Practice Perfect 715
Atelectasis Does Not Cause Postoperative Fever

Perhaps the most common question students are asked is to state the five Ws of postoperative fever. One can understand the purpose of this question: It requires a first order memorization while having a higher order clinical applicability to an important medical subject. Often called the “Rule of W,” it has some variations but goes something like this:

5 Reasons for Post-Operative Fever – the Rule of W?

Wind = atelectasis / pneumonia (24 - 48 hours)
Water = urinary tract infection (3 - 5 days)
Wound = wound infection (5 - 7 days)
Walking = venous thromboembolism (5 - 10 days)
Wonder drug = drug fever (anytime)

Many of us have been taught if the patient has a fever within the first 24 hours, the most common cause is atelectasis. I dutifully memorized this “fact” and prescribed incentive spirometry to all of my hospitalized patients, thinking I was doing something helpful. I was disconcerted to find out that atelectasis is, in fact, not a cause of postoperative fever. I thought at first that I was ignorant (very true) and should have known this, but during a recent academic session with students and residents, this very question came up using a well-known board review question system indicating it’s the continued presence of this inaccuracy in our knowledge base.

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As a very quick review, atelectasis is the loss of lung volume due to collapse of lung tissue.1 This may occur for several reasons including compression by a space-occupying lesion such as a tumor or infection, scaring of lung tissue, pleural effusion, pneumothorax, or blockage of an airway (termed obstructive atelectasis). In the operative setting obstructive atelectasis may theoretically occur as a result of breathing gas with a high fractional inspiration of oxygen (FiO2 or simply the amount of oxygen in the gas).

Yes, my friends, atelectasis does not cause postoperative fever. Let’s take a look at the research to support this claim. You will be even more perturbed to know the evidence against atelectasis has been building since the 1990s! I’ll point out here that most of the research is in general and cardiac surgery patients, and no studies exist that include lower extremity surgery. However, since atelectasis is most common in cardiac and general surgery it is fair to extrapolate the findings to podiatric surgery.

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Engoren2 in 1995 performed a retrospective analysis of 100 patients who underwent open heart surgery with the intent to see if atelectasis and postoperative fever were related. Patients were followed through postoperative day two with daily chest radiographs (a total of 190 radiographs taken) and continuous bladder thermometry. He found the incidence of atelectasis increased from 43% (day 0) to 69% (day 1) to 75% (day 2) while the incidence of fever decreased during this same period from 37% to 21% to 17% (day 0 to day 2), indicating a lack of association between the two conditions.

To more fully answer this question, in 2011 Mavros3 and colleagues performed a systematic review that included eight studies, of which one of the studies showed a relationship between atelectasis and early postoperative fever. They determined, “…there is no clear evidence that atelectasis causes fever at all.” Similarly, in 2011 Kane and associates4 found the same to be true for pediatric patients undergoing cardiac surgery. During their retrospective analysis of 203 patients, atelectasis increased during the first three days postop with no associated fever.

Despite the lack of prospective studies, experts have made it clear that atelectasis is not associated with postoperative fever, stating the following: “Early postoperative fever occurring in the first three days after surgery often requires no further diagnostic workup other than a review of the patient's history and medications and a focused physical examination.5

The obvious next question then is from where does postoperative fever come? Fever immediately in the OR or within hours after the surgery include inflammation from the surgery itself (mediated by IL-1, IL-6, TNF, and interferon gamma), malignant hyperthermia, or a pre-existing infection, while within the first three days is termed early postoperative fever. According to UpToDate5 the differential diagnosis for fever during the first three days is:

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  • Continued stress-mediated inflammation as a direct consequence of surgery
  • Trauma- or burn-mediated inflammation (very specific history that is easy to obtain)
  • Infections predating the operation
  • Myocardial infarction (fever is uncommon with MI but possible with Dressler syndrome or inflammatory pericarditis resulting from the MI)
  • Urinary tract infection (after genitourinary surgery or in-dwelling catheters)
  • Early surgical site infection (especially with Group A Streptococcus and Clostridium perfringens where surgical site infectious signs are also present)
  • Pneumonia (if a history of aspiration during anesthesia or continued intubation postop)

Note that none of these differentials includes atelectasis.

Let’s wrap this up by getting practical. A patient with a postoperative fever in the first three days may or may not have atelectasis, but the atelectasis is NOT the cause of the fever. More likely, the patient has a benign fever resulting from cytokine release related to the surgery. Perform a detailed history and physical to rule out the other important differentials, and if no obvious cause is noted then observe and expect fever reduction within a couple of days.

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This brings up one last question, and it relates to incentive spirometry. Since spirometry is intended to reduce atelectasis and postoperative fever, and we now know atelectasis is not a cause of postoperative fever, should we stop ordering spirometry? That, dear readers, is a question for another day!

Best wishes.

Jarrod Shapiro, DPM
PRESENT Practice Perfect Editor
[email protected]
  1. Stark P, Muller NL, Finlay G. Atelectasis: Types and Pathogenesis in Adults. UpToDate. Last update 1/27/2020.
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  2. Engoren M. Lack of association between atelectasis and fever. Chest. 1995 Jan;107(1):81-84.
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  3. Mavros MN, Velmahos GC, Falagas ME. Atelectasis as a cause of postoperative fever: where is the clinical evidence? Chest. 2011 Aug;140(2):418-824.
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  4. Kane JM, Friedman M, Mitchell JB, Wang D, Huang Z, Backer CL. Association between postoperative fever and atelectasis in pediatric patients. World J Ped Congenit Heart Surg. 2011 Jul;2(3):359-563.
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  5. Weed H, Baddour LM, Ho VP, Cochran A, Collins KA. Fever in the Surgical Patient. UpToDate. Last update 11/15/2019.
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