Understanding Expired CO2 Fraction
Expired carbon dioxide fraction shows how much carbon dioxide is present in exhaled gas. It is written as FECO2. The value may be shown as a decimal, percent, or parts per million. It helps students connect ventilation, gas exchange, and partial pressure ideas.
Why This Value Matters
A higher fraction means a larger part of the expired breath is carbon dioxide. A lower fraction can appear when ventilation is high compared with carbon dioxide production. The number also changes when dead space, breathing pattern, or measurement method changes. This calculator is for learning and planning. It should not replace clinical equipment.
Two Calculation Paths
The volume path uses carbon dioxide production and minute ventilation. Carbon dioxide production is commonly entered in milliliters per minute. Minute ventilation is entered in liters per minute. The tool converts ventilation to milliliters per minute. Then it divides carbon dioxide output by expired ventilation.
The pressure path uses mixed expired carbon dioxide pressure. It divides that pressure by dry gas pressure. Dry gas pressure equals barometric pressure minus water vapor pressure. At body temperature, water vapor pressure is often entered as 47 mmHg. You can change that value for special teaching cases.
Reading The Results
The result panel gives the main fraction, percent, ppm value, and estimated pressure. It also shows optional breath based values when respiratory rate is entered. These checks make the answer easier to inspect. They also help catch wrong units before exporting a report.
Good Data Habits
Use consistent units. Enter ventilation as total expired liters per minute. Enter carbon dioxide production as milliliters per minute. Use a realistic barometric pressure for the setting. Keep notes about the device, method, and patient condition when using examples. Small changes in pressure and ventilation can shift the fraction. Always review the assumptions beside the final answer. Save CSV or PDF copies when comparing several teaching cases.
Common Mistakes To Avoid
Do not mix liters and milliliters. Do not enter end tidal carbon dioxide when the method needs mixed expired pressure. End tidal values usually represent late exhaled gas. Mixed expired values represent the full collected breath. Label each source clearly. This makes review easier before sharing saved results online.