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Post-operative complications and post-operative fever
The cause of fever or deterioration after surgery is sought by the day it appears: in the first hours — the response to surgery, malignant hyperthermia or necrotising infection; on days 3–5 — pneumonia, urinary infection and line infection; on days 5–7 — wound infection and anastomotic leak; and after a week — abscess and thromboembolism.
Why it matters in the exam
Post-operative questions present a patient with fever, tachycardia, abdominal pain, low urine output or confusion, and ask for the diagnosis and the next step. The key is timing: fever on day one is usually an inflammatory response to surgery (atelectasis is not a proven cause of fever), tachycardia and abdominal pain on days 5–7 after a bowel anastomosis are a leak until proven otherwise, and sudden breathlessness in the second week raises suspicion of pulmonary embolism.
Other recurring topics: malignant hyperthermia during anaesthesia (rising end-tidal CO2, muscle rigidity, fever — treated with dantrolene); post-operative confusion in an older patient (the main risk factor is pre-existing cognitive decline; prevention without drugs, and avoiding benzodiazepines); low urine output (first check that the catheter is not blocked, then assess volume); and post-operative ileus versus mechanical obstruction. Remember that a post-operative myocardial infarction is usually silent, and that an anastomotic leak sometimes shows only as tachycardia and a recovery that is "slower than expected".
Key points
- Fever on day one — usually the response to surgery; malignant hyperthermia — dantrolene.
- Days 3–5 — lungs, urine and line.
- Days 5–7 — wound infection and anastomotic leak (tachycardia, pain, CT).
- After a week — abscess, thrombosis and embolism, drug fever and C. difficile.
- Delirium — look for a cause and use non-drug treatment; urine output below 0.5 mL/kg/hour — check the catheter first.
Summary table
| Timing | Main causes | Test or action |
|---|---|---|
| During surgery and up to 24 hours | Inflammatory response to surgery, malignant hyperthermia, transfusion reaction, early necrotising infection | Malignant hyperthermia — stop the trigger and give dantrolene 2.5 mg/kg |
| Days 3–5 | Pneumonia, urinary infection, intravenous line infection | Chest X-ray, urine and cultures; remove unnecessary lines |
| Days 5–7 | Wound infection, anastomotic leak | Examine the wound; contrast CT if a leak is suspected |
| After day 7 | Intra-abdominal abscess, deep vein thrombosis and pulmonary embolism, drug fever, C. difficile | CT, venous ultrasound, CT pulmonary angiography |
| Confusion (delirium) | Age, pre-existing cognitive decline, pain, drugs, infection, urinary retention | Look for the cause, non-drug measures; haloperidol only when there is danger; no benzodiazepines |
| Low urine output | Below 0.5 mL/kg/hour | Check the catheter, assess volume, review drugs and kidney function |
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Sources
- Sabiston Textbook of Surgery, 21st edition (2022) — Surgical Complications
- ESAIC guideline on postoperative delirium, 2023 (update) — Risk factors, prevention and treatment
- European Malignant Hyperthermia Group guidelines, 2020 — Recognition and dantrolene treatment of a malignant hyperthermia crisis
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.