The astute clinician will recognize that although a common cause of fever in the ICU is infection, many cases are of noninfectious fever.
Fever in the intensive care unit (ICU) patient is a common problem that results in the performance of many diagnostics tests. This increases both the costs of medical care and the exposure of the patient to uncomfortable procedures.
Proper management demands implementing a simultaneous algorithm for the workup of noninfectious fever.
Fever is thought to be a protective mechanism against infection. Many animal species are known to develop fever in response to a microbiologic organism. In humans, fever is thought to enhance several parameters of immune function and potentially enhance survival.
In addition, hyperthermia also increases cardiac output, oxygen consumption, carbon dioxide production, and energy expenditure, which may be harmful to patients with low cardiopulmonary reserve or cere-brovascular injury. Maternal fever may also be a cause of fetal malformations or spontaneous abortions.
Normal body temperature is 37.0 °C with circadian variation of between 0.5 °C and 1.0 °C. Several methods are used to measure body temperature. Taking the pulmonary artery mixed venous temperature is the most accurate method for measuring core body temperature.
Infrared ear thermometry is nearly equivalent to taking pulmonary artery and brain temperatures. Rectal temperatures obtained with a mercury thermometer or electronic probe are often a few tenths of a degree higher than core body temperature.
Oral temperatures can be influenced by drinking and eating or warmed air in ventilator circuits. Axillary measurements are unreliable. The Society of Critical Care Medicine defines a fever as a temperature greater than 38.3 °C. Most infectious causes of fever follow a diurnal pattern.
There are many causes of noninfectious fever. With the exception of drug fever and transfusion reaction, noninfectious fever usually does not lead to a fever greater than 39.8°C.
Most causes of noninfectious fever will be suggested based on a good history and physical exam.
A recent operation, chest pain with electrocardiogram (ECG) changes, and a quadriparetic patient with asymmetric lower extremity swelling or a large sacral decubitus ulcer are all commonly encountered scenarios causing noninfectious fever in the ICU patient.
Routine laboratory tests, such as a complete blood count to look for evidence of bleeding, leukocytosis, and eosinophilia; a liver panel and an amylase and lipase test; ECG with cardiac enzymes; and a check of lactic acid level can help to quickly rule in or rule out many of the most common causes of noninfectious fever.
Imaging studies such as a chest radiograph; computed tomography of the head, chest, abdomen, and pelvis; right upper quadrant ultrasound; and lower extremity venous duplex may also be necessary to complete the workup.
LIST OF CAUSES OF NONINFECTIOUS FEVER IN THE INTENSIVE CARE UNIT
- Alcohol/drug withdrawal
- Acalculous cholecystitis
- Postoperative fever (48 hours postoperative)
- Decubitus ulcer
- Drug fever
- Cerebrovascular accident/subarachnoid hemorrhage
- Myocardial infarction
- Pancreatitis
- Ischemic bowel
- Cirrhosis
- Gastrointestinal bleeding
- Hematoma
- Aspiration pneumonitis
- Acute respiratory distress syndrome (both acute and fibroproliferative phase)
- Deep vein thrombosis/pulmonary embolism
- Phlebitis/thrombophlebitis
- Adrenal insufficiency
- Intravenous contrast reactions
- Neoplastic fevers
Drugs are a commonly considered etiology of fever; in reality very few cases are cited in the literature. Drugs commonly associated with drug fever are the Beta-lactam antibiotics, procainamide, and diphenylhydantoin. Drug withdrawal fever should always be considered in a patient with a history of substance abuse. In many cases this abuse history may not be known to the clinician, so clinical suspicion should be high.
Suggested Readings
Fink M. Textbook of Critical Care, 5th ed. Philadelphia: Saunders/Elsevier, 2005:1186.
Marik P. Fever in the ICU. Chest 2000;117:855 869.