Hypoxia Research Laboratory
Pulse Oximeter Test Facility
Info for Manufacturers
This laboratory has developed methods that permit us to test multiple pulse oximeters simultaneously. We induce sudden profound and brief stable arterial oxygen desaturation in normal, paid volunteers and sample arterial blood when a stable level of hypoxia has been attained, for analysis in a gold standard bench CO-oximeter. This section describes the program, arrangements, and costs. 6 to 8 subjects can be studied in a single day, with 20-25 arterial blood samples from each subject. 10 to 12 subjects can be studied over two days, with 20-25 arterial blood samples each.
The key to this is a computer program that permits the inspired gas mixture to be adjusted by an operator who observes a breath-by-breath display of the arterial saturation computed from end tidal PO2 and PCO2, which is continuously monitored by mass spectrometry. Typically, saturation is determined once with air breathing and then reduced suddenly to one of 6 levels, range as requested, e.g. 94%, 90%, 85%, 80%, 75% and 70%, for about 30-60 seconds at each level. An arterial blood sample is obtained from an indwelling catheter at the end of each hypoxic plateau. The operator changes the inspired oxygen concentration at the end of each blood sampling, and the sudden change this produces in the oximeter recording is used as a time marker for subsequent analysis.
A "run" takes 5-7 minutes, during which several plateaus are obtained, e.g. 90%, 80%, and 70%; the run is terminated by a breath of 100% O2 followed by room air. Two runs together compose the six levels of saturation previously mentioned. Saturation of each arterial blood sample is determined by direct oximetry in a Radiometer OSM-3 multi-wavelength oximeter.
Normally, each tested oximeter should provide an electrical analog output signal that we record with LabVIEW in the computer for subsequent plotting and statistical analysis. The timing of the arterial sample on the pulse oximeter recording is obtained from the record of that oximeter using the abrupt fall to a lower plateau or rise produced by re-oxygenation. The mean oximeter output between 6 and 12 seconds before the sudden change of SpO2 is recorded and is read by cursor on a color terminal, and the value transferred to a file for statistical analysis in Excel. The output files include data collected at 2 Hz for each oximeter, and are available on CD or other media, for analysis. A study normally consists of one normoxic and 19-24 hypoxic comparisons for each subject.
In many modern pulse oximeters, no analog output is provided. If the manufacturer chooses to record the data in a portable computer at a rate of at least 1 Hz, that data can also be submitted to us for data analysis without extra charge. If we are not asked to analyze data, the charge will be as shown for the first 4 instruments, with additional oximeters counted as non-recorded instruments in the following table.
If a manufacturer prefers to collect and analyze the data, the continuous digital signal of each oximeter should be read, for comparison with the blood sample, 9 seconds before the record shows a sudden fall or rise in oxygen saturation, not at the time of blood sampling. This procedure accounts for the delays of finger circulation and uses the estimated delay from the lung to the sample site. There is no useful correlation between the actual time of blood sampling and the oximeter recording because of the extreme variability of tissue blood flow lag.
These studies are done with approval of the UCSF Committee on Human Research (H1094-01706-21, exp. date April 6th, 2007). The study takes about 1 hour of each subject's time. Reduction of the data requires several days. Manufacturer’s representatives may be present for these tests, and may mount the probes. An extra charge is made if no representative is present, requiring us to mount the probes.
In all cases, the blood analysis data are provided, including the SaO2, MetHb, COHb and Hgb concentration.
The data analysis report will consist of the following:
1. Graphic plots of the saturation values of each pulse oximeter at each blood sample time plotted against SaO2, the hemoximeter (blood) value.
2. Regression equations for the overall response of each instrument.
3. Plot of the bias values of all samples and all instruments against SaO2.
4. Tables of the mean error or bias, its standard deviation, standard error, 95% confidence interval, maximum and minimum and RMS, all computed both overall and by several sub-ranges of desaturation.
Technically, we can record data if each oximeter control unit provides a single ended analog output signal with BNC terminal mounted on the box. We provide cables to connect this to our computer. The oximeter probe leads should be at least 8 ft long. If no analog outputs are supplied, the manufacturer will be responsible for data recording.
Manufacturers must provide their own pulse oximeters and probes. Each individual manufacturer is charged an amount determined by the number of subjects, the number of samples per subject, and the number of oximeters (as shown by the cost table on the next page) plus the facility fee and UCSF overheads. Sites may include the fingers, ears, forehead and bridge of the nose. Data are not published without specific permission of the manufacturer, and in general, no plans now exist for publication of future data.
The costs of performing the study, paying the subjects, developing the computer facility and program, plotting the individual responses, and of personnel salaries require that we obtain payment for these studies. These tests are also used to support the physiology research of this laboratory.
No extra charge is made for dual recording of oximeters by both manufacturers and us. If the manufacturer chooses not to be present for the tests, an additional 10% charge will be added. If two manufacturers both agree to share a study date, 15% will be taken off the charge to each manufacturer.
We charge a 7% fee to maintain the equipment in the testing facility. Also, UCSF adds an additional 22% overhead charge to the amounts computed from the following table. A 50% cancellation charge is applied to studies cancelled within 1 week of the study date. A contract for each study, in accord with University requirements, must be in place prior to the start of the study. Our department's business contact is Ms. Christie Chu (chuch@anesthesia.ucsf.edu); she will help with contract information and payment coordination.
A fee schedule for the testing is available on request. Please contact Dr. Bickler (bicklerp@anesthesia.ucsf.edu).