Vapourised Hydrogen Peroxide (VHP) sterilisation – a sustainable approach

What are the environmental benefits of VHP vs ETO?

ETO is a carcinogen and can pose an increased cancer risk to populations local to sterilisation facilities. VHP, on the other hand, oxidises readily to oxygen and water, meaning, when handled correctly, it has no direct toxic emissions. Vapourised Hydrogen Peroxide sterilisation processes also use lower temperatures and shorter cycle times, so have significantly lower carbon emissions compared with ETO (see figure below).

What concerns do regulatory agencies have surrounding the use of ETO?

One of the key concerns for regulatory agencies around the use of ETO is the increased risk of cancer in communities nearby ETO medical sterilisation facilities. This risk was highlighted in 2019 when the United States Environmental Protection Agency (EPA) reported that ETO levels near a medical sterilisation facility had been measured to be above safe levels. They further stated that these background levels of ETO corresponded to an increased cancer risk of approximately 1 in 100 local residents.

Following this, in 2023, the EPA announced new tighter standards and increased monitoring of ETO emissions, aiming to reduce these emissions by 80%. Concerns have since been raised by the medical industry that the time and effort needed to implement these changes could impact the availability of vital medical devices. Now, following a review of its own, the FDA has classified VHP as an efficacious and safe sterilisation process, with stated aims of increasing VHP adoption and reducing ETO use.

What are the environmental and process benefits of using Vapourised Hydrogen Peroxide to sterilise medical devices?

Vaporous Hydrogen Peroxide has various benefits compared with ETO:

• It is not cancer causing
• It degrades to water and oxygen, so does not require lengthy chamber degassing
• It has lower carbon emissions.

Like ETO, VHP is an effective sterilisation agent and penetrates complex surfaces and device materials. Furthermore, VHP is compatible with a broad range of plastics, metals, ceramics and coatings commonly used in devices themselves (though not with card and paper packaging – as shown in the figure in the section above).

Industrial VHP chambers are also smaller scale compared to those for ETO. While this can pose limits in terms of scalability, it does bring some advantages. The smaller VHP chambers are more easily installed on-site and or even in-line, reducing reliance on off-site sterilisation facilities and associated transportation carbon costs.

There are also substantially reduced carbon emissions associated with Vapourised Hydrogen Peroxide sterilisation compared to ETO. This is due to numerous energy savings, such as VHP sterilisation processes requiring lower temperatures than ETO. Furthermore, ETO requires the chamber to be ventilated with warm air for several hours following sterilisation to ensure no traces remain on the devices, which is not required for VHP.

VHP also avoids some additional carbon costs incurred by ETO processes, namely those associated with technologies directed at ensuring legal limits for environmental ETO are not exceeded. For example, an in-line ETO abator catalyses ETO, breaking it down to form water and carbon dioxide, but requiring additional energy to do so.

What historical concerns have there been around VHP sterilisation?

Despite the benefits listed above, Vapourised Hydrogen Peroxide sterilisation has itself gone in and out of favour in the past. Widely adopted in the 1990s to replace ETO, concerns developed around the robustness of the process.

A 2018 note published by the United Kingdom Medicines Health Regulatory Authority (MHRA) described risks associated with the process fragility of VHP sterilisation. For example, they noted evidence that fatty acids from a fingerprint may “protect” contaminating organisms from VHP. Other risks with VHP sterilisation include the ability to ensure an efficacious concentration within long lumens, and residual moisture reducing process efficacy. The MHRA’s view being that while VHP sterilisation processes may be well controlled and validated and can be safe and efficacious, the potential for human error nonetheless posed risks to its widespread adoption. They did not impose a ban on the use of VHP, however; rather asking that manufacturers did so in dialogue with the agency.

How can the concerns associated with VHP be mitigated?

The recent publication of an ISO standard in 2022 (ISO 22441:2022) describing the steps required to validate and control a VHP sterilisation process has helped ensure these are efficacious and safe. The FDA has since adopted this as a harmonised standard, indicating its acceptance of this process. A European standard, BS EN 17180, is also currently under review.

Chamber design and process optimisations

Sterilisation providers Steris describe how sterilisation chamber design and process optimisations may alleviate some of the limitations of Vapourised Hydrogen Peroxide sterilisation. Historically, VHP sterilisation demonstrated some unreliability with penetrating long lumens; however, this has now been overcome with process innovations, such as increasing the concentration of VHP injected into the chamber and inclusion of an air injection to push VHP into the lumens. Similar efforts have gone into developing methods to detect and eliminate residual moisture. Another limitation is that industrial VHP chambers are smaller scale compared to those for ETO. However, this can be mitigated through the use of multiple machines to enable bulk processing.

Packaging and labelling materials

Liquids, powders and cellulose-based materials such as paper and cardboard degrade are degraded by Vapour Hydrogen Peroxide. It is important to avoid paper and cardboard elements, such as those often used for packaging or labelling of manufactured products or sub-assemblies, since their presence can adversely impact the sterilisation process efficacy due to depleting VHP concentrations. Alternative VHP compatible packaging can, for example, include polyethylene or polypropylene.

For sterilisation of surgical tools, which are typically wrapped in cloth and placed in metal or plastic trays, it is important to avoid cotton and nylon. Alternative fabrics should instead be used, which again could include those made from polyethylene or polypropylene fibres. It is important that plastic packaging is incinerated for energy (e.g. as toxic or medical waste if necessary). While incineration releases carbon dioxide, it is important to avoid disposing of plastic through landfill where it may release harmful plastic microparticles into the ground water and oceans.

What does the adoption of VHP sterilisation mean for process sustainability?

Overall, VHP has numerous environmental benefits compared with ETO, with a reduced risk of cancer to local populations and a significantly reduced carbon footprint. Adopting VHP for future sterilisation processes will reduce the environmental impact of medical device sterilisation. However, doing so will require appropriate consideration of packaging and process design to ensure robust sterilisation.