Relationships between capnogram parameters by mainstream and sidestream techniques at different breathing...

Area of Science:

• Respiratory Physiology
• Medical Instrumentation

Background:

• Capnography is vital for monitoring lung function in critical care settings.
• Mainstream capnography provides direct CO2 measurement, considered a reference standard.
• Sidestream capnography measures CO2 remotely, potentially impacting accuracy.
• Limited data exists comparing these methods during spontaneous breathing.

Purpose of the Study:

• To compare mainstream and sidestream capnography in spontaneously breathing adults.
• To analyze differences in capnogram shape and dead space indices.
• To evaluate performance across various respiratory rates.

Main Methods:

• Simultaneous time and volumetric capnography using mainstream and sidestream techniques.
• 35 spontaneously breathing adults.
• Controlled respiratory rates: 10, 12, and 20 breaths/min.
• Statistical analysis: Correlation and Bland-Altman.

Main Results:

• Excellent correlation and agreement for end-tidal CO2 (ETCO2) and physiological dead space.
• Strong correlations but moderate agreement for phase 3 slope and exhaled CO2 volume.
• Weaker correlations for phase 2 slope and anatomical dead space.
• Both methods detected significant changes in capnography parameters with altered breathing rates.

Conclusions:

• Mainstream capnography is more accurate for absolute values of shape factors and dead space fractions.
• Sidestream capnography can effectively detect and track changes in ventilation and dead space.
• Both techniques are valuable for monitoring spontaneously breathing patients, with distinct strengths.