Medical Applications of the High Powered Parallel Waterjet

Using fluidjet technology not only improves surgical debridement, it has a number of other medical uses.

During the past decade the treatment of chronic wounds became focused on wound bed preparation. This process consists of manipulating a wound to bring it into a physiologic state compatible with healing.

The process has been codified with the acronym TIME. The T refers to tissue necrosis. All unhealthy tissue, including tissue with inadequate blood supply, severely damaged tissue and dead tissue must be removed from the wound. The I is for infection. Bacterial burden must be below 100,000 bacteria/gm in order for a wound to heal. The M stands for moisture balance. Wounds heal best in a moist environment. Finally the E means edge. The advanced edge of the tissue at the wound perimeter must be primed for healing. Healing can be facilitated by means of appropriate dressings, applications of advanced technological wound coverage systems or by surgery.

Effective debridement is the key to advancing through the TIME cascade. Surgeons have cut away tissue using sharp instruments, including lasers, ultrasound, electrocautery and radiofrequency devices, all of which have major drawbacks.

The VersaJet is a high-powered parallel oriented fluidjet debridement instrument which was developed by HydroCision of Andover, MA, and brought into clinical use by Smith and Nephew of Hull, UK.

Despite its success in numerous industrial applications, the question is if there is any basis for the use of highpressure waterjet technology in surgical applications. After all, the scalpel is a well-established cutting device, simple and inexpensive.

Further, low-pressure "jets" of fluid have proven adequate for many medical applications, such as in wound cleaning. Why, then, introduce a complicated high-pressure technology in such a demanding field?

There are two attributes of waterjet devices that represent potential advantages over other incisional modalities.

Tissue Differentiation: A conventional scalpel in the hands of a skilled surgeon can "differentiate" certain tissues; for example, it can resect fatty tissue away from stromal, or muscular tissue. However, the surgeon is using the scalpel to dissect through tissue planes and if these planes are not actually planar, but are topographically irregular, he is unlikely to achieve an exact separation.

A great advantage, then, accrues to a device that can be pre-set to precisely remove layers of soft tissue to an exact level, even in surgical sites which are inhomogeneous, difficult to access, and/or difficult to visualize.

Fluidjet devices can be "tuned" by proper nozzle design and operating parameters to do just this. In fact, the earliest fluidjet devices were indicated for use in dissecting away soft, parenchymal tissue in the liver and for dissecting tumors in the brain. More advanced technology, coupled with the use of higher fluid pressures, provides the potential for exquisite control of precision tissue excision, a capability which is particularly useful in wound debridement.

Ablation: A major disadvantage of the early, lower-pressure fluidjet devices for liver and kidney dissection was the fact that the fluidjet tended to disperse the tissue removed at the site. As a result, various means of incorporating an external vacuum had to be utilized in an attempt to retrieve the dispersed tissue.

Obviously, failure to accomplish this completely could represent some hazard, depending on the nature and area of dispersion of the resected tissue. In addition, great care must be taken to avoid inadvertently directing the waterjet against uninvolved contiguous areas.

A major advance ensued from the recognition that waterjets from the basis of the very old technology of "eductor pumps." Such pumps have been used in mines for centuries to pump out slurries of coal, for example.

By the addition of a "collector" device, designed according to very specific criteria, it is possible to capture the fluidjet itself, while concomitantly creating a vacuum at the point of capture.

When properly designed, this configuration results in intense cavitation at the collection point, so not only is the excised tissue drawn into the collector, but it is macerated almost to the cellular level and driven out of the collector tube without need for any external vacuum connection.

An important further advantage of the collector configuration is that the jet is fully controlled, that is, its action is constrained to the region between the jet nozzle and the collector, and so the danger of impinging on uninvolved contiguous areas is greatly minimized.

Further, bacteria and wound contaminants will likely be removed along with the ablated tissues. By designing an appropriately contoured handle, the cutting edge of the fluidjet can effectively reach relatively inaccessible areas of a wound.

Operating parameters of greatest importance for surgical applications are quite different from those for industrial applications. First, it is essential that the working fluid be sterile, since it is exposed to the site of surgery. All surgical procedures are performed under sterile conditions. This is a substantial hurdle, since power must be transmitted to the working fluid without the transmission of bacterial or viral contamination. This immediately gives rise to the question of re-sterilization of those components that carry the working fluid.

Realizing that most fluidjet surgical devices will incorporate very small diameter tubes and very fine nozzles leads to the conclusion that re-sterilization of such devices is extremely difficult to validate. In particular, the need for sterilization is compounded by the need for absolute cleanliness, since a single residual particle – even though sterile -- can clog a jet orifice.

Consequently, that part of the system which carries the sterile working fluid is a pre-sterilized, single-use, device. This strategy imposes the need for low manufacturing costs, consistent with those disposable devices, but does alleviate the need for the long useful lifetimes that would be required for reusable devices.

A second technical hurdle is the need to reduce the size of a complete fluidjet system from the typical floor-mounted or truck-mounted industrial system to a size which allows mounting in typical operating room "towers" or on instrumentation carts.

This hurdle is mitigated by the fact that the pressure required for surgical applications are not as high as typically used in industry. Generally, pressures from several thousand psi to 15,000 psi are sufficient for wound debridement as opposed to the 50,000 to 100,000 psi range used for industrial applications. Similarly, it is essential to reduce the size of the "working end" of the system to millimeter dimensions, a realm unheard of in industry.

Finally, it is obviously necessary to ensure that the stringent safety requirements consistent with operating room use are incorporated into the fluidjet system. This includes meeting well-prescribed electrical safety regulations, but also involves overcoming any hazard from fluids under high pressure, as well as from the spread of infective contamination from spray generated by the device.

Other considerations, such as noise and ease of use, which are exacerbated in the often frenetic operating room environment, are essential.

The VersaJet has resolved these hurdles. The overall system consists of a reusable power and control console for pressurizing normal saline (a biologically compatible isotonic fluid) up to 15,000 psi. The pressure required for the particular wound is adjusted on the console. The console, in addition to meeting international regulatory requirements for electrical and mechanical safety, has a low noise level, minimal operator interaction and a size commensurate with "tower" mounting in the operating room.

Handpieces are disposable, including the entire sterile fluid path from saline bag, through the integral "pump cartridge," to the highpressure flexible tubing. The pump cartridge was designed to be easily inserted into a receptacle in the console and incorporates a sterile barrier, so that contamination from the non-sterile console is avoided. A foot pedal operates the handpiece that comes with either an 8 or 14 mm working area.

There are numerous recognized applications for the waterjet in surgery. The VersaJet has FDA approval as a wound debridement instrument. It is effective in removing granulation tissue, fibrinous debris or frank necrosis in all wound types, including fasciitis wounds. In very severe and extensive wounds near important anatomical structures, the VersaJet is capable of delicately and precisely removing tissue to an almost microscopic level so as not to injure these structures.

In combination with a negative pressure wound therapy system, a healthy wound can often be achieved in cases that were not possible with scalpel debridement. This is also true in patients with loss of abdominal domain.

It has been found that the Versa- Jet can clean off exposed viscera in cases of open abdomens. This allows more rapid closure with less risk of fistula.

The VersaJet is much more accurate and rapid than scalpel surgery in debriding necrotic muscle in compartment syndrome.

In burn wounds, VersaJet is not useful for the removal of dry eschar, which is too dense for it to cut. However, in chemical burns, friction burns and more superficial flame burns, it is a fast, less bloody and very effective debridement tool.

At this time, the VersaJet does not have FDA approval for burn debridement in the U.S., but it has been used extensively for this purpose in the U.K.

The instrument is exceptionally useful in cleaning up acute traumatic wounds. Patients who have crush injuries, electrical burns, compartment syndromes, gunshot wounds and open comminuted fractures are traditionally treated with serial debridements and wound irrigations in the operating room prior to any attempt at closure. The VersaJet enables the surgeon to more accurately clean the wound so that the number of debridement sessions required to get a properly prepared wound bed is significantly reduced.

The VersaJet is extremely useful for the removal of particulate foreign bodies, such as "road dirt." Road dirt consists of soil and grit that is ground into the tissues when a injured person is dragged against the ground.

Unless road dirt is removed from the wound early after the injury it gets incorporated into the healing skin and forms a traumatic tattoo. At that point it is almost impossible to get rid of it other than by directly excising it. The VersaJet readily and completely removes this material from an acute wound leaving a healthy wound bed. Similarly, the VersaJet facilitates removal of silicone gel following implant rupture.

VersaJet is useful for defatting flaps and skin grafts. When a full thickness skin graft is required, a piece of skin is cut away from one area of the body, all of the underlying fat is removed and it is then placed elsewhere on the body. The waterjet is a quick effective way to remove the excess fat from the underside of the graft.

Orthopedic surgeons have found the VersaJet to be a quick and effective way of debriding infected prostheses. When a patient who has a total joint prosthesis becomes infected, the prosthesis is generally removed and a spacer impregnated with antibiotics is placed in the joint space for a period of months prior to replacing the prosthesis.

With the VersaJet, the infected prosthesis can be removed, the wound completely cleaned and a new prosthesis inserted in one sitting, saving multiple operations and months of disability for the patient. The Versa Jet is used to remove osteomyelitic bone and metallosis from the worn out prosthesis.

The VersaJet, a high-powered parallel cutting water jet, was developed for the purpose of wound debridement. The process of development required solutions to many challenging technical problems. The result, however, is a device with remarkable accuracy and precision.

As more experience is gained with this new approach to surgery, more applications for this device will undoubtedly develop. There are many potential applications that can be realized as well by adapting the instrumentation to different surgical environments.

The VersaJet has empowered the surgeon to achieve better outcomes for patients while saving scarce economic resources for the hospitals at the same time. It has led to a paradigm shift in surgical thinking. TMD

This article was drawn, with permission, from a paper that received the "Best Application Paper" award at the 2005 WJTA American Waterjet Conference. It was jointly authored by Mark S. Granick, M.D., Ramazi O. Datiashvili, M.D., Parham A. Ganchi, M.D., Ph.D., and Donald C. Freeman, Jr., Ph.D.