Indirect calorimetry in a patient on total parenteral nutrition shows a respiratory quotient of 1.15. What does this value indicate?

• A Predominant fat oxidation with adequate caloric delivery
• B Predominant carbohydrate oxidation at measured energy expenditure
• C Overfeeding with net lipogenesis from excess carbohydrate ✓
• D Protein catabolism as the dominant fuel source

Explanation

Respiratory quotient reflects substrate use: approximately 0.7 for pure fat oxidation, 0.8 for protein, and 1.0 for carbohydrate. An RQ above 1.0 means more carbon dioxide is being produced than oxygen consumed, which occurs when excess carbohydrate calories are converted to fat (de novo lipogenesis), a sign of overfeeding. It also raises ventilatory load, relevant in patients with limited respiratory reserve.

Reference: Sabiston Textbook of Surgery, 21st ed.

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