Surgical Gowns are one part of an overall infection-control strategy and are commonly used to help prevent the gown wearer from transferring microorganisms that could harm vulnerable patients, such as those with weakened immune systems.

The AAMI (Association for the Advancement of Medical Instrumentation) is the standard that establishes the classification system (Levels 1-4) for protective apparel used in health care facilities based on liquid barrier performance using standardised test methods (FDA.gov, 2021).

  • Level 1: Minimal risk – to be used, for example, during basic care, standard isolation, cover gown for visitors, or in a standard medical unit
  • Level 2: Low risk – to be used, for example, during the blood draw, suturing, in the Intensive Care Unit (ICU), or a pathology lab
  • Level 3: Moderate risk – to be used, for example, during the arterial blood draw, inserting an intravenous (IV)line, in the Emergency Room, or for trauma cases
  • Level 4: High risk – to be used, for example, during long, fluid intense procedures, surgery, when pathogen resistance is needed, or infectious diseases are suspected (non-airborne)

Within this standard, AAMI has identified AATCC (American Association of Textile Chemists and Colourists) 42 and AATCC 127 as the key test requirements to test the efficacy of surgical gowns.

AATCC Test Method 42

This test is called the Water resistance: Impact Penetration Test, and indicates how the fabric will resist strikethrough when fluids splash or spray onto the fabric.

A 500±10mL water can sprays against the taut surface of a test specimen backed by a weighted blotter. The blotter is then reweighted to determine water penetration and the specimen is classified accordingly (SGS, 2021).​ This test does not have a fail / pass benchmark as it is an observation test only, with results recorded after each observation.​ It is the AAMI PB70 standard that determines the pass/fail of the fabric based on the Acceptance Quality Limit (AQL) requirement.

https://www.youtube.com/watch?v=ULqH3T2xL_E

 

AATCC Test Method 127

This test is called the Water resistance: Hydrostatic Pressure Test, and shows how the fabric will resist strikethrough when water pressure is applied to the surface of the fabric. Hydrostatic pressure tests the fabric for fluid resistance by measuring the force required for water to penetrate it (including seams) (SGS, 2021).

One surface of the test specimen is subjected to a hydrostatic pressure, increasing at a constant rate until three points of leakage appear on its other side (SGS, 2021). ​ This test also does not have a fail / pass benchmark as it is an observation test only, with results recorded after each observation.​ The AAMI PB70 standard will determine whether the fabric passes/fails based on the AQL requirement.​

https://www.youtube.com/watch?v=09elg5Z1kLE

 

Testing Methods for AAMI Level 4 Gowns

AAMI uses a range of factors to establish barrier effectiveness, including a material’s resistance to water, and blood penetration and efficacy in critical zones (including a gown’s front chest, sleeves, and sleeve seams). AAMI standards require a surgical gown to pass ASTM F1670 and ASTM F1671 in the critical zones to be labelled an AAMI level 4 surgical gown.

ASTM F1670

This test is called the “Resistance of Materials Used in Protective Clothing to Penetration by Synthetic Blood”

and is used to evaluate the resistance of materials used in protective clothing to penetration by synthetic blood under conditions of continuous liquid contact. Protective clothing pass/fail determinations are based on visual detection of synthetic blood penetration.

 

ASTM F1671

This test is called the “Resistance of Materials used in Protective Clothing to Penetration by Blood-Borne Pathogens” and is used to measure the resistance of materials used in protective clothing to penetration by blood-borne pathogens using a surrogate microbe under conditions of continuous liquid contact. Protective clothing material pass/fail determinations are based on the detection of viral penetration.

What areas are included in the critical zone?

There are typically 4 different areas that must pass within the critical zones, including two in the front chest and two on the sleeves. If a product passes ASTM F1670 and ASTM F1671 in all applicable areas, then it qualifies as an AAMI level 4 surgical gown.

 

Table 1: AAMI PB 70 Classification of Barrier Performance of Surgical Gowns, other Protective Apparel, Surgical Drapes and Drape Accessories

Table 1: AAMI PB 70 Classification of Barrier Performance of Surgical Gowns, other Protective Apparel, Surgical Drapes and Drape Accessories

LevelTestLiquid ChallengeResultExpected Barrier Effectiveness
1AATCC 42 Impact PenetrationWater!ERROR! undefined variable 'g'Minimal water resistance (some resistance to water spray)
2AATCC 42 Impact PenetrationWater1.0 gLow water resistance (resistance to water spray and some resistance to water penetration under constant contact with increasing pressure)
AATCC 127 Hydrostatic PressureWater!ERROR! undefined variable 'cm'
3AATCC 42 Impact PenetrationWater!ERROR! undefined variable 'g'Moderate water resistance (resistance to water spray and some resistance to water penetration under constant contact with increasing pressure)
AATCC 127 Hydrostatic PressureWater!ERROR! undefined variable 'cm'
4ASTM F1670 Synthetic Blood Penetration TestSurrogate BloodNo penetration at 2 psi (13.8kPa)Blood and viral penetration resistance (2psi)
ASTM F1671 Viral Penetration TestBacteriophage Phi-X174No penetration at 2 psi (13.8kPa)

Reference List:

AATCC 127 Hydrostatic Pressure Test » SGS-IPS Testing. (2021). Retrieved 3 May 2021, from

AATCC 42 Water Resistance » SGS-IPS Testing. (2021). Retrieved 3 May 2021, from https://ipstesting.com/find-a-test/aatcc-test-method/aatcc-42-water-resistance/#:~:text=AATCC%2042%20Water%20Resistance%20is,of%20fabrics%20to%20rain%20penetration

ANSI/AAMI PB70:2012 (ANSI/AAMI PB 70:2012) – Liquid barrier performance and classification of protective apparel and drapes in health care facilities. (2021). Retrieved 3 May 2021, from https://webstore.ansi.org/standards/aami/ansiaamipb702012pb70?gclid=CjwKCAjwm7mEBhBsEiwA_of-TC8tsVlCkBrcWVdbHDc9Evx1hMmet8Xy_8kxOlk2TpNPkWaKCN21nhoCP2YQAvD_BwE

ASTM International (2021). ASTM F1671 / F1671M – 13 Standard Test Method for Resistance of Materials Used in Protective Clothing to Penetration by Blood-Borne Pathogens Using Phi-X174 Bacteriophage Penetration as a Test System. Retrieved 20 May 2021, from https://www.astm.org/Standards/F1671.htm

ASTM International (2021). ASTM F1670 / F1670M – 17a Standard Test Method for Resistance of Materials Used in Protective Clothing to Penetration by Synthetic Blood. Retrieved 20 May 2021, from https://www.astm.org/Standards/F1670.htm

FDA (2021) Medical Gowns. Retrieved 20 May 2021, from https://www.fda.gov/medical-devices/personal-protective-equipment-infection-control/medical-gowns

NHMRC – Australian Guideline for The Prevention and Control of Infection in Heathcare. Table B2 1: application of standard and transmission-based precautions.