Discussion on the power supply of clean operating room in medical IT distribution system

1 Introduction

With the rapid development of medical electronic and electrical technology, modern medical care is increasingly dependent on electrical and electronic equipment. People's environmental requirements for hospital operating rooms are getting higher and higher, and some designs in the past are far from meeting people's requirements for safety and security. In particular, a large number of devices in the operating room touch the organs such as the human body and the brain, and in the event of electrical leakage, electrical accidents are likely to occur. How to protect hospital patients and medical personnel from electric leakage accidents has become very important, and has been widely concerned by relay protection experts and doctors at home and abroad. Many national and international standards have special provisions for medical distribution systems in the medical field, especially those where life is critical, such as operating rooms, intensive care units, cardiac care units, etc., with the aim of ensuring The medical electrical equipment inside provides a safe and reliable power source to ensure patient safety.

2 The necessity of medical IT power distribution system

2.1 electric shock to the human body

There are three main consequences of current flowing into the body. The first is burns, especially where current flows into and out of the body. This is followed by muscle paralysis, which may temporarily stop breathing. The third is that the electric shock causes ventricular fibrillation in the heart. This ventricular fibrillation causes dysfunction of the ventricles and heart valves, thereby stopping blood circulation. The first two results can cause discomfort, but rarely cause permanent damage, and ventricular fibrillation needs to be treated as soon as possible, otherwise it will cause brain damage or death. Under normal circumstances, the human body's natural reflection of electric shock can avoid or reduce the damage of current to the human body. First, the skin's skin resistance can limit the flow through the body. Second, the muscles contract when exposed to an electric shock, which generally allows the body to quickly disengage from the power source. However, it is well known that when the electric leakage current of the human heart is greater than 10 uA, the patient will die, which is called micro electric shock in medicine. In the medical process, in order to perform measurement, diagnosis or treatment for various purposes, the patient is often connected to various electrical devices, and the electrodes may enter the human body or be firmly attached to the surface of the human body (eg, electrocardiogram, electroencephalogram), and possibly The fluid is distilled from the human body and processed into the body (eg, kidney dialysis), which will cause the body to lose the protection of skin resistance. When the patient is under anesthesia, or loses the natural reflection of the electric shock due to loss of pain, the human body cannot be disconnected from the Power Supply, which is life-threatening to the patient.

2.2 Relevant regulations for the design of medical IT power distribution systems

Generally, the earth leakage protection switch such as RCD used in general-purpose buildings has a motion response value of mA (30 mA), which is far from meeting the needs of the medical field. Therefore, internationally, in the medical field, operating rooms, ICUs, CCUs and other important places, in addition to local equipotential bonding as required, the power distribution system usually uses a local neutral point ungrounded power supply system (ie IT system or Isolated Power Supplies system) powered. Powering these places through a single-phase 3KVA-10KVA isolation Transformer can first prevent leakage currents in other circuits from entering the operating room, ICU, and CCU medical electrical equipment through the grounding wire, posing a threat to patient safety; The load connected to the power supply (such as various medical electrical equipment) has a ground fault. Because it cannot form an electrical circuit to the ground, it can only produce a small capacitive leakage current, which can effectively control the direct leakage current to the heart and other organs. It greatly protects the patient from the leakage current. Domestically, the corresponding safety design specifications have also been introduced. Article 12.8.6 of the Code for Electrical Design of Civil Buildings stipulates that medical supplies for life-sustaining, surgical and other medical electrical equipment and systems located in the “patient area” should be used in Class 2 medical facilities. IT system. In addition, Section 8.3.4 of the "Technical Specifications for Hospital Cleansing Department" stipulates that: the cardiac surgery operating room must be provided with a functional grounding system for the isolation transformer. The national standard "Building Electrical Installations, Sections 7 - 710: Requirements for Special Installations or Locations - Medical Locations" (GB 16895.24–2005 / IEC 60364–7–710: 2002), has a corresponding division of medical facilities. Real-time monitoring instruments used on the surface or in vivo of the patient; instruments used for surgery; devices that maintain the patient's life and body functions; devices used to open the heart and brain. In such cases, the interruption of the power supply of the medical device may cause life-threatening to the patient; a weak leakage current may cause a 'micro-shock'. In a Class 2 location, each room must be equipped with at least one medical IT power supply (isolated power supply) that must be fitted with an insulation monitor. For example: anesthesia room, operating room, surgical preparation room, surgical gypsum room, surgical recovery room, cardiac catheterization room, intensive care unit, cardiac care room, angiography room, premature infant care room, etc. All of them belong to Class 2 power supplies locations. In the application group 2 medical facilities, an isolated power system with insulation monitoring, that is, an IT system, must be used.