Faulty Analysis Method of A Patient Monitor | SpO2 Related Fault Analysis and Troubleshooting
The measurement of SpO2 by the monitor uses the light absorption characteristics of Hb and HbO2-εcd in blood and based on Lambert Beer's law I=I0e (where I and I0 are the incident and transmitted light intensity respectively, ε, c, d are respectively material absorption coefficient, solution concentration, and light travel path). There are 2 common faults:
In the normal, there is no blood oxygen waveform and digital display in the normal boot conditioning waveform and digital display, which is generally caused by the damage of the blood oxygen probe or the failure of the blood oxygen module.
Troubleshooting steps: Connect the blood oxygen probe correctly and start the test.
(1) Determine whether the blood oxygen probe is in good condition. You can check whether the diode in the probe is lit normally or replace it with a new probe directly to eliminate it. If the probe is determined to be damaged, it needs to be replaced. The damage to the PO2 probe is generally divided into two types:
①The light-emitting diode or photodiode in the finger sleeve is burnt;
②The inner wire of the connector is desoldered. At this time, you can unscrew the connector and re-solder the line.
(2) Check whether the machine probe connection port and its line are normal. Probe connection failure can be caused by the port to which the probe is connected, the connected line, or the connector falling off or loose. At this time, it is necessary to disassemble the machine to re-fix the ports and lines, and then connect the probe to test.
If the possible faults mentioned in the previous two steps have been eliminated, but the machine still has no blood oxygen waveform and digital display, the oxygen module fault should be considered and need to be repaired or replaced.
The blood oxygen waveform and numbers are displayed, but the waveform interference is large or the blood oxygen measurement value is inaccurate. The blood oxygen waveform interferes greatly or the measured value is inaccurate, which is generally caused by external environmental factors.
(1)Exclude the interference of the patient's own activities, and make the patient quiet before testing. Care should be taken to detect the effects of light in the environment. From the light absorption characteristics of HbO2 and Hb shown in Figure 1 and Lambert Beer's law (I=I0e), it can be seen that when there is strong light (especially red light and infrared light) in the detection environment, it may cause changes in I0 and I, resulting in inaccurate measurements.
(2)Note the effect of dyes. If the patient is injected with a dye before the SpO2 measurement, it will change the blood concentration (c) and the absorption coefficient (ε), affecting the final measurement result.
(3)Avoid taking measurements on the same side as NIBP or using the same finger for extended periods of time. The long-term compression of the same finger by the SpO2 probe finger cuff and the compression effect of the cuff on the arm during NIBP measurement may lead to poor blood circulation in the finger, which may easily cause measurement errors and patient discomfort.