10 WHAT DOES POSTOPERATIVE FEVER MEAN?
Alden H. Harken M.D.

1. What is a fever?

Show answer Normal core temperature varies between 36°C and 38°C. Because we 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?

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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?

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* Stop the anesthetic.
* Give sodium bicarbonate (2 mEq/kg IV).
* Give dantrolene (calcium channel blocker at 2.5 mg/kg IV).
* Continue dantrolene (1 mg/kg every 6 hours for 48 hours).
* 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, coagulopathy.
4. Management: halt anesthetic; administer dantrolene over 48 hours, supplemental sodium bicarbonate; actively cool patient.

4. What causes fever?

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

5. Can fever be treated?

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Yes. Aspirin, acetaminophen, and ibuprofen are cyclooxygenase inhibitors that block the formation of prostaglandin E2 in the hypothalamus and effectively control fever.

6. Should fever be treated?

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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?

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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.

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* Order blood cultures, urine Gram stain and culture, and sputum Gram stain and culture.
* Look at the surgical incisions.
* Look at old and current IV sites for evidence of septic thrombophlebitis.
* If breath sounds are worrisome, obtain a chest x-ray.

9. What is the most common cause of fever during the early postoperative period (1-3 days)?

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The traditional answer is atelectasis. A total pneumothorax does not cause fever, however. Why does a little atelectasis cause fever, whereas a lot of atelectasis (pneumothorax) does not? The most likely explanation is that sterile atelectasis (and early postoperative lung collapse typically is not infected) has nothing to do with fever.

10. Do surgical incisions compromise spontaneous breathing patterns?

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Yes. Vital capacity was measured in a large group of patients 24 hours after various surgical procedures. An upper abdominal incision was the worst, followed by lower abdominal incision, then (counterintuitively) thoracotomy, median sternotomy, and extremity incision.

11. Should atelectasis be treated with incentive spirometry?

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Yes-but not to avoid fever.

12. Define a wound infection.

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A wound infection contains > 105 organisms per gram of tissue. An infected incision appears erythematous (red), edematous (swollen), and tender.

13. Are certain wounds prone to infection?

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Each milliliter of human saliva contains 108 aerobic and anaerobic, gram-positive and gram-negative bacteria. All human bite wounds must be considered as contaminated. Animal bite wounds typically are less contaminated. (It is safer to kiss your dog than your fiancé[e].)

14. Do incisions become infected early after surgery?

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The incision must be examined in a patient with a fever (39°C) < 12 hours after surgery. Look for a foul-smelling, serous discharge in a particularly painful wound (all incisions hurt) with or without crepitus. Gram stain of the serous discharge for gram-positive rods confirms or excludes the diagnosis of clostridial infection.

15. Summarize the therapy for clostridial gas gangrene.

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* The wound should be opened immediately, with fluid resuscitation of the patient. The mainstay of therapy is aggressive surgical debridement of necrotic tissue (skin, muscle, fascia). Make a big hole, and do not worry about closing it.
* Give penicillin, 12 million U/day IV for 1 week.
* Hyperbaric oxygen is not helpful.

16. Are nonclostridial necrotizing wound infections a cause of concern?

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Hemolytic streptococcal gangrene, idiopathic scrotal gangrene, and gram-negative synergistic necrotizing cellulitis are distinct entities but have been lumped into the single category of necrotizing fasciitis. All require the same initial approach:

1. Fluid and electrolyte resuscitation
2. Broad-spectrum antibiotics (”triples”)
3. Aggressive surgical debridement of all necrotic tissue

17. What are triple antibiotics?

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A shotgun approach to potentially life-threatening infections when the patient is seriously ill and the surgeon is seriously concerned:

1. Gram-positive coverage (e.g., ampicillin)
2. Gram-negative coverage (e.g., gentamicin)
3. Anaerobic coverage (e.g., metronidazole [Flagyl])

To avoid overgrowth of yeast and resistant bacteria, focus on the culprit bacteria as soon as the cultures define it.
KEY POINTS: CLOSTRIDIAL VERSUS NONCLOSTRIDIAL NECROTIZING WOUND INFECTIONS

1. Clostridial infection involves underlying muscle resulting in myonecrosis or gas gangrene.
2. Nonclostridial infection involves subcutaneous fascia (also known as necrotizing fasciitis).
3. Similar management: fluid and electrolyte resuscitation, antibiotics (high-dose penicillin for clostridial infection, broad-spectrum triples for necrotizing fasciitis), and aggressive surgical debridement of necrotic tissue.

18. Give the doses for triple antibiotics.

19. Which surgical procedures predispose to wound infections?

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Gastrointestinal procedures, especially when the colon is opened.

20. When do wound infections typically occur?

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12 hours to 7 days postoperatively.

21. How is a wound infection treated?

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The wound should be opened and completely drained.

22. Is it necessary to irrigate an infected wound?

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Tap water irrigation decreases the bacterial load and promotes healing. Alcohol is toxic to tissues. Sodium hydrochlorite (Dakin solution) and hydrogen peroxide kill fibroblasts and slow epithelialization. As a rule of thumb, put nothing into a wound that you would not put in your eye.

23. When do urinary tract infections (UTIs) occur?

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The longer the urethral (Foley) catheter is in place, the more likely the infection. Urologic instrumentation at the time of surgery may accelerate the process considerably. Germs crawl up the outside of the urethral catheter, and by 5-7 days after surgery most patients harbor infected urine.

24. How is a UTI diagnosed?

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Urine culture with > 105 bacteria/mL defines a UTI. White blood cells on urinalysis are highly suspicious.

25. Name the most common late causes of postoperative fever.

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Septic thrombophlebitis (from an IV line) and occult (usually intraabdominal) abscesses tend to present ≥ 2 weeks after surgery.

References
WEB SITES

1. http://www.mhacanada.org
2. http://www.anes.ucla.edu/dept/mh.html

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