Ultrasound in Wound Care.

To the Editor:

I am writing to comment on the research report by Klucinec et al entitled "Effectiveness of Wound Care Products in the Transmission of Acoustic Energy" (May 2000). The authors have done a great service to providers of wound care and their patients in demonstrating that various wound dressings have a high degree of variability in transmission of acoustic energy. However, I am concerned that some readers may miss the full impact of the article.

First, only 4 hydrogels and 4 transparent film dressings were examined. In light of the variability of transmission found among these dressings, I believe that no assumption can be made about the transmission rates of any of the other hydrogels or transparent film dressings on the market (at least 14 hydrogels and 20 film dressings, by my count). This means that clinicians who want to provide known doses of ultrasound in wound treatment using a dressing interface would be limited to choosing among the dressings examined in this study. It would have been helpful to know why these brands of film dressings and hydrogels were chosen.

Second, and more importantly, I contend that this study should not be seen as demonstrating the ability of hydrogel or film dressings to effectively transmit any acoustic energy in an actual clinical setting. In order to ensure optimal dressing-to-tissue contact, the authors chose to place a layer of ultrasound gel between the pig tissue and the dressing. This method, in my view, was appropriate for the intent of the research, to compare dressing transmission rates, in order to eliminate an unknown variable: the direct dressing-to-skin transmission rate. However, elimination of this unknown is not possible in the clinic.

To prevent a dressing-to-skin interface with a hydrogel dressing, sterile ultra sound gel would have to be used. If the hydroget were available, the added expense of a hydrogel dressing would be unnecessary; the wound could be treated with the ultrasound gel as the interface. Use of a liquid hydrogel as the interface is unsatisfactory, as, to my knowledge, the transmission characteristics of these materials (with many brands available) have not been established.

In the case of film dressings, no liquid interface (ultrasound gel or liquid hydrogel) can be used, as this would prevent the dressing from adhering to the skin. The dressing would peel up as soon as the sound head begins to move. Because there is likely to be air trapped in the interface between the film dressing and dry skin, it seems unlikely that adequate or reliable transmission could ever be established.

I believe the results of this study indicate the need for caution in choosing ultrasound coupling methods when treating wounds. Ultrasound coupling utilizing direct skin contact through an ultrasound gel interface (for periwound treatment) or an underwater technique (for wound bed treatment) has been shown to effectively transmit acoustic energy.[1] I do not believe that current knowledge allows accurate determination of dosages when treating through a dressing interface, even for those dressing brands whose "laboratory" transmission rates have been determined.

Robert I Burks, PT, MPT, CHT 503 Eldora Rd Pasadena, CA 91104

References

[1] Docker MF, Foulkes DJ, Patrick MK. Ultra sound couplants for physiotherapy. Physiotherapy. 1982;68:124-125.

Author Response:

We would like to thank Mr Burks for his insightful comments. Mr Burks rightly identifies that the major contribution of our report is demonstrating the wide variability in transmissivity of the various wound care products.

Mr Burks points out that we studied only a small subset of the hydrogel and film dressings that are commercially available. Our selection of 4 hydrogels and 4 film dressings was by convenience, based on products commonly used by colleagues in the Indianapolis area and available to us at no cost. Although each of the many different products in each category is similar in function, the different products vary widely in characteristics such as size, thickness, makeup (eg, percentage of water for the hydrogels), and adhesiveness. Because of this variability, we agree with Mr Burks that clinicians cannot generalize our results to dressings we did not study.

Mr Burks is correct in his identification of the gel interface between the dressings and the pig tissue as a limitation of our in vitro model. We appreciate his discussion of the clinical difficulties associated with the use of wound care products with ultrasound and of the ways in which the clinical use of these products differs from our experimental model. In our report, we made every effort to confine our conclusions to the transmissivity of the products themselves. Like Mr Burks, we believe that "current knowledge does not allow accurate determination of dosages when treating through a dressing interface."

We would like to add that Mr Burks cited a 1982 article published in Physiotherapy as his evidence for the effectiveness of ultrasound transmission through water. This article provides few details about how the transmissivity data were collected, leading us to question the validity of this information. There is a growing consensus that water is a poorer conductor of ultrasound than ultrasound gel and gel pads.[1-4] Investigations of temperature rise in muscle1 and tendon2,3 with a continuous wave at a frequency of 1 MHz revealed less temperature increase when sound was transmitted through water. Our own research,[4] using methods similar to those reported in our wound care products article, showed that only 31% of the acoustic energy was transmitted via a tap water bath. Although our studies did not address wound healing, these results suggest that the conducting medium affects the dose of acoustic energy that reaches the target tissue.

Brian Klucinec, PT, MS, ATC Physical Therapist Joyner Sportsmedicine Institute Inc 2525 9th Ave, Suite IA Altoona, PA 16602

Matthias Scheidler, PT, MS Physical Therapist Hancock Memorial Hospital and Health Services Greenfield, Ind

Craig Denegar, PT, PhD, ATC Associate Professor Dept. of Orthopedics and Rehabilitation Associate Professor in Kinesiology Pennsylvania State University University Park, Pa

Elizabeth Domholdt, PT, EdD Professor and Dean Krannert School of Physical Therapy University of Indianapolis Indianapolis, Ind

Sharon Burgess, PT, MS Assistant Professor of Physical Education Ball State University Muncie, Ind

References

[1] Draper D, Sunderland S, Kirkendall D, Ricard M. A comparison of temperature rise in human calf muscle following applications of underwater and topical gel ultrasound. J Orthop Sports Phys Ther. 1993;17:247-251.

[2] Forrest G, Rosen K. Ultrasound: effectiveness of treatments given under water. Arch Phys Med Rehabil. 1989;70:28-29.

[3] Forrest G, Rosen K. Ultrasound treatments given in degassed water. Journal of Sports Rehabilitation. 1992;1:284-289.

[4] Klucinec B, Scheidler M, Denegar C, Domholdt E, Burgess S. Transmissivity of coupling agents used to deliver ultrasound through indirect methods. J Orthop Sports Phys Ther. 2000;30:263-269.

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