How to use FingerSims

There are two types of testing that create questions concerning the numbers generated by the simulators and they are NIBP and SPO2 Simulators.  Both are not exact sciences and have more to do with the algorithms used by the Medical Device Manufacturer than the accuracy of the testing device.  Because of patents, each manufacture uses their own algorithm to determine the SPO2 reading.  The only true and accurate measurement of SPO2 is by drawing blood and sending it through a blood gas machine.  The Pulse Oximeter Finger cuffs were developed to give an approximation of the Oxygen level and show any trends, up or down, in the patients O2 levels.  Because these are not actual readings and only a result of calculations, there are many factors that can introduce errors in the readings.

BC Group manufactures the FingerSims at our St. Charles manufacturing facility. Each FingerSim is made by hand and checked for quality before they are shipped to our customers. A set of FingerSims consists of three Fingers with values of 80%, 90% and 97% saturation. The FingerSims are not an item that can be calibrated or recalibrated. At the time they are manufactured, a color dye is injected into each FingerSim that determines what level of saturation will be simulated. Pulse Oximeter manufacturers all use different wavelength light when calculating the Oxygen Saturation. As the light passes thru the patient’s finger or the FingerSim, some of the light is absorbed and as a result, a SPO2 reading is provided in percent of saturation. Because of the difference in wavelength you will see slight differences in the readings when using the FingerSims on the various manufactures. The important thing is that the FingerSims are consistent within each manufactures product. If you use the 97% Finger on a Nonin Oximeter™ you might get 97% where you might get 96% on a Nellcor product. You will notice that if the reading is slightly low or high on a particular manufacture’s product, it will be consistently high or low on that same model in the future. This is only true if all the environmental conditions are identical each time the test is performed.

It is worth noting that the devices being tested have a tolerance, and that the FingerSims have a temperature drift (as stated in the User Manual).  For example, the Welch Allyn Service Manual states to check the SPO2 function at 81% for a reading of 81% +/- 3%.  The FingerSims are calibrated at 72.5 °F, and will yield a higher reading at higher temperatures.  Different types of ambient lighting can also affect the SPO2 reading.  For best results, completely cover the finger cuff during testing.  Were the FingerSims allowed to acclimate to the room temperature?  If they were carried in a technicians pocket, the liquid inside might have a temperature closer to body temperature rather than room temperature.  Bringing the FingerSims in from cold weather can affect the performance of the FingerSims.

If readings are higher or lower than the stated value on any FingerSim, any or all of the above variables can be effecting those readings.  The important thing is to make sure the monitor alarms go off when the value drifts below the accepted range.

Keep in mind that the FingerSims are the only SPO2 Simulator that passes the red and infrared light, that is used by the Pulse Oximeter devices, through the FingerSims like they would a human finger.  All other simulators emit a signal into the Pulse Oximeter devices sensor and look at the red and infrared light coming out of the device, it never passes completely through the Simulator.

The FingerSims absorb light very much like a human finger based on the color dye in each Finger. They differentially absorb the light like the oxygenated and deoxygenated hemoglobin in a human Finger. They Test the Finger Probes the way they are designed to work, passing light through the Finger and measuring the results that pass through to the sensor.

We do have a Certificate of Conformity (COC) and a Statement of Calibration that can be provided upon request. Before the dye is injected into the Fingers it is checked for consistency and that it conforms to our standard in manufacturing that particular percent FingerSim. Once it is injected into the FingerSim, all FingerSimss are verified for accuracy before shipping. If they do not conform, they are destroyed since they cannot be re-calibrated.

Medical treatment is typically not given based on the readings coming from a finger cuff on a patient because they know the limitations of the technology.  If the patient is truly going into a crisis, the body will restrict the flow of blood to the extremities and provide the majority of the flow to the core body to protect the vital organs.  As a result, the readings of SPO2 coming from a finger are not meaningful at all other than to set off an alarm.  Blood gas would be drawn to determine the real levels.