Thirty per cent of patients will become febrile, while up to 90% of patients with sepsis will experience fever, during a stay in the intensive care unit (ICU). Fever in critically ill patients may be of infective, non-infective, or mixed origin. The confirmation of the source of fever is often difficult which leads to a diagnostic dilemma and a difficult decision (to treat or not to treat) often resulting in a variability of treatment response from the medical and nursing staff.

The Society of Critical Care Medicine practice parameters define fever in the ICU as a (core) temperature above 38.3°C. The condition is caused by an imbalance between heat production and heat loss. In the clinical context, excessive heat generation is much more common than defective heat loss. The resulting disturbance may be transient and/or trivial or it may portend serious illness.

This module focuses on the differential diagnosis of fever rather than on the antimicrobial treatment of infection.