Fever in the ICU: an approach

What it is

Fever is common in critically ill patients and is usually defined in the ICU as a core temperature of 38.3 °C or higher. It is a physiological response: inflammatory cytokines raise the hypothalamic set point. About half of ICU fevers are caused by infection, mainly ventilator-associated pneumonia, catheter-related bloodstream infection, urinary infection from the bladder catheter, surgical site infection, Clostridioides difficile colitis, sinusitis from nasal tubes and intra-abdominal infection. The other half are non-infectious: drugs, transfusion reactions, venous thromboembolism, pancreatitis, acalculous cholecystitis, postoperative inflammation, adrenal insufficiency, thyroid storm, alcohol withdrawal, central fever after brain injury, and hyperthermic syndromes such as malignant hyperthermia or neuroleptic malignant syndrome. A very high temperature, above about 41 °C, points away from infection. The approach is a focused search, not a reflex: measure the temperature reliably, examine the patient from head to toe including every line and wound, take cultures before antibiotics, order imaging guided by the findings, and decide whether the patient is unstable enough to need antibiotics at once. Lowering the temperature does not improve outcome in most patients, but it is treated in those who cannot tolerate it, such as after brain injury or cardiac arrest.

What to assess

• The history of the stay: days since admission, operations, new lines, new drugs, transfusions and the timing of the fever.
• The lines and tubes: insertion sites, how long each has been in, endotracheal and nasal tubes, drains and the bladder catheter.
• The skin, wounds and pressure areas, the calves for thrombosis, the chest, the abdomen and the sinuses.
• Haemodynamic state: new hypotension, rising lactate or new organ failure suggests sepsis and urgency.
• Patients who may not mount a fever: older adults, those on steroids or immunosuppressants, and those on RRT or ECMO.

How it is done (and why)

1. Confirm the temperature with a core or reliable method — peripheral readings miss or exaggerate fever.
2. Assess stability: blood pressure, perfusion, lactate and new organ failure — instability calls for antibiotics within the hour.
3. Examine every line, wound, tube and skin fold, plus chest, abdomen and calves — the source is often visible.
4. Draw two sets of blood cultures before antibiotics, peripheral and from the line — this separates line infection from other bacteraemia.
5. Send samples guided by the clinical picture: respiratory secretions, urine from the catheter port, stool if diarrhoea — target, do not shotgun.
6. Order imaging by suspicion: chest film, ultrasound of the abdomen and gallbladder, CT — find collections that need drainage.
7. Review the drug chart and recent transfusions — stopping a culprit drug is the test and the treatment of drug fever.
8. Remove or replace lines that are no longer needed or look infected — source control matters more than antibiotic choice.

Common sources and the first test

Findings that change the plan

• Temperature above about 41 °C: think drug fever, malignant hyperthermia, neuroleptic malignant syndrome, heat stroke or a transfusion reaction.
• Diarrhoea with fever and a high white count: test for C. difficile and stop unnecessary antibiotics.
• Fever with a new tense right upper abdomen in a long-stay patient: suspect acalculous cholecystitis and image the gallbladder.
• Fever with tachycardia, hypoxaemia and a swollen leg: suspect venous thromboembolism.
• Rash, eosinophilia or a pulse slower than expected for the fever, with a well-looking patient: consider drug fever.
• Fever in the first two days after surgery is usually inflammatory; a later fever deserves a full search.

Next step

• Write down the suspected source, the cultures sent and the reason for starting or withholding antibiotics.
• Call a senior at once if fever comes with hypotension, rising lactate or new organ failure: treat as possible septic shock.
• Review cultures at 48–72 hours to narrow or stop antibiotics.
• Treat the fever itself when it harms: brain injury, after cardiac arrest, limited cardiac or respiratory reserve, or distress.
• Ask for infectious diseases or surgical help when the source is not found or needs drainage.

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Elsewhere in DurgiPedia

• Fever
• Acute-phase response and fever (CRP, ESR, procalcitonin)
• Body temperature and fever patterns
• Measuring body temperature: sites, devices and technique
• Central venous catheter care

Connections

← All of anaesthesia

Educational content; it does not replace supervised training, your institution's protocols or the anaesthetist's or intensivist's decision. It contains no doses and no ventilator or infusion settings.

Sources: Fever in the Intensive Care Patient (StatPearls (NCBI Bookshelf), 2023).

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