107 Rate of CO2 production
The rate of CO₂ production is the volume of carbon dioxide formed by the body's metabolism per minute. CO₂ is the end product of the oxidation of glucose, fats and amino acids in the mitochondria (via the citric acid cycle). In a steady state it equals the CO₂ exhaled, about 200 mL/min at rest. The ratio of CO₂ produced to oxygen consumed, the respiratory quotient (RQ), depends on which fuel is being burned. CO₂ production rises with metabolic rate: in exercise, fever, sepsis, burns, hyperthyroidism and with overfeeding.
Clinical significance
CO₂ production matters most in people with limited breathing capacity. When it rises, ventilation must increase to keep PaCO₂ normal. In patients with severe COPD, neuromuscular weakness or on a ventilator, high CO₂ production (for example from fever or overfeeding with carbohydrate) can cause hypercapnia and make weaning from the ventilator harder. Indirect calorimetry measures VO₂ and VCO₂ to calculate energy expenditure with the Weir equation and to adjust nutrition.
Lower production
Hypothermia, hypothyroidism, deep sedation and anaesthesia, starvation.
Higher production
Exercise, fever and sepsis, burns and trauma, hyperthyroidism, shivering, excessive carbohydrate intake, malignant hyperthermia.
Matching nutrition to measured energy needs avoids both underfeeding and overfeeding, which increases CO₂ production and the work of breathing.
References
- Weir JB de V. New methods for calculating metabolic rate with special reference to protein metabolism. J Physiol. 1949;109(1–2):1–9. doi:10.1113/jphysiol.1949.sp004363
- American Thoracic Society; American College of Chest Physicians. ATS/ACCP statement on cardiopulmonary exercise testing. Am J Respir Crit Care Med. 2003;167(2):211–277. doi:10.1164/rccm.167.2.211
This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.
Published on 7 May 2024