Pattern recognition

Patterns of fever

The pattern of fever can be understood under the following headings:

a) Severity

Temperature not exceeding 37.8 C is classified as low grade fever. The clinical significance is that it usually indicates chronic illness (eg. infection, chronic inflammation, or malignancy). It often excludes acute bacterial infection.

Hyper pyrexia (core temp > 41C) indicates failure of the thermoregulatory mechanisms. The non-infectious cause of hyperexia (eg. heat stroke, heat exhausion, malignant hyperthermia) must be differentiated from infectious causes.

b) Periodicity

Fever types can be classified as:

• Continuous fever: The fever does not fluctuate more than 1° C in 24 hours.

• Remittent fever : The daily fluctuations exceed 2degree C.

• Intermittent fever: The fever persists only for several hours a day. When it occurs daily it is called Quotidian; on alternate days: Tertian; once in three days: Quartan fever.

A Relapsing fever pattern is seen with Borrelia, rat bite fever, there is fever for 3 to 6 days followed by a fever free interval of one week and then fever once again. Intermittent fever also occurs with antipyretic therapy and cooling measures, hence this is of little help in discriminating, the varied etiologic factors resulting in the febrile episode.

c) Chills and rigors

A Chill is a subjective (feeling cold) voluntary phenomenon representing adaptation of the body to conserve heat (uncommon in infants). A Rigor is an involuntary muscle contractions (shivering) to generate heat. It occurs in conditions like malaria, filaria, deep seated abscesses, bacterial endocarditis etc.

d) Inter febrile clinical state

A careful observation of the patients between two febrile paroxysms is a useful guide to arrive at the etiology of the fever.

A child who continues to be toxic, lethargic, apathetic even when the temperature reaches normal may have more severe infection usually bacterial. In contrast, a child whose inter-febrile state is that of well being and who is not toxic and resumes his normal level of activity when the temperature is normal could have a more benign cause or a parasitic infestation like malaria.

e) Core temperature mismatch

The temperature difference between the core and the peripheral temperature is particularly important in the diagnosis and management of :

• Sepsis

• Peripheral circulatory failure

• Hypothyroidism

• Malnutrition

• Febrile seizures

• Moribund child

f) Relationship between core temperature and other vital signs:

For every degree Fahrenheit (above 100º F) rise in the body temperature the heart rate rises by 10/min. A dissociation between the temperature and pulse rate is seen in cases of typhoid, psittacosis, brucellosis, legionnaire's disease, described as relative bradycardia.

Fever is also accompanied by an increase in the systolic blood pressure and a wide pulse pressure.

The respiratory rate also increases with increase in the body temperature (3.8 for every 1 degree F).

Factitious fever is accompanied by low pulse rate and normal respiratory rate.

g) Drugs and fever patterns

Drugs can induce fever and alternatively, antipyretics(APS) and analgesics can disrupt the patterns of fever.

h) Fever related nonspecific symptoms

Symptoms and signs accompanying fever might not always indicate a particular system involvement.

These fever related symptoms include flushing, sweating, lethargy, apathy, anorexia, body-aches and behavioural responses like wearing cooler clothes and switching on the fan. However, fever related symptoms like vomiting and headache might indicate a more serious problem like intra cranial infection.