Historically, mnemonics have been used in medicine to facilitate learning and provide clinicians with tools to enhance their care of patients. These memory devices are often applied on hospital wards, in EDs, and in primary care settings long after surgical rotations end. While some mnemonics have been tried and tested, others go invalidated in clinical trials and may actually contribute to incomplete or misguided assessments of patients. This can be especially problematic when diagnosing postoperative complications. “Oftentimes in surgery, index complications can initiate a cascade of other problems, resulting in high morbidity and costs,” explains Joseph A. Hyder, MD, PhD.

In the 1980s, the Rule of W mnemonic was first developed to chronicle the most common causes of postoperative fever in the order in which they occur. Although there is some variation in how it is taught, the five W’s are often shared as:

  1. Wind (atelectasis).
  2. Water (urinary tract infection [UTI]).
  3. Wound (wound infection).
  4. Walking (venous thromboembolism [VTE])
  5. Wonder drug (drug fever).

“Over time, the Rule of W has undergone numerous variations, but no research has been conducted to establish how the rule was formed or explore its veracity, including whether or not teaching of the rule may be broadened to include patients without fever,” Dr. Hyder says. “These are important shortcomings because multimodal perioperative analgesia, with drugs like acetaminophen and NSAIDs, has become increasingly common to help decrease rates of postoperative fever.”


A Simplified Approach

In a study published in the Journal of Surgical Education, Dr. Hyder and colleagues aimed to develop a simple, evidence-based mnemonic that can be applied to the teaching and diagnosis of postoperative complications. In the study, the timing and relative frequency of common postoperative complications was identified in a diverse surgical population. These findings were then applied to create a mnemonic that is analogous to the Rule of W but with an evidence base and applicability to postoperative patients without fever.

The study consisted of more than 614,000 patients, with nearly 10% of these individuals experiencing index complications of pneumonia, UTI, superficial surgical site infection (sSSI), deep/organ space (dSSI), VTE, kidney injury, and/or myocardial infarction (MI) within 30 days. The median time to complication differed significantly by postoperative day (POD) based on index complications (Figure). “For example, on POD 0, the most common complication was MI,” Dr. Hyder says. “Pneumonia was the most common complication on POD 1 and 2 while pneumonia and UTIs were significantly more common than other complications on POD 3.” On POD 4, the most common complication was sSSI. From POD 5 to POD 30, sSSI and dSSI were the two most common complications. Risk of VTE declined only slightly through POD 30.


A Revised Mnemonic

As a test of timing patterns, the authors calculated the median time to event for each index complication from the Rule of W over 30 days (Table). For additional verification, the median time to complication was tested during the first 14 PODs when competing diagnoses were most dynamic. The median time to events differed significantly during this postoperative interval. Based on the findings, the research team summarized a revision of the Rule of W as follows:

  1. Waves (ie, electrocardiogram waves)
  2. Wind (pneumonia)
  3. Water (UTI)
  4. Wound (sSSI and dSSI)
  5. Walking (VTE)

“Our study validates the Rule of W among surgical patients independent of fever and encourages data-driven modifications,” says Dr. Hyder. The revised mnemonic begins with Waves of the electrocardiogram because MI is the most common complication on POD 0. The next complication is still Wind, but this was revised from atelectasis to pneumonia, which represents a new target for prevention, diagnosis, and treatment. There is a striking distinction from the original Rule of W in that VTE was never the most common complication. “Our findings suggest that clinicians should be vigilant about finding VTE because risks for this complication persist 3 to 4 weeks postoperatively,” Dr. Hyder adds.


Thinking Critically

The more generalized Rule of W suggested in the study may have a role in efforts to prevent cascading complications in surgical patients by promoting prompt diagnosis and early rescue treatments. “Our research can be used as a starting point for critical thinking to enhance training,” Dr. Hyder says. “The findings add confidence to teachers and learners who apply the Rule of W when forming an initial differential diagnosis and creating diagnostic strategies.”


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;72:430-437. Available at: http://www.jsurged.org/article/S1931-7204(14)00305-5/abstract.

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