Abstract: The measurement of sub-bandage pressure is commonly reported as a means of comparing the possible effectiveness of compression therapies. While there remain several key challenges to the collection and interpretation of this data, a factor cited as a modifier of sub-bandage pressure is the technique by which the bandage is applied to the leg. Two elastic compression bandages were applied to an in-vitro limb model with differing numbers of layers (1 or 2) and at different application tensions (2N to 10N) using either a spiral or figure-eight application technique. Few differences were observed between the sub-bandage pressures and the shear component between bandage layers, regardless of bandage type or application technique. Sub-bandage pressures increased with the number of bandage layers applied and the bandage application tension. This exploratory study revealed what appeared to be relatively small differences between sub-bandage pressures when an elastic bandage was applied using either of the 2 application techniques with a possible trend for sub-bandage pressures to be higher for a given application tension when a spiral technique was used to apply the bandage. However, when the bandages were applied using the 2 techniques, there was a maximum 6 mmHg difference for a given bandage applied at a known tension, and it is possible that this small difference related to the challenges of maintaining a constant bandage application tension rather than marking a real difference in the sub-bandage pressures generated using different application techniques.

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ompression bandaging remains the primary treatment for venous leg ulcers, and multilayer systems are apparently more effective than single-layer bandages.¹ To date, controversy remains as to whether elastic or inelastic bandages differ in their relative efficacy. While these general comments on the effectiveness of compression bandages can be drawn from randomized, controlled trials, many of the comparisons between bandage systems depend upon surrogate outcome measures, such as sub-bandage pressure and its effect upon local blood flow.^2–4 Surrogate outcome measures, such as sub-bandage pressure, can be measured in vivo or in vitro, but regardless of whether the bandages are applied to human legs or model limbs, uncertainty remains regarding the selection of appropriate pressure sensors, their placement upon the leg, and the interpretation of the gathered data.^5,6 One unexplored issue that may influence sub-bandage pressure is the technique used to apply the bandage to the leg. In practice, 2 main bandage application techniques exist: application in a spiral pattern with a 50% overlap between successive bandage layers or application in a figure-eight pattern, again, with a 50% overlap between each layer. Application in a spiral fashion has been assumed to apply higher sub-bandage pressures for any given compression bandage.⁷ However, there does not appear to be any available data to substantiate this observation. The present study compared sub-bandage pressures of 2 elastic bandages (Tensopress, Smith & Nephew Ltd, Hull, United Kingdom, and Setopress, SSL International Plc, London, United Kingdom) applied to a model limb using the 2 application techniques. In addition to the measured sub-bandage pressures, forces acting between bandage layers (nominally described as shear forces in this study) were also compared when the bandages were applied using the 2 application techniques.

Methods

       A solid cylindrical limb model (38.3 cm diameter) was used to explore the effects of bandage application technique on sub-bandage pressure. The central portion of the model limb was covered with 2 layers of foam dressing (Allevyn, Smith & Nephew Ltd, Hull, United Kingdom) to simulate soft tissue and to prevent point loading upon the pressure sensors when they were covered with a compression bandage. Three strain-gauge temperature-compensated transducers² were mounted on the foam layer surrounding the model leg at approximate 5 cm intervals. When bandaged, the first sensor would be covered with a single layer of bandage, and 2 layers of bandage each covered the remaining 2 sensors.

Figures 1-2

       The compression bandages (Tensopress and Setopress, both 10 cm in width) were attached to the model leg using a single piece of adhesive tape (Mefix, Mölnlycke Health Care Limited, Bedfordshire, United Kingdom) and were suspended vertically from the point of attachment. In both the spiral and figure-eight application techniques, the model leg was supported at an angle to facilitate application at a constant tension. Figure 1 illustrates the application using a spiral technique with the model leg at 6 degrees, while Figure 2 shows the figure-eight application. In this second application technique, the model leg was positioned either at 6 degrees or 12 degrees as each layer of bandage was applied. In all cases, the bandages were applied by manual rotation of the model leg. Each bandage was applied at a range of constant tensions between 2N and 10N with the tension increasing in 2N increments. The bandages were tensioned using known volumes of fluid within a container attached to the free end of the bandage. Each set of measurements at the various application techniques and tensions was repeated 5 times with the median (range) sub-bandage pressures reported.
       In addition to the measurement of sub-bandage pressure, an assessment of the magnitude of any shear component was also undertaken. In this case, 2 strain-gauge sensors were placed together in line with the circumference of the tube. One sensor was enclosed in a fine nylon sac to reduce any shear forces that may act on it. The presence and magnitude of any shear forces were assessed by subtracting the reading from the sensor within the nylon sac from the reading obtained from the second sensor. Since the accuracy of the sensors was +/- 2 mmHg, any difference of 4 mmHg or less was considered to be an artifact and treated as a zero shear component.

Tables 1-2

Results

       Tables 1 and 2 illustrate the sub-bandage pressures recorded under 1 and 2 layers of the 2 compression bandages when applied at tensions between 2N and 10N. Sub-bandage pressure increased as the number of bandage layers and the applied tensions increased. Both tested bandages applied similar sub-bandage pressures for any given application tension or number of applied layers. Application of either bandage (Tensopress or Setopress) using a spiral application technique resulted in slightly higher sub-bandage pressures than did either bandage applied in a figure-eight configuration. This difference was small—a maximum observed divergence between sub-bandage pressures recorded beneath the bandages of either application techniques was 6 mmHg (2 layers of Tensopress applied at 8N). Little differences were seen in the shear component measured between the layers of either bandage applied using the 2 techniques; there appeared to be greater shear when Setopress was applied at 10N using a figure-eight application (spiral application shear component 1 mmHg; figure-eight application shear component 10 mmHg). In no other case did the difference in the shear component between bandages, application technique, or tension exceed the accuracy of the sensors (combined accuracy 4 mmHg).

Discussion

       The sub-bandage pressures measured beneath the 2 compression bandages were similar at each application tension and equivalent as the number of bandage layers increased for both bandage application techniques. At higher application tensions, there was a trend for the bandages applied in a spiral fashion to apply higher sub-bandage pressures. While bandage application technique may have an effect on sub-bandage pressure, this appeared to be relatively small in this study (maximum median increase in sub-bandage pressure with 2 layers of bandage applied in a spiral rather than as a figure-eight was 6 mmHg with the “typical” rise being around 3 to 4 mmHg), and the clinical relevance of such small changes may be open to question. Part of this apparent, albeit small, difference between the bandage application techniques may have been due to the challenge of applying the bandages by hand while trying to maintain a constant tension.

Conclusion

       From the results of this exploratory study, it may be concluded that bandage application technique plays a small role, if any, in determining sub-bandage pressure for elastic bandages applied at known tensions.