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What does Postoperative Fever Mean?


1

What is a fever?

Normal core temperature varies between 36°C and 38°C. Because humans hibernate a little at night, we are cool (36°C) just before rising in the morning; after revving our engines all day, we are hot at night (38°C). A fever is a pathologic state reflecting a systemic inflammatory process. The core temperature is >38°C but rarely >40°C.

2

What is malignant hyperthermia?

A rare, life-threatening response to inhaled anesthetics or some muscle relaxants. Core temperature rises >40°C. Abnormal calcium metabolism in skeletal muscle produces heat, acidosis, hypokalemia, muscle rigidity, coagulopathy, and circulatory collapse.

3

How is malignant hyperthermia treated?

  • a.

    Stop the anesthetic.

  • b.

    Give sodium bicarbonate (2 mEq/kg intravenously [IV]).

  • c.

    Give dantrolene (calcium channel blocker at 2.5 mg/kg IV).

  • d.

    Continue dantrolene (1 mg/kg every 6 hours for 48 hours).

  • e.

    Cool patient with alcohol sponges and ice.

Key Points: Malignant Hyperthermia

  • 1.

    Rare, familial (autosomal dominant with variable penetrance), catastrophic response to inhaled anesthetics or muscle relaxants

  • 2.

    Mechanism: Abnormal calcium metabolism in skeletal muscle

  • 3.

    Clinical manifestations: Core temperature >40°C, trismus, hypercapnia, tachycardia, tachypnea, hypertension, cardiac dysrhythmias, metabolic acidosis, hypoxemia, myoglobinuria, or coagulopathy

  • 4.

    Management: Halt anesthetic; administer dantrolene over 48 hours, supplemental sodium bicarbonate; actively cool patient

4

What causes fever?

Macrophages are activated by bacteria and endotoxin. Activated macrophages release interleukin-1, tumor necrosis factor (TNF), and interferon, which reset the hypothalamic thermoregulatory center.

5

Can fever be treated?

Yes. Aspirin, acetaminophen, and ibuprofen are cyclooxygenase inhibitors that block the formation of prostaglandin E 2 in the hypothalamus and effectively control fever.

6

Should fever be treated?

This is controversial. No evidence suggests that suppression of fever improves patient outcome. Patients are more comfortable, however, and the surgeon receives fewer calls from the nurses.

7

Should fever be investigated?

Yes. Fever indicates that something (frequently treatable) is going on. The threshold for inquiry depends on the patient. A transplant patient with a temperature of 38°C requires scrutiny, whereas a healthy medical student with an identical temperature of 38°C 24 hours after an appendectomy can be ignored.

8

Summarize a fever work-up

  • a.

    Order blood cultures, urine Gram stain and culture, and sputum Gram stain and culture.

  • b.

    Look at the surgical incisions.

  • c.

    Look at old and current intravenous sites for evidence of septic thrombophlebitis.

  • d.

    If breath sounds are worrisome, obtain a chest x-ray.

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