From the Guidelines
Fever is defined as a single temperature measurement greater than or equal to 38.3°C, according to the most recent guidelines from the Society of Critical Care Medicine and the Infectious Diseases Society of America 1. This definition is used to evaluate new fever in adult patients in the ICU. The normal body temperature range is subject to various factors such as age, gender, diurnal variation, and sampling site. Fever occurs as part of the body's immune response to infection, inflammation, or other medical conditions, and it can be managed with medications like acetaminophen or ibuprofen. While fever itself is usually not dangerous in adults, very high fevers above 103°F (39.4°C), fevers lasting more than three days, or fevers accompanied by severe symptoms like difficulty breathing, confusion, or stiff neck warrant medical attention. Some key points to consider when evaluating fever include:
- The definition of fever may vary depending on the patient population and clinical setting
- Not all patients with infection manifest fever, and the absence of fever in patients with infection is associated with worse outcomes 1
- Fever can be managed with medications like acetaminophen (325-650mg every 4-6 hours, not exceeding 3000mg daily) or ibuprofen (200-400mg every 6-8 hours with food)
- Staying hydrated is crucial during a fever, as the elevated temperature increases fluid loss through sweating. It's also important to note that the definition of fever has been consistent across various studies, with a single oral temperature measurement greater than or equal to 38.3°C being a commonly used threshold 1. However, the most recent and highest-quality study should be prioritized when making a definitive recommendation, which in this case is the 2023 guidelines from the Society of Critical Care Medicine and the Infectious Diseases Society of America 1.
From the Research
Definition of Fever
- Fever is a complex physiological response involving the innate immune system and should not be characterized merely as a temperature above the normal threshold of 37.0°C (98.6°F) 2.
- It is a cardinal symptom of most infectious diseases, but can also be caused by non-infectious conditions 3.
- Fever is part of a systemic inflammatory response by the immune system to infection, and is characterized by a regulated rise in body temperature that is defended by fully functional thermoregulatory mechanisms 4.
Characteristics of Fever
- The normal daily variation in body temperature is typically around 37.0°C (98.6°F), and fever is defined as a temperature above this threshold 2.
- In practice, fever is often defined as a temperature above 38°C (rectal or tympanic), 37.5°C (oral), or 37.2°C (axillary) 5.
- Fever can be distinguished from other forms of hyperthermia, such as exercise hyperthermia or hyperthermia due to inadequate means of heat dissipation, by its regulated rise in body temperature and its response to aspirin-like drugs 4.
Causes and Treatment of Fever
- Fever can be caused by a variety of conditions, including infections, inflammation, and other diseases 6.
- The treatment of fever depends on the underlying cause, and may include the use of antipyretic drugs, such as acetylsalicylic acid, or other medications 6.
- In some cases, fever may not require treatment, and may even be beneficial in helping the body to fight off infection 3.