Sterilizing Medical Equipment

Medical professionals are legally obligated to provide patients with a standard of care. One of the key requirements for meeting this standard of care is the proper sterilization of medical equipment. On any given day, approximately one in 31 patients contracts a healthcare-associated infection (HAI), many of which are preventable through rigorous instrument processing.

Healthcare organizations are audited by various groups; chief among them are The Joint Commission, DNV, and the Center for Medicare & Medicaid Services (CMS). Healthcare institutions are required to comply with policies outlined by their organizations and the standards to which they audit, as well as the recommended practices of the Association for the Advancement of Medical Instrumentation (AAMI), the Association of periOperative Registered Nurses (AORN) and the Healthcare Sterile Processing Association (HSPA).

Key Takeaways:

• Sterile processing is a regulated function, with healthcare facilities audited against standards set by The Joint Commission, DNV, CMS, AAMI, AORN, and HSPA.
• Always refer to the manufacturer’s Instructions for Use (IFUs) before sterilizing any instrument to avoid damaging it and to ensure proper sterilization.
• Steam sterilization is the default method for most surgical instruments, though ethylene oxide and vapor hydrogen peroxide are suitable for certain applications.
• The key difference between a gravity cycle and a vacuum cycle is how they remove air from the load. This difference determines both contact time and which instruments they can safely process.

The Risks of Improper Sterilization of Medical Instruments

There are many risks associated with the improper sterilization of medical instruments; that said, the three most significant are as follows:

1. Using the incorrect sterilization process for a product or piece of equipment can damage that item. Certain sterilization techniques utilize temperatures that can melt some materials, such as plastics. This is unacceptable for any item but, for a major piece of equipment such as the robotic arm for a Da Vinci Surgical System, it presents a major problem, both for procedure readiness and for replacement cost. Another issue with choosing the incorrect sterilization process is that if a medical instrument is processed using a method that has not been validated for processing, that instrument might not come out sterile.Any medical facility found using the incorrect sterilization processes is subject to reimbursement penalties or other enforcement actions by CMS, or potential revocation of accreditation by The Joint Commission or other accrediting agencies. That’s why, when sterilizing any instrument, it’s important that you refer to Instructions for Use (IFUs), which are the manufacturer’s guidelines for processing that instrument. If, for any reason, the IFUs are unclear, it’s recommended that you contact the manufacturer directly for instruction or refer to the IFU for a similar piece of equipment.
2. Improper sterilization has the potential to spread disease or result in an HAI. Regardless whether you use steam sterilization or a low-temperature sterilization option, to ensure patient safety, it is essential to follow IFUs, clean the device correctly, verify cleaning, and to select the correct sterilization process. Anything less could jeopardize the health of your patients and put your medical facility at risk.
3. Some devices require longer exposures than others because of the way they’re built and, in some cases, because they were improperly validated. To that end, referring back to IFUs and creating common classes for instruments so that you can process more than one item at a time is critical. ANSI/AAMI ST90:2017/(R)2024 establishes a formal process for creating product families that can be sterilized under common conditions. Some conditions are more critical than others — for example, if you attempt to use a vacuum cycle to sterilize a device that is only supposed to be sterilized using a gravity cycle, that device might explode. Again, the importance of following IFUs cannot be overstated.

How Do Healthcare Facilities Determine Which Instruments to Sterilize?

Not every piece of medical equipment requires the same level of processing. The standard framework used across healthcare to make this determination is the Spaulding classification, which was originally developed by the microbiologist Earle Spaulding in the 1950s and is still the basis for guidance from the Centers of Disease Control and Prevention (CDC) and AAMI today.

The Spaulding classification divides surgical instruments and other medical equipment into three categories based on their risk of transmitting infection:

• Critical instruments contact sterile tissue, the vascular system, or sterile body cavities. Because any microbial contamination presents a direct infection risk, these instruments must be fully sterilized before and after each use. Surgical instruments, implants, cardiac catheters, and biopsy forceps all fall into this category.
• Semi-critical instruments contact mucous membranes or non-intact skin, but do not enter sterile tissue. These instruments require high-level disinfection at minimum, a process that eliminates all microorganisms except a small number of non-harmful bacterial spores.
• Non-critical instruments contact only intact skin and therefore carry the lowest infection risk. These items require low-level disinfection between uses, not sterilization; common examples include blood pressure cuffs, pulse oximeters, and stethoscopes.

Know the Difference Between Point-of-Use Cleaning, Decontamination & Sterilization >>

How Do Hospitals Sterilize Surgical Tools?

Strange as it might sound, sterilizing surgical tools and other medical instruments isn’t as simple as just sterilizing them. Instead, it requires a three-step process that ends with sterilization.

1. Point-of-use cleaning: Instruments should be immediately cleaned at their point of use, typically by wiping off any visible soil and applying an enzymatic gel or foam spray to prevent blood and tissue from drying onto instrument surfaces. This step is time sensitive: Biofilm can form within minutes on instruments left to dry, and dried bioburden can be difficult to remove through mechanical cleaning.
2. Decontamination: Instruments are transported to the decontamination area of the facility’s sterile processing department (SPD), where they undergo mechanical cleaning using either a washer-disinfector or ultrasonic cleaner, followed by inspection. Decontamination must precede sterilization as it removes any remaining organic soil or bioburden that might prevent sterilants from reaching all surfaces.
3. Sterilization: Once cleaned, inspected, and packaged, instruments can be sterilized according to their IFUs.

Sterilization Techniques for Medical Devices

There are a few different techniques that medical professionals can use to sterilize instruments, devices, and other equipment:

• Autoclaving, also known as steam sterilization, uses saturated steam under pressure and high temperatures — from 250°F to 275°F (121°C to 135°C) — to kill microorganisms on the surface of items. There are two main types of of steam sterilization, each based on how air is pulled out of the autoclave chamber and how steam is vented in:
  • Gravity displacement is the oldest and simplest form of steam sterilization. It admits steam in from the top of the autoclave chamber and pushes air out of the bottom. Gravity displacement is ill-suited for complex instruments, but it is ideal for simple devices or those that will be damaged by a vacuum. Gravity displacement takes longer than the alternatives and offers less throughput.
  • Dynamic air removal refers to the process by which an autoclave alternates steam and vacuum pulses or steam pulses and venting to ambient pressure (known as steam flush pressure pulses, or SFPPs) to remove air from the chamber and instruments and allow steam to penetrate the load.Vacuum cycles are preferable for most applications because they can pull air out and ensure contact of the steam with the entire instrument in a sequence of three to four pulses. Vacuum cycles also actively remove air from instruments, making sterilization faster — there’s nothing between the steam and the instruments themselves.
• Ethylene oxide (EtO) is a man-made chemical which, when exposed to contaminated instruments, penetrates the microbial cell walls of any microorganisms and changes their structure, effectively killing them. EtO is compatible with a wide range of materials, making it suitable for instruments that cannot be processed using steam or high temperatures. However, despite its prevalence in medical device sterilization, there is mounting evidence that EtO increases the risk of certain cancers.
• Vapor hydrogen peroxide (VHP) is another form of low-temperature sterilization and a common alternative to EtO. With this form of sterilization, H2O2 vapor fills the sterilizer chamber, inactivating any microorganisms on the surface of an item. There are a number of different VHP manufacturers, including those that use gas plasma or ozone to help destroy residual hydrogen peroxide once sterilization is complete.

The Benefits of Steam Sterilization

Steam sterilization is the optimal sterilization method for the vast majority of medical instruments, equipment, and devices due to its:

• Speed: A standard steam sterilization cycle runs between 30 and 60 minutes from door close to cycle completion. By comparison, a VHP typically takes 45 to 75 minutes, while EtO can take up to 12 hours or more, including aeration. For high-volume SPDs supporting active operating rooms, the throughput advantage of steam is considerable and can spell the difference between sterilization keeping pace with surgical schedules and it becoming a bottleneck.
• Cost: Autoclaves are often less expensive to operate per cycle than their low-temperature alternatives. EtO sterilizers require costly sterilant cartridges, specialized ventilation infrastructure to manage toxic emissions, and compliance with OSHA exposure limits and EPA emissions requirements — regulatory burdens that have led many facilities to reduce or eliminate EtO use entirely. VHP sterilizers carry a higher per-cycle cost than steam and require instrument loads to be completely dry before processing, since residual moisture can cause cycle cancellations and, in some systems, requires instruments to be reprocessed.
• Versatility: The majority of medical equipment used in hospitals, including stainless steel instruments, wrapped packs, rigid containers, and even porous materials such as drapes and gowns, are heat- and moisture-stable and can be processed with steam. EtO’s primary advantage is its ability to penetrate dense packaging and long, narrow lumens, while VHP is well-suited to the heat-sensitive electronics and optics found in some powered instruments and scopes. While EtO and VHP both have their uses, they serve defined niches rather than competing with steam across the full instrument inventory.
• Safety: Steam sterilization uses only water and heat, produces no toxic byproducts, and requires no special handling of sterilants. By comparison, EtO is a known carcinogen subject to increasing regulatory pressure, and several states have already enacted strict emission limits on its use. VHP decomposes into water and oxygen and has a favorable environmental profile, but OSHA’s permissible exposure limit for hydrogen peroxide is 1 ppm over an eight-hour time-weighted average, and VHP systems must be validated to maintain safe ambient levels.

The case for autoclaving isn’t that EtO and VHP are inadequate. In fact, both are validated, effective sterilization methods in the appropriate circumstances. Instead, it’s that for the instruments it can process, nothing can compare to the combination of speed, affordability, and operational simplicity that steam offers for high-volume sterile processing.

Steam Sterilization Process

All medical instrument sterilization processes share three common features: air removal, a steam injection and sterilization phase and steam removal and drying. The difference between gravity and vacuum steam sterilization cycles comes down to how air is removed from the load and how steam penetrates into the load.

Gravity Cycle

1. Once the sterilizer door has been closed and sealed and the cycle started, the chamber drain valve opens.
2. Steam is admitted into the sterilizer chamber, which pushes the air downward because hot steam is less dense than air. Gravity cycle gets its name from this downward air flow.
3. The steam pushes the air out of the load.
4. After a predetermined period of time, or when the chamber drain temperature reaches 100°C / 212°F, the drain valve closes, allowing the chamber to pressurize with steam.
5. When the chamber temperature reaches the programmed temperature, the steam valve cycles in order to maintain that temperature without overheating.
6. At the end of the cycle, the steam valve closes, and the drain valve opens. Normally, the steam either mixes with water or runs through a cooling heat exchanger on its way to the sanitary drain in order to cool it and avoid damaging the drain.
7. On some gravity steam sterilizers, a vacuum device — either a pump or ejector — turns on to help dry the load after the steam pressure has fallen to a temperature that the vacuum device can tolerate. Once the drying phase is complete, HEPA-filtered air enters the chamber to return it to atmospheric pressure. The cycle is now complete.

Vacuum Cycle

1. The door is closed and sealed, and the cycle starts.
2. The chamber drain valve opens.
3. Steam is admitted into the sterilizer chamber, which pushes the air downward.
4. The steam pushes the air out of the load and preheats it.
5. After a predetermined period of time, the steam valve closes.
6. A vacuum device turns on and removes air from the chamber and the load.
7. Once the sterilizer has reached the programmed vacuum level, the vacuum valve closes, and the vacuum device shuts off.
8. Steam enters the chamber to reach the programmed pressure.
9. Once the chamber has reached the programmed pressure, the steam valve closes.
10. Steps five through seven are repeated twice or more, ending with an evacuation.
11. After the last evacuation, the drain valve closes, and steam enters the chamber to pressurize it.
12. Once the chamber reaches the programmed temperature, the steam valve cycles to maintain that temperature without overheating.
13. At the end of the cycle, the steam valve closes, and the drain valve opens. Normally, the steam either mixes with water or runs through a cooling heat exchanger on its way to the sanitary drain in order to cool it and avoid damaging the drain.
14. Once the steam pressure has fallen to a programmed level, the vacuum device turns on to help dry the load. Once the drying phase is complete, HEPA-filtered air enters the chamber to return it to atmospheric pressure. The cycle is complete.

Steam Sterilization Cycle Guide

The key difference between the two approaches listed below — gravity and dynamic air removal, or vacuum — is that with air being removed, there is no blockage of steam penetration into the load. For this reason, dynamic air removal cycle exposure times are much shorter than gravity cycle exposure times for the same temperature.

Gravity Cycles
Item Type	Exposure Time at 121°C / 250°F	Exposure Time at 132°C / 270°F	Exposure Time at 135°C / 275°F
Wrapped Instruments	30 minutes	15 minutes	10 minutes
Textile Packs	30 minutes	25 minutes	10 minutes
Unwrapped Nonporous Items (Instruments)	Cycle not defined	3 minutes	3 minutes
Unwrapped Nonporous and Porous Items in Mixed Load	Cycle not defined	10 minutes	10 minutes

 

Dynamic Air Removal Cycles
Item Type	Exposure Time at 132°C / 270°F	Exposure Time at 135°C / 275°F
Wrapped Instruments	4 minutes	3 minutes
Textile Packs	4 minutes	3 minutes
Wrapped Utensils	4 minutes	3 minutes
Unwrapped Nonporous Items (Instruments)	4 minutes	3 minutes
Unwrapped Nonporous and Porous Items in Mixed Load	4 minutes	3 minutes

Where to Find Steam Sterilization Equipment

Hospitals and other facilities looking to acquire an autoclave for medical use are advised to contact Consolidated Sterilizer Systems. We offer medical series steam sterilizers designed to sterilize at temperatures between 250°F and 275°F, as well as stainless steel vessel construction in a variety of sizes and program control options.

To learn more about our medical series steam sterilizers or what Consolidated can do for you, contact us today.

Frequently Asked Questions

Q: What is the best way to sterilize medical equipment?

A: The best way to sterilize medical equipment for instruments and devices that can tolerate high heat and moisture is steam sterilization. Steam is faster, less expensive per cycle, and more broadly applicable than its low-temperature alternatives. However, for instruments that cannot tolerate heat or moisture, vapor hydrogen peroxide is often the safest and most effective sterilization method. Before sterilizing any piece of equipment, be sure to consult the manufacturer’s IFUs for specific guidance.

Q: How often should medical equipment be sterilized?

A: How often medical equipment should be sterilized depends on the type of instrument and how frequently it’s used. All reusable critical instruments — those that come into contact with sterile tissue or the vascular system — must be sterilized before each use on a new patient, without exception. Any packaged instrument with compromised, wet, or damaged packaging must be reprocessed regardless of when it was sterilized. Again, always consult the manufacturer’s IFUs to confirm how often to sterilize a particular instrument or piece of equipment.

Q: What is the Spaulding classification?

A: The Spaulding classification is the framework healthcare facilities use to determine what level of processing a reusable instrument requires before it can be safely used on another patient. It categories instruments into three tiers: critical, semi-critical, and non-critical.

Q: Why can’t all medical equipment be sterilized the same way?

A: Not all medical equipment can be sterilized the same way because instruments are made from different materials with different tolerances. Steam sterilization subjects instruments to temperatures between 250°F and 275°F (121°C and 135°C) under elevated pressure, which can damage electronics, fiber optics, certain adhesives, and heat-sensitive plastics. For these instruments, low-temperature methods such as EtO and VHP sterilization is more appropriate.

Q: What happens if a facility uses the wrong sterilization method?

A: If a facility were to use the wrong sterilization method — one not specified by the instrument’s IFUs — that instrument could come out damaged or not fully sterile. From a compliance standpoint, facilities that use the wrong sterilization method could be subject to CMS reimbursement penalties, enforcement action, and loss of accreditation by The Joint Commission or the DNV.