IEC 60601-1 patient applied parts for Medical Electrical Equipment

In this blog, “IEC 60601-1 patient applied parts for Medical Electrical Equipment-Notes 1-2-3,” the author uses many figures to explain critical concepts. 

Note 1: Figures that explain APPLIED PART concepts

In IEC 60601-1, Figures 3 and 4 (shown below) are used to show where different parts of ME EQUIPMENT are located, and to help explain some of the defined terms in a pictorial way.

 

In both figures, the APPLIED PART is intended to come into contact with the PATIENT. Figure 3 shows a CLASS I medical device as per sub-clause 3.13. The device is PROTECTIVELY EARTHED (i.e., grounded), in addition to providing BASIC INSULATION. Figure 4 shows a CLASS II medical device per sub-clause 3.14. The device is not PROTECTIVELY EARTHED. Instead, Figure 4 shows how the design uses two levels of protection, which is a basic tenet of the IEC 60601-1 standard. The two levels of protection used are either DOUBLE or REINFORCED INSULATION.

Figures A.1 to A.7 provide examples of the way APPLIED PARTS and PATIENT CONNECTIONS are identified to apply the requirements for PATIENT LEAKAGE CURRENT and PATIENT AUXILIARY CURRENT. APPLIED PART circuits can provide isolation to other parts of the circuitry in the medical device, and these figures present several options for compliance with SPACINGS (i.e., CREEPAGE and AIR-CLEARANCE), DIELECTRIC WITHSTAND (i.e., HiPot test) and INSULATION requirements. The following discussion is limited to Figures A.1 and A.2. For additional information about Figures A.3-A.7, purchase a copy of IEC 60601-1, edition 3.0 (http://bit.ly/IEC60601-1) or edition 3.1 (http://bit.ly/IEC60601Consolidated).

Figures A.1 and A.2 show an ECG monitor that includes the monitor, PATIENT cable, PATIENT leads, and ECG electrodes. The critical elements of figure A.1 are:

1)     the APPLIED PARTS includes the electrodes and those parts of the PATIENT leads, or PATIENT cable that need to physically contact the PATIENT in NORMAL USE (sub-clause 3.8 definitions),

2)     application of RISK MANAGEMENT might id other parts of the PATIENT leads or PATIENT cable that needs to treated as APPLIED PARTS because of the probability they will come in contact with the PATIENT, (sub-clause 4.6 requirements), and

3)     the PATIENT CONNECTIONS consist of the ECG electrodes, which are part of the same function of the APPLIED PART.

Figure A.2 below shows the required F-TYPE APPLIED PART insulation incorporated in the medical device itself. The components within the dotted line form the PATIENT circuit.

Note 2: Parts that are not APPLIED PARTS may need to be treated as an APPLIED PART

Sub-clause 4.6 and Annex A, sub-clause 4.6, provide additional details that apply to the following paragraph below.

Parts of medical devices that are not APPLIED PARTS, but which touch the PATIENT during the NORMAL USE of the device, may need to be treated as APPLIED PARTS. In this case, the part shall not be marked as an APPLIED PART. A RISK ASSESSMENT PROCESS needs to be conducted to determine whether the parts that come in contact with the PATIENT but aren’t APPLIED PARTS should meet the requirements of APPLIED PARTS. Figures A.4 through A.7 all have a statement that roughly states: “The application of RISK MANAGEMENT might identify some parts of the device/system as having to be treated as APPLIED PARTS because of the probability they will come in contact with the PATIENT.” If your RISK ASSESSMENT determines that sub-clause 4.6 is applicable, then all applicable requirements and tests for APPLIED PARTS should be applied to the parts identified in the RISK ASSESSMENT—except for sub-clause 7.2.10 for marking of APPLIED PARTS. These requirements apply to this standard and the relevant collateral and particular standards in the 60601 series of standards. An example of the type of parts that could fall under sub-clause 4.6 could be computer system interface cable (I/O).

Note 3: Definition of associated term PATIENT CONNECTION

A PATIENT CONNECTION is part of the APPLIED PART, as shown in figure A.1. Sub-clause 3.78 defines a PATIENT CONNECTION as: “Individual point on the APPLIED PART through which current can flow between…PATIENT and ME EQUIPMENT in NORMAL…or SINGLE FAULT CONDITION.” In this example, the conductive part of the ECG electrode is considered the PATIENT CONNECTION.

IEC 60601-1 assumes the PATIENT is earthed as a NORMAL CONDITION per sub-clause 8.5.4, 4^th dashed item because there are many opportunities in the normal operation of medical electrical devices where the PATIENT can accidentally become grounded. Therefore, some PATIENT LEAKAGE CURRENT tests are configured with the LEAKAGE CURRENT measuring device (see Figure 12) directly connected to earth on one side and passing thru the measuring device to the APPLIED PART circuit that is being tested. The boxed-in area in Figure 15 is the portion of the PATIENT LEAKAGE CURRENT test measuring circuit that is connected from the PATIENT CONNECTION (item 4) thru the measuring device to earth (left-hand corner of the figure—symbol sometimes called “upside-down Christmas tree”).

 

Leo Eisner is the owner and founder of Eisner Safety Consultants (http://bit.ly/LeoEisner). If you need help with IEC 60601 compliance, email Leo directly at Leo@EisnerSafety.com or call him at +1 (503) 244-6151.  You can also connect on LinkedIn at http://bit.ly/ConnectwithLeo.