Notes on Practice: Keys to Understanding the Science of Compression Wrapping

  Compression therapy is a widely used treatment for various forms of edema. In an orthopedic setting, it is commonly used to limit postoperative edema and edema due to trauma. In wound care, compression therapy has many uses, including the management of complications associated with venous, lymphatic, and sickle cell disorders. When applied properly, compression wraps are instrumental to successful management of these conditions. When applied poorly, at best the condition does not improve and at worst the condition deteriorates or leads to iatrogenic complications. The risk of complications associated with compression wrapping can be reduced by taking a complete history and physical and by gaining a general understanding of the principles of compression wrapping.   A history and physical is necessary to identify conditions that likely will lead to complications. These include unstable congestive heart failure, the presence of a deep vein thrombosis, acute cellulitis, and vascular compromise. The assessment of these factors and others has been described elsewhere, and is not the purpose of this review.¹   The second component of safe and effective use of compression requires an understanding of the interaction of each factor relating to the total pressure the wrap will exert on the limb. LaPlace’s Law states the amount of resting pressure a bandage will exert on the limb can be determined from the number of layers, width, and tension of the bandage, as well as the circumference of the limb to which the bandage is applied.   LaPlace’s Law: P(mmHg) = [T(kgf) x N x 4630] / [C(cm) x W(cm)].   In clinical practice, it is more important to understand the concept than it is to calculate an exact sub-bandage pressure. For this reason, the equation can be simplified even more, as the constant (4630) and the units can be eliminated, leaving the equation P = TN/CW.

Compression Components

  Bandage options.   Short-stretch bandages. The first thing that must be considered is whether the bandage being applied is a short- or long-stretch bandage. As the name implies, short-stretch bandages will change very little from their resting length when they are stretched. Examples of short-stretch bandages are those bandages commonly used in lymphedema management and paste bandages (often referred to as non-stretch). The short-stretch bandage has a high dynamic pressure and a low resting pressure because of the small amount of elasticity in the bandage. As a result, when someone is ambulating (dynamic) in a short-stretch bandage, the pressure will increase as the muscles contract but the bandage does not expand. This is beneficial — it promotes venous return by assisting the calf muscle pump. When the person wearing a short-stretch bandage elevates the limb (resting), sub-bandage pressure is reduced because the lack of elasticity in the bandage prevents recoil. Gravity-eliminated positions will lead to lower pressures in the vessels and, therefore, could lead to occlusion if the bandage pressure remained high. For this reason, short-stretch bandages are recommended for people wearing bandages while sleeping.   Long-stretch bandages. The typical long-stretch bandage is an elastic bandage that can be stretched to multiple times its resting length. If fully stretched, these bandages can provide a high dynamic and high resting pressure. The high dynamic pressure could be beneficial, but is often difficult to apply with uniform tension (see below) throughout. The high resting potential is problematic, and usually causes the wearer to remove the dressing at some point due to discomfort or signs of poor perfusion to the foot. On the other hand, if a long-stretch bandage is applied without tension, it will not be effective at producing either dynamic or resting tension. Many varieties of bandages fit between the two extremes of the non-stretch bandage and the elastic bandage, but the principle is the same: the more the bandage is stretched during application, the higher the pressure it will produce.   Tension. Bandage tension relates to how much the bandage is stretched while it is being applied. With an elastic bandage, the further the bandage is stretched, the higher the tension it will produce. Because tension (T) is in the numerator of the equation, an increase in tension leads to an increase in sub-bandage pressure if other factors remain the same.   Layers. In LaPlace’s Law, N represents the number of layers of the bandage applied. Like tension, this variable is also in the numerator so more layers applied leads to a higher sub-bandage pressure. Clinically, this variable becomes important when choosing a wrapping technique.   Technique. The most common wrapping techniques are spiral and figure 8 (also known as herring bone or criss-crossing). Spiral wrapping creates a 50% overlap of the wrap, resulting in exactly two layers of bandaging covering the leg (see Figure 1a). Figure 8 wrapping goes up the leg and then comes back down, creating a criss-crossing pattern which results in more layers and thus a higher pressure (see Figure 1b). Many of the multilayer compression bandaging systems will combine these techniques with some layers being applied in a spiral fashion and others in a figure 8.   A mistake made by clinicians not familiar with this concept is wrapping the remainder of a dressing around the top of the limb when the garment is too long. This increases the number of layers proximally and creates a tourniquet effect due to sub-bandage pressures that will be higher proximally than distally   Width. The width (W) of the bandage is the easiest parameter to change, as a different size bandage can be selected based on the goal. Bandage width is in the denominator of the LaPlace Law equation; a wider bandage will result in a smaller sub-bandage pressure if all other factors remain constant. The most clinically relevant aspect of bandage width is in the wrapping of the foot or hand, which is common with lymphedema. Because these areas are so much smaller than the leg, narrower bandages are used. This will increase the pressure, so care must be taken to ensure other factors are controlled, including limiting the number of elastic layers and not applying excessive tension.   Circumference. Limb circumference (C) is also inversely related to sub-bandage pressure. When applying a compression wrap to a thin leg, risk of breakdown is higher than when the same wrap is applied to a large leg. This portion of the equation works to the clinician’s advantage in a normally shaped limb, because it creates a natural pressure gradient with a higher pressure distally where the limb is small compared to the larger circumference proximally. It is more accurate to think of this variable in terms of radius of curvature rather than overall limb circumference, because even large limbs have prominent areas that will be subjected to higher pressures. The least complicated example of this principle in practice is a normal shaped limb with a prominent tibial crest and a muscular calf. When compression is applied, relatively low pressure is exerted on the posterior calf because the radius of curvature is large. The radius of curvature is much smaller on the tibial crest because the anterior portion almost comes to a sharp point. The small surface area to which the wrap is applying tension at this point results in a high pressure. This is the reason compression wraps that are too tight typically lead to breakdown over bony prominences, such as the tibial crest, malleoli, fibular head, and base of the fifth metatarsal, while less prominent areas remain intact. These areas should be padded appropriately to make them less prominent under the compression wrap (see Figure 2).   Patients with abnormally shaped limbs due to trauma and lymphedema also pose problems relating to limb size. As mentioned previously, the normal anatomy favors a compression gradient as the limb gets larger moving proximally. When areas of the distal limb are larger than proximal portions, the proximal portions will be subjected to higher pressures, potentially trapping the edema in the distal segments. This can be addressed by applying padding to restore the normal size gradient of the limb. If the compression wrap is wrapped too high, this same problem can occur as the calf gets smaller as it approaches the knee. This can be remedied by ending the compression wrap at the largest portion of the calf.

Summary

  Compression therapy is an excellent strategy for the management of edema, but it is not without risk. These risks are minimized when knowledge about the principles of compression are applied. By adjusting therapy according to these principles, compression wrapping can be used effectively, even in those with limbs that are not typical in size, shape, or would otherwise be subject to damage.

Resource

  McCulloch, JM. Assessing the circulatory and sensory systems. In: McCulloch JM, Kloth LC. Wound Healing Evidence-Based Management, 4th ed. Philadelphia, PA: FA Davis;2010:94–101. – Ed Mahoney, PT, DPT, CWS Assistant Professor of Physical Therapy Louisiana State University Health Sciences Center Shreveport, LA