What is the respiratory quotient?
The respiratory quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed. This is based primarily on the patient’s diet.
A diet high in lipids has an RQ of 0.7. An all protein diet has an R/Q of 0.8. An all carbohydrate diet has an RQ of 1.0. A mixed diet of all of these has an RQ of 0.8, or 80%
What is the RQ used for?
- Patients with severe COPD who retain carbon dioxide may benefit by reducing their RQ.
- An elevated RQ may indicate overfeeding, while a decreased respiratory quotient may indicate underfeeding.
- The RQ is an important component of the alveolar air equation. The respiratory quotient allows us to approximate how much oxygen is leaving the alveoli. This is necessary to calculate the alveolar air equation.
What is the alveolar air equation?
The alveolar air equation calculates the pressure of oxygen within the alveoli. The alveolar air equation must also be calculated to then calculate the A-a gradient. The A-a gradient reflects the difference between oxygen pressure in the alveoli and oxygen pressure in the arteries. The A-a gradient helps us determine why a patient is hypoxemic.