The long-held belief that atelectasis (collapse of part of a lung) is a common cause of early postoperative fever (EPF) is widely considered a myth in modern medical understanding.1
The primary reasons why atelectasis is not typically considered the cause of postoperative fever are:
Lack of Causal Evidence: Multiple clinical studies and systematic reviews have failed to establish a clear causal link between the presence of atelectasis and the development of a fever in the immediate postoperative period (usually the first 48–72 hours).2
For example, studies have shown that the incidence of atelectasis can increase in the days following surgery, while the incidence of fever may decrease over the same period, indicating they are independent events.3
Alternative Explanation: Inflammatory Response: The most likely cause of early postoperative fever is the body's normal, self-limiting inflammatory response to the trauma of surgery and general anesthesia.4
This is known as a stress-mediated inflammation, where damaged cells release alarm signals called Damage-Associated Molecular Patterns (DAMPs) that activate immune cells to release fever-inducing pyrogenic cytokines (like IL-6 and IL-1).5 This is a physiologic response, not an infection.6
High Incidence of Both: Both atelectasis and low-grade fever are very common after surgery (atelectasis can be seen in up to 90% of patients), leading to a frequent association that was misinterpreted as causation.
A patient may have both conditions, but the atelectasis is simply an incidental finding, not the source of the fever.7
What actually causes early postoperative fever?
In the absence of a clear source of infection, EPF is most often attributed to the benign inflammatory response to the surgical stress.8 More serious causes of fever (often remembered by the "5 Ws" mnemonic) usually occur later:
Wind (Pneumonia)9
Water (Urinary Tract Infection)10
Wound (Surgical Site Infection)11
Walking (Deep Vein Thrombosis/Pulmonary Embolism)12
Wonder drugs (Drug fever or transfusion reactions)13
A patient with a low-grade fever within the first two days post-op who has no other signs of infection is generally expected to have the fever resolve on its own, stemming from the inflammatory process.
This video further discusses the concept of whether atelectasis is truly a cause of fever: Does Atelectasis Cause Fever? - Medical