Accuracy of two pulse oximeters during maximal cycling exercise

Area of Science:

• Physiology
• Medical Devices
• Biomedical Engineering

Background:

• Pulse oximetry is a non-invasive method for measuring oxygen saturation of haemoglobin (SaO2).
• Previous validation studies often used plastic syringes for arterial blood sampling, potentially affecting accuracy.
• Understanding device-specific performance is critical for reliable clinical data.

Purpose of the Study:

• To compare SaO2 measurements from two specific pulse oximeters (Ohmeda Biox 3700e and Criticare 504 USP) against arterial blood CO-oximetry.
• To assess the impact of using ground glass syringes for arterial blood sampling on SaO2 measurement accuracy.
• To evaluate pulse oximeter performance under normobaric and hypobaric conditions during maximal exercise.

Main Methods:

• Twenty male subjects (trained cyclists and untrained) underwent maximal cycle ergometer tests in a hypobaric chamber at two different pressures (745 mm Hg and 695 mm Hg).
• Arterial blood samples were collected in ground glass syringes for CO-oximetry analysis.
• Simultaneous SaO2 measurements were taken using Ohmeda Biox 3700e and Criticare 504 USP pulse oximeters at rest, 7 minutes into exercise, and at VO2max.

Main Results:

• Both pulse oximeters demonstrated correlations with CO-oximetry (Criticare: r=0.94, Ohmeda: r=0.91) when all data were combined.
• The Ohmeda Biox 3700e consistently underestimated SaO2 (mean bias: -2.5 +/- 1.9%).
• The Criticare 504 USP overestimated SaO2 (mean bias: 0.9 +/- 1.5%), with less bias than the Ohmeda.

Conclusions:

• Individual pulse oximeter validation is essential for accurate SaO2 readings.
• The potential influence of dyshaemoglobins on pulse oximeter accuracy warrants consideration.
• Ground glass syringes may offer a more reliable method for arterial blood sampling in validation studies.