Basic Sciences as Applied to Surgery
Basic Sciences as Applied to Surgery tests whether you can translate anatomy, physiology, pathology, microbiology, pharmacology, immunology, and perioperative nutrition into bedside decisions. The board favors mechanisms and numbers that change management, not isolated facts.
Fluids, electrolytes, and nutrition
- Total body water is about 60% of lean weight; intravascular volume is small, so crystalloid distributes widely. Use balanced isotonic crystalloid for resuscitation; 0.9% saline causes hyperchloremic metabolic acidosis.
- Maintenance with the 4-2-1 rule; replace deficits and ongoing losses. Correct chronic hyponatremia slowly (≤8–10 mEq/L/24 h) to avoid osmotic demyelination.
- Enteral nutrition is preferred when the gut works; start within 24–48 h after major surgery in the ICU. Refeeding syndrome: check phosphate, potassium, and magnesium.
Hemostasis, microbiology, pharmacology
- Primary hemostasis is the platelet plug; secondary hemostasis is fibrin. Give prophylactic antibiotics within 60 min of incision (120 min for vancomycin or fluoroquinolones); redose for long cases or major blood loss.
- Wound healing: hemostasis, inflammation, proliferation, remodeling. Cortisol, diabetes, radiation, malnutrition, and smoking impair it; vitamin C and zinc are cofactors.
Worked example: A 70 kg man has been NPO 8 h. Maintenance = 4×10 + 2×10 + 1×50 = 110 mL/h; 8-h deficit = 880 mL. Give maintenance plus deficit with isotonic fluid and add KCl only after urine output is established and potassium is known. Reasoning: 4-2-1 estimates hourly needs; deficits are replaced over time, not as a bolus, and potassium is never added blindly.
Traps: choosing hypotonic fluid for resuscitation; forgetting that third-space losses are isotonic; treating a high anion gap without calculating it; assuming albumin improves outcome in critical illness.