Hemodialysis therapy is a new treatment for patients with renal failure. At present, hemodialysis therapy is also the most widely used method for treating renal failure at home and abroad. However, because the treatment target is mostly critical patients, and the risk of treatment is high, any glitch may cause serious medical accidents, so blood The safety protection requirements of the dialysis unit are extremely high. According to the characteristics of hemodialysis equipment, this paper analyzes the requirements of safety protection from two aspects: electrical safety and functional safety.
First, electrical safety requirementsThe hemodialysis device is mainly composed of power supply components, heaters, motors, temperature sensors, pressure sensors, conductivity sensors, etc. According to the requirements of GB9706.1-1995, the electrical safety involved 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 the two key issues related to patient protection against electric shock and leakage current. Figure 1 Typical 1 Typical insulaTIon of haemodialysis equipment
When the hemodialysis device is being treated, the device is in contact with the blood through the dialysate. According to the conventional medical electrical device design concept, the application part directly used for the heart or in contact with the blood should be designed into a CF type, but all the blood. The application part of the dialysis unit is type B, which is determined by its special structure. At this stage, it has not been able to design a CF type structure.
A component that must be in contact with the patient during the functioning of the device, as defined in the application section. When the dialysis device is running, the dialysate exchanges substances through the semi-permeable membrane and blood. The semi-permeable membrane does not have any isolation. Therefore, the entire dialysate operating part should be regarded as the application part, which includes Dialysis solution preparation system, temperature sensor, dialysate pressure sensor, conductivity sensor and heater. 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. Therefore, the application part of the hemodialysis device is a B-type application part.
2. Anti-shock analysis between electrical partsAs shown in Figure 1, there are four ways to get through the various insulations to the application part from the external power supply to the patient. One is from the network power through the intermediate circuit, and then through various sensors and dialysate contact; the second is from the network power through the heater and dialysate contact; the third is the battery (the battery can be regarded as a specific grid power) through the intermediate circuit across each The sensor is in contact with the dialysate; the fourth is that various external uncertain power sources may be in contact with the dialysate across the intermediate circuit and sensor through the SIP/SOP interface. The above four routes are analyzed separately for points A to G shown in Fig. 1 below. Welcome to reprint, this article from the electronic enthusiast network ()
a) The influence of the network power supply on the patient through the intermediate circuitAs can be seen from Figure 1, the network power supply is in contact with the patient through Part A isolation and G-part insulation high impedance. Part A represents the primary and secondary of the power supply of the equipment network. It is required to achieve double insulation between the two parts. If this part is broken down, the power supply of the network is directly added to the intermediate circuit and each sensor, which may cause serious danger. In addition, the G part uses a semiconductor sensor, and utilizes the characteristics of the PN junction to realize an isolation method of insulating high impedance, which plays a role of limiting leakage current. However, since the semiconductor is unreliable, it is easy to break down and cannot be used as a highly perfect component. Therefore, in Chapter 17 of GB9706.1-1995, if the insulation between the application part and other live parts depends on the insulation properties of the junction of the semiconductor device, it is necessary to short the junction each 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 influence of the net power supply on the patient via the heaterIt can be seen from Fig. 1 that the power supply of the net is directly heated by the heater (point B). The insulating filling material of the heating rod is generally magnesium oxide, and the insulation level is required to achieve basic insulation, but the filling material can generally be Double insulation is achieved. Therefore, the insulation of the network power through the heater and dialysate to the patient is sufficient.
c) The impact of the battery on the patientAs can be seen in Figure 1, the battery is part of the intermediate circuit and is considered to be a specific power source. The battery is isolated from the application by the sensor. For sensor analysis see a). Generally, 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, over discharge, reverse polarity and other fault tests. Because the above faults are very likely to cause the battery to catch fire or even the danger of explosion.
d) the effect of external voltage on patientsThe device transmits signals to and from external devices via the SIP/SOP interface. This connection constitutes a medical electrical system and its safety should meet the requirements of GB9706.15. If the manufacturer has no clear statement on SIP/SOP, considering that 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 is directly under a single fault state. It is added to the SIP/SOP interface. Therefore, there should be isolation between the SIP/SOP interface and the intermediate/patient circuit. The reference voltage required for this isolation is the network voltage, because this situation occurs only in the case of a single fault. The degree of basic insulation is sufficient.
3, the patient's leakage current requirementsBecause the application part of the device is directly in contact with human blood, the patient's leakage current flows through the extracorporeal circulation blood circuit, which may cause serious consequences such as ventricular fibrillation, heart pump failure or tissue necrosis. In the case of a ground fault, the leakage current of the patient will increase sharply, reaching the value of the ground leakage current when the device is normal. Therefore, the product should be designed to limit the leakage current to the ground.
Second, functional safety protectionThe device is designed to treat the patient in an invasive manner and can be life-threatening when the safety system fails, requiring a safety 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 hemodialysis equipment must have: Welcome to reprint, this article from the electronic enthusiast network ()
1. Over-temperature protection of dialysate and replacement fluidWhen the temperature of the dialysate exceeds 41 °C, hemolysis reaction will occur in the blood. In order to minimize the risk of over-temperature, the state stipulates that the dialysis device must have a protection system independent of any temperature control system, that is, in addition to controlling the temperature. In addition to the sensor, there must be an independent temperature protection system. In general, the temperature control sensor's temperature control range does not exceed 40 ° C, while the temperature protection system's over temperature alarm is 41 ° C. It is impossible to over-temperature alarm when the device is working normally, that is, it is impossible to 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, let the temperature sensor fail, so that the heater is continuously heated. When the dialysate temperature exceeds the set value, its temperature protection system must be triggered to achieve the following alarm actions: triggering sound, light alarm and blocking dialysis The liquid flows to the dialyzer.
2, ultrafiltration protectionUltrafiltration is one of the important indicators of hemodialysis equipment. When there is a large error in the ultrafiltration system, the accumulation of excessive time will cause life danger to the patient. The protection system that the device must have should be independent of any ultrafiltration control system. In addition, the output of the prevention device deviates from the set value of the control parameter to create 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 alarmIf the blood pressure exceeds the set range and the duration exceeds the set delay, the hemodialysis unit must stop the blood pump operation, close the vein clamp, and give an audible and visual alarm. The focus of the test is the accuracy of the blood pressure alarm and the actions it achieves. The venous clamp is powered by electromagnetic or hydraulic pressure and blocks blood flow by clamping the extracorporeal blood circuit tube.
4, air alarmAir detection is based on the principle of ultrasound. Ultrasonic waves travel faster in liquids and solids than in gas. When the venous loop bubbles flow through the air detector, the ultrasonic receiving sensor gets a voltage drop that is less than normal and is processed by the CPU. There are two ways to detect air: one is to detect the presence of bubbles. When there are ≥200μl of bubbles passing through the detector, the detector must act; the other is a liquid level detector. This protection method is when a bubble passes. In the case of a gas device, the air bubbles can be removed, but if the degassing device causes the liquid level to drop beyond the detector due to a large amount of air, it is necessary to operate. In the detection process, it is mainly to check the sensitivity of the alarm to the bubble size and speed. When the bubble is relatively small and the blood flow rate is relatively fast, the air detector "failure" state often occurs, so when checking the bubble alarm, it should be The blood pump speed is adjusted to the fastest, and a single bubble is measured at the minimum value of the limit.
The protective action of air entry must include the following conditions: triggering sound and light alarms, stopping blood pump operation, interrupting the flow of any replacement fluid, clamping the venous return tube, and minimizing ultrafiltration.
5, blood leakage protectionThere are several possible causes of blood loss in vitro. One is that the tube is detached or ruptured, and the blood loses blood to the outside. This situation will cause the venous pressure to be low. One is the coagulation alarm. This may be because the blood pump stops or because The blood itself is caused by the mechanism; the most common type of blood loss is blood leakage, which is mainly caused by a membrane rupture, which causes blood to flow to the dialysate. Device leaking blood
The protection is realized by the result of blood leakage, and the sensitivity of the blood leakage protection system can be measured by artificially simulating blood leakage during the detection.
The blood leak detector consists of a light source and a photoresistor, which is measured by measuring the light transmission intensity in the waste liquid line. The light beam is irradiated onto the photoresistor through the waste liquid. If the waste liquid is mixed with blood, the light transmission is weakened, and the photoelectric effect changes to cause an alarm. When triggering a blood leak alarm, the system should give an audible and visual alarm, stop the blood pump at the same time, and interrupt any replacement fluid flow to reduce the ultrafiltration to a minimum.
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