What is a pressure ulcer ?

Pressure ulcers occur when there is a localised area of cellular damage to tissue which was previously viable. Damage can involve superficial tissue, to multiple tissue layers. Damage can be caused by extrinsic factors and exacerbated by intrinsic factors.

The cause of pressure ulcers in the majority of cases is direct pressure applied to the supporting tissue layers. The ulcers being caused by unrelieved pressure that results in capillary occlusion. The capillary pressure that is widely quoted is 32 mmHg [Landis - see References] but this is a mean value and capillary pressures can be much lower or higher (11-120 mmHg) than the mean depending on the patient's health, age, fitness, nutrition, or area over which the pressure is being applied. Pressure ulcers are found to be more common over bony areas of the body. When the skin and underlying tissue is compressed between bone and a hard support surface, damage to the tissues can occur within two hours, resulting in damage to the microcirculation and ischaemia. Direct pressure ulcers such as these are referred to as Type I pressure ulcers [Barton et al - see References].

Shear Force

Shear forces are the forces transferred internally to the patient and the supporting surface when they are placed under load usually in opposite directions to the applied load or movement. Thus shear force components act in the opposite direction to patients load or movement. It is important to note that shear force components may work in many directions between the support surface and the patient dependent on the direction of loading. Shear occurs when the patient is moved or handled incorrectly, eg. being dragged instead of lifted clear of the supporting mattress surface. Shear forces are also created when the bed is tilted in any direction causing a load on the patients tissues due their weight. Shear is an important factor to consider in elderly patients because of the loss of elastin, which leaves their skin with minimum flexibility and elasticity. The damage is caused when underlying muscle fibres and subcutaneous tissues are ripped and separated. When this occurs there is a release of clotting factors within the tissue and blood clots occur which block the microcirculation. Shear force ulcers are referred to as Type II ulcers [Barton et al - see References].

Friction

Friction is the resistance to movement between two surfaces when subjected to forces parallel to the two surfaces. When this  occurs between two surfaces shear forces are produced within those two surfaces. Therefore the greater the friction between two surfaces the greater the shear force component is within the two surfaces. Friction occurs between the patient and the support surface. eg support mattress covers, or X-ray trolley. Friction is increased by moisture and temperature which change the characteristics of the support surface. This is an important consideration if the patient is incontinent or has a raised body temperature. It is more common in areas where the papillary layer, which anchors the dermis, such as in the back. Friction ulcers often occur when the patient repeatedly slips down the bed, especially with the use of back rests or when the bed is elevated. Friction ulcers are referred to as Type II ulcers [Barton et al - see References].

Intrinsic factors

Any systematic condition that compromises the peripheral vascular circulation, eg. renal failure, congestive cardiac failure, diabetes. Patients with a terminal illness especially patients with cachectic conditions. If the patient suffers from immobility due to physical illness, disability or psychological state. Patients who are sedated ranging from anaesthesia to antidepressants. Patients who are malnourished, being emaciated or having a deficient diet. Patients who are incontinent causing excoriation and maceration of the skin.

Removal of extrinsic factors

The use of the correct lifting equipment and positioning techniques to minimise skin injury. Use a 30 degree tilt when placing patients on their side in bed. The maintenance of ambient room and body temperature is important. It is also important to avoid the use of damaged equipment such as back rests, chairs, supports. If the patient has to undergo further investigations it is important to avoid long waiting times in X-ray or casualty, on hard surfaces not equipped with special mattresses.

Minimising intrinsic factors

Refer all patients to the dietitian for nutritional assessment when they fall into a high risk category without an active ulcer, or they have an established ulcer. If the patient has a pressure ulcer, the patients calorie intake should be  3500-4500 calories per day, to combat catabolic effects of tissue breakdown. An adequate fluid intake should be maintained to combat dehydration and levels of vitamin C, zinc and iron should also be maintained to enhance wound healing. Incontinence should be controlled with bladder training or use of incontinence device. If incontinence cannot be controlled, avoid the use of incontinence pads which can increase friction. Treatment of any underlying systemic diseases should also be continued.

Pressure ulcer cleansing

Skin Care

Inspect skin and document daily. Avoid the use of hot water and rubbing (friction) or massage over bony prominences. The use of mild cleansing agents and moisturisers on dry skin is recommended. See dressing selection page for dressings.
 
 For further information see the Wound Management Good Practice Guidance, Published by the Journal of Wound Care.

* Wound healing research Unit WHRU
* Dundee University
* SMTL Links Page
* US National Library of Medicine
* Merck Manual
* Tissue Viability Society
* Waterlow Score Website