INSPECTION OF MEDICAL DEVICES

Transcription

1 INSPECTION OF MEDICAL DEVICES Safety And Maintenance For Industrial Systems Sapienza Università di Roma, Ing. Silvia Ruggieri 1

2 Safe MD development Physiological effects of electricity and Consequences of dangerous voltage IEC vs. IEC Commonly used terms and definitions How is testing performed? Final test AGENDA 2

3 Achievements: Significant improvement of health care in all medical specialties Reducing the number of seriously ill people Reduction of mortality Consequences: increased complexity of medical devices and their applications increased incidence of adverse effects of implementation of MD in the U.S. approx. 10,000 cases of patient injury due to the application of MT MEDICAL DEVICES 3

4 Causes of unintended consequences: improper handling insufficient or improper staff practice (training) in handling with MD insufficient experience example, medical staff rarely read manuals for the users (User Manual) equipment malfunction Demand for MD developers: developement of safe devices (failure-safe) MEDICAL DEVICES 4

5 In a clinical environment patient is exposed to various risks, more than a typical workplace or at home frequent invasive (blood) operations - penetration through skin or mucous membranes presence of potentially hazardous chemicals and substances - anesthetics, medicines, medical gases sources of infection - particularly "hospital infection" various sources of energy that penetrate into or through the patient: current, voltage, ionizing and non-ionizing radiation, sound and ultrasound, electric and magnetic field, UV radiation, lasers, microwave radiation, mechanical stress, etc. DANGER TO PATIENTS 5

6 Electrical MD security is considered: physiological effects of electricity possibility (risk) of failures and their consequences methods of patients and staff protection standards describing electrical safety electrical safety testing modes Understanding the possible dangers and risks Implementation in achieving security SAFE MD DEVELOPMENT 6

7 Body (tissue) becoming a part of an electrical circuit The amount (amplitude) of electricity often depends on the ratio of voltage present and the sum of all (serially connected) impedance Usually, the highest impedance is the impedance of the skin The consequence of current flow: nerve and/or muscle tissue stimulation heating of tissues (a result of tissue resistance) burns PHYSIOLOGICAL EFFECTS OF ELECTRICITY 7

8 I t curves for sensory and motor responses PULSED CURRENT 8

9 Further consideration are based on the following parameters Human body with contact to el. circuit at left and right hand Body weight: 70 kg Applied current time: 1 s to 3 s Current frequency: 60 Hz PHYSIOLOGICAL EFFECTS OF CURRENT 9

10 THRESHOLD OF PERCEPTION Current density is just large enough to excite nerve endings in the skin Subject feels tingling sensation Lowes values with moistered hands (decreases contact resistance): 0.5 ma at 60 Hz 2 ma to 10 ma DC The subject meight feel a slight warming PHYSIOLOGICAL EFFECTS OF CURRENT (1) 10

11 LET-GO CURRENT The let-go current is defined as the maximal current at which the subject can withdraw voluntarily For higher current nerves and muscles are vigorously stimulated Involuntary contraction or reflex withdrawals may cause secondary physical injuries (falling off the ladder) The minimal threshold for the let-go current is 6 ma PHYSIOLOGICAL EFFECTS OF CURRENT (2) 11

12 RESPIRATORY PARALYSIS, PAIN, FATIGUE Higher current causes involuntary contraction of muscles and stimulation of nerves what can lead to pain and cause fatigue Example: stimulation of respiratory muscles lead to involuntary contraction with the result of asphyxiation if current is not interrupted Of course, today s ethics commission would never allow these experiments on human beings. PHYSIOLOGICAL EFFECTS OF CURRENT (3) 12

13 VENTRICULAR FIBRILLATION The heart is especially susceptible to electric current. Just 75 ma to 400 ma (AC) can rapidly disorganize the cardiac rhythm and death occurs within minutes Only a brief high-current pulse from a defibrillator can depolarize all the cells of the heart muscle simultaneously Within the U.S. occur approximately 1,000 death per year due to cord-connected appliances PHYSIOLOGICAL EFFECTS OF CURRENT (4) 13

14 SUSTAINED MYOCARDIAL CONTRACTION When current is high enough to stimulate the entire heart muscle, it stops beating Usually the heart-beat ensues when the current is interrupted Minimal currents range from 1 A to 6 A (AC), like used in defibrillators PHYSIOLOGICAL EFFECTS OF CURRENT (5) 14

15 BURNS AND PHYSICAL INJURY Resistive heating cause burns Current can puncture the skin Brain and nerve tissue may lose all functional excitability Simultaneously stimulated muscles may contract strong enough to pull the attachment away from the bone or bread the bone PHYSIOLOGICAL EFFECTS OF CURRENT (6) 15

16 Unintended consequences are usually a result of human involvement in the circuit, in some way connecting to the grid (inattention, failure) Several levels of action perception contractions (let-go) paralysis (respiratory), pain, fatigue ventricular fibrillation tetanic contraction burns and physical injuries ELECTRICITY GRID 16

17 Fibrilation Convulsion Consequences depende on the voltage current relation, but also on individual susceptibility Expected values Intact skin R K = 2~5 kω Damaged skin - injuries, surgical procedures R O = 100Ω ~ 1kΩ CONSEQUENCES OF DANGEROUS VOLTAGE 17

18 Fibrilation Convulsion Focus on the worst possible scenario, for example, a person holding two conductors at different potentials in his hands resulting muscle spasms, inability to release captured conductors In case of intact skin, R ext = 2~5 kω, cramps can occur even at a voltage of few dozen ma In case of damaged skin - injuries, surgical procedures, R int = 100Ω ~ 1kΩ, fibrillation may occur at voltages of several volts and current of few dozen ma CONSEQUENCES OF DANGEROUS VOLTAGE 18

19 The consequences of current passage through the tissue depend on the contact point with the source of voltage Even greater power will not necessarily cause fatal consequences, eg. fibrillation, when going through the limbs MICROSHOCK VS. MACROSHOCK 19

20 Macroshock is caused by current passing through the body through the skin, and the current that can cause harmful effects is relatively high and significantly depends on the point of contact Microshock is caused by the passage of relatively low current, but the source of electricity was brought directly into contact with the heart, for example, during cardiac catheterization (catheter in the heart is a diagnostic procedure). Another point of contact can be anywhere on the body (eg limbs). Current of 10 μa is considered safe limit to prevent microshock MICROSHOCK VS. MACROSHOCK 20

21 Macroshock = current spreads through the body Two factors reduce danger in case of an electric shock High skin resistance (15k Ohm to 1 MOhm at 1 cm2) Spatial distribution Many medical devices Reduce the skin resistance with ionic gel (good electrode contact), or Bypass the natural protection by bypassing the skin (thermometer in the mouth, intravenous catheters, etc.) Many fluids conduct electricity (blood, urine, intravenous solution, etc.) Result Patients in medical-care facilities are much more susceptible to macroshocks MACROSHOCK HAZARDS 21

22 Ground fault with short circuit to a metal chassis: A. not grounded chassis macroshock B. grounded chassis safe Figure: Macroshock due to a ground fault from hot line to equipment cases for (a) ungrounded cases and (b) grounded chassis. MACROSHOCK HAZARDS PROTECTION 22

23 Microshock = all current flows through the heart Microshock accidents generally result from leakage-currents in line-operated equipment differences in voltage between grounded conductive surfaces due to large currents in the grounding system Microshock currents can flow either into or out of the electric connection to the heart Result Patient is only in danger of microshock if there is some electric connection to the heart MICROSHOCK HAZARDS 23

24 Leakage-current flows: A. through the ground wire no microshock occurs B. through the patient if he touches the chassis and has a grounded catheter etc. C. through the patient if he is touching ground and has a connected catheter etc. Figure: Microshock leakage-current pathways. Assume 100 μa of leakage current from the power line to the instrument chassis, (a) Intact ground, and 99.8 μa flows through the ground, (b) Broken ground, and 100 μa flows through the heart, (c) Broken ground, and 100 μa flows through the heart in the opposite direction. MICROSHOCK HAZARDS PROTECTION 24

25 ZONE 1: no reactions (~1mA) ZONE 2: no dangerous physiological effect (~10mA) ZONE 3: reversible disorders, muscle contractions, breathing difficulties (~100mA) ZONE 4: probable cardiac arrest, respiratory arrest, severe burns (~200mA) LET'S DO SOME CALCULATIONS 25

26 Reasonably safe current value: MD WITHOUT APPLIED PARTS I c = 10 ma ~ 20 ma Maximum safe contact voltage for the patient: U L = 25 V ca, 60 V cc Esternal contact: R ~ 10 kω ZONE 2 LET'S DO SOME CALCULATIONS 26

27 Reasonably safe current value: MD WITH APPLIED PARTS OF THE CF TYPE I c 10 μa Maximum safe contact voltage for the patient: U L = 10 mv Internal contact: R ~ 1 kω For heart current value > 10 μa: VENTRICULAR FIBRILLATION!!! LET'S DO SOME CALCULATIONS 27

28 Generally, patients are only occasionally and accidentally exposed to risk of getting in touching with devices whose conductive parts may be energized. In hospitals, especially in intensive care units, patients are deliberately connected to the diagnostic and/or therapeutic electrical devices/equipment: particularly careful with the isolation of any conductive parts connected to the heart or its vicinity from all other conductive parts all conductive parts in the vicinity of the patient must be connected to a single point grounding (eg, metal bed, cupboard, etc.) periodic testing of the grounding impedance must be provided Tolerable difference in potential between the grounded conductive parts in clinical areas: in the general minor of 500 mv intensive care and other critical cases minor of 40 mv PROTECTIVE GROUNDING 28

29 Under normal conditions, increasing patient safety is provided by: formation of isolated parts of the grid installation of automatic monitoring of impedance grounding (line isolation monitor) POWER IN CLINICAL ENVIRONMENTS 29

30 The principle of redundancy can be applied to the safety of medical devices and equipment For example, it is required that electrical medical equipment is safe even in case of a breakdown on the conductive contact with patient Grounding impedance must be sufficiently low so that the patient may not get in touch with any dangerous voltage EQUIPMENT SAFE DURING THE FIRST FAILURE 30

31 Occur between conductors that are not in direct contact (touch) and are at different potentials For devices that are powered from the grid, leakage currents are: capacitive character (spreading capacity) operative character (current through the insulation, dust, humidity...) LEAKAGE CURRENTS 31

32 Pathways of leakage current through the patient with intact ground lead LEAKAGE CURRENTS PATHWAYS 32

33 Pathways of leakage current through the patient with broken protective ground lead, patien connected to ground through a catheter LEAKAGE CURRENTS PATHWAYS 33

34 Pathways of leakage current through the patient with broken protective ground lead, patien connected to ground by an electrode or unintentianally. LEAKAGE CURRENTS PATHWAYS 34

35 The International Electrotechnical Commission, or IEC, has done the industry a great service by introducing a series of standards for the safety and efficacy of medical electrical equipment, better known as IEC As IEC was put into practice, though, experts observed that these standards overlooked the necessity of ongoing testing of the equipment after it had entered the field. Thus, a new set of standards for this very purpose was introduced: IEC HOW DETECT AND ERADICATE POTENTIAL ELECTRIC HAZARDS? 35

36 IEC 60601, Medical Electrical Equipment General Requirements for Safety was introduced in 1977 and put forth a set of requirements for the manufacturers of medical equipment. These requirements were designed to detect and eradicate any potential electric hazards presented by the equipment being produced (e.g. leakage currents, protective grounding, etc.). Assuming the equipment was utilized properly for the duration of its lifespan, these tests were meant to curb possible defects later on. They were further utilized on equipment already in service as a means of routine tests and after-repair tests; however, this practice presented some unforeseen difficulties: for example, IEC outlines type-testing in laboratory conditions, but often those conditions are not available or applicable once the device is already in use. And so, thirty years after IEC appeared on the scene, in 2007, IEC 62353, Medical Electrical Equipment Recurrent Test and Test After Repair of Medical Electrical Equipment emerged to accommodate the needs of in-service devices. IEC is specifically designed around testing equipment in the field, and is therefore more practical, more effective, and more safe than using IEC in those particular circumstances. IEC VS. IEC

37 Electrical equipment, designed for treatment, monitoring or diagnoses of patients, powered from not more than one connection to mains supply and which are necessarily in physical or electrical contact with the patient or transfers energy to or from the patient or detects such energy transfer to or from the patient. Combination of equipment of which at least one is classed as medical electrical equipment and as such specified by the manufacturer to be connected by functional connection or use of a multiple portable socketoutlet. WHAT IS AN ELECTRICAL MEDICAL DEVICE? 37

38 WHAT IS AN ELECTRICAL MEDICAL DEVICE? 38

39 WHAT IS AN ELECTRICAL MEDICAL DEVICE? 39

40 Applied part: Part of the medical equipment, which is designed to come into physical contact with the patient, or parts that are likely to be brought into contact with the patient. COMMONLY USED TERMS AND DEFINITIONS IN IEC /

41 F-Type applied part: Applied part which is electrically isolated from earth and other parts of the medical equipment. i.e. floating. F-Type applied parts are either type BF or type CF applied parts Type B applied part: Applied Part complying with specified requirements for protection against electric shock. Type B applied parts are those parts, which are usually Earth referenced. Type B are those parts not suitable for direct cardiac application. Type BF applied part: F-Type applied part complying with a higher degree of protection against electric shock than type B applied parts. Type BF applied parts are those parts not suitable for direct cardiac application. Type CF applied part: F-Type applied part complying with the highest degree of protection against electric shock. Type CF applied parts are those parts suitable for direct cardiac application. COMMONLY USED TERMS AND DEFINITIONS IN IEC /

42 Patient environment: Volumetric area in which a patient can come into contact with medical equipment or contact can occur between other persons touching medical equipment and the patient, both intentional and unintentional. COMMONLY USED TERMS AND DEFINITIONS IN IEC /

43 Class I: Equipment protection against electric shock by (earthed) additional protection to basic insulation through means of connecting exposed conductive parts to the protective earth in the fixed wiring of the installation BASIC INSULATION + PERMANENT CONNECTION OF THE PROTECTIVE EARTH CONDUCTOR AND OF THE METALLIC PARTS Class II: Also referred to as double insulated. Equipment protection against electric shock is achieved by additional protection to basic insulation through means of supplementary insulation, there being no provision for the connection of exposed metalwork of the equipment to a protective conductor and no reliance upon precautions to be taken in the fixed wiring of the installation BASIC INSULATION + DOUBLE OR REINFORCED INSULATION EMD CLASSIFICATION 43

44 IEC requires testing before initial start-up, after repair, and periodically. The manufacturer is obligated to provide information about the testing of the device, with which the operator of the testing should carefully comply. WHEN ARE THE TESTS SPECIFIED BY IEC PERFORMED? 44

45 Tests of device safety must be performed by qualified technician who have received adequate training for attending to devices under testing conditions. Individuals who perform safety tests must be able to recognize any threats posed by devices that do not meet safety standards. WHO SHOULD PERFORM THESE TESTS? 45

46 Before testing, accompanying documentation must be examined Whenever and wherever possible, the device must be disconnected from the mains supply power; otherwise, special measures must be implemented for the prevention of hazards resulting from working on live devices. All tests carried out must be documented in depth. Testing documents must at the very least contain the following entries: Designation of the test location (e.g. company, department, authority) Name of the person(s) who performed and evaluated the test Designation of the tested device and accessories (e.g. type, serial number, inventory number) Executed tests including measured values, measuring methods and utilized measuring instruments Function test Final evaluation Date and ignature of the person who prepared the evaluation Identification of the tested device (if required by the operating service provider) HOW IS TESTING PERFORMED? 46

47 In most cases, 70% of all faults are detected during visual an inspection. The following inspections can be included: 1. Housing / Enclosure - Look for damage, cracks etc. 2. Integrity - Look for obstruction of moving parts, connector pins etc. 3. Cabling (supply, applied parts etc.), Look for cuts, wrong connections etc. 4. Fuse rating - check correct values after replacement. 5. Markings and labelling - check the integrity of safety markings. 6. Integrity of mechanical parts - check for any obstructions. VISUAL INSPECTION 47

48 1. Protective Conductor Resistance Measurement 2. Leakage Current Measurement: 1. Device Leakage Current 2. Leakage Current from the Application Part 3. Insulation Resistance Measurement (not obligatory) ELECTRICAL MEASUREMENT TESTS 48

49 1) Protective Conductor Resistance Measurement Protective conductor resistance measurements are performed on Class I devices to ensure that all accessible conductive parts (which, in the event of a fault, may become live) are appropriately secured to the protective conductor terminal. All devices must conform to the following protective conductor connection limit values: ELECTRICAL MEASUREMENT TESTS (1) 49

50 2) Leakage Current Measurement Leakage current measurement requirements only apply universally to AC components; DC leakage current measurements must be determined and explicitly expounded upon in accompanying documentation by manufacturers (complying also with IEC DC limit values). The measured value must be corrected to the value which corresponds to the measurement at nominal line voltage. The following leakage currents are measured: 1. Device Leakage Current 2. Leakage Current from the Application Part ELECTRICAL MEASUREMENT TESTS (2) 50

51 There are three methods to choose from for measuring leakage current; selection of which should be based on the design of the device: ELECTRICAL MEASUREMENT TESTS (2) 51

52 ELECTRICAL MEASUREMENT TESTS (2) 52

53 ELECTRICAL MEASUREMENT TESTS (2) 53

54 ELECTRICAL MEASUREMENT TESTS (2) 54

55 3) Insulation Resistance Measurement Insulation resistance is a helpful measurement to find insulation faults caused by dust, wetness or pollution but the measurement may be forbidden by some manufacturers to avoid damage on sensitive parts. Furthermore, there is no limit value specified in IEC 62353, but the following values can serve as a reliable guideline: ELECTRICAL MEASUREMENT TESTS (3) 55

56 4) Function Test Function tests regarding safety will be specified by the manufacturer, and should be executed accordingly. Function tests also fall under essential performance characteristics and special requirements of IEC Most of the time, additional test instruments will be required (such as with infusion pumps and defibrillators). ELECTRICAL MEASUREMENT TESTS (4) 56

57 DOCUMENT EXAMPLE 57

58 IN 45 MINUTES, YOU MUST EXECUTE A RISK ANALYSIS OF 1 ELECTROMEDICAL DEVICE THAT CHOOSE FROM THESE LISTED: EXTERNAL DEFIBRILLATOR ECG MONITOR OPERATING TABLE SCIALYTIC LAMP ELECTROSURGERY FINAL TEST 1/2 58

59 IN THE REST OF TIME, YOU MUST DESCRIBE HOW YOU WILL MAKE THE SAFETY TEST ON THE ELECTROMEDICAL DEVICE YOU CHOSE BEFORE AND COMPILE THE MAINTENANCE REPORT FROM YOU PREPARED. FINAL TEST 2/2 59