respiratory quotient
Ratio of carbon dioxide production to oxygen consumption, reflecting metabolic substrate utilization and respiratory efficiency.
Full Definition
The respiratory quotient (RQ) is a physiological measurement calculated as the ratio of carbon dioxide production (VCO2) to oxygen consumption (VO2), expressed as RQ = VCO2/VO2. This ratio typically ranges from 0.7 to 1.0 in healthy individuals and provides valuable information about metabolic substrate utilization and overall metabolic state. An RQ of 0.7 indicates predominantly fat metabolism, while an RQ of 1.0 suggests carbohydrate metabolism. Values above 1.0 may indicate hyperventilation, lipogenesis, or metabolic alkalosis. In critical care settings, RQ measurements help optimize nutritional support, assess metabolic efficiency, and guide weaning decisions for mechanically ventilated patients. The measurement is obtained through indirect calorimetry using specialized equipment that analyzes expired gases. Understanding RQ patterns assists respiratory therapists and clinicians in tailoring interventions to individual patient metabolic needs.
Usage
Usage note: Commonly abbreviated as RQ in clinical documentation.
In Context
- "The respiratory quotient of 0.85 indicated a mixed substrate metabolism pattern in the mechanically ventilated patient." — Metabolic assessment report
- "Indirect calorimetry revealed an elevated respiratory quotient of 1.2, suggesting overfeeding with excessive carbohydrate administration." — Nutritional consultation note