ISO Standards – a tool to overcome prescribing your “favourite” cushion

As a therapist, it can feel overwhelming to work out what the best cushion for pressure care may be. It is also important that we try to not to have a favourite cushion too – as when we do, it means that we are forgoing part of the clinical reasoning process. Just because one cushion may have worked for the previous three clients you have worked with, does not mean that it will meet the needs of your next.

With so many cushions on the market, and new ones being released regularly, it can be difficult to work out the key difference of each cushion and remove the marketing or sales pitch which can often come with them. This being said – how I hear you ask can we tell the difference between cushions and compare apples with apples? What makes a cushion a “good” cushion? ISO standards and performance metrics will soon become a new tool in your clinical toolbox to help you determine a potential short list of cushions you may want to trial with your client. They help to remove any bias as these results provide you with lab-based data.

Performance metrics are quantitative measures used to evaluate the effectiveness and efficiency of products. In the realm of assistive technology, such as wheelchair cushions, these metrics are essential for ensuring that products meet the necessary standards for safety, quality, and performance. As a Clinician, you can leverage these metrics to make informed decisions that align with the individual needs and goals of the user.

Performance metrics for wheelchair cushions, as outlined by the International Organization for Standardization (ISO), include various standardized tests that assess aspects such as skin protection, durability, flammability, microclimate and stability. These metrics are derived from mechanical bench tests that simulate the interaction between the cushion and a simplified body form, known as an "indenter." By using lab-based tests, we can remove as many variables as possible and compare cushions side by side.

The Clinical Practice Guideline (CPG) for the prevention and treatment of pressure injuries was published in 2019. This publication offers a clinical perspective that can be applied to the development and application of ISO tests.

The CPG recommend selecting a seated posture and system that:

• Is acceptable for the individual
• Minimises the pressures and shear exerted on the skin and soft tissues at high-risk areas
• Provides adequate support
• Maintains stability
• Maintains the individual’s full range of activities

Two ISO tests which relate to the CPGs recommendations and best practice around skin protection include.

• Immersion and Envelopment: These tests measure how well a cushion can distribute pressure by immersing the body and enveloping its contours. This is crucial for preventing pressure injuries.
• Contact Area: Assessed through pressure mapping, this metric evaluates the distribution of pressure across the cushion, indicating its effectiveness in pressure redistribution.

In 2017, the Wheelchair and Cushion Standards group at University of Pittsburgh was awarded a RERC grant to evaluate and further develop RESNA (Rehab Engineering and Assistive Technology Society of North America) and ISO performance standards. They applied a subset of test methods from the ISO 16840 standard suite to a diverse cohort of approximately 50 cushions from multiple manufacturers. Permobil was asked to contribute specific cushions as part of this national scientific testing effort. The results of this testing are presented in the Interactive Data Exploration Tool: wheelchairstandards.com (I would really encourage you to have a look at all their data and tests on their website. It is a great resource). Using Contact Area testing as an example, this test assess the distribution of pressure on a loaded cushion, recorded 60 seconds after the cushion is loaded. Contact area represents the total load bearing area. High Contact Area results indicate a large base of support.

Permobil has identified their cushions which the University of Pittsburgh tested as discussed below. The results are available in the Permobil Scientific Report: Guidance to individualized cushion selection based on performance metrics. Cushion ‘AT’ is a ROHO Single Compartment High Profile Inflated to 0.5” clearance under test load and demonstrated the highest contact area score across the cushions tested. Black (K) is reference foam. 

What does this mean clinically? Well … Contact Area and Immersion are both tests specific to skin protection. Therefore, these may be two tests of particular relevance if you want to determine which products may best meet the needs for a user with high or very high risk of a pressure injury.

You may then consider which options performed high in both tests and then consider other key needs for that particular user, The most relevant cushions would be brought out to the user to trial to see if any are more suited to the user’s unique preferences.

So, if you want to consider using ISO tests as part of your clinical reasoning process and reduce the risk of having a “favorite” cushion, I encourage you to consider the following:

1. Commit to seeking out and reviewing product standards testing results​. Permobil has released some results which you can access here.
2. Identify individual needs through thorough clinical assessment​
3. Match proven product characteristics to client's unique presentation​
4. Confirm products selected have provided expected results through trial, follow-up and training
5. Ask about the materials in use and expected durability
   

Honestly when I was first introduced to this topic it did take me a little while to get my head around it. I would encourage you to use the resources available and if in doubt, please do not hesitate to reach out. We all love a deep dive on all things ISO in our team. A good place to start with some case studies applications can be found here – Understanding Cushion Performance Metrics.

References:

1. WHO. ICF model. https://www.who.int/standards/classifications/international-classificationof-functioning-disability-and-health.
2. International Organization for Standardization (ISO). https://www.iso.org/about-us.html.
3. International Organization for Standardization (ISO). ISO 16840, Wheelchair Seating – Parts 1-14. International Organization for Standardization.
4. European Pressure Ulcer Advisory Panel, National Pressure Injury Advisory Panel, Pan Pacific Pressure Injury Alliance. Prevention and Treatment of Pressure Ulcers/Injuries: Clinical Practice Guideline. The International Guideline.; 2019.
5. University of Pittsburgh. (2021, November). Pressure mapping. Wheelchairstandards.com. https://wheelchairstandards.com/pressure-mapping-sorted-by-cushion-category/
6. University of Pittsburgh. (2021, November). Pressure mapping. Wheelchairstandards.com. https://wheelchairstandards.com/pressure-mapping-sorted-by-cushion-category/

Author

Tilly Brook MOccThy (Hons) (OT)

Director Clinical Services