Normal PETCO2 Values Obtained by Capnography
Under normal conditions, PETCO2 is in the range of 35 to 40 mm Hg. 1
Standard Reference Range
The normal PETCO2 range is 35-40 mmHg according to the American Heart Association guidelines for advanced cardiovascular life support 1, 2
This range reflects normal physiologic conditions where CO2 is produced in the body and delivered to the lungs by circulating blood 1
The PETCO2 value represents the partial pressure of carbon dioxide in exhaled air at the end of expiration 1
Physiologic Basis
Because CO2 is a trace gas in atmospheric air, CO2 detected by capnography in exhaled air is produced in the body and delivered to the lungs by circulating blood 1
Under normal conditions with adequate cardiac output and ventilation, PETCO2 closely approximates arterial CO2 (PaCO2), which has a normal range of 35-45 mmHg 2, 3
The PETCO2 reflects three primary physiologic processes: CO2 production from cellular metabolism, alveolar ventilation, and pulmonary blood flow 2
Clinical Context and Variations
Values >50 mmHg indicate hypoventilation and potential respiratory compromise, while values <30 mmHg indicate significant hyperventilation 2
An absolute change from baseline >10 mmHg is clinically significant and may indicate respiratory depression before oxygen desaturation occurs 2
During cardiopulmonary exercise testing, normal PETCO2 at rest is typically 36-42 mmHg, with a 3-8 mmHg increase during exercise representing a normal response 1
Important Clinical Caveats
Waveform capnography is the gold standard for PETCO2 measurement, ensuring accuracy and confirming proper endotracheal tube placement 2
Technical factors can cause falsely low PETCO2 readings, including bronchospasm, mucous plugging, ETT kinking, alveolar fluid, hyperventilation, air leaks, and mouth breathing 2
In specific clinical scenarios (cardiac arrest, mechanical ventilation with high PEEP, pulmonary embolism), PETCO2 may not accurately reflect PaCO2 and arterial blood gas analysis may be necessary 4