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Pre-Surgery Fasting: Why 8–12 Hours, Not 24 — Evidence-Based Rationale

Current guidelines (ASA, ESPEN, ERAS) recommend 6 hrs for solids, 2 hrs for clear liquids — not 24 hours. Prolonged fasting causes harm.

Physiological Rationale for Short Fasting

  1. Aspiration Prevention: Gastric volume <25 mL and pH >2.5 reduce pneumonitis risk. Achieved with 6-hr solid / 2-hr clear liquid fast.
  2. Gastric Emptying: Solids: 6–8 hrs; clear liquids: 60–90 min. Anesthetics delay emptying — but prolonged fasting increases volume/acidity.
  3. Metabolic Stability: Avoids catabolism, insulin resistance, hyperglycemia, dehydration, ketosis — all worsen outcomes.
  4. Patient Comfort: Reduces thirst, hunger, anxiety, headache, nausea.
  5. ERAS Alignment: Carbohydrate loading (clear carb drink 2–3 hrs pre-op) improves insulin sensitivity, reduces LOS.

Special Cases

  • Gastroparesis, bowel obstruction, pregnancy, difficult airway — individualized (may need longer).
  • Pediatrics: 6 hr solids / breast milk 4 hr / clear liquids 1–2 hr.

24-hour fasting is outdated, harmful practice. Follow modern, evidence-based preoperative fasting guidelines.

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