression.
- Travel history
- Household pets
- Hobbies
- Use of tobacco, alcohol, illicit drugs
- Blood transfusion history
- Immunizations
- Drug allergies
- Ethnic origin
- History of psychiatric disorders
- Prosthetic or implanted devices
- Exposure to chemicals
- Sexual practices
- Family history: Tb, Infectious disease
2. Look out for any changes in the physical exam:
- Vital signs
- Pay close attention to : mucus membranes, skin, lymph nodes, HEENT, nail beds, CV system, chest exam, abdominal exam, GU (male and female)
- Invasive line insertion sites
What lab/diagnostic tests are used to diagnose a fever?
- CBC: may show anemia, leukocytosis with left shift (bacterial) or leukopenia (viral),bandemia
- Urinalysis
- Blood chemistries: serum glucose, Liver function tests
- Erythrocyte sedimentation rate: lacks sensitivity and specificity, but elevation warrants additional testing
- Cultures and analysis: blood culture, urine, sputum, stool, invasive line catheter tips, CSF, peritoneal fluid, liver biopsy, bone marrow aspiration, lymph node biopsy
- Immunologic serologies: HIV, ANA, rheumatoid factors
- Imaging: CXR, abdominal ultrasound, CT scan or MRI (not both), Endoscopy (crohn’s disease); radionuclide studies (Ventilation –perfusion scans); echocardiogram
What are the changes seen in the body due to a fever?
- For every increase of 1 degree above 37 degrees C., there is a 13% increase in oxygen consumption.
- Elevated core temperatures can increase the demand for oxygen; therefore, can aggravate pre-existing cardiac or pulmonary conditions.
- Reducing fever with antipyretics also reduces systemic symptoms of headaches, myalgia’s and arthralgia’s.
- Patients with autoimmune diseases being treated with biologic agents, such as tumor necrosis factor-alpha inhibitors, are at increased risk for routine and opportunistic infections. In these patients, a low-grade fever may serve as an early warning sign of a serious illness.
What are the treatment options for patients with fever?
- The combination of aspirin (NSAID’s) and acetaminophen is more effective than either alone.
- Inhibitors of cyclooxygenases, such as aspirin and NSAIDs are potent antipyretics.
- Acetaminophen is a poor cyclooxygenase inhibitor in peripheral tissue and does not display noted anti-inflammatory activity; however, acetaminophen is an outstanding antipyretic and should be used as the initial antipyretic.
- The decision to treat, or reduce fever, with antipyretics assumes that there is no diagnostic benefit for allowing the fever to persist.
- In rare cases, such as malaria, the observation of the pattern of fever can be helpful diagnostically.
What should you consider when treating geriatric patients with fever?
- The ability to develop a fever in older adults is impaired.
- Baseline fever in older adults is lower than in younger adults
- Older adults with severe infections may only display a modest fever.
- Older adults are at greater risk due to immune senescence, co-morbidities (DM, CAD, COPD) and communal residence (long term care)
- The most common causes of fever in the geriatric population include:
- Connective-tissue diseases (RA, Polymyalgia rheumatic, etc.)
- Malignancies- colon ca, lymphoma, leukemia
- Intra-abdominal infections and Tb
- Medication effect.
