Deployed Sterilization

Written by CHERYL GERBER

STERILIZING MEDICAL EQUIPMENT IN THE HARSH AND CHALLENGING DEPLOYED ENVIRONMENTS THAT MANY MEDICAL TEAMS FIND THEMSELVES FACING IS A DAUNTING CHALLENGE.

The DoD is evaluating options for lightweight medical sterilizers that will be used in austere environments by mobile, forward surgical teams that cannot transport the heavy, outdated sterilizers used in stationary combat support hospitals. For decades, the primary method of sterilization has been steam under pressure in a bulky autoclave known as Big Bertha. Weighing in at 250-400 pounds, Bertha uses nine kilowatts of electric power and contains a three-foot chamber 20 inches in diameter.

Forward surgical teams (FST) consider Bertha’s weight a major disadvantage. “We are addressing problems that the big brick-and-mortar hospitals don’t face. They don’t pack up and move every two weeks,” said Mark Arnold, engineer and product manager for the Army at Fort Detrick, Md.

But weight isn’t the only drawback. “All of the services are using Bertha, so we all have the same problem. It’s really a matter of obsolescence more than ineffectiveness. The Bertha sterilizer was built in the 1960s and its heyday was Vietnam. Given its shortcomings, it’s not a bad sterilizer, but the company isn’t in business anymore. You can’t get repair parts,” said Chuck Bolin, project officer, Marine Corps, Medical Research and Development Systems Command, Quantico, Va.

However, despite its bulk and obsolescence, Bertha has major advantages. For one, it can run off any power source. When it’s necessary to lug Bertha out to the field, where there’s no conventional source of power, the old sterilizer can still perform. “The good thing about the Berthas is the burner plates underneath them that use any kind of combustible fuel. You can light it much like you light a Coleman camp stove to boil the water to make the steam you need to sterilize material,” Bolin said.

In addition, Bertha’s use of steam is nontoxic, compared with another sterilization method, ethylene oxide, a volatile gas that requires an 8- 12-hour aeration cycle to release its toxicity. “When you use ethylene oxide, one of the residuals generated is ethylene glycol, a toxic antifreeze. You have to aerate overnight to get rid of what is left on the instruments after sterilization,” Arnold said. As a result, ethylene oxide is now rarely used.

The Army has created add-ons to Bertha to work around the disadvantages and stretch the return on investment. “We can now recover water from the exhaust, reprocess it and return it to the boiler,” Arnold said. “But previously we had to stop the sterilizer, let it cool down for an hour or more and then someone had to stand on a box and pour water from a bucket into the back part of the sterilizer in order to refill the sterilizer boiler to produce steam. It consumed two-and-ahalf gallons of water every time you ran a cycle to sterilize equipment,” he said.

Nonetheless, Bertha’s disadvantages have outweighed the advantages. The time required for sterilization and the wet process count high among the drawbacks. “You need a long dry cycle, and sometimes, if you are in a humid environment, you’d open Big Bertha after the sterilization process and get condensation that would re-contaminate the products,” Bolin pointed out.

These problems alone are intolerable in field locations where soldiers are brought in on stretchers and need surgery on the spot. While FST doctors use disposable sterile instruments to get around the lack of a portable lightweight sterilizer, disposables present supply-chain dependency and medical waste problems that could be mitigated by using a portable sterilizer.

Bertha’s obsolescence also means it cannot sterilize modern medical devices used for new surgical and exploratory procedures. The devices often include plastic, fiber optics and other sensitive materials, which cannot tolerate the high, 130-degree-Celsius temperatures generated by the big steam pressure cooker. Given the intense heat, Bertha can only sterilize conventional, metal medical devices.

In addition, many Berthas do not have the retrofitting provided by the Army that reprocesses water from the exhaust. In some cases, a Bertha requires up to five gallons of distilled water, which is seldom readily available in the field. Austere operational environments often necessitate the use of alternate water sources, which result in deterioration of the autoclave heating elements and can degrade the sterilized product.

To address these limitations, the Office of Naval Research’s (ONR) Small Business Innovative Research (SBIR) program solicited the development of a lightweight sterilizer with alternative technology. The solicitation recently closed and is now under evaluation. Two of the companies that submitted proposals are offering new technologies— gas plasma and ozone—with the required light weight.

Phygen Inc. of Minneapolis is developing a gas-plasma sterilization process that can overcome most of the disadvantages presented by steam autoclaves like Big Bertha. The method employs a chamber that is evacuated with a vacuum pump and receives a small injection of vaporized hydrogen peroxide. The chamber electrode is energized with high voltage, and ionized gas in the chamber generates the sterilizing plasma.

Gas-plasma sterilization has been around for a while, but it only provided one form of sterilization—oxidation—as a result of hydrogen peroxide forming free radicals. This does not provide deep-enough sterilization. “Phygen’s sterilization technology delivers more effective sterilization than what is available in gas plasma today. Our Phyonic technology provides three forms of sterilization,” said Dave Bell, founder and CEO of Phygen. “It ionizes material, creates ultraviolet light, and oxidation occurs with a chemical reaction,” he said.

While ions and free radicals etch biological material, ultraviolet light produced by the plasma destroys genetic material. The third form is created when oxygen and peroxide vapor that is not dissociated oxidizes biological material. “This is more effective because it creates a higher kill rate. It is lethal to the things you want to kill,” he said.

In addition, Phygen’s low-temperature discharge plasma sterilizes at 55 degrees Celsius, as it uses active atoms rather than a heating-up process. As a result, medical professionals can sterilize modern medical devices made of plastic or fiber optics that would be destroyed in the heat of Bertha’s steam.

The gas-plasma technology requires several milliliters of peroxide for each cycle, compared with gallons of distilled water required by the steam autoclave. The gasplasma device is also expected to require less power. Sterilization can be accomplished in 38 to 58 minutes, and the weight of the device can be reduced by 50 to 70 percent, depending on user requirements, resulting in considerably improved portability. This can be essential in austere environments, such as the mountainous or desert regions in Afghanistan and Iraq, where portability is a must.

Finally, gas plasma is a dry process, which eliminates the condensation and consequent re-contamination problem that can occur with the wet steam process. The dry gas-plasma technology can be used in low-temperature environments, where ice could destroy equipment that relies on a wet process.

Gas-plasma sterilization also takes less time. “With steam autoclaves, first you have to heat water to 270 degrees for ten minutes minimum, then put it on a dry cycle, which could take a few hours,” Bolin said. By contrast, the gas-plasma sterilizer consists of plugging in the device to standard, single phase AC receptacle or DC power for initial warm up to reach standby mode (estimated to take 15 to 45 minutes depending on user configuration), after which each sterilization cycle takes no more than 58 minutes.

However, the power source of the gas plasma sterilizer is not as flexible as that of old Bertha. “As we transition to the gasplasma sterilizer, we will lose the versatility of power source and become power dependent,” Bolin said. “You lose the ability to sterilize products even if you don’t have a power source.”

However, gas plasma uses a range of voltages and is expected to have a power consumption of 1200 to 1500 watts, the equivalent of a hair dryer, compared with Bertha’s steam process, which operates on three phase 240 power and consumes about 9000 watts of energy. “Just about everything we need in operating rooms is power-dependent. Nowadays we [USMC] use forward resuscitative surgical suites, and they have two small 3-kilowatt generators designed for 18 surgeries in 72 hours. Within the surgical company of a medical battalion, we also have a big generator,” Bolin said.

Nonetheless, Phygen intends to incorporate power-supply versatility into the design of its future sterilizers. “This will be user-driven,” Bell said. “We’re now in conversations with Army, Navy and Marines about their requirements,” he said.

Another alternative to steam is ozone sterilization, which is already commercially available. Lynntech Inc., College Station, Texas, which licenses its proprietary ozone technology, also submitted a response to ONR’s SBIR solicitation, proposing its ozone-based lightweight sterilizer.

“We provide a cold sterilization method for plastic and sensitive equipment with fiber optics, which cannot be sterilized in a steam autoclave,” said Tony Giletto, Lynntech manager of operations and technology development and a senior research scientist.

“Using Lynntech’s proprietary product, you can make ozone from water, and your only waste product is oxygen, which is harmless, so it’s green chemistry,” he said.
 
“By introducing humidified ozone into the sterilization chamber, we generate ozone under pressure from water, without a pump, resulting in a humid, high-concentration ozone gas stream,” said Scott McKenzie, Lynntech manager of technology commercialization and a senior research scientist.

Lynntech is now actively seeking a partnership with a company that can bring a portable, lightweight version of the ozone sterilizer to market. Because the current technology takes hours to sterilize, it could be more appropriate for combat support hospitals.

Lynntech’s Ozone Sterilization Unit is also lighter in weight and more compact than Bertha. Although the proposed unit has a larger chamber than Bertha, it is expected to weigh approximately 100 pounds less. The cycle time of the ozone sterilizer will be less than that of Bertha but probably longer than that of gas plasma.

In late 1997, Ozone received FDA approval, with “Generally Recognized As Safe” status, for use as a germicidal tool in the food-production industry. It has recently been approved as a sterilizing agent for medical instruments. Since it is generated on demand from water and electricity, no storage of chemicals is required.

Lynntech was funded in November 2005 by the Army to develop a lightweight and portable steam sterilizer the size of a thermos or canteen. It must use no electricity to sterilize medical and dental instruments in the field. “It’s a phase-one SBIR, so the technology is still in the research stage,” Giletto said.

Phygen also received funding from NIH and the Army in May 2005 to develop a plasma sterilizer, according to Mark Arnold, program manager on the contract. Arnold was encouraged by Phygen’s performance at NIH. “Phygen got a blockbuster score for a phase-two proposal for SBIR through NIH. A phase-one award is on the public domain on the NIH Web site,” he noted.

Although gas plasma or ozone can meet the requirements of mobile FSTs, they cannot provide water sterilization. “Water and solutions for irrigation to clean wounds with sterile water will need stationary sterilizers,” Arnold noted. So an FST will still have to haul a certain amount of sterilized water around.

However, the increasingly mobile services are looking to lighten their weight loads as much as possible. As such, they await the new lightweight sterilization devices that will contribute to achieving that goal. “We are looking forward to getting Phygen’s prototype of the plasma sterilizer in here so we can test it. We expect to get a prototype sometime this summer,” Arnold said.

The Marines would like to see the lightweight, mobile sterilizers fully deployed within the next two years. “Our objective is for new sterilization technology, such as gas plasma, to be mature enough to deploy in 2008,” Bolin said. ♦

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