Fever above 38ºC (100.4ºF) is common in the first few days after major surgery [1,2]. Most early postoperative fever is caused by the inflammatory stimulus of surgery and resolves spontaneously [3-7]. However, postoperative fever can be a manifestation of a serious complication.
A thorough differential diagnosis of postoperative fever includes infectious and noninfectious conditions that occur following surgery. Fever may arise due to a surgical site infection (SSI), or from other hospital-related conditions, including nosocomial pneumonia, urinary tract infection, drug fever, and deep vein thrombosis (table 1). In evaluating a postoperative patient with fever, it is important to consider a broad differential, and not to assume that fever is due to infection.
Fever as a manifestation of infection may be reduced or absent in immunocompromised patients including those receiving glucocorticoids, cancer chemotherapy, post-transplant immunosuppression, and also in some patients who are elderly or have chronic renal failure.
The evaluation of fever in immunocompromised patients is discussed elsewhere. (See "Infectious causes of fever and rash in non-HIV immunocompromised hosts" and "Approach to the immunocompromised patient with fever and pulmonary infiltrates" and "Overview of neutropenic fever syndromes" and "Diagnostic approach to the adult presenting with neutropenic fever".)
PATHOPHYSIOLOGY OF POSTOPERATIVE FEVER
Fever is a manifestation of cytokine release in response to a variety of stimuli [8-10]. Fever-associated cytokines, including interleukin (IL)-1, IL-6, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma, are produced by a variety of tissues and cells (algorithm 1). There is some evidence that IL-6 is the cytokine most closely correlated with postoperative fever  (see "Pathophysiology and treatment of fever in adults").