Myth of the Month

What is the most likely cause of this patient’s fever?


A 63-year-old man undergoes cardiac bypass surgery. He is able to be extubated at 8 hours. The next morning he has a fever to 38.5° C His exam shows no redness at the surgical site, or at his IV sites. His lung exam is unremarkable. His urinalysis is without white blood cells. His white blood cell count is 8,500, and his chest x-ray shows atelectasis without other abnormalities.

Dr. Douglas S. Paauw, University of Washington, Seattle

Dr. Douglas S. Paauw

What is the most likely cause of this patient’s fever? The research papers cited below suggest what it isn’t and what it might be.

One of the earliest things I was taught in my clinical years were the causes of postoperative fever, or the 5Ws, which are wind, water, wound, walk, and wonder drug.

Atelectasis was touted as the cause of early postoperative fever. This became clear fact in my medical student mind, not something that I had ever questioned. But investigation into whether there is evidence of this shows it is only a myth. In actuality, there is scant evidence, if any, for atelectasis causing fever. Frequently, no cause of postoperative fever has been found, despite aggressive attempts to look for one.

What the research says

Fanning and colleagues prospectively looked at 537 women who were undergoing major gynecologic surgery.1 Postoperative fever occurred in 211 of them. In 92% of these patients, no cause for fever was found.

Atelectasis is frequently seen postoperatively. Schlenker and colleagues reported that, in patients with postoperative atelectasis, temperature elevation on the first postoperative day was directly related to the degree of atelectasis, but the white blood cell count elevation was inversely related.2

In this study, atelectasis was diagnosed by auscultation, with chest x-rays ordered at the discretion of the physician. There was little correlation with the auscultatory findings and presence or absence of atelectasis in the patients who did receive chest x-rays.

Engoren did a study to prospectively evaluate 100 postoperative patients with daily chest x-rays and continuous temperature monitoring.3 Results from the day of surgery (day 0) to the second postoperative day showed an increase in presence of atelectasis from 43% on the day of surgery to 79% by day 2.

Fever, defined as temperature greater than 38° C, fell from 37% on the day of surgery to 17% by day 2. Engoren found no association between fever and degree of atelectasis.

Mavros and colleagues did a comprehensive review to determine whether there was evidence to support atelectasis causing fever.4 They concluded that there was no clinical evidence supporting the concept that atelectasis is associated with early postoperative fever.

A possible cause of fever

Mavros and colleagues’ paper suggested that early postoperative fever was caused by stress derived by surgery, which can increase the patient’s interleukin-6 levels and thermostatic set point. This was demonstrated in a small study by Wortel and colleagues, who measured IL-6 levels in the portal and peripheral blood of patients following pancreaticoduodenectomy.5 They found IL-6 levels correlated strongly with peak body temperature.

In conclusion, atelectasis is not a well-established cause of postoperative fever.

Dr. Paauw is professor of medicine in the division of general internal medicine at the University of Washington, Seattle, and he serves as third-year medical student clerkship director at the University of Washington. He is a member of the editorial advisory board of Internal Medicine News. Dr. Paauw has no conflicts to disclose. Contact him at


1. Fanning J et al. Infect Dis Obstet Gynecol. 1998; 6(6):252-5 .

2. Schlenker JD and Hubay CA. Arch Surg 1973;107:846-50

3. Engoren M. Chest. 1995;107(1):81-4 .

4. Michael N et al. Chest. 2011;140(2):418-24

5. Wortel CH et al. Surgery. 1993;114(3):564-70 .

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