Respiratory quotient is the ratio of VCO2 and VO2:
RQ = CO2 eliminated/O2 consumed
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. The respiratory quotient (RQ) is affected by extremes of substrate use by the body. Underfeeding, which promotes use of endogenous fat stores, should cause decreases in the RQ, whereas overfeeding, which results in lipogenesis, should cause increases in the RQ. 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.
Defined by: Ravi Balireddy, MD