The effect of sensor malpositioning on pulse oximeter accuracy during hypoxemia

Area of Science:

• Medical Devices
• Clinical Monitoring
• Respiratory Physiology

Background:

• Pulse oximeters are widely used for non-invasive monitoring of arterial oxygen saturation (SpO2).
• Previous research indicated potential inaccuracies with malpositioned sensors in normoxemic individuals.
• The performance of pulse oximeters with malpositioned sensors during hypoxemia remained uninvestigated.

Purpose of the Study:

• To evaluate the behavior of various pulse oximeters with both correctly and incorrectly positioned sensors.
• To assess oximeter performance across a broad spectrum of arterial oxygen saturation (SaO2) levels, including hypoxemia.
• To identify potential discrepancies between measured SpO2 and actual SaO2 under different sensor placement conditions.

Main Methods:

• Eight different pulse oximeters were tested on 12 healthy volunteers.
• Five oximeters were intentionally used with malpositioned sensors.
• Subjects underwent controlled breathing of oxygen-nitrogen mixtures to achieve SaO2 levels ranging from 100% down to 70%, with arterial blood gas analysis for calibration.

Main Results:

• Malpositioned sensors significantly altered pulse oximeter performance, with variations observed between manufacturers and models.
• Some devices consistently underestimated SpO2, while others showed a trend of underestimation at high SaO2 and overestimation at low SaO2.
• Analysis revealed a reduced sensitivity of SpO2 to SaO2 changes (decreased slope) in many cases, alongside significant inter-subject variability.

Conclusions:

• Sensor malpositioning substantially alters pulse oximeter calibration curves.
• In hypoxemic conditions, inaccurate readings due to malpositioned sensors can mask severe oxygen desaturation, leading to underestimation of hypoxemia.
• Recommendations include frequent verification of sensor placement and avoidance of difficult-to-access sensor sites.