Pathology of Fever

Fever or pyrexia is an elevation in body temperatures, when cytokines causes the set point of the Hypothalamus Thermoregulatory Centre to be altered. .

Fevers that are controlled by the Hypothalamus do not rise above 41degrees Celsius, indicating a built-in thermostatic safety mechanism.

Above 41 is usually as a result of convulsions, hyperthermia or impairment of the control centre.

Fever is a non-specific response that is mediated by exogenous pyrogens (Bacteria or virus) and endogenous pyrogens released from host cells. Endogenous pyrogens are Interleukin -1, Interleukin -6 and tumor necrosis factor. These are known as cytokines. Cytokines are synthesized by cell types such as endothelial cells, epithelial cells, lymphocytes, fibroblasts and monocytes. Interleukin 1 an inflammatory mediator produces other signs of inflammation such as malaise and anorexia.

In the case of Bob, he has been pulling at his ear, indicating an ear infection or Acute Otitis Media. The exogenous pyrogens isolated from cultures of the middle ear are: SPneumonae, H.influenza and less commonly, Group A streptococci and Staphylococcus aureus.

When these bacteria enter the body, they act as antigens and trigger the immune system. White cells are produced to help promote the body’s defence against infection. In addition prostaglandins are generated .The prostaglandins bind to receptors in hypothalamus and induce changes in its set point. To meet the new set point the body produces and conserves heat. Several hours may pass before the body temperature reaches the new set point.

Once the set point is increased, the blood flowing through the hypothalamus is perceived as being below the correct temperature, so heat conservation and generation is initiated until blood temperature reaches the new set point. Fever is established.

There four phases to a fever are: Prodomal, Chill, Flush and Diaphoresis.

Prodomal: - The child feels unwell but the temperature is normal. This is the stage where exogenous and endogenous pyrogens are acting to reset the hypothalamic set point.

Chill: - The child is cold and shivering and the body temperature is increasing. The body thermostat is set at 39 degrees Celsius but the blood is still at 37 degrees C. The hypothalamus detects a difference and initiates heat generating mechanism until the blood temperature reaches the new set point.

Vasoconstriction and piloerection occurs before shivering starts. This is an uncomfortable sensation of being chilled and there is an onset of generalized shaking although temperature is rising.

The skin is pale and covered with gooseflesh at this stage. One curls up to conserve body heat.

Once the shivering has caused the body temperature to reach the new set point, shivering ceases and warmth develops. This is know as the flush stage

Flush: In this stage, cutaneous vasodilation occurs, the skin becomes warm and flushed and dry and the temperature is elevated. The temperature reaches the new set point. It will remain elevated until a new set point is determined by removal of pyrogens (e.g destruction of bacteria by antibiotics, in Bob’s case amoxillin (40-45 mg /kg).

Diaphoresis: The hypothalamus set point drops. The child is flushed and feels hot, the temperature is falling. The hypothalamus detects the blood as being too hot and initiates heat loss. This is the stage of febrile response marked by sweating. Diaphoresis assists in evaporative heat loss. When the fever breaks, the client becomes ‘Afebrile”.

If a drop in temperature occurs suddenly, a crisis can occur. An abrupt and large peripheral vasodilation can cause a child to go into shock.

Not everybody proceed through the four stages of fever. Sweating may be absent. Fever may develop gradually and there may be no indication of chill or shivering.

There is an increase in respiration, elevated heart rate, dehydration due to sweating and increased vapor loss due to increased heart rate.

Purpose of fever

Fever signals the presence of infection and the need for medical treatment.

During a febrile episode, there are increased motility and activity of white blood cells.

High temperature stimulates interferon which inhibits growth of viruses. Fever also reduces the concentration of iron in the blood plasma, suppressing growth of microbial agents which grow best at normal body temperature.

Patterns of fever

Sustained: A constant body temperature continuously above 38 degrees C. and does not fluctuate.

Intermittent: Fever spikes accompanied by usual temperature levels in between. Temperature returns to acceptable value at least once in 24 hours.

Remittent: Fever spikes and falls but not returning to normal temperature levels.

Relapsing: Periods of febrile episodes accompanied by acceptable temperature values.

Febrile episodes and periods of normal temperature (Normothermia) may be longer than 24 hours.

Diagnosis of Acute Otitis Media

Symptoms: Pain ,discomfort and fever.

Pneumatic otoscopy can determine evidence of middle ear infection. Diagnosis of AOM in children can be established by ear pain, marked redness or distinct fullness or bulging of the tympanic membrane. In infants and young children , unaccustomed tugging and rubbing of the ear may be indicative of ear pain.