Safety protection of hemodialysis device
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1. Electrical safety requirements
The hemodialysis device is mainly composed of power components, heaters, motors, temperature sensors, pressure sensors, conductivity sensors and other components. According to the requirements of GB9706.1-1995, the electrical safety content is very wide, but it is easy to cause harm to patients. There are still two aspects: protection against electric shock and leakage current. This section uses a specific product insulation diagram to describe two key issues related to patient protection against electric shock and leakage current. Figure 1 Insulation diagram of a typical hemodialysis device (figure 1 Typical insulaTIon of haemodialysis equipment) Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
1. Determination of application type
When the hemodialysis device is in treatment, the device is in contact with the blood through the dialysate. According to the conventional medical electrical device design concept, it is directly used in the heart or the application part in contact with the blood. The application part of the dialysis device is B type, which is determined by its special structure. At this stage, it has no ability to design for the CF type structure.
According to the definition of the application part, the device must be in contact with the patient when the function of the device is running. During the operation of the dialysis device, the dialysate exchanges substances through the semi-permeable membrane and blood. The semi-permeable membrane does not play any role in isolation. Therefore, the entire dialysate operation part should be regarded as the application part, which includes The dialysate preparation system, temperature sensor, dialysate pressure sensor, conductivity sensor and heater are included. Among them, the heater is a protective grounding component, which determines that the hemodialysis device can provide basic anti-shock capability and has a specific protection against leakage current, so the application part of the hemodialysis device is the B-type application part.
2. Anti-shock analysis among various electrical parts
As shown in Figure 1, from the external power supply to the patient, there are four ways to pass through various insulation to reach the application part. One is from the network power supply through the intermediate circuit, and then through various sensors and dialysate contact; The second is from the network power supply through the heater and the dialysate contact; The third is the battery (battery can be regarded as a specific grid power supply) through the intermediate circuit across each Sensors are in contact with dialysate; Fourth, various uncertain external power supplies may contact the dialysate through the SIP / SOP interface, across the intermediate circuit and the sensor. The following four points are analyzed for points A to G shown in FIG. 1 respectively. Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
a) Influence of the network power supply on the patient via the intermediate circuit
It can be seen from Figure 1 that the network power is in contact with the patient through the A part isolation and G part insulation high impedance. Part A represents the primary and secondary of the device's network power supply. Double insulation is required between these two parts, because if this part is broken down, the network power supply is directly added to the intermediate circuit and each sensor, which may cause serious danger. In addition, the G part uses a semiconductor sensor, which uses the characteristics of the PN junction to realize the isolation method of high-insulation insulation, which plays a role in limiting the leakage current. Therefore, GB9706.1-1995 stipulates in Chapter 17, if the insulation between the application part and other live parts depends on the insulation performance of the semiconductor device junction, you must short one junction at a time to simulate the breakdown of the critical junction to verify the single Whether the leakage current and the patient auxiliary current in the fault state exceed the allowable value.
b) The effect of the network power supply on the patient via the heater
As can be seen from Figure 1, the network power supply directly heats the dialysate through the heater (point B). The insulating filler material of the heating rod is generally magnesium oxide, and the insulation level requires basic insulation, but its filler material is generally acceptable. Achieve double insulation. Therefore, the insulation of the network power supply to the patient via the heater and the dialysate is also sufficient.
c) The impact of the battery on the patient
As can be seen from Figure 1, the battery is part of the intermediate circuit and is considered a specific power source. The battery is isolated from the application part by the sensor. For the analysis of the sensor, see a). Usually the leakage current generated by the battery is relatively small, and the laboratory pays more attention to the safety assessment of the battery itself, such as short-circuit, overcharge, overdischarge, reverse polarity and other fault tests. Because the above failures are very likely to cause the battery to fire or even explode.
d) Influence of external voltage on patients
The device transmits signals with external devices through the SIP / SOP interface. This connection constitutes a medical electrical system, and its safety should meet the requirements of GB9706.15. If the manufacturer does not have a clear statement on SIP / SOP, considering the safety factor of the external device is uncontrollable, the worst case is that the external device communicating with the dialysis device has insufficient power isolation strength, and the network power supply is directly Added to the SIP / SOP interface, therefore, there should be isolation between the SIP / SOP interface and the intermediate circuit / patient circuit. The reference voltage required for this isolation is the grid voltage, because this situation occurs only when a single fault occurs, so it is required It is sufficient to achieve basic insulation.
3. Requirements for patient leakage current
Because the application part of the device is in direct contact with human blood, the patient's leakage current flows through the extracorporeal circulation blood circuit, and this current can cause serious consequences such as ventricular fibrillation, heart pump failure, or tissue necrosis. In the case of a ground fault, the patient's leakage current will increase sharply, reaching the value of the ground leakage current when the device is normal, so the product should be designed to limit the ground leakage current as much as possible.
Second, functional safety protection
The device is used to treat patients in an invasive manner. When the safety protection system fails, it may cause life threatening. This requires a safety protection system that is completely independent of the control system. To meet this independent protection system structure, the device must implement a dual system, dual CPU structure, and the safety protection sensor must also be independent of the control sensor. The following is the safety protection that the hemodialysis device must have: Welcome to reprint, this article comes from the electronic enthusiast website (http: //)
1. Over-temperature protection of dialysate and replacement fluid
The dialysate temperature will cause hemolysis reaction when the temperature exceeds 41 a??. In order to minimize the risk of overtemperature, the state stipulates that the dialysis device must have a protection system independent of any temperature control system, that is, in addition to the temperature control In addition to the sensor, there must be an independent temperature protection system. In general, the temperature control range of the temperature control sensor will not exceed 40 ?° C, and the overtemperature alarm of the temperature protection system is 41 ?° C. It is impossible for the over-temperature alarm to occur when the device is working normally, that is, we cannot detect the over-temperature alarm when the device is in normal use. In order to check the over-temperature alarm, the temperature control sensor and the protection sensor are generally separated Come, that is to say, the temperature control sensor fails to make the heater continue to heat. When the dialysate temperature exceeds the set value, its temperature protection system must be triggered to achieve the following alarm actions: trigger audible and visual alarms and prevent dialysis The fluid flows to the dialyzer.
2. Ultrafiltration protection
Ultrafiltration is one of the important indicators of hemodialysis devices. When there are large errors in the ultrafiltration system, the excessive accumulation of time will cause danger to patients' lives. The protection system that the device must have should be independent of any ultrafiltration control system. In addition, the output of the device is prevented from deviating from the setting value of the control parameter and causing a safety hazard. When the output of the device deviates from the set value of the control parameter, the action of the protection system must trigger an alarm of sound and light.
3. Blood pressure alarm
If the blood pressure exceeds the set range and the duration exceeds the set delay, the hemodialysis device must stop the operation of the blood pump, close the venous clamp, and sound and light alarm. The focus of the inspection is the accuracy of the blood pressure alarm and the actions it implements. The venous clamp uses electromagnetic or hydraulic power to block blood flow by clamping the extracorporeal blood tube.
4. Air alarm
Air detection is based on the principle of ultrasound. Ultrasonic waves propagate faster in liquids and solids than in gases. When bubbles in the venous circuit flow through the air detector, the ultrasonic receiving sensor gets a voltage drop that is smaller than normal and is processed by the CPU. There are two methods of air detection: one is to detect the presence of air bubbles. When bubbles a‰￥200??l pass the detector, the detector must act; the other is the liquid level detector. This protection method is to remove air bubbles In the case of air degassing device, air bubbles can be removed, but if the degassing device has too much air to cause the liquid level to drop beyond the detector, it must act. During the detection process, the sensitivity of the alarm to the size and speed of the bubble is mainly checked. When the bubble is relatively small and the blood flow rate is relatively fast, the "failure" state of the air detector often occurs, so when checking the bubble alarm, the alarm should be The speed of the blood pump is adjusted to the fastest speed, and the single bubble is measured at the minimum value of the limit.
The protective actions for air entry must include the following conditions: triggering audible and visual alarms, stopping the operation of the blood pump, interrupting the flow of any replacement fluid, clamping the venous return tube, and minimizing ultrafiltration.
5. Blood leakage protection
There are several possible causes of extracorporeal blood loss. One is that the tubing is detached or ruptured and the blood is lost to the outside world. This situation will cause the venous pressure to be low; the other is the blood coagulation alarm. This may be because the blood pump stops or because The blood itself is caused by a mechanism; the most common type of blood loss is blood leakage, which is mainly caused by a rupture of the membrane, which causes blood to flow to the dialysate. Device leakage
The protection is based on the result of blood leakage to realize the alarm. During the detection, the sensitivity of the blood leakage protection system can be measured by artificially simulating blood leakage.
The blood leak detector is composed of a light source and a photoresistor, which is realized by measuring the light transmission intensity in the waste liquid pipeline. The light beam irradiates the photoresistor through the waste liquid. If the waste liquid is mixed with blood, the light transmission is weakened, and the alarm is triggered after the photoelectric effect is changed. When a blood leak alarm is triggered, the system should issue an audible and visual alarm while stopping the blood pump and interrupting the flow of any replacement fluid to reduce ultrafiltration to a minimum. Welcome to reprint, this article comes from the electronic enthusiast network (http: //)
Four Burner Gas Cooker,Stainless Steel Gas Stove,Ce Table Outside Gas Cooker,4 Burner Glasstop Gas Cooker
xunda science&technology group co.ltd , https://www.gasstove.be