What Is Postoperative Fever? – Causes, Symptoms, Treatment

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What Is Postoperative Fever?/Postoperative Fever is defined as a temperature higher than 38 C (or greater than 100.4 F) on two consecutive postoperative days or higher than 39 C (or greater than 102.2 F) on any postoperative day. Knowledge of differential diagnosis, as well as a systematic approach, proves useful in narrowing down the differential diagnosis and instituting proper management.

Fever, as a manifestation of sepsis, should be promptly identified and managed appropriately to lower mortality rates in such cases.

Postoperative fever refers to an elevated body temperature (≥ 38.5°C) occurring after a recent surgical procedure. Diagnosing the cause of postoperative fever can sometimes be challenging; while fever in this context may be benign, self-limited, or unrelated to the surgical procedure, it can also be indicative of a surgical complication, such as infection.


Systemic Inflammatory Response Syndrome (SIRS):

Four criteria that include:

  • Temperature higher than 38 C or less than 36 C
  • Heart rate higher than 90 beats per minute
  • Respiratory rate greater than 20 per minute
  • White blood cell count greater than 12 x 10/L or less than 4 x 10/L

Two of the 4 criteria are needed to identify a patient with SIRS.

Two of the SIRS criteria plus a suspected source of sepsis is required to diagnose sepsis.

  • Sepsis plus organ dysfunction is consistent with severe sepsis.
  • Severe sepsis plus refractory hypotension (refractory to fluid resuscitation) is consistent with septic shock.

Signs of Organ Dysfunction

  • Systolic BP less than 90 mm Hg or mean arterial pressure less than 65 mm Hg.
  • Drop-in BP greater than 40 mm Hg (especially in hypertensive patients)
  • Lactate greater than 2 mmol/L
  • Urine output less than 0.5 mg/kg/hr for 2 consecutive hours
  • Drop-in Glasgow coma scale (GCS) or abbreviated mental test scores

Causes of Postoperative Fever

The timing strongly influences etiology.

  • Underlying conditions (e.g., immunosuppressed patients) may have a reduced inflammatory response or reduced fever while at the same time having a serious infection.
  • Differential diagnosis includes infectious (e.g., nosocomial or surgical site infections) and non-infectious (e.g., deep vein thrombosis, pulmonary embolus, myocardial infarction, drug-related, transfusion-related, endocrine-related for example adrenal insufficiency or thyroid storm) causes.
  • Fever is more likely to be due to infection as the time interval following surgery increases.
  • Fever in patients may have more than one cause at the same time, and infectious and non-infectious causes may coexist.


  • Wind – This refers to respiratory problems, such as pneumonia or atelectasis, a lung condition that’s sometimes caused by anesthesia.
  • Water –  The fever may be caused by a urinary tract infection.
  • Walking – This refers to venous thromboembolism (VTE), which is a potential complication of surgery.
  • Wound – This is an infection of the surgical site.
  • Wonder drugs – Some medications, including certain antibiotics or medications containing sulfur, can cause a fever in some people. A central line site can also become infected and cause a fever.
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Early Postoperative Fever


  • Soft-tissue infection (including Necrotizing Fasciitis)
  • Pneumonia
  • Clostridium difficile
  • Abdominal surgery complications (e.g. anastomotic leak or abscess)
  • Urinary Tract Infection
  • Infected Joint Replacement (or another infected prosthesis)
  • Catheter-Related Bloodstream Infection (CRBI)


  • Atelectasis is NOT a cause of fever (see above)
  • Pulmonary Embolism
  • Alcohol Withdrawal
  • Adrenal Insufficiency
  • Consider Hydrocortisone IV in addition to other management

Symptoms of Postoperative Fever

As you recover, also keep an eye out for any signs of infection around your surgical site or any areas that received intravenous medication. Common signs of infection include:

  • swelling and redness
  • increasing pain or tenderness
  • drainage of a cloudy fluid
  • warmth
  • pus
  • bad smell
  • bleeding

Other signs that your postoperative fever might be more serious include:

  • unexplained leg pain
  • severe headache
  • trouble breathing
  • painful urination
  • frequent urination
  • nausea or vomiting that won’t stop
  • a tear near the surgical site
  • severe constipation or diarrhea

Diagnosis of Postoperative Fever

Immediate Fever

Fever occurs immediately after surgery or within hours on postoperative days (POD) 0 or 1.

  • Malignant hyperthermia: high-grade fever (greater than 40 C), occurs shortly after inhalational anesthetics or muscle relaxant (e.g., halothane or succinylcholine), may have a family history of death after anesthesia. Laboratory studies will reveal with metabolic acidosis and hypercalcemia. If not readily recognized, it can cause cardiac arrest. The treatment is intravenous dantrolene, 100% oxygen, correction of acidosis, cooling blankets, and watching for myoglobinuria.
  • Bacteremia: High-grade fever (greater than 40 C) occurring 30 to 40 minutes after the beginning of the procedure (e.g., Urinary tract instrumentation in the presence of infected urine). Management includes blood cultures three times and starting empiric antibiotics.
  • Gas gangrene of the wound: High-grade fever (greater than 40 C) occurring after gastrointestinal (GI) surgery due to contamination with Clostridium perfringens; severe wound pain; treat with surgical debridement and antibiotics.
  • Febrile non-hemolytic transfusion reaction: Fevers, chills, and malaise 1 to 6 hours after surgery (without hemolysis). Management: Stop transfusion (rule out hemolytic transfusion reaction) and give antipyretics (avoid aspirin in the thrombocytopenic patient).

Acute Fever

Fever occurs in the first week (1 to 7 POD).

  • POD 1 to 3: atelectasis: After prolonged intubation, the presence of upper abdominal incision, inadequate postoperative pain control, lying supine. Should be prevented by incentive spirometry, semi-recumbent position, adequate pain control, early ambulation. Clinically may be asymptomatic or with increased work of breathing, respiratory alkalosis, chest x-ray with volume loss. Treatment includes spirometry, chest physiotherapy, semi-recumbent position (improves expansion of alveoli by preventing pressure from intra-abdominal organs on the diaphragm and hence improving functional residual capacity)
  • POD 3: Unresolved atelectasis resulting in pneumonia (respiratory symptoms, Chest x-ray with infiltrates or consolidation, sputum culture, empiric antibiotics and modify according to culture result and sensitivity), or development of urinary tract infection (urine analysis and culture, treat with empiric antibiotics and modify according to culture result and sensitivity)
  • POD 5: Thrombophlebitis (may be asymptomatic or symptomatic, diagnose with Doppler ultrasound of deep leg and pelvic veins and treat with heparin)
  • POD 7: Pulmonary embolism (tachycardia, tachypnea, pleuritic chest pain, ECG with right heart strain pattern (a low central venous pressure goes against diagnosis), arterial blood gas with hypoxemia and hypocapnia, confirm the diagnosis with CT angiogram, and treat with heparin if recurrent pulmonary embolism while anticoagulated with therapeutic INR, Inferior vena cava filter placement is the next step
  • POD 7 (5 to 10): Wound infection: Risk increases if the patient is immunocompromised (e.g., diabetic), abdominal wound, duration of surgery greater than 2 hours, or contamination during surgery. Signs include erythema, warmth, tenderness, discharge. Rule out abscess by physical exam plus ultrasound if needed. If an abscess is present, drainage and antibiotics are needed. Prevention is by careful surgical technique and prophylactic antibiotics (e.g., intravenous cefazolin at the time of induction of anesthesia as well as postoperatively if needed)

Subacute Fever

Fever occurs between postoperative weeks 1 and 4.

  • POD 10: Deep infection (pelvic or abdominal abscess and if abdominal abscess could be sub-hepatic or sub-phrenic). A digital rectal exam to rule out the pelvic abscess and CT scan to localize intra-abdominal abscess. Treatment includes re-exploration vs. radiological guided percutaneous drainage.
  • Drugs: Diagnosis of exclusion includes rash and peripheral eosinophilia

Delayed Fever

Fever after more than 4 weeks.

  • Skin and soft tissue infections (SSTI)
  • Viral infections

The above differential diagnosis is for causes that are categorized based on timing. However, there are many other causes that may have specific signs on physical exam and occur after specific surgery that are not included in the above differential.

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Initial assessment includes general appearance, GCS, and vital signs to determine how sick the patient is.

  • Airway, Breathing, Circulatory, Disability, Exposure (quick assessment to identify and simultaneously provide appropriate management)
  • Check patient notes (the type of procedure, timing of the procedure, intraoperative complications, anesthesia records, patient comorbidities, last ward rounds)
  • Check patient Intake and Output (including the type of stools, if the patient with type 7 stools rule out Clostridium difficile enterocolitis)
  • Check patient orders (is the patient being treated with antibiotics or not, receiving deep vein thrombosis prophylaxis or not)
  • System based assessment (pulmonary, cardiac, gastrointestinal, urinary)
  • Sites of infection that are visible (i.e., skin for bedsores, cellulitis, vascular access sites)
  • Besides tests – vital signs should be monitored. If the patient is hypotensive, venous blood gas is needed to measure serum lactate. It will guide fluid resuscitation; if the patient is tachycardic, bedside ECG might be important to confirm their rhythm, might rule out myocardial infarction; oxygen saturation 96% to 98% in patients with healthy lungs or 89% to 92% in carbon dioxide retaining patients, for example, COPD patients; monitor blood glucose levels because high blood glucose levels point towards septic response; urinalysis to rule out urinary tract infection
  • Blood tests – WBC, CRP especially if trending upward might point towards a septic response, hemoglobin level would point toward the oxygen-carrying capacity of the blood, liver function tests to rule out liver injury, coagulation parameters, and platelets to rule out disseminated intravascular coagulation, renal function to rule out kidney injury or electrolyte abnormalities
  • Microbiology – Cultures (blood, urine, wound, and sputum if producing it), if suspecting line sepsis (blood culture from the line, remove the line and send the tip to the lab)
  • Imaging – Chest x-ray (prove or rule out pneumonic process), abdominal imaging (ultrasound, CT scan to rule out collections)
  • Venous doppler – of the legs to rule out deep vein thrombosis


Treatment can include oxygen, fluid balance, intravenous fluids, and a urinary catheter, or antibiotics.

  • Drugs: antibiotics, analgesia, antiemetics
  • Incentive Spirometry
  • Venous thromboembolism prophylaxis (low molecular weight heparin and wearing pneumatic stocking)
  • Escalation (relay information to a senior health professional and ask for further advice from  infectious disease physician)

Additional support can be provided via anti-pyrexials and analgesia. It is important to ensure the patient remains hydrated; observations should be increased and a fluid balance started

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A low threshold of suspicion should be present for suspected sepsis. Any new rise in temperature whilst on antibiotics should prompt repeating the septic screen (and investigating other potential causes than infection). Any concerns should warrant an early senior review.

Infection Source Empirical Antibiotic Regime
Lower Respiratory Tract Co-Amoxiclav 625mg PO TDS for 5 days
Lower Urinary TractUpper Urinary Tract Trimethoprim 200mg PO BD for 3 daysCo-Amoxiclav 625mg PO TDS for 14 days
Surgical Site or Cellulitis Flucloxacillin 500mg PO QDS for 5 days
IV line(Central Line) Flucloxacillin 500mg PO QDS for 5 days(Vancomycin, levels requires close monitoring, follow local guidelines for dosing)
Intra-Abdominal Cefuroxime 1.5g IV TDS + Metronidazole 500mg TDS IV
Septic Arthritis Flucloxacillin 2g IV QDS
Unknown source Cefuroxime 1.5g IV TDS + Metronidazole 500mg TDS IV + Gentamycin 5mg/kg STAT


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