During our medical school and residency years, many of us learned the “Rule of W” as a helpful mnemonic for causes of postoperative fever: Wind (pulmonary causes, including atelectasis), Water (urinary tract infection), Wound (infection), Walking (deep venous thrombosis), and Wonder Drugs (drug fever). Classic teaching has been that noninfectious causes predominate during the first 48 hours post op, with infectious diseases taking over after that. Atelectasis is also very common in the immediate postoperative period, seen in up to 90% of patients by postoperative day 3, and is often taught as the primary cause of fever in the immediate postoperative period.1,2 But is this backed up by the evidence?
A 2011 systematic review looked at the association between atelectasis and fever. Eight studies involving 998 postoperative patients were included, with the majority of cases being postcardiac or abdominal surgeries. Seven of the eight studies failed to show a significant association between early postoperative fever (EPF) and atelectasis; in the one “positive” study, atelectasis was assessed only once on postop day 4. The authors of the review concluded that “there is no clinical evidence suggesting that atelectasis is a major cause of early EPF”.3 A subsequent study of postoperative fever in pediatric patients showed similar negative results.4 This begs the question – does atelectasis cause fever at all? Likely not. In an animal study from 1963, experimentally induced atelectasis resulted in fever, but the fever appeared secondary to infectious causes (i.e. pneumonia in the affected lung) and resolved with antibiotic administration.5 It seems more likely that EPF is due to other factors, such as the increase in pyrogenic cytokines seen in the postoperative period.3
So, what should the new generation of medical students and residents be taught? In an article reviewing complications seen in a cohort of over 600,000 surgical patients, the authors proposed a new “Rule of W” to reflect the most frequent postoperative complications, in order of timing: Waves (myocardial infarction), Wind (pneumonia), Water (urinary tract), Wound (infection), and Walking (deep venous thrombosis).6
Atelectasis and early postoperative fever are both commonly seen after surgery, but the relationship appears to be simply an association, not causal. The “Rule of W” can be an effective mnemonic for the causes of postop fever – just make sure you use the updated version.
Dr. Sehgal is clinical associate professor of medicine, division of hospital medicine, South Texas Veterans Health Care System and University of Texas Health Sciences Center at San Antonio. He is a member of the editorial advisory board for The Hospitalist.
1. Carter AR, et al. Thoracic Alterations After Cardiac Surgery. AJR. 1983;140(3):475-81.
2. Chu DI, Agarwal S. Postoperative Complications. In: Doherty GM. eds. CURRENT Diagnosis & Treatment: Surgery, 14e New York, NY: McGraw-Hill; 2014.
3. Mavros MN, Velmahos GC, Falagas ME. Atelectasis as a Cause of Postoperative Fever. Chest. 2011;140(2):418-24. doi: 10.1378/chest.11-0127.
4. Kane JM, Friedman M, Mitchell JB, Wang D, Huang Z, Backer CL. Association Between Postoperative Fever and Atelectasis in Pediatric Patients. World J Pediatr Congenit Heart Surg. 2011;2(3):359-63. doi: 10.1177/2150135111403778.
5. Lansing AM, Jamieson WG. Mechanisms of fever in pulmonary atelectasis. Arch Surg. 1963;87:168-74.
6. Hyder JA, Wakeam E, Arora V, Hevelone ND, Lipsitz SR, Nguyen LL. Investigating the “Rule of W,” a Mnemonic for Teaching on Postoperative Complications. J Surg Educ. 2015;72(3):430-7. doi: 10.1016/j.jsurg.2014.11.004.