Last updated: Dec 2004
Keywords: compression bandaging; four-layer system; chronic venous insufficiency; venous ulceration; pathophysiology of compression; wound healing.
Sustained compression is the most important factor in the conservative management of venous leg ulcers.
Compression using four-layer bandaging causes a variety of physiological and biochemical effects involving haemodynamic and lymphatic function.
Four-layer bandaging provides sustained compression but also tackles the complex clinical problems associated with leg ulceration.
Four-layer bandaging has been in existence for more than 15 years, during which time it has been used in numerous studies and in many populations throughout the world. This short series reviews the development of the four-layer compression bandage system together with the evidence that contributes to a greater understanding of why it is effective in promoting healing in venous leg ulcers. This article looks at the development of the four-layer system and current understanding of the mechanisms of action.
Compression therapy is widely accepted as the cornerstone of venous leg ulcer treatment and often has a dramatic effect on outcome, with patients reporting reduced pain and improved mobility and general quality of life as a result of their ulcers healing , .
Unlike many clinical developments in wound care, four-layer bandaging was not developed by the wound care industry but by a clinical group at Charing Cross Hospital, London, with an appreciation of what was required for an effective compression system. The group used Stemmer's theoretical framework, which suggested that an external pressure of at least 40mmHg at the ankle was required to achieve ulcer healing in patients with chronic venous insufficiency, with lower levels of compression required for those with varicose veins and higher levels for those with venous and/or lymphatic disorders . The concept underlying the development of the system was the requirement for sustained compression, which could be achieved using a multi-layer bandage system.
In the four layer technique a wool bandage is applied from the base of the toes to just below the knee joint. This is followed by the application of a crepe bandage. Next an elastic compression bandage is applied in a figure of eight, followed by a final cohesive layer.
The development of the four-layer bandage system also took account of the considerable clinical problems experienced, such as high levels of exudate and disproportionate limb size and shape. In addition, there was a practical requirement to reduce the number of visits required as most patients were seen daily, with the aim to develop a system that required weekly application only. This has contributed significantly to the cost-effectiveness of the four-layer bandaging system as it has resulted in significant reductions in nursing time , .
In attempting to review four-layer bandaging, it is important to consider what is known concerning the role of compression in promoting venous ulcer healing. Although it has been shown to impact on haemodynamic and lymphatic function, the exact mechanisms of action remain poorly understood , , , . Partsch has described the current thinking behind the mechanisms of compression, which is summarised below .
The reduction of oedema is a vital aspect of an effective compression system . Compression helps to counteract the loss of capillary fluid by ultrafiltration and also reduce its accumulation in the interstitium (Starling's equilibrium). Where there is an oncotic pressure gradient across a semi-permeable membrane (ie a capillary wall), it causes fluid to be drawn across the capillary membrane to achieve equal concentrations on both sides. Starling's equation summarises the relationship between these factors (Box 1). This suggests that the application of external compression counteracts the loss of capillary fluid by increasing local tissue pressure and reinforces reabsorption by squeezing fluid into the veins and lymph vessels .
It is thought that compression acts on the venous system in a number of ways to improve healing. In patients with competent valves, the flow of the blood back to the heart is achieved through the combined action of the calf muscle pump and the foot pump. In those with venous disease the valves may be damaged, causing the blood to flow back into the veins of the lower leg (venous reflux), producing high ambulatory pressures in the venous circulation in the upright position (ambulatory venous hypertension) . Patients with venous disease and ulceration often have ambulatory pressures in excess of 90mmHg , which compares with 10-20mmHg in individuals with functioning valves.
Compression has been shown to reduce venous reflux ,  and increase blood flow towards the heart, which may be a significant factor in achieving ulcer healing . In particular, four-layer bandaging has been found to significantly decrease venous reflux in patients with proven popliteal deep venous incompetence . The same study also found that elastic, long-stretch bandage systems applied with pressures of up to 40mmHg failed to reduce reflux .
In a standing individual blood flows slowly through the veins. During walking blood flow is increased due to the combined action of the calf muscle pump and the foot pump. Many patients with chronic venous disease develop a significant reduction in calf muscle pump function . This may be due to reduced general mobility, or more importantly, ankle mobility . Studies have shown that in patients with reduced or absent ankle movement, venous ulcer healing is significantly reduced , , . External compression has been shown to have a significant effect on the venous pump, with an increased expelled volume , .
By applying an adequate level of compression the diameter of veins may be reduced in both the superficial and deep system, although this does not occur in all patients . Reducing the diameter of the veins has the effect of decreasing the venous blood volume in the lower limb , . Using radioactive methods, Partsch showed that by applying an external pressure of 40mmHg the venous volume is reduced in the horizontal position; a similar effect was found in the upright position using air plethysmography .
Compression therapy has been shown to improve superficial skin lymphatic function as well as lymph transport within the subfascial system . Stimulation of lymph formation and lymph flow through enhanced vasomotion within the lymphatics increases overall lymph transport and therefore the removal of fluid from the interstitial tissues to the venous system .
A number of studies have shown the important effect of compression on stimulating fibrin removal through fibrinolysis , , , . Removal of protein-rich oedema through enhanced lymphatic function is also important in slowing and reversing the proliferation of dermatosclerotic connective tissue. Compression has been shown to normalise skin lymphatics in lipodermatosclerosis .
A number of authors have examined the effect of compression on venous and arterial microcirculation. It is thought that compression may play an important role in preventing transient ischaemic reperfusion injury to the endothelium and therefore the development of venous ulceration , . Mayrovitz and Larsen found that compression accelerates blood flow in the microcirculation and suggest that this may promote the movement of neutrophils through the microcirculation. This helps to prevent tissue necrosis by reducing the risk of neutrophil margination and adherence to the endothelium together with a reduction in the risk of activation and release of free radicals . Improved blood flow was not maintained when the sub-bandage pressure fell over time, reinforcing the need to provide a sustained level of compression .
One study noted that distal toe perfusion was reduced in healthy volunteers, even though sub-bandage perfusion pressures remained unaltered . This was thought to be due to a compensating reflex vasodilatory effect beneath the bandage. However, these effects were not adequate to compensate for reductions in distal perfusion . This study reinforces the need for caution in the over-ambitious use of compression in patients with significant concurrent peripheral vascular disease.
The four-layer bandaging has gained considerable momentum as a treatment method in the last 15 years. While widely accepted as the cornerstone of venous ulcer treatment, and based on sound pathophysiological principles, the exact mechanisms which lead to healing remain poorly understood. However, providing the right materials and application technique are used, there can be few interventions that have such dramatic effects on outcome in patients with venous leg ulceration.
The second article will consider clinical indications for use and application of the four-layer bandaging system.
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