1.2 Pathophysiology of fever

At the end of this session you will be able to:

1. Demonstrate a clear understanding of the pathophysiology of fever and apply it to your practice

In addition you will be able to:

2. Identify the two key pathophysiological mechanisms associated with fever
3. Identify the four phases of fever and recognise what phase of fever a child is in
4. Discuss how understanding pathophysiology can contribute to your management of a child with fever

Pathophysiology of fever is complex and dynamic.

Thermoregulation is controlled by the thermoregulation centre within the hypothalamus.

This centre responds to input from the blood bathing the hypothalamus and from peripheral receptors. The centre aims to maintain body temperature at a particular (normal) set point – usually at about 37°C.

Normothermia is maintained by a balance between heat production and heat loss.
(for further information about heat transfer see Graduate Research

Any substance that causes fever is called a pyrogen.

Exogenous pyrogens are ones that come from outside the body and include microbes, viruses and toxins.

Endogenous pyrogens are induced, within the body, in response to exogenous pyrogens. Browne et al (2001) propose three pathophysiological mechanisms that are important to consider in the management of children with fever (see Table 1).

Table 1: Three key pathophysiological mechanisms related to fever (developed from Browne et al. 2001)
Fever can result when:
1.	The thermoregulatory set-point is elevated above the normal set-point. This most commonly occurs as a result of bacterial and viral infection which induces the action of cytokines (endogenous pyrogens); which through the action of prostaglandins turns up the thermostat. The body responds to this by producing physiological changes (including metabolic, endocrine, behavioural and autonomic processes) aimed at elevating body temperature. This produces the signs and symptoms associated with fever.	For a fever resulting from an elevated set-point the use of antipyretics and other controlled measures such as cooling may be appropriate
2	Heat production exceeds heat loss. This can occur in salicylate overdose, malignant hyperthermia, hyperthyroidism and excessive environmental temperatures.	For fever resulting from either excessive heat production or defective heat loss, antipyretics are not effective.
3	Heat loss mechanisms are defective This can occur in heat stroke, anticholinergic drug toxicity and ectodermal dysplasia.	For fever resulting from either excessive heat production or defective heat loss, antipyretics are not effective.

Porth (1994) cited in Casey (2000) identifies the four phases of fever. Understanding these phases gives practitioners insight into what is happening and this means they can provide an explanation to the child’s parents (see Figure 1).

Figure 1: The Four Stages of Fever (adapted from Port 1994; Casey 20000

1.2 Pathophysiology of fever

Table 1: Three key pathophysiological mechanisms related to fever (developed from Browne et al. 2001)

Dosing made easy