Pulse Oximetry In-Depth Description

DESCRIPTION OF CO-OXIMETER VALIDATION BLOOD TESTS (REGULATORY ACCURACY – CLINICAL TRIAL)
SpO₂ accuracy performance of the Test Pulse Oximeter is evaluated during stationary (non-motion) conditions over the specified range (usually 70-100% SaO₂) as compared to arterial blood samples assessed by CO-Oximetry.

A minimum of 10 healthy non-smoking adult subjects, ranging in pigmentation from light to dark, are enrolled in the study to meet the study design requirements defined by ISO 9919 Pulse Oximeter Standard and by the FDA’s Guidelines for Pulse Oximeters.

The subjects have an arterial catheter placed in the radial artery to allow for simultaneous blood samples during stable plateaus of induced hypoxic levels that cover the specified oxygen saturation range.

The subject rests comfortably in a reclined position. The subject is given a gas mixture of medical grade oxygen and nitrogen to induce hypoxia in a stair stepped manner to the minimum target SaO₂ level (based on the specified range for the Test Pulse Oximeter).

Data is collected from all pulse oximetry systems simultaneously. The oxygen saturation (SpO₂) and pulse rate values are automatically recorded via computer from each pulse oximetry system. At each stable plateau, blood samples are drawn during non-motion conditions and immediately analyzed on multiple CO-Oximeters.

The data is analyzed to derive a statistical comparison between the test device and the Reference CO-Oximeters. Comparison is made to the average of more than one reference device.

Reference CO-Oximetry is used as the basis for comparison for each sensor SpO₂ reading. Anomalous values are removed from the analysis prior to pairing of the SpO2 and SaO₂ data. Statistical analysis is performed on a minimum of 200 data points collected on at least 10 subjects over the specified SaO₂ range.   The Accuracy Root Mean Square (ARMS) calculation is used to determine the SpO₂ accuracy performance which provides documentation for the SpO₂ accuracy claims for the device under test. The formula used in this calculation is:

Description of Pulse Oximetry Statistics:  The A_rms statistic (Accuracy Root Mean Square) is required by regulatory agencies when overall accuracy of a device is evaluated.  The A_rms calculation is affected both by Precision and by Bias.  The name comes from the fact that it is the square root of the mean of the squares of the values.  The values being the differences of each data pair (test reading – reference reading).  Another way of describing the Arms calculation is that it looks at a ‘moving’ mean or SD of pairs where the reference value is different for each test-reference pair.  The A_rms statistic provides one number which includes both Precision and Bias in a single number and can tell the clinician the general Accuracy of the pulse oximeter.

More information on the technical aspects of this type of study can be found in the journal publication written by Mr. Batchelder of CLINIMARK titled: Batchelder, PB; Raley, DM; Maximixing the laboratory setting for testing devices and understanding statistical output in pulse oximetry.  Anesthesia & Anesthesia. 2007 Dec;105(6Suppl):S85-94. Review (PubMed index at PMID: 18048904)

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