UKMLA Surgery: Acute Abdomen & Peri-op Masterclass

Surgery is where UKMLA candidates often under-read and over-rely on the question stem. The AKT and CPSA both lean heavily on acute abdomen differentials, peri-operative assessment, and post-operative complications — and the examiners build stems that punish candidates who haven't separated "how do I diagnose appendicitis?" from "when does appendicitis become surgical?" from "what are the post-operative complications of appendicectomy?"

This pillar covers the three surgery buckets the GMC content map emphasises: acute abdomen (with recognition algorithms by quadrant), pre-operative assessment (ASA grade, frailty, anaesthetic risk), and post-operative care (VTE prophylaxis, pyrexia workup, analgesia prescribing, ERAS). We end with a UKMLA pattern library — twelve surgical SBA stems where the diagnosis and first-line action should click within thirty seconds.

Use this alongside our gastroenterology high-yield guide for pancreatitis, cholangitis, and bowel-obstruction biochemistry, our emergency presentations masterclass for AAA rupture and acute limb ischaemia, and our prescribing safety guide for peri-operative anticoagulation management.

1. The Acute Abdomen: Differentials by Quadrant

The acute abdomen is the catch-all term for sudden-onset severe abdominal pain needing urgent surgical or medical evaluation. The first question every UKMLA stem asks is: where is the pain? Map the differential geographically.

Right upper quadrant (RUQ):

• Biliary: biliary colic, acute cholecystitis, ascending cholangitis
• Hepatic: hepatitis, liver abscess, congestive hepatomegaly
• Right basal pneumonia (referred)
• Right kidney: pyelonephritis, renal colic
• Subphrenic abscess

Epigastric:

• Peptic ulcer disease, perforated ulcer
• Pancreatitis
• MI (inferior, atypical presentation) — always consider in middle-aged + risk factors
• AAA
• Ruptured oesophagus (Boerhaave's)
• Gastritis

Left upper quadrant (LUQ):

• Gastric / splenic disease (rupture, infarct, abscess)
• Left basal pneumonia
• Left pyelonephritis, renal colic
• Pancreatitis (may be LUQ or diffuse)

Right iliac fossa (RIF):

• Appendicitis (most common in young adults)
• Mesenteric adenitis (children, post-URTI)
• Crohn's terminal ileitis
• Meckel's diverticulitis
• Ovarian cyst torsion, PID, ectopic pregnancy (always β-hCG in women of reproductive age)
• Caecal pathology (carcinoma, volvulus)

Left iliac fossa (LIF):

• Diverticulitis (most common in older adults)
• Sigmoid volvulus
• Ovarian/gynaecological pathology
• Constipation
• Sigmoid carcinoma

Suprapubic:

• UTI, urinary retention
• PID, endometriosis, ovarian pathology
• Ectopic pregnancy, miscarriage

Diffuse / central:

• Early appendicitis (before migration)
• Small bowel obstruction, mesenteric ischaemia
• Peritonitis from any perforation
• AAA, ruptured AAA
• DKA, Addisonian crisis (medical mimics)

UKMLA trap: middle-aged man with epigastric pain and shock — think MI and AAA before pancreatitis. Always get an ECG and check femoral pulses.

2. Appendicitis — Alvarado, Imaging, Management

Appendicitis is the commonest surgical emergency in the UK (lifetime risk ~7%). Classic presentation: central abdominal pain migrating to RIF over 12–24 hours, anorexia, nausea, low-grade fever, rebound tenderness and guarding at McBurney's point.

Alvarado score (MANTRELS):

• Migration of pain (to RIF): 1
• Anorexia: 1
• Nausea/vomiting: 1
• Tenderness in RIF: 2
• Rebound: 1
• Elevated temperature (>37.3°C): 1
• Leukocytosis (>10): 2
• Shift of WCC to left (neutrophils): 1

Score ≥7 → surgery; 5–6 → admit and observe or image; <5 → discharge with safety-net advice.

Signs:

• Rovsing's sign (LIF palpation → RIF pain)
• Psoas sign (hip extension → RIF pain) — retrocaecal appendix
• Obturator sign (hip flexion and internal rotation → pain) — pelvic appendix

Investigation:

• FBC, CRP, U&E, clotting, β-hCG, urinalysis (exclude UTI).
• Ultrasound first-line in children and pregnant women; sensitivity 80–90%.
• CT abdomen in adults with atypical presentation (high sensitivity/specificity).
• MRI if CT contraindicated (pregnancy).

Management:

• Laparoscopic appendicectomy first line.
• Conservative antibiotic-only management (amoxicillin-clavulanate) is an option for uncomplicated disease in selected patients (not standard UK practice — surgery still default).
• Complications: perforation (peritonitis), appendix mass (phlegmon — may be managed conservatively with interval appendicectomy), appendix abscess (drainage).

SBA trap: pregnant woman with RIF pain — suspect appendicitis, get an ultrasound first, surgery if confirmed (appendicitis in pregnancy has higher perforation rates with delay). β-hCG mandatory.

3. Cholecystitis vs Biliary Colic vs Cholangitis

Three biliary conditions on a single spectrum of gallstone disease.

Biliary colic:

• Transient obstruction of cystic duct → intermittent RUQ/epigastric pain, often post-fatty meal, lasting minutes to a few hours.
• Afebrile, no peritonism.
• USS confirms stones.
• Management: analgesia, elective cholecystectomy.

Acute cholecystitis:

• Persistent obstruction + inflammation of gallbladder wall.
• Constant RUQ pain, fever, Murphy's sign positive (arrested inspiration on RUQ palpation).
• WCC and CRP elevated; LFTs usually normal or mildly deranged.
• USS: thickened gallbladder wall (>3 mm), pericholecystic fluid, sonographic Murphy's.
• Management (NICE CG188): IV fluids + analgesia + IV antibiotics (e.g. co-amoxiclav); laparoscopic cholecystectomy within 1 week of presentation (preferred over delayed).

Ascending cholangitis:

• Infection of the biliary tree, usually obstructive cause (stone, stricture, malignancy).
• Charcot's triad: RUQ pain + fever/rigors + jaundice (50–75% have all three).
• Reynolds' pentad: Charcot's + hypotension + confusion (severe).
• LFTs obstructive pattern: raised ALP, GGT, bilirubin.
• USS/MRCP shows duct dilatation.
• Management: IV fluids + broad-spectrum antibiotics (piperacillin-tazobactam) + urgent ERCP for biliary drainage within 24 hours. High mortality if drainage delayed.

UKMLA trap: jaundiced patient + fever + rigors + RUQ pain → cholangitis → broad-spectrum antibiotics and urgent ERCP, not "trial of conservative management."

4. Pancreatitis (see GI guide) + Surgical Indications

Pancreatitis is covered in depth in the gastroenterology guide. Surgical relevance:

• Gallstone pancreatitis — cholecystectomy during the same admission for mild disease (NICE NG104), or delayed until inflammation settles in severe disease.
• ERCP within 72 hours if gallstone pancreatitis with cholangitis or persistent biliary obstruction.
• Complications needing surgical/radiological intervention: infected pancreatic necrosis (walled-off necrosis drainage), pseudocyst (endoscopic or surgical drainage if >6 weeks, symptomatic, or >6 cm).
• Severity scoring: Glasgow-Imrie, APACHE II, CRP >150 at 48 hours predicts severe disease.

5. Bowel Obstruction: SBO vs LBO, Operative Triggers

Bowel obstruction is a surgical emergency. Key split: small bowel vs large bowel, with different causes and operative thresholds.

Small bowel obstruction (SBO):

• Causes (60–70% adhesions from previous surgery; others: hernias, malignancy, Crohn's stricture, intussusception): AIMS — Adhesions, Intussusception/Inflammation, Malignancy, Strictures/Stones (gallstone ileus).
• Presentation: colicky central pain, vomiting (early, bilious → faeculent), absolute constipation (late), abdominal distension.
• Imaging: erect AXR — central distended loops >3 cm, valvulae conniventes (complete across lumen). CT abdomen + contrast identifies cause and transition point.
• Management: "drip and suck" — NG tube for decompression, IV fluids, electrolyte correction, catheter for fluid balance, analgesia, antiemetics. 70–80% resolve conservatively. Surgery if: strangulation (peritonitis, fever, WCC, lactate), closed-loop obstruction, no resolution in 48–72 hours, obstructed hernia.

Large bowel obstruction (LBO):

• Causes (60% colorectal cancer; others: diverticular stricture, volvulus, faecal impaction):
• Presentation: slower onset, distension prominent, later vomiting, absolute constipation.
• Imaging: AXR — peripheral distended loops >6 cm (caecum >9 cm indicates impending perforation), haustra (incomplete across lumen). CT with contrast for cause and staging.
• Management: IV fluids, NG decompression, catheter. Surgery more often needed — right hemicolectomy (caecal/ascending), Hartmann's (sigmoid with perforation/unstable), defunctioning stoma, or bridging stent (as neoadjuvant to elective resection).
• Sigmoid volvulus: "coffee bean sign" on AXR. First-line: flexible sigmoidoscopy and rectal tube decompression. Recurrent → sigmoidectomy.
• Caecal volvulus: requires surgery (decompression rarely works).

SBA traps:

• SBO + fever + rising lactate → strangulation → theatre now.
• Elderly with constipation, distension, "coffee bean" on AXR → sigmoid volvulus → flexible sigmoidoscopy + rectal tube.

6. Perforated Viscus — Recognition and Management

Perforation presents with sudden severe abdominal pain, peritonitis (rigid abdomen, rebound, guarding), shock if delayed.

Causes:

• Peptic ulcer (gastric/duodenal) — commonest upper GI; NSAIDs a classic cause.
• Diverticulitis (sigmoid).
• Appendix, caecum (obstructive cancer).
• Trauma.
• Boerhaave's (oesophageal rupture from vomiting).

Investigation:

• Erect CXR — free air under the diaphragm (up to 30% false negative).
• CT abdomen with contrast — definitive.
• Bloods: FBC (WCC), CRP, U&E, LFT, amylase (exclude pancreatitis), lactate (perfusion), VBG, group and save.

Management:

• IV fluids, broad-spectrum antibiotics (piperacillin-tazobactam), NG tube, catheter.
• Urgent laparotomy — washout, source control, repair vs resection ± stoma.
• Hartmann's procedure for perforated diverticulitis with faecal peritonitis.

7. AAA — Screening, Rupture Presentation

Abdominal aortic aneurysm is a focal aortic dilatation >3 cm.

Screening: UK NHS AAA screening programme — one-off abdominal ultrasound for men aged 65. Women not routinely screened (lower prevalence).

Asymptomatic AAA surveillance (UK):

• 3.0–4.4 cm: annual USS.
• 4.5–5.4 cm: 3-monthly USS.
• ≥5.5 cm (or rapid expansion >1 cm/year, or symptomatic) → elective repair (EVAR or open) per vascular MDT.

Ruptured AAA:

• Classic triad: abdominal/back/flank pain + hypotension/collapse + pulsatile abdominal mass.
• Often misdiagnosed as renal colic in the elderly — never diagnose new-onset renal colic in age >60 without excluding AAA.
• Management: do not delay — stable patients may have CT angiography to decide between EVAR and open repair; unstable patients go straight to theatre. Mortality of ruptured AAA remains 50–80%.

SBA trap: 75 y/o man with "renal colic" and hypotension → get a CT aorta, not a KUB.

8. Peripheral Vascular Disease — ABPI, Fontaine

Intermittent claudication: cramping pain in calf/thigh/buttock on walking, relieved by rest. Fontaine classification:

• I: asymptomatic
• II: intermittent claudication (IIa >200 m, IIb <200 m)
• III: rest pain
• IV: tissue loss (ulcers, gangrene) — critical limb ischaemia

ABPI (ankle-brachial pressure index):

• 1.3: abnormally stiff vessels (calcified — diabetes, CKD)

• 1.0–1.3: normal
• 0.9–1.0: acceptable
• 0.5–0.9: mild/moderate PAD (claudication)
• <0.5: severe PAD/critical limb ischaemia

Management (NICE NG236):

• Claudication: smoking cessation, exercise programme (supervised), statin (atorvastatin 80 mg), antiplatelet (clopidogrel 75 mg preferred over aspirin for PAD), optimise risk factors (BP, DM). Endovascular (angioplasty/stent) or bypass surgery if lifestyle-limiting or failed conservative.
• Critical limb ischaemia (rest pain >2 weeks OR tissue loss): urgent vascular referral, revascularisation preferred, amputation if not salvageable.

UKMLA trap: diabetic with ABPI 1.4 and absent distal pulses — calcified non-compressible vessels; don't be falsely reassured; use toe pressures or duplex USS.

9. Acute Limb Ischaemia — 6 Ps, Timing

Acute limb ischaemia is sudden interruption of arterial supply threatening limb viability. 6 Ps (same as compartment syndrome — different context):

1. Pain (sudden onset, severe)
2. Pallor (then marbled dusky)
3. Pulselessness
4. Paraesthesia
5. Paralysis (late)
6. Perishingly cold

Causes:

• Embolus (80%) — AF commonest source; rupture of atheromatous plaque; cardiac (recent MI with mural thrombus, endocarditis, prosthetic valve).
• Thrombosis in situ on pre-existing PAD.
• Trauma, dissection, paradoxical embolus.

Rutherford classification:

• I: viable (no sensory loss, no motor deficit, detectable Doppler)
• IIa: marginally threatened (minimal sensory loss, no motor deficit)
• IIb: immediately threatened (sensory loss beyond toes, mild-moderate motor deficit) — revascularise within 6 hours
• III: irreversible (profound sensory loss, paralysis, no Doppler) — amputation

Management:

• Immediate IV heparin (50–100 units/kg) and analgesia.
• Urgent vascular review.
• Investigation: CT angiogram or on-table angiography.
• Definitive: embolectomy (Fogarty catheter), thrombolysis (tPA), bypass, or primary amputation.
• Post-reperfusion: watch for compartment syndrome (fasciotomy if in doubt), rhabdomyolysis, hyperkalaemia.

10. Hernias — Inguinal, Femoral, Incisional

Inguinal hernias:

• Commonest hernia. Above and medial to the pubic tubercle.
• Direct (through Hesselbach's triangle — lateral to epigastric vessels medially) — older adults, bulge anterior.
• Indirect (through deep ring → inguinal canal → superficial ring, lateral to epigastric vessels) — all ages, controlled by pressure over deep ring.
• Elective repair (open Lichtenstein or laparoscopic mesh) — risk of strangulation lower than femoral but still indicated if symptomatic.

Femoral hernias:

• Below and lateral to the pubic tubercle, through the femoral canal.
• More common in women.
• Higher risk of strangulation (narrow neck) — always repair, even if asymptomatic.

Other hernias:

• Umbilical / paraumbilical: common, often congenital in children (resolve by age 3–5).
• Incisional: through previous surgical scar. Risk factors: obesity, wound infection, poor technique, immunosuppression.
• Richter's: only part of bowel wall herniates (not full circumference) — can strangulate without obstruction.
• Spigelian: through semilunar line.
• Obturator: through obturator foramen — elderly thin women, Howship-Romberg sign (pain down medial thigh).

Incarceration vs strangulation:

• Incarcerated: irreducible, not necessarily ischaemic.
• Strangulated: vascular compromise — pain out of proportion, erythema, fever, bowel obstruction. Emergency surgery.

SBA traps:

• Femoral hernia in elderly woman with bowel obstruction → strangulated → emergency repair.
• Post-operative incisional hernia in obese patient → elective mesh repair.

11. Pre-op Assessment — ASA Grade, CPEX, Frailty

ASA physical status classification (American Society of Anesthesiologists):

• ASA I: normal healthy patient.
• ASA II: mild systemic disease (smoker, mild DM, controlled HTN).
• ASA III: severe systemic disease (poorly controlled DM, COPD, HF).
• ASA IV: severe systemic disease that is constant threat to life (recent MI, severe HF, active ACS).
• ASA V: moribund, not expected to survive 24 hours.
• ASA VI: brain-dead, organ donor.
• Add "E" for emergency surgery.

Pre-op investigations (NICE NG45 — tailored by ASA and surgery grade):

• ASA I/II, minor surgery: usually none.
• ASA I/II, major surgery: FBC, U&E, ECG if >65.
• ASA III+: FBC, U&E, ECG, consider CXR, echo, PFT.

Specific considerations:

• Anticoagulation: bridging for high-risk mechanical valves; DOACs stopped 24–48 hours before (longer for renal impairment); warfarin stopped 5 days before (INR <1.5 target). See prescribing safety.
• Diabetes: variable rate insulin infusion (VRIII) if long starve, complex surgery, or diabetes poorly controlled.
• Steroids: patients on long-term steroids (>5 mg prednisolone for >3 weeks) need stress dose — IV hydrocortisone 50–100 mg at induction and post-op.
• Frailty: Clinical Frailty Scale ≥5 → multidisciplinary input, consider comprehensive geriatric assessment (see geriatrics guide).
• CPEX (cardiopulmonary exercise testing): anaerobic threshold <11 ml/kg/min predicts poor outcome from major surgery.

UKMLA trap: diabetic on long-acting insulin for elective AAA repair — start VRIII and stop usual insulin at NBM; resume when eating.

12. WHO Surgical Safety Checklist

The three-phase checklist prevents wrong-site, wrong-patient, wrong-procedure surgery.

Sign-in (before induction):

• Patient identity, procedure, consent confirmed.
• Site marked.
• Allergies known.
• Airway/aspiration risk assessed.
• Blood loss >500 ml anticipated → IV access + group and save.

Time-out (before skin incision):

• Team introductions.
• Patient, procedure, site confirmed.
• Anticipated critical events.
• Antibiotic prophylaxis given.
• VTE prophylaxis planned.
• Imaging available.

Sign-out (before patient leaves theatre):

• Procedure performed recorded.
• Swab, needle, instrument count correct.
• Specimens labelled.
• Equipment problems noted.
• Key recovery concerns communicated.

Expected knowledge: the checklist exists, its three phases, and that failure to comply is a "never event."

13. Post-op Pyrexia Ladder (4 Ws + Catheter)

Timing of post-operative fever narrows the differential. Classic "Ws":

Also consider: transfusion reaction (within 24 hours), aspiration pneumonia (post-extubation), endocarditis (if cardiac valve surgery), line sepsis.

UKMLA trap: post-op day 6 after bowel anastomosis, patient develops fever, tachycardia, abdominal pain → CT abdomen looking for anastomotic leak → theatre if confirmed.

14. VTE Prophylaxis and ERAS Principles

VTE prophylaxis (NICE NG89):

• All inpatients assessed on admission using a VTE risk assessment tool (Department of Health form).
• Mechanical: anti-embolism stockings (contraindicated in PAD, severe leg oedema), intermittent pneumatic compression.
• Pharmacological: LMWH (enoxaparin 40 mg OD, reduced to 20 mg in severe renal impairment) or fondaparinux. DOACs approved for elective hip/knee replacement.
• Duration: 7 days for most surgical patients; 28 days for major abdominal/pelvic cancer surgery, 35 days for hip replacement, 14 days for knee replacement (the lengths are worth memorising — they are popular SBA content).
• Withhold if active bleeding, severe thrombocytopenia, head injury, upcoming neuraxial procedure (time intervals per product).

ERAS (Enhanced Recovery After Surgery):

• Pre-op: carbohydrate loading (non-clear fluids up to 2 hours pre-op permitted in some protocols), no prolonged starvation, optimise anaemia, no bowel prep for most colorectal cases.
• Intra-op: multimodal analgesia, avoid opioids where possible, goal-directed fluid therapy, minimally invasive surgery, warming.
• Post-op: early mobilisation, early feeding, early catheter removal, early discontinuation of drains, multimodal analgesia.
• Reduces length of stay and complications.

15. Pain Ladders and Post-op Analgesia Prescribing

WHO analgesic ladder (adapted for post-op):

Step 1 — non-opioid: paracetamol 1 g QDS (max 4 g/day; reduce to 3 g if <50 kg or hepatic impairment). NSAIDs (ibuprofen 400 mg TDS, naproxen 500 mg BD) — avoid in renal impairment, active PUD, uncontrolled HF, >65 without PPI.

Step 2 — weak opioid: codeine 30–60 mg QDS (max 240 mg/day), tramadol 50–100 mg QDS. Check CYP2D6 ultra-rapid metaboliser risk (morphine toxicity).

Step 3 — strong opioid: oral morphine (Oramorph 5–10 mg PRN or immediate-release 10–20 mg QDS + PRN), IV/SC morphine (1–2 mg increments titrated), PCA (patient-controlled analgesia — 1 mg morphine bolus, 5-minute lockout, hourly max).

Adjuncts:

• Regional anaesthesia: epidural, spinal, nerve blocks (TAP block for abdominal surgery).
• Gabapentin/pregabalin for neuropathic pain and enhanced recovery.
• Ketamine (sub-anaesthetic doses) in refractory pain, chronic opioid users.
• Lignocaine infusion (colorectal ERAS).

Oral morphine conversions (repeat from prescribing safety):

• Codeine 10 mg : morphine 1 mg (10:1)
• Tramadol 10 mg : morphine 1 mg (10:1)
• Oxycodone 1 mg : morphine 1.5–2 mg (1:1.5)
• Subcutaneous morphine 1 mg : oral morphine 2 mg (1:2)
• IV morphine 1 mg : oral morphine 2–3 mg

Breakthrough dose: 1/6 of the total 24-hour oral morphine equivalent.

UKMLA traps:

• Patient on MST 60 mg BD (total 120 mg/day) → breakthrough dose 20 mg immediate-release (1/6 of 120).
• Converting oral morphine 60 mg to SC → 30 mg SC (half).
• Post-op epidural + additional oral morphine PRN → risk of respiratory depression; coordinate with anaesthetics.

The UKMLA Surgery Pattern Library

Twelve high-yield stems:

1. Central pain migrating to RIF + Rovsing's + WCC 14 → appendicitis → CT/USS and laparoscopic appendicectomy.
2. Jaundice + fever + RUQ pain → cholangitis → IV antibiotics + urgent ERCP.
3. Elderly + "renal colic" + shock → rule out ruptured AAA first; CT aorta.
4. Coffee-bean sign on AXR in constipated elderly → sigmoid volvulus → flexible sigmoidoscopy + rectal tube.
5. Sudden severe abdo pain + rigid abdomen + free air on CXR → perforated viscus → laparotomy.
6. AF patient with sudden cold painful leg, absent pulses → acute limb ischaemia → IV heparin + urgent vascular input.
7. Elderly woman with femoral hernia and bowel obstruction → strangulated → emergency repair.
8. Post-op day 2 pyrexia → atelectasis/pneumonia → chest physio, analgesia, reassess.
9. Post-op day 5 cancer bowel surgery with fever + abdo pain + tachycardia → anastomotic leak → CT + theatre.
10. Claudication at <100 m + ABPI 0.5 → PAD → supervised exercise + statin + clopidogrel; consider revascularisation if lifestyle-limiting.
11. Diabetic for elective AAA repair on long-acting insulin → start VRIII at NBM.
12. On MST 60 mg BD, worsening pain → breakthrough 20 mg Oramorph + reassess regular dose (consider 30% uplift).

Putting It All Together

Surgical SBAs reward candidates who keep three parallel maps in mind: the acute abdomen map (pain location → differentials → first-line imaging), the peri-op map (ASA + frailty + specific drug/condition considerations), and the post-op map (timing of fever → likely cause → investigation). Layer on top the pattern library — twelve stems that account for most of the surgical marks on UKMLA.

Pair this pillar with the gastroenterology high-yield guide for pancreatitis, UGI bleed, and diverticulitis detail, our emergency presentations masterclass for AAA rupture and acute limb ischaemia decision trees, the prescribing safety guide for peri-operative anticoagulation and post-op opioid prescribing, and the geriatrics guide for CFS-based decisions in older surgical patients. The obstetrics and gynaecology pillar covers the pregnancy-abdomen differentials (ectopic, ovarian torsion, HELLP) that overlap with surgical SBAs.

If a surgical stem feels murky, the usual fix is to ask the three questions again: where is the pain, what is the clock (sudden? days? post-op day?), and what single investigation gives you the fastest route to a diagnosis? Ready to practice? Start with an MLA Prep surgery mini-mock and see which stems you close on first read.