A Closer Look At Ultrasonic Debridement

Can ultrasonic debridement facilitate improved wound healing? Sharing insights from their clinical experience as well as the literature, these authors discuss the mechanism of ultrasonic debridement, how it compares to other debridement methods and offer perspectives on the advantages and weaknesses of ultrasonic debridement.

   Ultrasound in medicine continues to help the clinician treat and evaluate numerous conditions and pathologies. Diagnostic ultrasound at frequencies of 5 to 12 MHz provides the ability to view the musculoskeletal system for pathology in addition to evaluating arterial and venous blood flow. Therapeutic ultrasound for physical therapy uses frequencies ranging from 0.7 to 3.3 MHz. This treatment provides the benefits of both thermal and non-thermal effects on soft tissue.1

   Low-intensity pulsed ultrasound (at 1 kHz) provides a mechanical stimulus that helps bones heal as in the case of both traumatic and surgical nonunions.2 Low-frequency ultrasound (22 kHz to 35 kHz) has also found a home in wound care. One may utilize this modality to remove devitalized tissue as a selective method of wound debridement.

   Debridement of non-viable tissues is necessary for wound improvement and healing, and is considered a cornerstone of acute or chronic wound management. Research has shown that removing non-viable tissues decreases the incidence of infection and accelerates the rate of closure.3,4

Reviewing The Different Methods Of Debridement

Methods of debridement include sharp debridement, mechanical debridement, autolytic debridement, biosurgical debridement and chemical (enzymatic) debridement.
The term surgical or sharp debridement does not necessarily imply aggressive debridement. The level of invasiveness defines aggressive debridement. Sharp debridement describes the use of surgical instruments such as scissors, scalpels, curettes or other sharp blades to remove devitalized tissue.

   Sharp debridement can be invasive (aggressive) or non-invasive (conservative). For example, removing eschar from a pressure ulcer that you have clearly differentiated from viable tissue is considered conservative even if you use a blade or scissor. Sharp debridement, if the physician performs it conservatively, does not require anesthesia or hemostasis. This is the fastest type of debridement.

   Autolytic debridement is a form of chemical debridement but does not involve treating the wound with a therapeutic agent. It is the process by which the wound bed clears itself of devitalized tissue and cellular debris via phagocytic cells and endogenous proteolytic enzymes present in the wound or in wound fluid.

   Autolytic debridement usually requires the use of a moist, hypoxic environment provided by an occlusive dressing. The debridement by autolysis of deep pressure ulcers or diabetic neuropathic foot ulcers is not as predictable as with venous ulcers or more superficial pressure ulcers, and may take a longer time.5

   Chemical debridement involves the application of topical agents (enzymatic or non-enzymatic) that chemically disrupt or digest devitalized extracellular proteins present in the wound. Most of the research work in the field of chemical debridement has dealt with the use of enzymes with proteolytic action.6

   Biosurgical debridement involves myiasitic maggots, which feed on dead tissue, resulting in the cleaning of the wound bed.7

   Mechanical debridement may be aggressive or conservative. Mechanical debridement methods include hydrosurgery, forceful irrigation (high-pressure saline debridement), therapeutic ultrasound hydrotherapy and the use of wet-to-dry gauze dressings. The difference between mechanical debridement and other methods is that mechanical debridement does not discriminate between viable and nonviable tissues.

What The Literature Reveals About The Mechanisms Of Ultrasonic Debridement

Ultrasonic debridement is a form of mechanical debridement. It employs an electrical current, which piezoelectric crystals then convert to mechanical vibrations. The mechanical vibrations stimulate a probe, which in turn amplifies the vibrations. This mechanical energy converts into acoustic energy, which subsequently transfers to the tissue in the wound bed and peri-wound tissue.8

   The process involves the application of a saline solution. Given that ultrasound does not travel easily through air, the saline solution serves as a contact media for the ultrasound waves to travel from the probe into the tissues via direct contact.

   During this process, there is additional acoustic phenomena, including cavitation, which is the creation and destruction of small bubbles within the fluid surrounding the probe.9 During cavitation, the bubbles oscillate in size and shape. The oscillation of the bubbles is dependent on the frequency of the ultrasound wave. The bubbles expand and rapidly collapse, causing shockwave formation. This implosion due to cavitation causes erosion of tissues.10 Ultrasonic debridement provides both mechanical and hydrodynamic effects directly in the wound bed. This method causes necrotic tissue disruption, fragmentation and emulsion.11

   In addition to the removal of debris and necrotic tissue from the wound bed, one recent study involving the Qoustic Wound Therapy System (Arobella Medical) revealed that low frequency ultrasound reduces the bacterial numbers through direct damage to bacterial cell walls.12 Therefore, ultrasound may be quite effective in treating pathogenic bacteria, particularly those resistant to antibiotics.

   Further microbiological studies are needed to confirm the effectiveness of ultrasonic debridement for the treatment of localized wound infection and bacterial colonization.

Key Insights On Utilizing Ultrasound Debridement Devices

One may perform debridement using an ultrasonic generator during a typical clinic visit. The ultrasonic debrider allows the operator the ability to direct the probe selectively on devitalized tissue while avoiding healthy granulation tissue. Depending on the unit, there are a number of features that allow the physician to tailor the debridement for each particular wound.

   Some ultrasonic debridement generators have interchangeable probes. The probes and hand pieces are autoclavable, and therefore are reusable. Depending on the device, the type of probes varies. Some are contoured to be abrasive and have a variety of cutting edges while others are beveled and designed to address undermining and sinuses. There are also more classical probes (curette-like) with a sharp circular blade or scoop. With these probes, the doctor can be more or less aggressive, depending on the situation and the probe he or she chooses.

   Some ultrasonic debridement generators provide controls to vary the acoustic power. For example, the SonicOne® (Misonix) also has controls that provide both a continuous mode and intermittent mode. This is particularly useful if the wound is painful or the patient experiences pain during the debridement process. In our experience, lowering the acoustic power and changing from continuous to intermittent mode reduces the amount of pain the patient will feel.

   Of particular importance is the misconception that ultrasonic debridement is not painful. In our experience, unless the wound is neuropathic, all of the methods we have used cause some degree of pain. In most cases, pre-treatment of the wound with topical lidocaine 4% or 5% ointment for 10 to 15 minutes is sufficient for a minimally aggressive procedure. We apply the lidocaine ointment (about the thickness of a dime) to the wound and cover with an occlusive dressing. Depending on the particular patient, wound etiology and the aggressiveness of the procedure, you may allow the patient to take preemptive oral analgesia 45 minutes prior to the procedure.13,14

   In successful ultrasonic debridement, removal of devitalized tissues is based on the degree of cavitation caused by bubbles from within a saline solution. Depending on the unit, such as the Sonoca 180 (Soring) or Qoustic Wound Therapy System™ Model AR1000, a bag of saline solution will be useful as it provides a continuous drip of saline during the procedure (gravity fed solution). The SonicOne has a variable adjustable pump that has the ability to control the amount of saline one uses during debridement. One may pump saline from any bottle or bag because the stream is not gravity fed.

   The physician would drape the extremity or wound in the usual sterile fashion. We suggest placing absorbent pads below and around the area you are debriding. These pads capture the saline as it runs off the area you are cleaning. Then choose a probe. Depending on the particular unit and the application, there are a number of great choices available.

Assessing The Pros And Cons Of Ultrasonic Debridement

Although we are familiar with all of the marketed ultrasonic debridement devices, we have the most experience with the SonicOne device. We have studied the rates of wound healing in venous ulcers that underwent surgical debridement (using curettage debridement) and those that underwent ultrasonic debridement.

   On average, we found that wounds that underwent ultrasonic debridement healed at a faster rate than those that underwent standard sharp debridement. All patients received standard wound care with a non-adherent primary dressing and standard compression therapy with either a three- or four-layer bandage.

   A previous study reported faster wound healing with a low intensity, non-contact ultrasound device (MIST Therapy®, Celleration).15 However, in this study, researchers used the MIST device solely as an adjunct to wound therapy and not as a debridement device. In our experience, the level of clinical debridement obtained from non-contact low intensity therapeutic ultrasound is marginal in comparison to the high intensity ultrasonic debridement devices that produce cavitation.

   It is important to note that on average, an ultrasonic debridement procedure takes more time than a standard sharp debridement procedure. For example, we found that the mean time to perform ultrasonic debridement was approximately 20 minutes whereas a standard sharp debridement was only 10 minutes.

   Specifically, with the SonicOne, we found that the setup time averaged five minutes, actual debridement lasted an average 9.8 minutes and cleanup took an average of 5.5 minutes.

   In contrast, sharp debridement involved one minute of setup time, an average of 8.5 minutes for the debridement and one minute for cleanup.

   Although the time to perform the actual procedure is similar, the setup and cleanup time is significantly greater for the ultrasound methodology. Of course, you can circumvent this delay if you are able to schedule all or most of your debridement procedures in the same session.

   Of equal importance is the total number of procedures performed. We found that debridement with high intensity ultrasound lasted significantly longer than debridement performed with a curette. In a 12-week period, we recorded performing an average of 3.5 debridements per patient with the SonicOne in comparison to an average of 5.8 sharp debridement procedures per patient.

   As with any other surgical debridement procedure, the duration of high intensity ultrasonic debridement can vary depending on the physician or surgeon performing the procedure.

   As we mentioned earlier, both aggressive and conservative debridement can attain varied results. In our experience, if the circumstances allow, the more aggressive debridement is, the better. In comparison with sharp debridement, there is less bleeding with ultrasonic debridement. In most cases, one can easily achieve hemostasis with elevation and compression without the need of cautery.

In Conclusion

Ultrasonic debridement devices have found a home in wound care. This innovative method of debridement can provide clinicians with a tool they can use to remove devitalized tissue selectively from the wound bed.

   This technology has a number of benefits and appears very promising. The first benefit is that ultrasound has a therapeutic effect on the tissue in and around the wound bed. A second great advantage is the reduction and destruction of pathogens that occupy chronic wounds.

   Dr. Wendelken is a licensed RN who specializes in emergency medicine. He is affiliated with the Calvary Hospital Center for Palliative and Curative Wound Care in Bronx, NY. He is an Adjunct Professor in the Department of Radiology at Temple University School of Podiatric Medicine. Dr. Wendelken is a principal in BioVisual Technologies, LLC, and is the inventor of the PictZar® Digital Planimetry software program.

   Dr. Markowitz is a staff physician at the Center for Curative and Palliative Wound Care at Calvary Hospital in Bronx, N.Y.

   Dr. Alvarez is the Director of the Center for Curative and Palliative Wound Care at Calvary Hospital in Bronx, NY. He is a Professor in the Department of Medicine at the New York Medical College in Valhalla, N.Y.

   For further reading, see “Key Insights On Mapping Wounds With Ultrasound” in the July 2006 issue of Podiatry Today, “Current Concepts In Wound Debridement” in the July 2009 issue or “Assessing Debridement Options For Diabetic Wounds” in the March 2007 issue.

   To access the archives, visit www.podiatrytoday.com.

References:

1. Wilkin LD, Merrick MA, Kirby TE, Devor ST, et al. Influence of therapeutic ultrasound on skeletal muscle regeneration following blunt contusion. Int J Sports Med 2004; 25(1):73-77. 2. Strauss E, Gonya G. Adjunct low intensity ultrasound in Charcot neuroarthropathy. Clin Orthop Relat Res 1998; 349:132-138. 3. Steed DL. Debridement. Am J Surg 2004; 187(5A):71s-74s. 4. Whitney J, Phillips L, Aslam R, Barbul A, Gottrup F, et al. Guidelines for the treatment of pressure ulcers. Wound Repair Regen 2006; 14(6):663-79. 5. Williams D, Enoch S, Miller D, Harris K, Price P, et al. Effect of sharp debridement using curette on recalcitrant nonhealing venous ulcers: a concurrently controlled, prospective cohort study. Wound Repair Regen 2005;13(2):131-7. 6. Wiseman DM, Rovee DT, Alvarez OM. Wound Dressings: design and use. In: Cohen K, Diegelmann R, Linbladt WJ (eds) Biochemical and Clinical Aspects of Wound Healing. WB Saunders, Philadelphia, 1999, pp. 562-580. 7. Greer K. Age-old therapy gets new approval. Adv Skin Wound Care 2005; 18(1):12,15. 8. Stanisic MM, Provo BJ, Larson DL, Kloth LC. Wound debridement with 25 kHz ultrasound. Adv Skin Wound Care 2005; 18(9):484-90. 9. Gong C, Hart D. Ultrasound induced cavitation and sonochemical yields. J Acoustical Society Am 1998; 104(4):2675-82. 10. Cain C, et al. Non-invasive ultrasonic tissue fractionation for treatment of benign disease and cancer- “histotripsy.” Therapeutic Ultrasound Group, Biomedical Engineering Dept. Univ. of Michigan. 11. Hall TL, Fowlkes JB, Cain AC. A real-time measure of cavitation unduced tissue disruption by ultrasound imaging backscatter reduction. IEEE Trans Ultrasonics Ferroelectrics Freq Control 2007; 54:569-575. 12. Conner-Kerr T, Alston G, Stovall A, et al. The effects of low-frequency ultrasound (35 khz) on methicillin-resistant Staphylococcus aureus (MRSA) in vitro. Ostomy Wound Management 2010; 56(5):32-42. 13. Friedman PM, Mafong EA, Friedman ES, Geronimus RG. Topical anesthetics update: EMLA and beyond. Dermatol Surg 2001; 27(12):1019-1026. 14. Alvarez OM, Kalinski C, Nusbaum J, Hernandez L, et al. Incorporating wound healing strategies to improve palliation in patients with chronic wounds. J Palliative Med 2007; 10(5):1161-1189. 15. Kavros SJ, Miller JL, Hanna SW. Treatment of ischemic wounds with non-contact, low-frequency ultrasound: the Mayo Clinic Experience. Adv Skin Wound Care 2007; 20(4):221-6. Additional Reference 16. Westerhoff W. Future prospects of proteolytic enzymes and wound healing. In Westerhoff W, Vanscheidt W (eds.): Proteolytic Enzymes and Wound Healing. Springer-Verlag GmbH & Co., New York, 1994, pp. 99-102.