Wounds, Surgical Infection and the Postoperative Patient
Surgery — Wounds and Surgical Infection, NMC MBBS licence examination syllabus (Nepal Medical Council).
Wounds, surgical infection and the postoperative patient
Almost every surgical infection question has the same answer: source control.
Surgical infection is one of the few areas of medicine where the decisive treatment is usually not a drug. An abscess drained heals; an abscess treated with escalating antibiotics does not. Dead tissue removed stops feeding the infection; dead tissue left behind keeps the patient septic no matter what is running through the cannula. This single idea — source control — organises most of the chapter.
The corollary is a habit worth building now: when an infected patient is not improving, the first question is not "which antibiotic next?" but "is there something here that needs draining or removing?" That question, asked early, is what separates a straightforward recovery from a prolonged one.
🩺 Where this lives: Surgical site infection is among the commonest healthcare-associated infections, and a substantial proportion of cases are considered preventable. What prevents them is unglamorous and systematic — prophylactic antibiotics timed before the incision rather than after it, keeping the patient warm and well perfused, controlling glucose, and careful handling of tissue. None of it is technically difficult. It is reliably done or reliably forgotten, and the difference shows up in the wound five days later.
💡 A note on doses. This chapter gives none. Prophylactic and therapeutic antibiotic choices depend on the procedure, the likely organisms and local resistance patterns, all of which change. Learn the principles and the timing here; take agents and doses from your local guideline.
How wounds heal
The clinically loaded distinction is between healing by primary and secondary intention — because it is a decision, not just a description. Apposing the edges of a clean wound gives fast healing and a fine scar. Apposing the edges of a contaminated wound seals bacteria and dead tissue into a closed space, which is the recipe for an abscess. A dirty traumatic wound is cleaned, debrided and left open, with closure considered later once it is clean.
Surgical site infection
💡 Exam angle: the timing of prophylaxis is asked repeatedly and is easy marks. Prophylactic antibiotics are given before the incision, so that tissue concentrations are adequate at the moment contamination occurs. Given after the operation, they do very little — the bacteria are already established in the wound. Note also that prophylaxis is short: continuing antibiotics for days after a clean operation adds resistance and side effects without adding protection.
Abscess and source control
WHY ANTIBIOTICS ALONE FAIL AGAINST A COLLECTION
An abscess is a cavity of pus walled off from the
circulation. Antibiotics reach tissue through blood — and
there is no blood supply in the centre of a collection.
The acidic, anaerobic environment also impairs the
activity of several antibiotic classes and of neutrophils.
So the drug reaches the wall and not the contents. The
patient improves slightly, then plateaus, then relapses
when the course stops.
SOURCE CONTROL means physically dealing with the focus:
DRAIN the collection (surgery or image-guided)
DEBRIDE dead and devitalised tissue
REMOVE infected foreign material where possible
DIVERT or REPAIR a leaking viscus
THE RULE THAT COVERS MOST QUESTIONS:
if a patient with an infection is not improving on
appropriate antibiotics, look for a COLLECTION or DEAD
TISSUE before changing the drug.
Necrotising soft tissue infection
This is the surgical infection that must not be missed, and the reason it gets missed is built into it: the infection travels along the fascial plane beneath the skin, so the surface can look far better than the patient is. Pain out of proportion to the visible findings is the classic early clue, along with rapid progression and systemic toxicity. The treatment is urgent surgical debridement — antibiotics and resuscitation support the operation, they do not replace it, and imaging must not delay theatre when the diagnosis is clinically suspected.
The postoperative patient
POSTOPERATIVE COMPLICATIONS WORTH RECOGNISING
ATELECTASIS early fever, basal crackles. Treated by
sitting up, mobilising, physiotherapy and
good analgesia — pain that prevents deep
breathing causes it.
WOUND DEHISCENCE the wound separates, classically around
day 5-10. A pink serous discharge from an
abdominal wound is a warning sign that may
precede it. BURST ABDOMEN is a surgical
emergency — cover the viscera with warm
saline-soaked swabs and return to theatre.
ANASTOMOTIC LEAK fever, tachycardia, pain and ileus after
day 5 in a patient who was recovering.
Deterioration after initial improvement is
the pattern to notice.
ILEUS absent bowel sounds, distension, vomiting,
no flatus. Usually settles with supportive
care; distinguish from mechanical
obstruction.
VENOUS THROMBOEMBOLISM surgery, immobility and malignancy
together give a high risk, which is why
thromboprophylaxis is assessed routinely.
THE UNIVERSAL RULE: a postoperative patient who deteriorates
after initially improving has a COMPLICATION until proven
otherwise.
Clinical reasoning: four presentations
🔍 Case 1 — not settling on antibiotics
PresentationA patient treated for a soft tissue infection has had five days of appropriate intravenous antibiotics. The fever swings, and there is a tender fluctuant area. A broader-spectrum antibiotic is proposed.
Key cluesA swinging fever and a fluctuant swelling.
ReasoningThis is a collection. Antibiotics cannot penetrate the avascular centre of an abscess, so the patient improves partially and then stalls — exactly the pattern described.
AnswerDrain it. Escalating the antibiotic without source control is the wrong move; antibiotics are the adjunct here, not the treatment.
🔍 Case 2 — a leg that hurts more than it looks
PresentationA diabetic patient has severe leg pain with only modest erythema. He is tachycardic, febrile and looks unwell. The pain seems disproportionate. A CT is being arranged before a surgical opinion.
TrapBeing reassured by unimpressive skin, and letting imaging delay theatre.
ReasoningPain out of proportion to visible findings, with systemic toxicity and rapid progression, is necrotising infection until proven otherwise. The skin looks well because the disease is in the fascial plane beneath it.
AnswerImmediate surgical review for urgent debridement, alongside resuscitation and broad-spectrum antibiotics. Do not wait for the scan.
🔍 Case 3 — improving, then not
PresentationA patient recovering well after bowel surgery becomes unwell on day 6 — fever, tachycardia, abdominal pain and a distended silent abdomen. The team attributes it to postoperative ileus.
Key patternDeterioration after initial improvement.
ReasoningThat pattern, at this timing, after an anastomosis, is an anastomotic leak until proven otherwise. Ileus does not usually produce fever and progressive systemic upset.
AnswerResuscitate, investigate urgently for a leak, involve the operating surgeon early. Source control — drainage or reoperation — is what treats it.
🔍 Case 4 — the dirty wound in the emergency department
PresentationA farmer presents several hours after a deep, soil-contaminated laceration with some devitalised tissue. Primary suturing is proposed to give a neat scar.
TrapPrioritising the cosmetic result over the biology.
ReasoningClosing a contaminated wound over dead tissue creates a sealed, anaerobic space — an abscess waiting to happen, and a setting in which tetanus and clostridial infection are a genuine concern.
AnswerThorough cleaning and debridement, leave the wound open, and consider delayed closure once clean. Check tetanus immunisation status and manage per protocol.
Commonly confused
Confusion
The distinction
Why it matters
Cellulitis vs abscess
An abscess is a drainable collection
Antibiotics treat one and fail against the other.
Cellulitis vs necrotising infection
Pain out of proportion, toxicity, rapid spread
One needs antibiotics, the other needs theatre now.
Escalating antibiotics vs source control
No drug reaches the centre of a collection
The commonest reason for failure to improve.
Primary vs secondary intention
Closure is a decision based on contamination
Closing a dirty wound creates an abscess.
Prophylaxis before vs after incision
Tissue levels must be present when cutting
Given afterwards it achieves little.
Ileus vs anastomotic leak
Fever and progressive toxicity point to a leak
Attributing a leak to ileus loses critical time.
Serous discharge vs normal ooze
Pink serous fluid may precede dehiscence
A warning that can be acted on.
Rapid revision
MUST-KNOW FACTS
1. Wound healing: INFLAMMATORY → PROLIFERATIVE → REMODELLING.
2. Remodelling continues for months; scars gain strength slowly.
3. Primary intention: clean wound, edges apposed, fine scar.
4. Secondary intention: left open, granulates up, broader scar.
5. NEVER primarily close a contaminated wound.
6. Delayed primary closure is the answer for a dirty wound.
7. Healing is delayed by infection, ischaemia, diabetes, steroids, smoking.
8. Wound classes: clean, clean-contaminated, contaminated, dirty.
9. PROPHYLACTIC ANTIBIOTICS GO IN BEFORE THE INCISION.
10. Prophylaxis is short — prolonging it adds resistance, not protection.
11. SSI prevention also means normothermia, glucose control, oxygenation.
12. IF THERE IS PUS, LET IT OUT.
13. Antibiotics cannot penetrate the avascular centre of an abscess.
14. Swinging fever + fluctuant swelling = collection.
15. Not improving on antibiotics? Look for a COLLECTION or DEAD TISSUE.
16. Source control: drain, debride, remove infected material, repair a leak.
17. Necrotising infection: PAIN OUT OF PROPORTION to the skin findings.
18. Also: rapid spread, systemic toxicity, crepitus, anaesthetic skin.
19. It spreads in the fascial plane, so the skin can look deceptively well.
20. Necrotising infection needs URGENT SURGICAL DEBRIDEMENT.
21. Imaging must not delay theatre when it is clinically suspected.
22. Postop fever days 1–2: respiratory — atelectasis.
23. Days 3–5: urinary — think about the catheter.
24. Days 5–7: the wound — take the dressing down and look.
25. Beyond day 5: deep collection, anastomotic leak, thromboembolism.
26. Anastomotic leak: deterioration AFTER initial improvement.
27. Burst abdomen is an emergency — cover with warm saline swabs, theatre.
28. Pink serous discharge from an abdominal wound may precede dehiscence.
29. Good analgesia prevents atelectasis by allowing deep breathing.
30. Assess thromboprophylaxis in every surgical patient.
31. Check tetanus status in every contaminated traumatic wound.
💡 Exam angle: when a stem describes an infected surgical patient who is not getting better, the intended answer is almost never a different antibiotic. It is drainage, debridement or a return to theatre. Train yourself to reach for source control first — it is correct far more often than escalation, and it is the reasoning the question is testing.
Syllabus points
The phases of wound healing
Primary versus secondary intention
Why contaminated wounds are not primarily closed
What delays wound healing
The surgical wound classification
Timing of prophylactic antibiotics
Why antibiotics fail against a collection
Source control: drain, debride, remove, repair
Necrotising soft tissue infection
Pain out of proportion as the early clue
Postoperative fever by timing
Dehiscence, anastomotic leak and ileus
Create a free account to tick topics off, take notes as you read, watch the video lessons and get a day-by-day study plan built around your exam date.