Test the arterial system before using compression
Ischemic necrosis could result
By Liza G. Ovington, PhD
Program Director
Wound and Continence Management
Home Health Care Division, Southeast Florida
Columbia Healthcare Corporation
Ft. Lauderdale, FL
External gradient compression plays a vital role in the management of chronic ulcers of the lower extremities by controlling the concomitant edema and facilitating the action of the calf muscle pump. The "calf muscle pump" refers to the system of deep veins housed within the calf and surrounded by a compressive sheath of muscles and fascia. When calf muscles are contracted, these internal veins are compressed, intramuscular pressure rises, and venous blood is "pumped" upward to the heart to relieve venous pressure and reduce volume.
Compression is measured as millimeters of mercury or mm/Hg; 10-15 mm/Hg is considered low pressure, 25-45 is considered moderate, and above 45 is considered high pressure.
It is critical to assess the patient’s arterial system before initiating any sort of compressive therapy. If there is inadequate arterial supply, external compression may precipitate a disastrous result: ischemic necrosis. A common way to assess the arterial supply is to obtain an ankle brachial index (ABI). This consists of taking the systolic blood pressure at the ankle and dividing it by the systolic blood pressure at the brachial artery. If the arterial supply is adequate, this ratio should result in a number close to 1 or above. (Blood pressure at the ankle should usually be higher that that at the arm.)
If the ABI yields a number lower than 0.6, it may not be advisable to institute compressive therapy.
There are a number of modalities for supplying external compression to the lower extremities. It is important to know their features and benefits when selecting a modality for use by a particular patient. With multiple options for compression, the most important task for the clinician is to find one with which the patient will be compliant. Here are some of the types of compression bandages:
Unna boots
A very common type of static (nonelastic) compression bandage, the Unna boot was developed in the late 1800s by a German dermatologist, Paul Unna, MD. The Unna boot has come to be a generic term used to refer to any type of gauze bandage that has been impregnated with a paste containing zinc oxide and used to achieve static gradient compression on the lower extremities.
Unna boots are wrapped around the patient’s leg from the toes to just below the knee and can be applied as a continuous spiral or in shorter but consecutive lengths. The gauze strip(s) should be applied snugly but not tightly. Once the paste bandage has been applied, a second layer of stretch gauze can be applied over the top in a continuous spiral up the leg and finally topped with a self-adhering elastic bandage such as Coban (3M Company). Unna boots can be left in place for up to seven days depending on the drainage from the ulcer.
One potential disadvantage of these zinc oxide bandages is that both the patient and the clinician applying the wrap may find them quite messy because the zinc oxide paste comes off on hands.
Elastic bandages
Strips of elasticized bandages can be used to deliver gradient compression by wrapping them from the toes to just below the knees, using a specific methodology of "50% stretch" (or tension) and "50% overlap" to achieve desired compression.
To achieve 50% stretch, pull the bandage out to full extension and then relax it to approximately half stretch. The same level of stretch applied consistently as you go up the leg will result in gradient compression (pressure is highest at the ankle and lessens as you go up the leg) if the leg is larger at the top of the calf than at the ankle. If you use a lot more or less than 50% stretch of the bandage, you may get too much or too little compression.
The term "50% overlap" means that each subsequent spiral of the bandage strip overlaps the previous spiral by one-half. Again, if the overlap is less or more than 50%, you may achieve significantly less or more than the desired compression.
Because 50% stretch is a subjective quantity to measure in an elastic bandage, there are several bandages that have a rectangle printed on or woven into the fabric of the bandage. If these rectangles are stretched until they form a square, then you have a visual signal that you have achieved 50% stretch. Judging 50% overlap is easier, but there also are bandages that have a visible midline so you are better able to judge the overlap from one spiral to the next.
Most of the elastic wrap bandages can be washed up to 15 times for reuse. However, placing them in a dryer deteriorates the elastic.
Multiple-layer bandage systems
There are several versions of multiple-layer compression bandages commercially available. They are available as pre-packaged systems of either three or four bandage layers. The first layer is usually some type of padding (such as cotton batting or cotton wool or cast padding), applied as a continuous spiral. This layer is used to absorb potential exudate from the ulcer and to protect bony prominence at the ankles and normalize the subsequent pressure achieved from the next layers.
The second layer is usually crepe, applied as a spiral, which serves to smooth the padding layer and add absorbency. The third layer is elastic, applied with 50% stretch and 50% overlap. The fourth and final layer is usually an elastic self-adherent layer applied in a spiral, which keeps all the other layers in place. It has been suggested that use of these multiple-layer bandages results in more reproducible sub-bandage pressures.
Note that all of the aforementioned compressive modalities, which have to be wrapped up the leg, usually require the skill of a trained health care professional. These bandages should be applied when edema is at its lowest and with the leg positioned horizontally rather than perpendicular to the ground. Again, as with the Unna boot, the elastic bandages can be left in place for up to seven days with medical supervision.
A potential drawback of these wrapped bandages is that the layers can slip on the leg and result in tight areas that could create a tourniquet effect at the ankle. If the patient has a very small ankle (less than 18 cm), it is critical to increase the ankle circumference by padding it to avoid this potential effect.
Tubular bandages and compression stockings
A variety of tubular compression products do not require wrapping skills and can be pulled on over the leg like a sock or stocking. In general, they are elasticized in the horizontal plane relative to the leg and must be ordered according to the circumference of the patient’s leg at different anatomical points to deliver adequate and correct compression. If patients have adequate manual dexterity and strength, they often can apply these bandages without the assistance of a health care professional.
Compression stockings usually are used when the patient does not have an open ulcer, and they are mainly a preventative modality. They are specially fitted to each patient. Certain types of compression stockings are available with zippers, which make them easier for a patient to put on even if they have some degree of manual weakness. Most of these stockings are washable (again, not to be placed in the dryer) and are available in different pressure ranges according to the patient’s leg size. Compression stockings should be applied before getting out of bed and kept on all day.
Listed at left are representative examples of the different types of compression products which are commercially available.
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