In this episode I’ll discuss causes of fever in critically ill patients.

Subscribe on iTunes, Android, or Stitcher

Elevated body temperature is detected in almost half of patients admitted to adult ICUs.

Its presence should trigger a thorough search for the etiology.

IDSA / SCCM guidelines define pyrexia in critically ill adults as a temperature of 38.3 °C or greater, with a lower threshold used in immunocompromised patients who are more likely to have a severe illness without significant elevation in body temperature.

A recent review article defined fever as 38 °C or greater, high fever as 39.5 °C or greater, and hyperthermia as 41 °C or greater.

Severe hyperthermia (41 °C or greater)

Severe hyperthermia is different from fever or pyrexia in that it occurs without an increase in the hypothalamic set point. For this reason, severe hyperthermia does not generally respond to anti-pyretic medications.

Causes of severe hyperthermia include medications, endocrine disorders, and heat stroke.

Medication-induced hyperthermia

I discussed medication-induced hyperthermia in episode 40. The 3 types of medication-induced hyperthermia are:

1. Malignant hyperthermia

2. Neuroleptic malignant syndrome

3. Serotonin syndrome

Muscular rigidity, significant hyperthermia, and autonomic instability are all common features of serotonin syndrome, malignant hyperthermia, and neuroleptic malignant syndrome. A thorough review of the patient’s current and recent medications is the best way to tell the difference between these 3 conditions.

Endocrine disorders

The 3 types of endocrine disorders that cause hyperthermia are:

1. Thyrotoxicosis

2. Pheochromocytoma

3. Adrenal Crisis

Heat stroke

Heat stroke may be classical or exertional.

In classic heat stroke, high environmental temperatures overwhelm a patient’s ability to dissipate heat. This typically occurs with elderly patients or patients with chronic disease.

In exertional heat stroke an otherwise healthy patient’s ability to maintain normal temperature is disrupted by strenuous physical activity.

Fever (generally 38 °C or greater but under 41°C)

Fever above 38 °C but under 41°C is usually associated with an increase in the hypothalamic set-point. It may be infectious or non-infectious.

Infectious fever

During infection, cytokines (such as Interleukin-1) act as pyrogens and cause an elevation in body temperature.

Non-infectious fever

Causes of non-infectious fever are numerous and common. Patients in a surgical ICU are more likely to have non-infectious fever than fever from an infectious source. Examples of non-infectious fever are:

Transfusion reactions

Drug fever (Discussed in episode 64. The most common causes are antineoplastics, antimicrobials, CNS agents, and cardiovascular agents)

Deep vein thrombosis or pulmonary embolism

Septic thrombophlebitis

Pancreatitis

Acalculous cholecystitis (Typically occurs in patients with significant hypotension or s/p non-biliary surgery)

Postoperative fever (May be due to lung atelectasis)

Neurological insults such as subarachnoid hemorrhage, traumatic brain injury, or intracerebral hemorrhage

Fever workup

The authors of a review in the journal Critical Care had the following to say regarding the workup of critically ill patients with fever:

Guidelines recommend a clinically driven, cost-conscious approach, rather than a protocolized, dogmatic approach, to obtaining cultures and imaging studies in critically ill patients with pyrexia. Based on existing literature that suggests a poor association between pyrexia and the likelihood of a positive culture, yet a high likelihood that pyrexia heralds the presence of an infection, most infections are likely diagnosed based on clinical and radiographic findings. Therefore, we suggest for immunocompetent patients with an elevated body temperature that investigations should be guided by the clinical probability of the etiology. Blood cultures should be obtained in any patient with rigors, and may be avoided in febrile patients without concomitant systemic inflammatory response syndrome.

If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.

<– Previous Post Next Post –>