Postoperative Fever

Postoperative fever is a temperature of 38.0 C or more after surgery. It is common, and most episodes in the first 48 hours are non-infectious.

Epidemiology. Up to 40% to 50% of patients have fever on days 1 to 2. Infection explains a minority of early fevers, and a much larger share after day 3.

Causes by timing.

• Days 0 to 2: inflammatory response to tissue injury, transfusion reaction, drug fever, malignant hyperthermia, adrenal insufficiency, thyroid storm, aspiration, and rarely necrotising soft tissue infection (streptococcal or clostridial).
• Days 3 to 7: surgical site infection, urinary infection, pneumonia, line infection, Clostridioides difficile, anastomotic leak, intra-abdominal abscess, venous thrombosis, pancreatitis, cholecystitis.
• After day 7: deep abscess, drug fever, sinusitis, parotitis, thrombophlebitis, haematoma, endocarditis.

Pathophysiology.

Surgical trauma releases interleukin-1, interleukin-6 and tumour necrosis factor alpha. These raise the hypothalamic set point through prostaglandin E2, and the size of the response follows the extent of surgery.

Hyperthermia without a raised set point (malignant hyperthermia, thyroid storm, serotonin syndrome) arises from heat production exceeding loss.

Look for a source: wound erythema, purulence or crepitus, calf swelling, cough, urinary symptoms, abdominal tenderness or distension, drain fluid, cannula phlebitis, diarrhoea, rash, meningism and new murmur.

Red flags.

• Hypotension, heart rate over 120/min, respiratory rate over 22/min, altered mentation or lactate over 2 mmol/L (sepsis).
• Pain out of proportion, skin blistering or crepitus (necrotising infection).
• Temperature over 40 C with rigidity and rising end tidal carbon dioxide (malignant hyperthermia).
• Neutropenia, prosthetic material or recent spinal procedure.
• Rash within hours of a new drug.

Review the operation, timing, drugs and transfusions, then examine fully. Send full blood count, C-reactive protein, procalcitonin, lactate, urea, electrolytes and liver tests.

Take two sets of blood cultures from separate sites before antibiotics when fever is over 38.5 C or sepsis is suspected. Send urine culture if symptomatic or catheterised with fever, wound swab, and stool for Clostridioides difficile if diarrhoea. Obtain chest radiograph if respiratory signs are present, venous duplex for suspected thrombosis, and CT of the abdomen and pelvis for suspected collection or leak.

Differential diagnosis.

• Inflammatory response.
• Surgical site infection.
• Pneumonia.
• Urinary infection.
• Line infection.
• Intra-abdominal collection or leak.
• Venous thromboembolism.
• Clostridioides difficile.
• Drug or transfusion reaction.
• Malignant hyperthermia.
• Adrenal or thyroid crisis.

Early fever without red flags. Examine, observe and do not start antibiotics empirically.

• Paracetamol: 1 g orally or IV every 6 hours (over 50 kg) as needed; maximum 4 g in 24 hours; use 2 to 3 g daily if under 50 kg, malnourished, chronic alcohol use or hepatic impairment; monitor liver enzymes if used beyond 3 days at high dose.

Sepsis. Give antibiotics within 1 hour, chosen for the likely source and local resistance.

• Piperacillin-tazobactam: 4.5 g IV every 6 hours; duration directed by source and response; maximum 18 g daily; monitor creatinine and full blood count; for creatinine clearance 20 to 40 mL/min give 3.375 g every 6 hours, under 20 mL/min give 2.25 g every 6 hours.
• Add vancomycin for suspected meticillin resistant Staphylococcus aureus: 25 to 30 mg/kg IV loading dose, then 15 to 20 mg/kg every 8 to 12 hours; monitor levels (area under the curve 400 to 600) and creatinine; extend the interval in renal impairment.
• Resuscitate with fluid and vasopressors as needed, and control the source (drain abscess, open the wound, remove an infected line, re-explore).

Necrotising infection. Urgent surgical debridement plus piperacillin-tazobactam 4.5 g IV every 6 hours (maximum 18 g daily; reduce for creatinine clearance under 40 mL/min), vancomycin 25 to 30 mg/kg IV loading dose then 15 to 20 mg/kg every 8 to 12 hours (area under the curve 400 to 600; extend the interval in renal impairment), and clindamycin 600 to 900 mg IV every 8 hours; duration directed by surgical findings; maximum clindamycin 2.7 g daily; monitor renal function and for Clostridioides difficile.

Malignant hyperthermia. Stop triggering agents, give 100% oxygen, and cool.

• Dantrolene: 2.5 mg/kg IV rapidly, repeated until signs settle; reconsider the diagnosis if cumulative dose reaches 10 mg/kg; monitor temperature, end tidal carbon dioxide, potassium and creatine kinase; caution in hepatic impairment.

Other causes. Treat thrombosis, withdraw implicated drugs, and give stress dose hydrocortisone for adrenal insufficiency (100 mg IV then 50 mg every 6 hours).

Monitoring. Temperature chart, vital signs, white cell count, C-reactive protein and cultures, and reassess the wound daily.

Referral and escalation. Surgical review for suspected collection, leak or wound infection. Critical care for sepsis with organ dysfunction. Infectious diseases advice for unexplained persistent fever, prosthetic infection or resistant organisms.

Special groups. Older adults may not mount a fever. Immunosuppressed and neutropenic patients need broader and earlier cover. In pregnancy use beta lactams and avoid tetracyclines and fluoroquinolones.