전 기 안 전 (Electrical Safety) 서울대학교병원 의공학과 김 희찬

목 차 Clinical Engineer A Historical Perspective Safety Issue Electrical Safety Physiological effects of electricity Important susceptibility parameters Perception threshold Electricity conduction mechanism Distribution of Electrical Power My Experience Macroshock Hazards Microshock Hazards

Clinical Engineer-definition Biomedical Engineers assist in struggle against illness and disease by providing materials and tools that can be utilized for research, diagnosis, and treatment by health care professionals. Clinical Engineer have achieved this position by assuming responsibility for managing the use of medical equipment within the hospital environment

The American Hospital Association : “a person who adapts, maintains, and improves the safe use of equipment and instruments in the hospital” The Association for the Advancement of Medical Instrumentation (AAMI) : “a professional who brings to health-care facilities a level of education, experience, and accomplishment which will enable him/her to responsibly, effectively, and safely manage and interface with medical devices, instruments, and systems and the user thereof during patient care” Clinical Engineer-definition

The American College of Clinical Engineering (ACCE) : “a professional who supports and advances patient care by applying engineering and managerial skills to health-care technology” The Board of Examiners for Clinical Engineering Certification : “an engineer whose professional focus is on patient-device interfacing; one who applies engineering principles in managing medical systems and devices in the patient setting”

A Historical Perspective Engineer’s first enter to clinical scene : late 1960s in response to concerns about electrical safety of hospital patient Ralph Nader (consumer activist) : “at the very least, 1200 Americans are electrocuted annually during routine diagnostic and therapeutic procedures in hospitals” Ladies Home Journal, April 24, 1970 Raise the level of concern about safe use of medical device

A Historical Perspective- cont. Overnight growth of a new industry : hospital electrical safety National Fire Protection Association (NFPA) : standards addressing electrical safety in hospital Joint Commission on the Accreditation of Hospital : “hospital must inspect all equipment used on or near a patient for electrical safety at least every 6 months” Hospital administrator’s options –Paying medical device manufacturer –Service contracting –In-house staff New engineering discipline – clinical engineering - was born.

Safety Issue In USA, about 10,000 device-related patient injuries each year Most injuries are attributable to improper use of a device as a result of inadequate training and lack of experience Medical personnel rarely read user manuals until a problem occurred “Everything that can go wrong eventually will go wrong” Murphy’s law

Electrical Safety Electric Shock : unwanted or unnecessary physiological response to current. Three phenomena : –(1) electrical stimulation of excitable tissue (nerve & muscle) –(2) resistive heating of tissue, and –(3) electrochemical burns and tissue damage

Physiological effects of electricity 70-Kg (max. current at which the subject can withdraw voluntarily:min. 6mA) (75~400mA) (1~6A)

Important susceptibility parameters Let-go current vs. frequency Fibrillation current vs. shock duration & weight

Perception Threshold D’Arsonval(galvanometer fame) : showed when current was passed through the human body, no sensation was perceived as the frequency was increased beyond Hz.(100W light bulb connected two human subjects (arm to arm) burn brilliantly with 1A current) Medical diathermy, Electro-surgical Unit (Bovie)

A cell model Cross-sectional view of skin layers

electrode(metal) wire(metal) electrode(metal) wire(metal) e-e- Charge carrier Tissue Electrolyte/Dielectric cell skin ions Charge carrier Electricity Conduction Mechanism Electrochemical Reactions e-e- Charge carrier

Effect of entry point on current distribution Fibrillation current : lead I > lead II, III For dog: 20  A, human : 80~600  A Safety limit : 10  A Important susceptibility parameters

Distribution of Electric Power Ex) 120V, 500W instruments, power-cord resistance 0.25  Then the voltage drop across the neutral to ground is 0.25(500/120) = 1.04V

My experience - Isolation transformer 와 3-prong plug 의 중요성 - 질문 : 다음과 같은 회로에서 Isolation transformer 를 쓰지 않는 것과 2 구, 3 구 플러그를 혼용해서 쓰는 것의 위험성 을 설명해 보시오.

Macroshock Hazards 질문 : 왼쪽 그림을 보고 macroshock 이 일어나는 과정을 설명하시오.

Microshock Hazards 질문 : 왼쪽 그림을 보고 microshock 이 일어나는 과정을 설명하시오.