Calibration of densitometers for indicator dye dilution

Area of Science:

• Biomedical Engineering
• Medical Diagnostics
• Analytical Chemistry

Background:

• Accurate calibration of densitometers is crucial for reliable indicator-dilution curve analysis.
• Indocyanine green (ICG) is widely used for measuring cardiac output and liver function.
• Understanding factors affecting ICG calibration is vital for clinical accuracy.

Purpose of the Study:

• To systematically investigate factors influencing the calibration of a Gilford monochromatic densitometer.
• To identify key variables affecting the accuracy of indicator-dilution curves recorded with indocyanine green.
• To provide recommendations for a robust and error-free calibration technique.

Main Methods:

• Systematic investigation of calibration parameters for a Gilford monochromatic densitometer.
• Testing variations in withdrawal speeds, sampling systems, hemoglobin, and hematocrit.
• Assessing the impact of dye storage and the presence of contrast media on optical properties.
• Evaluating the substitution of stored ACD blood for patient blood during calibration.

Main Results:

• Calibration was unaffected by withdrawal speeds (6.4-20.6 cm3/min), hemoglobin (10-17.5 g/dL), or hematocrit (30-60%).
• Significant variations in calibration were observed with different sampling systems.
• Calibration lines exhibited curvature and hysteresis; optical properties of ICG were altered by contrast media.
• Substitution of stored ACD blood increased random error but not systematic error.

Conclusions:

• Sampling system design is a critical factor in Gilford densitometer calibration for ICG curves.
• Contrast media can interfere with ICG optical properties, impacting calibration.
• A simple, validated calibration technique is recommended to minimize systematic errors in clinical practice.