Electrosurgical Accessory Testing

CITECH tests electrosurgical accessories (cables, monopolar and bipolar electrodes and return electrodes) more frequently than it tests any other devices. We are familiar with the content and philosophy of the ANSI/AAMI standard, HF18, and also with IEC 60601-2-2 and 60601-2-18. Our testing has been used in 510(k) submissions and to justify CE Marking. Still, testing some electrosurgical devices remains more art than science.

The following articles discuss some of the tests, as they relate to standards. If you have any questions about testing your electrosurgical accessory, please call us; we'll be glad to discuss them with you.

Recent Standards Activity

In mid-2006, IEC issued the 4th edition of IEC 60601-2-2. With several significant exceptions, the accessory requirements in the 4th edition are identical to those of ANSI/AAMI HF18:2001, reflecting AAMI’s participation in the IEC revision. Accordingly, AAMI officially withdrew HF18:2001 early in 2007; it will no longer sell HF18. FDA has not yet withdrawn its recognition of HF18:2001, although it now also recognizes IEC’s 4th edition. (A 5th edition of IEC 60601-2-2 is being finalized by the IEC committee, but has not been officially adopted yet.) CITECH can test to HF18 and/or the IEC 4th edition. For active accessories, IEC testing is more time-consuming.

The following articles do not reflect these recent changes;
we will update the articles in the near future.

 

Meeting Two Standards for Active ESU Accessories

There are two standards that cover electrosurgical units (ESUs) and their accessories. The domestic standard is ANSI/AAMI HF18; the most recent edition is dated 2001. The international standard is IEC 60601-2-2; the third edition (dated 1998-09) is currently in use. [Another international standard, IEC 60601-2-18, for endoscopic equipment, has not come into widespread use in this country.] This article focuses on the requirements of the two standards for active accessories.

Manufacturers seeking FDA clearance to market these accessories in the U.S. should meet HF18, while those marketing in Europe should meet the IEC standard. There are many similarities between the two standards, but there are also some significant differences. To help firms looking toward both markets, CITECH can develop a test program that demonstrates compliance with both standards without duplication.

Requirements of the IEC standard are at least as severe as those of the ANSI standard, where they cover similar tests. However, ANSI/AAMI HF18-1993 includes several tests of accessory cables that are not found in the IEC document, and IEC 60601-2-2 includes a cable dielectric withstand test not found in HF18. [FDA expects compliance with all of these cable tests.] There are two other areas where the differences between the standards are especially noteworthy-the dielectric withstand test voltage and the material used to wrap the active accessory for testing.

Both standards require that the dielectric withstand capabilities of the electrode be tested at 150% of a particular voltage, but there's an ocean of difference between them as to which voltage this is. The ANSI/AAMI standard requires that the electrode manufacturer specify a maximum voltage rating for the device (with testing at 150% of that value). This can be less than the maximum setting of the ESU, and it reflects the typical clinical use of the particular device. The IEC standard requires that the electrode withstand 150% of the maximum output of the ESU with which it is intended to be used. Although there are valid arguments for both approaches, the IEC requirement is usually much more difficult to meet, especially with the thin insulation required of laparoscopic electrodes.

The first (1986) edition of ANSI/AAMI HF18 required that the electrode be wrapped in foil for the dielectric withstand test. However, as the standard was used, it was noted that the foil would not conform well to the electrode; the inevitable creases in the foil caused stress points for high-voltage breakdown, causing inconsistent and unrealistic results. Therefore, since 1993, HF18 requires that the electrode be wrapped in a conductive, conforming material, such as saline-moist cloth; it specifically warns against the use of foil. The IEC standard, on the other hand, requires that the electrode be wrapped in foil; no alternative is allowed, and no rationale is offered. Based on our experience, we believe that this is wrong for the same reason that AAMI did.

The ANSI/AAMI standard 60 Hz test of the accessory is not found in the IEC standard. While the test is easier to conduct than the high-frequency dielectric withstand test that both standards require, we have never found a device to pass the high-frequency test but fail the 60 Hz test.

CITECH has worked with many clients to test electrosurgical electrodes against the requirements of the ANSI/AAMI and IEC standards. Below, we have prepared a table that compares the active accessory requirements of the two standards. If you would like to discuss your testing needs or have any questions pertaining to the comparison table, call CITECH.

Electrosurgical Accessory Test Requirement Comparison ANSI/AAMI HF18-2001 and IEC 60601-2-2 (3 ed)

Test HF18 60601-2-2 Sterilization Reusable devices: Do all tests except strain relief after 20 sterilizations (4.2.5.3) Reusable devices: Do high-frequency dielectric withstand tests after 20 sterilizations per Clause 44.7 (59.103.2) Cable dielectric withstand, mains frequency Test entire cable in water @ 3 kV for 5 min, after 12 hr soak (4.2.5.1) Test 10 cm length in saline @ 3 kV for 5 min after 24 hr soak (59.103.1) Cable dielectric withstand, high frequency None Test 10 cm in saline @ 1.5 times maximum output of ESU for 30 sec (59.103.1) Cable high frequency leakage Test 30 cm in special fixture @ 800 V, peak-to-peak; frequency 0.3 - 1 MHz (4.2.5.2) None Accessory handle dielectric withstand, 60 Hz Wrap in saline-moist cloth (not foil); apply 3 kV (1.5 kV for bipolar and gastroenterological) for 60 sec (4.2.5.4) None Accessory handle dielectric withstand, high frequency Wrap in saline-moist cloth (not foil); test @ 1.5 times manufacturer's rating, using ESU, for 30 sec; confirm switch operation (4.2.5.4) Wrap in foil (no alternative); test at 1.5 times maximum output of ESU for 30 sec; confirm switch operation (59.103.2) Fingerswitched handpiece liquid ingress None Pour 1L saline over handpiece; confirm fingerswitch operation (44.6) Cable strain relief Conduct steady pull and impact test on all strain reliefs (4.2.5.5) None

r2-5/13/2005

 

INSULATING ELECTOSURGICAL INSTRUMENTS

Dear Editor:

"Comparing Insulating Materials for Electrosurgical Instruments" (MD&DI, February 1996) by Peter Kleinhenz and Christine Vogdes is very informative, but suffers due to the authors' use of the 1986 version of the ANSI/AAMI standard, HF18. Our company has tested the dielectric withstand of electrosurgical active electrodes using both the 1986 and the 1993 editions of the standard. I would like to present a perspective on the two editions and the reasons for the major differences between them.

In 1986, as the Association for the Advancement of Medical Instrumentation (AAMI) was adopting the first edition of HF18, ECRI published an evaluation of hand-switched electrosurgical pencils (Health Devices, 15(6):151-177). Working from a draft of HF18, ECRI engineers applied a 4-kV, peak-to-peak sinusoid at 1 MHz to different models of pencils on the market. Surprisingly, most of them failed despite the fact that these same models were being exposed to much higher peak voltages in daily clinical use, apparently without a large incidence of dielectric breakdown. The failure of these pencils led ECRI to conclude that the test was too severe and not reflective of clinical conditions.

Instead, ECRI developed the method of wrapping the electrode in saline-moistened cloth and applying voltages from a high-power electrosurgical unit (ESU). This method was adopted in HF18-1993, with two changes: HF18 allows the manufacturer to specify a voltage rating for the electrode (rather than requiring all electrodes to meet a specified breakdown voltage), and requires testing at 150% of that rating.

The HF18-1993 high-frequency dielectric breakdown test differs from the 1986 test in two major respects. First, it requires that the electrode be wrapped in saline moistened cloth and placed on a metal plate, rather than placed on the plate unwrapped. This change ensures resting of the entire insulation (in the previous version, an insulation flaw that faced upward might not result in a failure). The second change employs an actual ESU as the voltage generator. This change was problematic for the AAMI committee because different ESU models have different waveforms, and the results may vary accordingly. Nevertheless, it is a much more realistic test method.

One reason that devices can withstand much higher peak voltages from an ESU rather than from a 4-kV signal as specified in the 1986 standard is that the ESU coagulation voltage (the highest output mode) is not a continuous sinusoid. Instead, it is a series of bursts of a damped sinusoidal voltage. Although the first few cycles of voltage may be 10 kV, peak-to-peak, the voltage quickly drops.

This damped waveform makes a big difference in dielectric breakdown because the insulation is not continuously subjected to high voltage. Dielectrics are not perfect; they have certain losses that can be characterized as a resistance parallel with the capacitor formed by the dielectric separating the saline-soaked wrap and the electrode conductors. These dielectric losses tend to increase at higher frequencies and may not be well characterized at electrosurgical frequencies by their manufacturers (e.g., plastics companies). Dielectric losses cause heating; heating causes insulation to melt, resulting in what appears to be dielectric breakdown. Therefore, subjecting a dielectric to a continuous 4 kV at 1 MHz can cause the insulation to melt and fail, something that would not happen in clinical use. The result is much more severe than applying a l0-kV (or higher) signal from an ESU.

Although we test active electrodes made with many different insulating materials, we do not know the material or dimensions used; such information is proprietary to our client and does not affect our application of the HF18 dielectric breakdown test. Thus, we cannot provide any information similar to the tables in the article. However, we can say that using the waveform from HF18-1986 will not provide results that correlate with the current edition of the standard or with the real use of electrosurgical electrodes.

Robert Mosenkis, CCE
President
CITECH
Plymouth Meeting, PA

The authors reply:

Mr. Mosenkis makes a number of valid points about the differences between the two HF18 versions and the performance of electrosurgical instruments using an actual ESU. Our intent was to show that the 1986 standard, still employed by some manufacturers, is a severe test. We also demonstrated that the actual performance of materials is as expected based on the fundamental electrical characteristics of the insulator. The results of our study were intended to show relative performance, using the more-severe 1986 method for differentiation. The relative performance of materials will remain the same under less severe testing conditions. Ultimately, it is up to instrument design engineers to test and specify the proper materials and associated insulation thicknesses for the intended use.

from Medical Device & Diagnostic Industry, May 1996

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