How it all began
From the time that an operating room gown first became a part of the surgeon’s armamentarium, its primary purpose was to protect the patient from the members of the surgical team. In that capacity, the garment was made of a relatively loosely woven, readily permeable, all carded cotton Type 140 (thread count) material generically known as "muslin". The material fulfilled the essential requirement of the application in that it 1) was considered effective in terms of providing what was believed to be a satisfactory aseptic barrier, 2) was readily available and 3) was economical to use.

Then in 1952, the surgical community was alerted to the fact that although the "muslin" material may have been considered an effective bacteriological barrier when it was dry, it lost its barrier capabilities once it became wet - even when multiple layers were used.1

The need for a liquid barrier
This disclosure triggered the textile industry to develop more satisfactory materials for this unique application. In responding to the challenge, both segments of the industry - the non-woven disposable and woven reusable, introduced a new generation of fabrics. Whereas both made claims about their performance capabilities, there was no similarity to the tests upon which those claims were predicated.

In the meantime, the American College of Surgeons’ (ACS) Committee on the Operating Room Environment (CORE) charged the entire textile industry with the responsibility to develop a test method that had the capability to simulate the stresses that they astutely described as "usual conditions of use".2

Not being able to either correlate the results of the tests being used by industry or consider them as simulating "usual conditions of use", a distinguished surgical researcher not only developed a test method but introduced the term for the phenomena of liquid penetration that has been commonly used ever since: "strike through". The published results of his study indicated that some of the non-woven materials that had passed their Mason jar test proved to be totally ineffective and that some were moderately effective. However, included with the number that performed quite well was one woven reusable.3 Be that as it may, it was these findings that supported the researcher’s appeal to the Surgical Device Classification Panel of the Food and Drug Administration’s (FDA) Bureau of Medical Devices for classification of aseptic barrier materials for surgical gowns and drapes as Class II medical devices: high priority, that is those in need of performance standards.4

One response to the FDA’s classification process has been the development of voluntary standards, user guidelines, and recommended practices by cooperative working groups composed of representatives from the clinical community, other healthcare professionals and industry. Thus it was that representatives from the three groups formed an ad-hoc committee to address the issue. Subsequently, the group was formally organized under the auspices of the Association for the Advancement of Medical Instrumentation (AAMI) and identified as the Committee on Aseptic Barriers.5 Unfortunately, because of a lack of consensus among its members, the Committee was disbanded and the task abandoned in May 1983.6

The emergence of HIV
With the emergence of the era of the hazards associated with the transmission of blood-borne pathogens, the primary purpose of the surgical gown suddenly changed from third person to first person - to protect the surgeon from the patient. This also meant that whatever degree of "strike-through" may have been tolerated in the past was no longer acceptable.

It was during this period that two clinical researchers,7,8 working independently of one another, reported on the barrier effectiveness of a variety of products that were on the market. What exemplified the need for a standard test method was the fact that some of the materials that had been found to be satisfactory under the conditions of one of the tests would have failed when subjected to he challenge of the other test that had been an especially designed device for this purpose. What is particularly noteworthy is that the results of the less challenging test, reported detecting penetration of human immunodeficiency virus (HIV) through plastic-reinforced materials in which "strike-through" was not visible.

Nevertheless, the results of these studies exemplified the need for a meaningful test method that could be adopted by both the clinical community and industry for use in assessing a material’s barrier capability. It was also reasonable to assume that whatever test method would be developed would measure a material’s ability to resist liquid penetration at various levels.9 Rating the materials in this manner would be in accord with the results of a comprehensive in-vivo study specifically designed for that purpose.10 More importantly, it would facilitate the selection process mandated by the Occupational Safety and Health Administration’s (OSHA) final rule that the garments be appropriate for the "task and degree of exposure anticipated".11

The development of new tests
With the pressing need for a test method, an industry-driven committee of the American Society for Testing Materials (ASTM) released a modification of one of its existing mechanical devices that had originally been developed for determining the effectiveness of protective clothing worn by chemical workers. The group incorporated the methodology in two tests—one for liquid penetration and one for viral penetration. Both methods were first adopted as ‘Emergency Standards’ and subsequently adopted as standards in 1995.12,13

However, rather than the results of either of the tests being reported on a comparative basis, they were identified as pass/fail with a ‘pass’ predicated on the material’s ability to resist penetration at a level of 2 pounds per square inch (psi). In responding to how that level of resistance was selected, the test’s developer and Chairman of the ASTM’s committee advised that it had a high correlation to the manual elbow-lean test (simple and manually executed) that had been used by one of its member manufacturers to demonstrate their material’s effectiveness.14

It should be noted that prior to the ASTM’s adoption of the test methods, several reports had been published in the clinical literature that indicated that the pressure exerted on surgical gowns and drapes in both in-vivo and in-vitro circumstances had been found to be far in excess of 2 psi.15,16,17 As observed by one of the researchers, "because conditions of use are known to vary greatly by type of procedure and task, all materials do not need to have the same level of resistance, yet the ASTM tests subject all to a single method".18

Notwithstanding the ASTM’s noble mission to help reduce the risk of occupational exposure to bloodborne pathogens, the fact of the matter is that our healthcare delivery system is financially strained at an unprecedented level and is being pressured to not only contain costs but reduce them. Under these circumstances, to indiscriminately provide all healthcare workers with what the industry group believes to be the maximum level of protection would be neither prudent nor fiscally responsible.

The new ‘standard’
The American National Standards Institute (ANSI)/AAMI has recently published a document which is said to provide a solution to this half-century need.19 Entitled "Liquid barrier performance and classification of protective apparel and drapes intended for use in health care facilities",20 it has been adopted by the Food and Drug Administration (FDA) and is considered to satisfy the agency’s need for Performance Requirements for those Class II Medical Devices.

The Standard establishes the use of four different test methods and two different liquids to classify the differences in the levels of a materials’ "barrier performance".

To accommodate the need for determining a material’s "barrier performance" for the "duration and level of anticipated exposure", AAMI’s Protective Barrier Committee selected two other tests, the American Association of Textile Chemists and Colorists (AATCC) #42-2000 water impact penetration test and their #127-1998 hydrostatic test for that purpose. (It should be noted that this same AAMI group had several years earlier maintained that neither of the two tests were suitable for use for this purpose.)21

Thus the new ‘standard’ establishes four (4) levels of barrier effectiveness.

For Level 1, the lowest of the four, the AATCC’s 42-2000 water impact penetration test is used. The material’s capability to resist penetration is determined by being challenged by a fixed amount of water sprayed on it while being held at a 45o angle. An absorbent blotter affixed under the fabric is then weighed to ascertain is weight gain. According to the ‘standard’, the blotter should not have gained more than 4.5 grams to be considered a Level 1 fabric.

For Level 2 fabrics, there are two tests that can be used. One is the same test used for Level 1 except that the weight gain of the blotter can be no more than 1 gram.

An alternate test is the AATCC’s 127-1998 hydrostatic head test. A sample of the fabric is clamped horizontally on the bottom of a metered glass cylinder. The hydrostatic pressure is steadily increased as the height of the water in the cylinder is raised. To be acceptable for a Level 2 barrier, it must resist penetration of water when it reaches a height of 20 centimeters.

For Level 3 fabrics, both of the AATCC tests may be used. However, for the impact penetration test, the weight gain of the blotter is again 1.0 gram. For the hydrostatic head test, the water level in the cylinder must be at least 50 centimeters.

For Level 4 fabrics, the ASTM’s mechanical device is used for both. For surgical gowns, the material must pass their F-1671 test for viral penetration; surgical drapes need only pass the F-1670 for resistance to penetration to synthetic blood. The test sample is mounted in a vertical position onto a cell that separates the challenge and a viewing port. The time and pressures protocols specify atmospheric pressure for five minutes, 2.0 pounds of pressure per square inch (psi) for one minute and atmospheric pressure for 54 minutes. The test is terminated if visible penetration occurs before or after 60 minutes.

Interpreting the results
For Levels 1, 2 and 3, the results of the water impact penetration test must stand on their own merit since there is no known method of correlating the weight of the blotter to the level of pressure exerted on it.

For the hydrostatic pressure test used for Levels 2 and 3, the correlation between the height (in centimeters) of water and the level of pressure is known. For Level 2, the equivalent of pounds per square inch (psi) at 20 centimeters is 0.20; when the level of water is raised to 50 centimeters the psi is 0.73.

The question that logically arises is how the barrier effectiveness of a material that is awarded a ‘pass’ (at 2 psi) when tested with the ASTM’s device can reasonably be compared to the psi of the Levels 2 and 3? Unfortunately, they cannot be. The culprit? Surface tension.

The role of surface tension
As defined in the document, surface tension is the "intermolecular forces acting on the molecules at the free surface of a liquid. Surface tension affects the degree to which a liquid can wet a material (i.e., the lower surface tension, the more easily the liquid wets a material’s surface)".22

Surface tension is measured by a unit of dynes per centimeter. Whereas water used in both of the AATCC tests measures around 72 dynes/cm, blood is around 42 dynes/cm. (It is viscosity that makes blood thicker than water.) This means that liquids, such as blood, that have a low surface tension, can penetrate fabrics more readily than those with a higher surface tension such as water.

Thus, in terms of interpreting the results of the tests for Levels 1, 2 and 3, they do NOT mean that under actual conditions of use, that they would not permit the penetration of blood.

Leakage in the ‘critical zone’
The ANSI/AAMI ‘Standard’ defines the Critical Zone as an "area of protective apparel or surgical drape where direct contact with blood, body fluids and otherwise potentially infectious material (OPIM) is most likely to occur".23

One of those areas of the surgical gown in which ‘leakage’ at the gown/glove interface was first reported in 1975 24. Some 20 years later, in a multi-center study of blood contacts in 8,502 surgical procedures, it was found that of the total of 1,043 contacts, 60% were experienced by surgeons and that 53% of those involved the fingers, hands and arms.25 A recent report on this "danger zone" included a proposed solution to this problem area that has yet to be pursued commercially.26,27

Nevertheless, it now appears in the list of Exclusions as one of the items that the ‘Standard’ does NOT cover.28 In response to an inquiry of the FDA about the Exclusion, they advised that "the Committee (AAMI’s Barrier Committee) excluded this subject because the standard is for the barrier properties of the gown and drapes, especially critical zone, and it is not possible to determine how an individual would select a gown that assured there would no be a potential problem with this interface".29

In the interim, until such time as some change(s) is made in the design and construction of this area, the protective capability of the surgeon’s gown, regardless of the material of which it is made, will continue to be compromised.

Another omission
It is to be noted that the ‘Standard’ classifies the patient drape as an item of protective clothing. In so doing, it calls for the inclusion of a ‘barrier’ quality material in the critical zone. As recently stated, the influence of a ‘barrier’ material on the incidence of surgical-site infections not been assessed by scientific studies.30 This confirms the statement made on their use more than twenty years ago. In a commentary on the factors that must be considered that can influence postoperative wound infection, the author stated that there is not convincing evidence for all of them - one of which was barrier materials. Thus he concluded that their use was predicated on "anecdotal experience and commercial interests rather than scientific studies".31

Conclusion
What the ANSI/AAMI ‘Standard’ does is assess a barrier material’s effectiveness using four different tests for liquid resistance for four different levels, three different challenges and then expresses the results in three unrelated ways.

The ‘Standard’ was developed with the intent of satisfying "Food and Drug Administration’s requirements for pre-market notification (Section 510 (k)) and medical device reporting" and to be "used mainly by device manufacturers in qualifying, classifying and labeling the barrier performance of their products".