A 50 kg woman undergoing elective surgery receives IV fluids for preoperative fasting replacement. Using the Holliday-Segar '4-2-1' rule, what is the maintenance fluid rate (mL/h) for a 50 kg adult?

• A 50 mL/h
• B 110 mL/h
• C 90 mL/h ✓
• D 150 mL/h

Explanation

The 4-2-1 rule: 4 mL/kg/h for first 10 kg = 40 mL/h; 2 mL/kg/h for next 10 kg = 20 mL/h; 1 mL/kg/h for remaining 30 kg = 30 mL/h. Total = 40 + 20 + 30 = 90 mL/h. This rule gives approximately 1500–1800 mL/day maintenance for a 50 kg adult, reflecting insensible losses and basal metabolic requirements.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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