TPN: Respiratory quotient

Respiratory quotient is the ratio of VCO₂ and VO₂ (carbon dioxide production). In other words: RQ = CO₂ eliminated/O₂ consumed. It is used in calculations of basal metabolic rate (BMR). Under typical metabolic conditions with stable respiratory function, the range of RQ in human metabolism is approximately 0.7 to 1.0. A value of 1.0 is consistent with pure carbohydrate oxidation, whereas a value of 0.7 is consistent with pure fat oxidation. Measurement of RQ in patients on TPN is important for two reasons: prevention of fat accumulation in the liver and alleviation of potential respiratory distress secondary to excess glucose. So the key is to keep the RQ somewhere between those two values.