Surgical sciences and principles of surgery (general surgery core knowledge)
Domain 1 - Surgical sciences and principles of surgery (general surgery core knowledge)
This domain tests applied basic science - wound healing, haemostasis, the metabolic response to injury, fluid compartments, surgical microbiology and tumour biology - as the explanation for a clinical decision. EMQ stems are short scenarios; you must pick the single mechanism, fluid or timing, not list everything you know.
Core rules
- Wound healing: haemostasis → inflammation (0–3 days) → proliferation (3 days–3 weeks) → remodelling (up to a year). Type III collagen is laid first and replaced by type I. Strength is ~5% at day 5, ~20% at 3 weeks and never exceeds ~80% of normal skin. Steroids, diabetes, uraemia, jaundice, radiotherapy and malnutrition impair healing; vitamin C is required for proline hydroxylation.
- Haemostasis: primary haemostasis is platelet adhesion (vWF–GP Ib) and aggregation (GP IIb/IIIa); secondary is the coagulation cascade. A prolonged APTT with normal PT suggests haemophilia or heparin; a prolonged PT with normal APTT suggests warfarin, vitamin K deficiency or liver disease. Protamine reverses heparin; vitamin K and fresh frozen plasma correct warfarin-related bleeding.
- Metabolic response (Cuthbertson): an ebb (hypovolaemic) phase then a flow (catabolic) phase driven by catecholamines, cortisol, glucagon, ADH and aldosterone, with insulin resistance, sodium and water retention and potassium loss. Excess saline worsens oedema and ileus.
- Fluid compartments: total body water ≈60% of lean weight - ICF 40%, ECF 20% (interstitial 15%, plasma 5%). Maintenance is 4-2-1 mL/kg/h, roughly 25–30 mL/kg/day.
- Surgical infection: wound classes are clean, clean-contaminated, contaminated and dirty. Prophylaxis is a single dose within 60 minutes of incision (vancomycin and fluoroquinolones within 120 minutes), re-dosed every two half-lives or after 1,500 mL blood loss - and never a substitute for source control.
Worked example
A 62-year-old man is readmitted on day 6 after right hemicolectomy with fever 38.6 °C, tachycardia, oliguria and lactate 3.8 mmol/L. A leak presents around day 5–7 because collagen deposition is at its trough while luminal flora and intraluminal pressure are high - anastomotic strength is minimal then. The answer is resuscitation plus CT abdomen/pelvis with IV contrast and surgical source control, not antibiotics alone.
Traps
A normal platelet count does not exclude a bleeding disorder; maintenance fluid is not a series of boluses; prolonged postoperative antibiotics are not prophylaxis; and 'poor healing' usually has a named cause - steroids, jaundice, ischaemia or malnutrition - that the question is testing.