Failure analysis and troubleshooting of monitor

As one of the most commonly used medical equipment, monitor is widely used in various clinical departments with high frequency of use. Therefore, the number of failures is relatively large. To ensure the normal operation of the monitor can not only provide comprehensive monitoring for patients, but also improve the work efficiency of medical staff, and provide important and effective information for disease analysis and diagnosis.

The following describes the monitor commonly used monitoring parameters ECG (electrocardiogram), SPO2 (oxygen saturation), NIBP (non-invasive blood pressure), RESP (respiration) related to the failure analysis and removal methods.

I. ECG related failures

Monitoring ECG is a process of detecting and receiving the potential difference of biological current produced by cardiac electrical stimulation by ECG lead line. There are two common faults in monitor:

Failure phenomenon: After the human body is correctly connected to the ECG electrode, the monitor prompts "no signal reception" or "electrode shedding".

Fault analysis and troubleshooting: monitor prompted "no signal reception" or "electrode shedding", is generally due to electrode shedding, damage or electrocardiogram module failure caused by the use of ECG analog signal generator for detection.

Elimination steps: correctly connect ECG analog signal generator and ECG lead line, and start detection.

(1) If the waveform and numerical value of the ECG signal are normal, the monitor and the ECG lead are normal, and the connection between the electrode and the human body should be checked. The electrode falling off or the electrode being melted for too long will lead to the display of the centerless electrical waveform.

(2) if the waveform and numerical value of the unintentional electrical signal are displayed, it is necessary to determine whether the ECG lead line is intact. Replaceable and intact ECG leads are tested again. If troubleshooting occurs, the original ECG leads are damaged and need to be replaced.

(3) If the failure has not been eliminated after replacing the intact ECG lead, the ECG module should be suspected of failure and the machine should be removed for maintenance or replacement.

Fault phenomena: ECG scanning baseline can not be displayed stably on the screen, drift uncertain; ECG waveform abnormal or interference, inaccurate measurement.

Troubleshooting: ECG baseline drift, abnormal waveform, inaccurate measurement, generally with external interference or machine settings.

Elimination steps:

(1) Check whether the place where the patient sticks the electrode is clean and wet, and if necessary, clean the skin with alcohol.Meilun

(2) Check whether the electrode is well-connected or needs to be replaced due to long-term use of melting; generally recommend that the electrode should be replaced after 3 hours of use.

(3) the internal moisture of the machine itself needs to be continuously booted 24h for drying.

(4) Move the machine to a place where there is less electromagnetic interference, restart the machine to observe, and eliminate the influence of electromagnetic interference from the surrounding machine.

(5) check the machine's AC power supply with or without earth wire. If it is not connected, it needs to be re connected.

(6) Check whether the selected ECG filtering mode or power frequency setting is correct, if not, choose the appropriate filtering mode and power frequency (usually set to 50Hz).

Two, SPO2 related failures

The measurement of SPO2 by the monitor is based on the absorption characteristics of Hb and HbO2-epsilon C D in blood and Lambert-Beer's law I=I0e (formulas I and I0 are incident and transmitted light intensities respectively, and epsilon, C and D are material absorption coefficient, solution concentration and light path). There are 2 common faults.

Fault phenomenon: in normal boot, no blood oxygen waveform and digital display.  Trouble analysis and troubleshooting: no blood oxygen waveform and digital display, generally due to the blood oxygen probe damage or blood oxygen module failure caused.

Elimination steps: connect the blood oxygen probe correctly and start the machine for testing.

(1) determine whether the oxygen probe is intact. It can check whether the diode in the probe is lit properly or replace the new probe with substitution method to eliminate it. If the probe is damaged, it needs to be replaced. The damage of PO2 probes is generally divided into two kinds.

(1) light emitting diodes or photodiodes burned in fingers.

2. If the inner conductor of the joint is removed, then the joint can be unscrewed and the welding line can be re welded.

(2) check the machine probe connection port and whether the circuit is normal. The connection or connection of the probe and the connection can cause failure of the probe connection. At this point, it is necessary to reassemble the ports and circuits before connecting the probes.Meilun

(3) If the possible faults mentioned in the first two steps have been eliminated and the oxygen waveform and digital display of the machine are still absent, the oxygen module faults should be considered and repaired or replaced.

Fault phenomenon: the blood oxygen waveform and number are displayed, but the waveform interference is bigger or the blood oxygen measurement value is not accurate.

Trouble analysis and troubleshooting: blood oxygen waveform interference is larger or the measurement value is not accurate, is generally caused by external environmental factors.

Elimination steps: exclude the interference of patients' own activities, and make patients quiet after testing. Attention should be paid to detecting the effects of light in the environment. From the absorption characteristics of HbO2 and Hb shown in Fig. 1 and Lambert-Beer's Law (I = I0e), it can be seen that the changes of I 0 and I may be caused by the exposure of strong light (especially red and infrared light) in the detection environment, resulting in inaccurate measurement.

Attention should also be paid to the effect of dyeing agents. If the patient is injected with a stain before SPO2 measurement, the blood concentration (c) and the absorption coefficient (e) will change, affecting the final measurement results.

Finally, avoid measuring with NIBP on the same side or using the same finger for a long time. The long time compression of the same finger by the finger sleeve of SPO2 probe and the compression of the arm by the sleeve pocket during NIBP measurement may lead to poor blood flow of the finger, and easily lead to measurement errors and patient discomfort.

Three, NIBP related failures

The monitor used vibration wave method to measure NIBP. In the process of measurement, the pulsation of the blood vessel wall caused by the blood flow will produce a gas vibration wave in the cuff. The vibration wave is transmitted through the trachea to the pressure sensor in the machine to detect the cuff pressure in real time. There are two common faults.

Fault phenomenon: When NIBP measurement, prompt "cuff error", "air pump leakage" or pressure error alarm.Meilun

Trouble analysis and troubleshooting: generally due to airway leakage, blockage or blood pressure module pump and vent valve failure caused.

Elimination steps:

(1) check whether the extension tube and cuff are damaged or folded or blocked, and replace it if necessary.

(2) check whether the port of the extension tube and the cuff and the machine are tight. If necessary, the port must be cleaned with alcohol.

(3) when the air pipe in the machine is broken off or loosened, it is necessary to remove the machine to reconnect and reinforce the inner pipe.

(4) exclude the malfunction of the air pump and vent valve on the NIBP module.

(1) Pump detection: remove the air pump to connect to 12V DC power supply, test whether the air pump work and output is normal, if not, the damage of the air pump need to be replaced;

(2) Exhaust valve detection: dust accumulation in the valve, resulting in valve closure is not strict or the valve airway blockage, will lead to monitor prompted leakage fault or pressure error alarm. At this time, the valve can be removed and cleaned by using a syringe. Replace the bleed valve or the NIBP module if necessary.

Fault phenomenon: the external gas path is intact, which can normally charge and deflate, but no blood pressure or blood pressure is allowed.

Troubleshooting:

(1) Choose the appropriate size of the cuff, and before the cuff is bound, remove the body surface barrier and extrude the air in the cuff pocket. Too loose or too tight cuff will make the air in the cuff can not normally feel the pulsation of the blood vessel wall to produce vibration waves, resulting in blood pressure can not be measured or inaccurate measurement.

(2) exclude the influence of patient's own activities. One of the most important drawbacks of measuring NIBP by vibration wave method is that it is easily disturbed by external vibration. Therefore, NIBP measurement should be carried out in a quiet state.Meilun

(3) the cuff binding position and patient posture should be correct. The results showed that there was a difference of about 8 mmHg between the position measured by NIBP and the heart height by 10 cm. Therefore, when measuring NIBP, the measurement position should be kept in line with the height of the heart.

(4) the failure of the blood pressure module should be considered. The damage of pressure sensor or signal processing system in this module will result in no measurement result or inaccurate measurement value. At this time, the module needs to be dismantling to repair or replace the module.

Four, RESP related failures

Electrical impedance measurement is mostly used in the monitor. It is mainly through RA and LL two electrodes to pick up the electrical signals caused by the change of respiratory impedance in the human body thorax, and through the analysis and processing of the machine system, the final respiratory frequency process is obtained.

Fault phenomenon: no breathing wave or abnormal breathing wave, measurement is not allowed. Troubleshooting: according to the measurement principle of RESP, respiratory signals. The detection is done by ECG electrode, so it is closely related to ECG. The following four factors should be excluded:

(1) to exclude patients from frequent activities and severe cough, they should be measured in a calm state.

(2) correctly position the electrode, especially the position of RA and LL two electrodes should be placed correctly.

(3) exclude the influence of lead wire, electrode quality and poor contact.

(4) respiratory module failure, need to be dismantling maintenance or replacement.