Measuring the Metabolic Cost of Fever

Fever is part of the body's immune response, often triggered by infection. Fever is commonly treated with medicines such as paracetamol, mainly because people feel unwell with fever. However fever does have a role in fighting infection: it enables the rest of the immune system to function more efficiently, and may directly stop bacteria and viruses from multiplying. In most cases however treating fever does not matter because the rest of the immune system can cope well enough to fight the infection (with or without additional treatment, like antibiotics). In critically ill patients however any advantage in the fight against infection may be crucial. In a large observational study of adult patients in the intensive care unit, patients who developed an early fever with temperature between 38.5-39.5 degrees C fared relatively better than patients who were colder. So it is possible that in critical illness fever may be beneficial. However in critical illness the body does have limited energy resources. In order to raise the body temperature energy is required. However the investigators do not know how much energy is required to generate a fever in critically ill children. This study will aim to try and measure the energy required to generate a fever in a critically ill child. The investigators will measure energy expenditure directly in children admitted to the intensive care unit by measuring the levels of oxygen and carbon dioxide they breathe in and out (a method called indirect calorimetry). This will enable the investigators to judge whether the benefits of a fever can be justified by the energy costs in the energy depleted state that is critical illness.