Postoperative fever and complications

• Fever is common after surgery. A mild low-grade fever up to 101.5 F (38.6 C) during the first 48 to 72 hours usually reflects normal healing (inflammation, wound repair, fluid shifts, anaesthesia effects) rather than infection. This is often called the "101.5 rule". ^[1]
• Most fevers that appear within the first 48 hours are benign and self-limiting. Fever that develops after the first 2 days is more likely to have an infectious cause, but non-infectious causes must still be considered. ^[2]
• Use the four Ws when evaluating postoperative fever: Wind (pneumonia, aspiration, pulmonary embolism, but not atelectasis alone), Water (urinary tract infection), Wound (surgical site infection), and "What did we do?" (drug fever, blood product reaction, line-related infection). ^[2]
• The cause varies with the postoperative day: immediate reactions such as malignant hyperthermia or transfusion reactions, early inflammatory fever and lung complications, then urinary infection and venous thromboembolism, and later surgical site infection, anastomotic leak, abscess, drug fever and postpartum endometritis. ^{[1][2][7][11][12]}
• A focused history and targeted examination (wound, lines, chest, abdomen, legs, mental state) beats a broad "shotgun" screen. ^[2]

By the end of this page you should be able to:

1. Explain why a low-grade early postoperative fever is often normal, and when fever should raise concern.
2. List the likely causes of fever for each postoperative day window.
3. Carry out a focused examination of the surgical wound and of all lines and drains.
4. Choose targeted, proportionate investigations instead of an undirected screen.
5. Use the algorithm to move from cause-by-day to a diagnosis and next step.
6. Outline practical prevention: skin preparation, prophylactic antibiotics, thromboprophylaxis, lung expansion, early mobilisation, and short catheter use.
7. Recognise and manage other early postoperative problems: ileus, wound dehiscence, urinary retention, and delirium.

There is an old teaching that atelectasis causes most early postoperative fevers. Contemporary evidence does not support that link on its own: a low-grade early fever is more plausibly part of the normal inflammatory response to surgery, and atelectasis is now listed as a pulmonary problem rather than a proven cause of fever. ^[2][5] At the same time the normal response is not harmless in every patient. Distinguishing the expected early fever from surgical site infection, leak, sepsis, or a rare catastrophe such as malignant hyperthermia is the core task. ^[1][7]

Clinicians sometimes speak of "physiologic" versus "pathologic" fever. In practice the distinction is made at the bedside by the timing, the height and pattern of the temperature, and the accompanying features, rather than by the number alone. ^[1]

The postoperative day is the strongest clue to the cause. The table is a guide, not a rule: more than one cause can coexist, and an individual patient may not follow the calendar.

Other causes belong in the differential whatever the day: infected intravenous lines and central lines, deep abscess, sinusitis from a nasogastric tube, Clostridioides difficile infection, false or factitious fever, and thrombophlebitis. ^[2] Postpartum endometritis deserves special mention: it is the most common postpartum infection, usually polymicrobial, and is 5 to 20 times more common after caesarean delivery than after vaginal delivery. ^[11]

Take the history with the postoperative day in mind. Ask about:

• The temperature itself: when it started, how high, its pattern, peaks, rigors, and sweating. A low intermittent grade over the first 2 days is usually reassuring; a new fever after a previously normal course is more worrying. ^[1][2]
• The procedure and anaesthesia: type of operation, wound class, duration, blood loss, mesh or implants, any difficulty or contamination, and whether volatile anaesthetics or succinylcholine were used. ^[7]
• Drugs: antibiotics, antipyretics, new medications started in hospital, propofol, or any infusion; drug fever is a diagnosis of exclusion after a careful medication review. ^[2]
• Lines and devices: every intravenous cannula, central line, arterial line, chest drain, nasogastric tube, urinary catheter, epidural catheter, and dressings, including insertion dates and sites. ^[2]
• Blood products: any transfusion and its timing, and whether fever, chills, back pain, red urine (haemoglobinuria), or breathlessness occurred during or shortly after it. ^[12]
• Obstetric history when relevant: mode of delivery, prolonged labour, membrane rupture, and postpartum bleeding. ^[11]
• Risk factors: diabetes, immunosuppression, malnutrition, obesity, smoking, chronic lung or kidney disease, known venous thromboembolism. ^[4]
• Forced daily activities: mobilisation, physiotherapy, respiratory exercises, and incentive spirometry use. ^[5]

Examination must be systematic and repeated, because findings change as complications declare themselves.

Inspect and palpate the whole incision, including any drain sites, under adequate light. Note erythema (and how far it extends), warmth, tenderness, induration, swelling, fluctuance, separation of wound edges, purulent or serous discharge, dehiscence, and evisceration. ^[4][10] Smell the dressing and any drainage. Remove the dressing when necessary, with clean technique, so that the deep wound can be seen. Early surgical site infection is diagnosed clinically, and signs often appear after the first week; fever, redness, tenderness and wound drainage are the usual clues. ^[2][4]

Wound healing is in its earliest stages at days 5 to 8, so dehiscence at that time is mechanical as well as biological. ^[10] If evisceration occurs, cover the exposed contents with a warm saline-soaked sterile dressing, keep the patient nil by mouth, and arrange urgent surgical review.

Inspect every line from hub to insertion site. Look for erythema, tenderness, purulent drainage, tunnel infection, and swelling along the tract. Palpate central venous sites, including the neck, infraclavicular area, and groin. Check urine colour, clarity, and any catheter bypassing; a catheter-associated urinary infection is a common source after day 3. ^[2][9] For a chest drain, inspect the insertion site, check the underwater seal and drainage character, and auscultate the chest. For a wound drain, inspect around the site and characterise the output. Do not forget to count lines: an overlooked idle cannula is a common source. Remove unnecessary cannulas. ^[2]

• Chest: respiratory rate, oxygen saturation, chest expansion, percussion, and auscultation for crackles, consolidation, pleural rub, or effusion. ^[5]
• Abdomen: distension, tenderness (generalised versus localised), guarding, rebound, bowel sounds, and visible peristalsis. Ileus, anastomotic leak, and intra-abdominal abscess each produce a different pattern. ^[8]
• Legs and pelvis: unilateral swelling, warmth, tenderness, or superficial thrombophlebitis suggestive of deep vein thrombosis. ^[2]
• Mental state: confusion, inattention, or a change from baseline (see Delirium). ^[13]
• Skin and joints: rashes, infection at remote sites, or seeded septic foci.

Investigate with a focused approach, directed by the postoperative day and the findings. Undirected panels waste resources and often mislead. ^[2]

• Vital signs and temperature trend: include respiratory rate and oxygen saturation, and record the postoperative day for every reading.
• Full blood count (with differential) for anaemia, leucocytosis, or leucopenia; a raised neutrophil count supports bacterial infection, but inflammation alone can raise it.
• Renal and liver function, electrolytes, glucose (target under 200 mg/dL perioperatively). ^[4]
• Inflammatory markers: C-reactive protein is useful for trend; procalcitonin is more specific for bacterial infection where available. Interpret both in context; they rise after surgery itself. ^[4]
• Cultures where there is a suspected source: blood (peripheral and from lines) if sepsis is possible, urine if pyuria or catheter-related infection is suspected, sputum or tracheal aspirate with respiratory signs, wound swab or pus, and cerebrospinal fluid only when indicated. Take cultures before antibiotics when this can be done without delaying treatment. ^[2]
• Urine dipstick and microscopy: useful for a water source; remember that asymptomatic bacteriuria is common with catheters and does not always explain fever. ^[9]
• Imaging: chest radiograph when respiratory signs are present; ultrasound for superficial collections and gallbladder; computed tomography with contrast for suspected anastomotic leak, deep abscess, or unexplained prolonged fever. Targeted venous ultrasound if deep vein thrombosis is suspected.
• Wound imaging: probe a deep collection with ultrasound before opening it, and obtain computed tomography if the infection seems to extend into tissue planes.
• Removed catheter tips are cultured when a line infection is suspected.

When fever persists beyond a few days despite treatment, do two things: revisit the history, examination, and drug chart, and image for a deep or secondary source. ^[2][4]

• Treat the underlying cause, not the number. Early low-grade inflammatory fever usually needs fluids, encouragement to mobilise and breathe deeply, and monitoring, rather than antibiotics. ^[1][2]
• Suspected sepsis: take cultures, resuscitate, and give empirical antibiotics that cover the likely source after local guidance; remove or control a focus of infection such as an abscess or infected wound; control lines when they are the source.
• Malignant hyperthermia: stop all trigger agents, hyperventilate with high-flow oxygen, cool actively, support circulation, and give intravenous dantrolene; it should be available wherever triggers are used. ^[7]
• Venous thromboembolism: if confirmed, anticoagulate according to protocol; for prophylaxis see below.
• Surgical site infection: open and drain collections, debride necrotic tissue, obtain cultures, and use antibiotics for spreading infection or systemic features. ^[4]
• Anastomotic leak: nil by mouth, intravenous fluids and antibiotics, imaging, and urgent senior or surgical review; re-operation may be needed.
• Wound dehiscence: support the wound and protect against evisceration; urgent surgical opinion.
• Postoperative delirium: reorient, optimise analgesia, sleep, hydration, and oxygenation; review medications; treat the underlying precipitant. ^[13]

Prevention spans the whole perioperative pathway. The measures below are the ones with evidence captured in the sources for this page.

These four problems are not all febrile, but each colours the assessment of a postoperative patient and two of them (ileus and delirium) frequently accompany early fever.

Prolonged ileus increases hospital stay, cost, and patient discomfort, and it can mimic a more serious obstruction. ^[8] Management is supportive and stepwise:

• Confirm that there is no mechanical obstruction or anastomotic leak (re-examine and image if worried).
• Nil by mouth with a nasogastric tube if there is vomiting or distension.
• Intravenous fluids and electrolyte correction (especially potassium and magnesium), adequate analgesia with opioid-sparing where possible, early mobilisation, and careful reintroduction of oral intake once flatus or stool returns and nausea settles. ^[8]

Dehiscence is partial or total separation of a previously closed wound because healing has failed. It typically occurs 5 to 8 days after surgery, when healing is still in its early stages. ^[10] Predisposing factors include ischaemia, infection, raised intra-abdominal pressure, diabetes, malnutrition, smoking, and obesity. ^[10]

Superficial separation is warned of by increased bleeding or drainage. Complete dehiscence can lead to evisceration, with herniation of intra-abdominal organs through the open wound. ^[10] Management: protect the wound, cover any exposed contents with a warm saline-soaked sterile dressing, keep the patient nil by mouth, give intravenous fluids and analgesia, and obtain urgent surgical review. If dehiscence is suspected, inspect early and do not simply re-dress and wait.

Postoperative urinary retention (POUR) is the inability to pass urine after surgery despite a full bladder. ^[9] Because the definition is not standardised, reported prevalence ranges widely, from 5 to 70 percent, so it is common in hospital practice. ^[9] Unrecognised POUR can lead to prolongation of stay, urinary tract infection, detrusor damage from over-distension, overflow incontinence, vesicoureteric reflux, and, in severe cases, renal failure. ^[9]

Risk is increased by pelvic and anorectal surgery, opiates, neuraxial anaesthesia, male sex, and older age. Management:

• Conservative measures first: privacy, warmth, ambulation where safe, analgesia, and running water.
• If these fail, catheterise (intermittent or short-term indwelling), documenting volumes.
• Avoid leaving a catheter in place longer than necessary; re-check a bladder scan or residual volume after removal and record voiding. ^[9]

Postoperative delirium is delirium occurring at any point between emergence from anaesthesia and hospital discharge; it may be hyperactive (agitated, restless), hypoactive (quiet, lethargic, low attention), or mixed. ^[13] Hypoactive delirium is easily missed and is the commonest form in elderly postoperative patients. ^[13]

Management is cause-directed and supportive: reorient and familiarise, optimise analgesia and sleep, ensure hydration and oxygenation, correct infection, electrolytes, and pain, and rationalise psychoactive drugs (minimise benzodiazepines and anticholinergics). ^[13] Any new fever in an older postoperative patient whose recovery has stalled should prompt a search for infection, hypoxia, or dehydration as the trigger, including at the wound and lines.

Refer urgently (same hour) for red-flag conditions listed above: malignant hyperthermia, sepsis, suspected anastomotic leak, necrotising soft tissue infection, line-related sepsis, pulmonary embolism, and wound dehiscence with evisceration. ^[2][7][10]

Routine referral is appropriate for a wound infection needing drainage, a suspected abscess on imaging, a urinary infection that does not respond to treatment, a surgical site infection in a patient with implants, and any fever that persists beyond a few days without a clear source. ^[2][4]

• Make the diagnosis at the bedside: a systematic examination of the wound, lines, chest, abdomen, and legs will find most sources without advanced testing.
• Draw blood cultures before antibiotics only if the laboratory can process them; do not let them delay treatment. Use the cheapest reliable imaging, such as clinical examination and plain radiographs, and reserve computed tomography for when it will change management.
• Early mobilisation, incentive spirometry or coached deep breathing, removal of unnecessary catheters, and thromboprophylaxis with fluids and early walking are available almost everywhere and prevent the problems that cause late fever. ^[5][6][9]
• Use generic antibiotics according to local resistance data; avoid broad-spectrum agents where a narrower drug fits the likely source. ^[3][4]
• Where dantrolene for malignant hyperthermia is unavailable, prevention (avoiding triggers and preparedness) and rapid cooling remain essential. ^[7]

• A low-grade fever up to 101.5 F (38.6 C) in the first 48 to 72 hours usually reflects normal healing; most fevers in the first 48 hours are benign and self-limiting. ^[1][2]
• Fever after the first 2 days is more likely to be infectious; always re-check the postoperative day when the temperature is taken. ^[2]
• Atelectasis is not, on its own, a proven cause of fever; early fever is more plausibly part of the normal inflammatory response. ^[2][5]
• Use the four Ws (Wind, Water, Wound, What did we do?) to organise the search; look for pneumonia, UTI, surgical site infection, and iatrogenic causes. ^[2]
• Malignant hyperthermia and transfusion reactions are the dangerous immediate causes; know the triggers, the rigidity, and the hypercarbia. ^[7][12]
• Surgical site infection develops after day 5 in many patients and is often diagnosed clinically at the wound; SSI occurs in 5 to 20 percent of operations and is up to 60 percent preventable. ^[2][4]
• Postpartum endometritis is 5 to 20 times more common after caesarean delivery than after vaginal delivery, and is often polymicrobial. ^[11]
• Discontinue prophylactic antibiotics within 24 hours in most operations; give the dose 30 to 60 minutes before incision and redose in long cases. ^[3][4]
• Thromboprophylaxis commonly starts 24 to 72 hours after surgery and continues for 7 to 30 days or until mobile, balanced against bleeding risk. ^[6]
• Postoperative urinary retention is common (5 to 70 percent reported), and delirium between emergence and discharge is easily missed when hypoactive. ^[9][13]

Postoperative ileus; delirium and perioperative neurocognitive disorders; wound care and surgical site infection; venous thromboembolism and thromboprophylaxis; urinary tract infection and catheter care; malignant hyperthermia; transfusion reactions; sepsis; pneumonia and postoperative pulmonary complications; diabetes and perioperative glucose control.