Understanding the "5 W's": What is the mnemonic for the most common causes of post op fever?

October 1, 2025 •

5 min read

Postoperative fever affects a significant percentage of surgical patients, with incidences ranging from 14% to over 90% depending on the procedure. A helpful tool for medical professionals and patients alike is the mnemonic for the most common causes of post op fever, a simple memory aid known as the “5 W's,” which helps organize the potential sources of temperature elevation during recovery.

Quick Summary

The "5 W's" is a classic mnemonic for recalling potential causes of a fever after surgery: Wind, Water, Wound, Walking, and Wonder Drugs. The mnemonic helps healthcare providers and patients prioritize common postoperative issues based on their typical onset timing.

Key Points

The 5 W's Mnemonic: The classic memory tool for postoperative fever stands for Wind, Water, Wound, Walking, and Wonder Drugs.
Timing is a Guide, Not a Rule: While traditional teaching linked each "W" to a specific timeline, modern evidence shows significant overlap, and a fever's cause should always be evaluated clinically.
Atelectasis (Wind): Traditionally a cause of early fever, it is now often viewed as an associated finding rather than the sole cause; use incentive spirometry to reduce risk.
Surgical Site Infection (Wound): Infections at the incision site typically occur several days after surgery, presenting with redness, swelling, and increased pain.
Deep Vein Thrombosis (Walking): Immobility increases the risk of blood clots, so early movement as approved by a doctor is a critical preventative measure.
Beyond the Mnemonic: Other important causes of postoperative fever exist, such as transfusion reactions, malignant hyperthermia, and abscesses, which require prompt clinical investigation.

For decades, medical professionals have relied on the “5 W's” or “Rule of W's” as a foundational memory tool for approaching postoperative fever. This mnemonic provides a systematic framework for considering the most frequent causes of elevated body temperature following a surgical procedure. By associating each 'W' with a specific category of complication, it simplifies the diagnostic process for care teams and helps patients understand the potential reasons behind their symptoms during recovery.

The "5 W's" Explained

The traditional mnemonic serves as a checklist, with each 'W' representing a potential cause of fever. The sequence was originally used to reflect the typical timeline of complications, though modern data has nuanced this understanding.

Wind (Atelectasis and Pneumonia)

What it is: The 'Wind' in the mnemonic refers to pulmonary complications. The most common of these is atelectasis, a partial or complete collapse of a lung or a section (lobe) of a lung. After surgery, patients may breathe shallowly due to pain or residual anesthesia, causing air sacs (alveoli) to deflate and collapse. While previously taught as a direct cause of early fever, contemporary evidence suggests it is more of an associated finding, and not the sole cause. However, poor lung function can lead to more serious conditions.
When it typically appears: Traditionally associated with the first 24 to 48 hours after surgery.
Associated symptoms: Shortness of breath, rapid heart rate, or a cough.
Treatment: Using an incentive spirometer, deep breathing exercises, and early mobilization are key.

Water (Urinary Tract Infection)

What it is: This 'W' stands for a urinary tract infection (UTI). A UTI can develop after surgery, especially if a urinary catheter was used during or after the procedure. Catheters provide a pathway for bacteria to enter the bladder, leading to infection.
When it typically appears: Fevers from UTIs most commonly occur around three to five days post-operation.
Associated symptoms: Painful or frequent urination, cloudy or foul-smelling urine, and suprapubic discomfort.
Treatment: Diagnosis involves a urinalysis and urine culture, followed by appropriate antibiotics.

Wound (Surgical Site Infection)

What it is: A surgical site infection (SSI) refers to an infection at or near the incision site. SSIs can be superficial, involving only the skin, or deep, affecting the tissues beneath the wound.
When it typically appears: Infections usually manifest around day five to seven after surgery, but severe types like necrotizing fasciitis can appear earlier.
Associated symptoms: Increased redness, swelling, warmth, pain, or pus/drainage from the incision.
Treatment: Treatment often involves wound drainage, debridement (removal of infected tissue), and antibiotics.

Walking (Deep Vein Thrombosis)

What it is: This refers to venous thromboembolism (VTE), which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). Immobility after surgery is a major risk factor for blood clots forming in the deep veins of the legs. A PE occurs if a DVT clot breaks off and travels to the lungs, a potentially life-threatening event.
When it typically appears: Often after day four, as patients begin to move around more, though it can happen at any time.
Associated symptoms: Swelling, pain, or redness in one leg (for DVT) or shortness of breath, chest pain, and increased heart rate (for PE).
Treatment: Preventative measures include early ambulation, compression stockings, and blood thinners. Treatment involves anticoagulants.

Wonder Drugs (Drug or Transfusion Fever)

What it is: This category includes fevers caused by a reaction to medications or blood products given during or after surgery. A medication can trigger a fever as an allergic reaction or side effect. Transfusion reactions are also a possibility, though less common.
When it typically appears: Can be seen at any time, but is often considered after other causes have been ruled out. Some variants of the mnemonic associate it with later fevers.
Associated symptoms: A fever not explained by infection, often accompanied by a rash.
Treatment: Discontinuation of the offending drug or product, and sometimes symptomatic treatment.

The Traditional "Rule of W's" Timing vs. Modern Evidence

The traditional teaching of the '5 W's' implied a predictable timeline for fever causes. However, recent evidence suggests that this timeline is not absolute and that causes can overlap. The table below compares the classic view with a more evidence-based perspective.


	Classic Teaching (General Guide)	Modern Evidence (More Nuanced)
Wind	Within 24-48 hours (mostly atelectasis).	Atelectasis is common but not the likely cause of fever; pneumonia can occur within days (peak POD 2).
Water	Around 3-5 days after surgery.	UTIs can emerge after a few days, particularly with indwelling catheters.
Wound	Typically around 5-7 days post-op.	Wound infections often appear later, though severe infections can be much earlier.
Walking	After day 4 to 6, as patients become more mobile.	DVT/PE risk is present throughout the postoperative period, not just with mobility changes.
Wonder Drugs	A diagnosis of exclusion, often for later fevers.	Can occur at any time, often within the first week after administration of the medication or transfusion.
Immediate Fever	Not typically covered; often attributed to surgical trauma.	Consider malignant hyperthermia, blood transfusion reactions, or pre-existing infection (0-1 days).

Beyond the Mnemonic: A Holistic Approach

While the mnemonic is an excellent starting point, a comprehensive evaluation is always necessary. A healthcare team will consider a wide range of factors, including the patient's medical history, the type and length of the surgery, and other potential complications. Other fever causes not covered by the standard mnemonic, such as intra-abdominal abscesses, colitis, or line infections, must also be considered.

To promote a healthy recovery and minimize the risk of complications, patients should be proactive. Following surgical discharge instructions is critical. This includes proper wound care, staying hydrated, and adhering to prescribed medications. Early mobilization, as approved by a healthcare provider, can significantly reduce the risk of pulmonary and vascular issues.

Conclusion

For anyone involved in postoperative care, from the patient to the medical student, knowing what is the mnemonic for the most common causes of post op fever is a valuable first step in understanding potential complications. The "5 W's"—Wind, Water, Wound, Walking, and Wonder Drugs—provides an effective and memorable framework for considering potential sources of fever. While the traditional timeline associated with these causes is now viewed with more flexibility, the mnemonic remains a powerful educational tool that underscores the importance of a systematic approach to assessing a patient during surgical recovery. However, it is imperative to remember that this mnemonic is a guide, not a substitute for a comprehensive clinical evaluation, especially if the fever is high, persistent, or accompanied by other concerning symptoms.

For further information on this topic, consult a reliable medical resource like the article on postoperative fever from the National Center for Biotechnology Information (NCBI): https://www.ncbi.nlm.nih.gov/books/NBK482299/.

Frequently Asked Questions

The 'Wind' in the mnemonic stands for pulmonary issues, most commonly atelectasis (partial lung collapse) or pneumonia. It is traditionally associated with fevers occurring within the first 48 hours after surgery.

You can remember the most common causes of post-op fever using the '5 W's' mnemonic: Wind (lungs), Water (UTI), Wound (surgical site infection), Walking (DVT/PE), and Wonder Drugs (medication-induced fever).

A fever from a surgical site infection (SSI) most commonly appears later in the recovery period, typically around five to seven days after the operation. It may be accompanied by redness, warmth, or drainage at the incision site.

'Water' refers to a urinary tract infection (UTI), which is a common cause of fever after surgery, especially if a patient had a urinary catheter during the procedure.

Yes, walking and early mobilization, when medically approved, are crucial for preventing certain causes of postoperative fever. It helps prevent deep vein thrombosis (DVT) and pulmonary complications like pneumonia.

'Wonder Drugs' refers to a drug-induced fever, where a patient has a fever as a reaction to medications (like antibiotics) or blood products received during or after surgery.

No, modern evidence challenges the long-held belief that atelectasis is the primary cause of early fever. While the two are often associated, atelectasis is not always the direct causal link, and other inflammatory or non-infectious causes should be considered.