The amount of carbon dioxide produced as a result of metabolism in designated as VCO ₂ . It may be reported in mL/min or mL/kg/min.

At standard temperature and pressure, the rate at which carbon dioxide enters the alveolar gas from the blood is equal to the metabolic production of carbon dioxide by tissue metabolism in the body.

Calculation of the VCO ₂ is important for a number of reasons:

• The value of along with the value of VO ₂ is utilized for the calculation of the Respiratory Quotient
• An important application of VCO ₂ monitoring in the ICU is the determination of physiological dead space ratio. An increase in dead space represents an impaired ability to excrete CO ₂ . Increased dead space fraction is a feature of the early phase of acute respiratory distress syndrome (ARDS)
• Monitoring of VCO ₂ has also been found to be useful in the detection of pulmonary embolism
• In the ICU setting, additional applications include monitoring of ventilation, optimization of PEEP, assessment of pulmonary perfusion, and non-invasive determination of cardiac output

VCO ₂ is calculated by:

• VCO ₂ (mL/min) = VE (FECO ₂ - FICO ₂ )

mL/kg/min is calculated by:

• VCO ₂ (mL/kg/min) = VCO ₂ (mL/min) / kg body weight

Variable Definitions:

• VCO ₂ = CO ₂ exhaled in mL/min
• VE = Volume of air expired in mL/min
• FECO ₂ = Fraction of CO ₂ in expired air
• FICO ₂ = Fraction of CO ₂ in inspired air

Interpretation:

For a healthy, resting person with a normal Respiratory Quotient (RQ = 0.8), a normal VCO ₂ is 180- 200 mL/min or 2.5-3.5 mL/kg/min.

Factors affecting VCO2

Factors that increase VCO2:

• Any increased muscular activity (exercise or pathological causes)
• Hypermetabolic states (sepsis, hyperthyroidism, etc)
• Hyperthermia
• Pain/Stressors

Factors that decrease VCO2:

• Hypometabolic states (hypothyroidism)
• Hypothermia
• Paralysis (anesthesia, mechanical ventilation, Guillain Barré)
• Sleep or sedation

References:

• Arena R, Humphrey R, Peberdy MA. Prognostic ability of VE/VCO2 slope calculations using different exercise test time intervals in subjects with heart failure. Eur J Cardiovasc Prev Rehabil. 2003;10(6):463-8.
• Arena R, Myers J, Aslam SS, et al. Peak VO2 and VE/VCO2 slope in patients with heart failure: a prognostic comparison. Am Heart J. 2004;147(2):354-60.
• Arena R, Peberdy MA, Myers J, Guazzi M, Tevald M. Prognostic value of resting end-tidal carbon dioxide in patients with heart failure. Int J Cardiol. 2006;109(3):351-8.
• Guazzi M, Arena R, Ascione A, et al. Exercise oscillatory breathing and increased ventilation to carbon dioxide production slope in heart failure: an unfavorable combination with high prognostic value. Am Heart J. 2007;153(5):859-67.
• Hospital Management.net. Monitoring every breath you take. http://www.hospitalmanagement.net/features/feature746/. Last accessed May 10, 2009.
• Ohio University. Exercise Physiology Lab - Oxygen Consumption & Aerobic Capacity. http://www.biosci.ohiou.edu/faculty/schwirian/bios446/eplab07&08vo2&aerobiccapacity.htm. Last accessed May 10, 2009.