THE LOW AIR LOSS BED SYSTEM IN TREATMENT OF BURN PATIENTS

Landi, 0., Catrani S., Mengozzi E, Greco 1, Erbazzi A., Arcangeli F., Feletti S.

Civisione Dermatologica, Centro Ustioni, Ospedale Bufalini, USL 39, Cesena, Italia

SUMMARY. In the new Mediscus Mark 5A-M low air loss bed the patient lies on a mattress formed by five groups of air sacs, adjustable in each section to different air pressure and made of material permeable to water-vapour. This prevents the formation of pressure sores and ensures that the patient's skin is kept dry in a comfortable and controlled warm air atmosphere. In cases of severe burns the patient can be nursed supine for long periods without being turned and there is no friction against painful burn wounds. When skin grafts are applied, the patient may be placed on the bed resting on the grafts without significant damage. The bed can be easily positioned in order to achieve maximum patient comfort and it can be adapted to accommodate any medical emergency. The recent experiences with two low air loss beds in the care of burn patients over a period of six months are described.

Damage to the skin and soft tissues following prolonged decubitus of the patient in a conventional bed is known to be caused by excessive pressure of the skeleton on the soft parts, with values 4-5 times as high as that of the pressure within the capillaries, which is about 26 mm Hg. If these local conditions persist, the collapse of the capillaries and the veins leads to functional circulatory disturbances, at first transitory but later permanent, followed by organic damage with cutaneous necrosis spreading to the subcutaneous tissue, the fascia, the muscles and the bones.
Further damage is caused by friction between skin and bedsheet due to gravitational slipping and by imperfect cutaneous evaporation at the pressure points.
All thesel negative conditions are aggravated in the burn patient, who presents impaired circulatory function, serious cutaneous damage, with necrosis and fluid losses due to exudation and evaporation. To obviate these conditions Scales proposed to support the critical burn patient on an air cushion - as if in levitation - without any physical membrane, according to the hovercraft principle. In view of the technical problems deriving from the considerable air loss and of the negative psychological effects induced by this method in the patient, we used an actual air cushion, covered in material which reduced air loss and offered a number of important advantages: the Low Air Loss Bed System (LALBS).
This system is intended to ensure body contact over the largest area possible, distributing an appropriately low pressure throughout the contact surface and allowing adequate evaporation at the contact points.
The LALBS model at our Burns Centre (Mediscus Mark 5A-M Bed, Fig. 1) consists of a series of 21 air sacs made of nylon and microporous polyurethane, impermeable to water but permeable--water-vapour, divided into five groups. Each group is maintained at a selected pressure and controlled by differently coloured manometers (Fig. 2). The same colours identify the five sections corresponding to the head, trunk, pelvis, thighs and legs. The pressure in the sacs can reach 36 cin H 2 0, but does not normally exceced 29 em H 2 0. In the sections for contact of the lower limbs, the pressure may be as low as half that for the trunk (Fig. 3).
An electric pump conveys air into the sacs and a system of valves maintains the air at the desired pressure in each of the five sections. The influx is about 1,400 litres per minute. The air is heated electrically and thermostatically controlled with a digital monitor. Air escapes through the lateral seams of the sacs together with water-vapour emitted by the patient. This continual flow maintains a constant

Fig. 1: The Mediscus Mark 5A-M Low Air Loss Bed System. Fig. 2: Control panel at foot of Mark 5A-NI bed with manometers for the 5 air sac sections, thermometer and digital thermostatic control monitor.

The patient rests directly on the sacs, in order to avoid alterations of decubital pressure or other undesired complications. In emergency conditions a sheet, if possible made of the same material as the sacs, is stretched between the sacs and the patient. Because of their smoothness and fine texture, the sacs permit easy moving of the patient on the surface of the bed (Fig. 4). Nursing manoeuvres are facilitated by the capacity of the new model of the LALBS bed to inflate instantly all the sacs to maximum pressure, thus creating a more rigid and uniform resting surface for the time required temperature in the patient's immediate environment, facilitates sterility and keeps the wound and contact surfaces dry.

Accidental perforation of a sac does not impair the functioning of the system, which continues to operate also when it is necessary to remove individual sacs for cleaning. All the sacs are cleaned daily with a 1% Savlon solution or soap and water. Bacteriological swabs are taken regularly from the sacs in the various sections and from the filters in the pumping system. Periodically all the sacs are specially washed at a temperature of 25 'C in a washing-machine, using soap powder, and then hung up to dry at ambient temperature.

Fig. 4: Movement of the patient on the bed surface is facilitated by the smooth, fine texture of the sacs and their continuous adaptation to body position.

Another feature of the new model is that the pumping, heating and control system is mounted directly at the foot of the bed. It is also now possible to deflate only the section corresponding to the pelvis, making it easier for the patient to get off and on the bed. All the sacs can be deflated in 5 seconds so that in the event of cardiac arrest resuscitation can be initiated with the necessary urgency.
Apart from these extreme conditions, the LALBS bed is satisfactory for all the patient's normal needs, in the various positions and clinical conditions. One electric and two pneumatic systems make it possible to raise the head and the foot sections of the bed by up to 30' and the whole support surface can be positioned in Trendelenburg or anti-Trendelenburg. A control panel enables staff and the patient himself to select the position preferred: this reduces nursing commitments and greatly increases comfort, as the burn patient no longer suffers pain at every change of position because of friction against the bedsheets.
Skin grafts, when applied, can be maintained in position for some days with vaselined gauzes and thin containing dressings, and then left uncovered, with little risk of trauma and considerable reduction in the time required for the graft to take and consolidate.
When it is necessary to apply a bandage, the procedure is facilitated by the patient's low resting pressure, so that it is easy to pass hand and bandage under the burns with minimum discomfort for the patient. The same holds true for drainage tubes, catheters, etc.
In cases of multiple trauma it is possible to use the orthopaedic traction apparatus accessory (Fig. 5), with which the two 1ALBS beds in our Centre were fitted some months ago.

RESUME. Le lit LALBS (Low Air Loss Bed System) à air chaud prévient les plaies de décubitus et permet au patient brûlé de maintenir les lésions sèches aussi aux points d'appui et de recevoir les médications sans mouvements douloureux. Dans ces conditions les greffes cutanées s'attaquent mieux et elles sont moins facilement traumatisées. Il y a un bon niveau de confort pour le patient et une réduction de l'assistance nécessaire des infirmiers.

BIBLIOGRAPHY 

1. Leeder CJ.: Use of the low air loss system in treatment of burns patients. Scand. J. Plast. Reconstr. Surg., 13: 159, 1979.
2. Scales J.: Pressure sore prevention. Care Science Pract., 1: 2, 1982.
3. Scales J.T., Lunn H.F., Jeneid P.A., Gillingham M.E., Redfern S.J.: The prevention and treatment of pressure sores using air-support systems. Paraplegia, 12: 118, 1974.
4. Wyllie F.J., McLean N.R., McGregor J.C.: The problem of pressure sores in a regional plastic surgery unit. J. Roy. Coll. Surg. Edinb., 29: 38, 1984.