전 기 안 전 (Electrical Safety)

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

Clinical Engineer-definition • 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 (1~6A) (75~400mA) (max. current at which the subject can withdraw voluntarily:min. 6mA)

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

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 2500-5000Hz.(100W light bulb connected two human subjects (arm to arm) burn brilliantly with 1A current) • Medical diathermy, Electro-surgical Unit (Bovie)

Cross-sectional view of skin layers A cell model

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

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

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 plug의 중요성 - 질문: 다음과 같은 회로에서 Isolation transformer를 쓰지 않는 것과 2구, 3구 플러그를 혼용해서 쓰는 것의 위험성을 설명해 보시오.

Macroshock Hazards 질문: 왼쪽 그림을 보고 macroshock이 일어나는 과정을 설명하시오.

Microshock Hazards 질문: 왼쪽 그림을 보고 microshock이 일어나는 과정을 설명하시오.

전 기 안 전 (Electrical Safety)