Fever in children

Mechanisms of development and significance of fever

The thermoregulatory center located near the floor of the third ventricle is responsible for maintaining homeothermy (temperature constancy). Depending on the mechanism of development, hyperthermia is divided into two types:

1. True fever. This is a regulated process. Triggered by pathogens (bacteria, viruses, inflammation), cytokines (especially IL-1) are produced, which stimulate the synthesis of prostaglandin E2 (PGE2). PGE2 acts on the hypothalamus and shifts the "set point" upward. The balance between heat production and heat loss is maintained, but at a new level.
2. Neurogenic hyperthermia. This occurs due to direct damage to hypothalamic neurons or impaired blood circulation in the central nervous system. This is not a shift of the set point, but a breakdown of the mechanism itself.

The process has a dual nature. On the one hand, it is a sanogenetic (protective) response: the immune system is activated, phagocytosis is enhanced, interferon is produced, and the replication of viruses and bacteria is suppressed. On the other hand, once compensatory mechanisms are exhausted, pathological changes begin: hypermetabolism, dehydration, cardiac and pulmonary strain (tachycardia and tachypnea), along with the risk of cerebral edema and febrile seizures.

Temperature norms and classification

Normal temperature depends on the measurement site. In the axillary (armpit) region, the norm is 36–37 °C. Mucosal values are higher and more stable: oral temperature is 0.3–0.5 °C higher than axillary, and rectal temperature is 0.5–1 °C higher.

Based on severity (measured in the axilla), four grades are distinguished:

• Subfebrile: 37.1–38.0 °C.
• Moderate febrile: 38.1–39.0 °C.
• High febrile: 39.1–40.0 °C.
• Hyperpyretic: above 40.0 °C.

Indications for antipyretic therapy

The strategy for prescribing antipyretics depends on age, medical history, and the measurement method. According to WHO guidelines, pharmacological temperature reduction in healthy children is indicated only at an axillary temperature of > 38.5 °C (or rectal > 39.0 °C). Below these values, fever is considered beneficial.

Thresholds are lowered for risk groups:

• > 38.0 °C: infants under 3 months; children with a history of febrile seizures; patients with severe cardiac, pulmonary, or neurological disorders.
• > 37.5 °C: development of "pale fever" (accompanied by peripheral vasospasm).
• At any values: pronounced pain syndrome (headache, myalgia) or significant deterioration in well-being.

Drug selection and safety profile

Centrally acting drugs lower temperature by inhibiting PGE2 synthesis in the hypothalamus and resetting the "set point" to normal. Safety is the primary criterion for selection in pediatrics.

• First-line drugs: paracetamol (10–15 mg/kg, max. 60 mg/kg per day) and ibuprofen (5–10 mg/kg, max. 30 mg/kg per day). Administered per os or per rectum. Alternating them is permitted in case of resistance.
• Reserve: metamizole sodium (5–10 mg/kg). Administered parenterally (IV, IM) only if first-line drugs are ineffective. Risk: agranulocytosis.
• Absolute contraindication: acetylsalicylic acid (aspirin). In infections, it causes life-threatening Reye's syndrome (acute hepatic encephalopathy).

Overdose risks:

• Paracetamol: hepatotoxicity (hepatic necrosis).
• Ibuprofen: gastrointestinal ulcers, allergies. In children under 3 months and in cases of dehydration, the risk of nephrotoxicity increases sharply.

Special situations: pale fever and intensive care

In "pale" fever (vasospasm), conventional antipyretics do not work. Antispasmodics (drotaverine, papaverine) and antihistamines (promethazine, chloropyramine) are required. In severe cases, a lytic cocktail is administered parenterally.

Physical cooling methods (sponging, enemas) are merely adjunctive in infections. They are non-physiological because they provoke vasoconstriction and increase heat production (strictly prohibited in pale fever).

Red flag: the appearance of signs of circulatory failure (hemodynamic disturbances) is a direct indication for emergency hospitalization, as it may indicate shock or severe toxicosis.

Class and exam questions

What else to study on this topic

• Pathogenetic cytokine cascade and PGE2 synthesis
• Differential diagnosis of hyperthermia types
• Calculation of first-line drug dosages and the lytic cocktail
• Emergency care for febrile seizures
• Criteria for hemodynamic disturbances and shock diagnosis

Other topics in "Chapter 13. Main syndromes requiring emergency care"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.