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A New Concept in Patient Care: The Air-Fluidized Bed
A NEW CONCEPT IN PATIENT CARE: THE AIR-FLUIDIZED BED Thomas S. Hargest, B.A., and Curtis P . Artz, M.D.
The air-fluidized bed brings to the nurse a totally new concept in patient support and care. In the past, the patient has been supported by various types of mattresses. In an air-fluidized bed, the patient floats within the bed itself on a fluid which is composed of air and ceramic t3pheres.l This fluid is not to be confused with liquid which is wet. While an air-fluidized bed is difficult to describe, the principle behind it is reasonably simple: a particle of any size or shape can be suspended in an air stream when the volume and pressure are adequate to support it. The British Hover bed makes use of this principle in the actual suspension of burned patients in air to form eschar; however, it is not utilized in a continuous mode because of excessive air requirements and the drying effect.2 While the air-fluidized bed operates on a Thomas S. Hargest obtained his B.A. degree from Lafayette College, Easton, Pennsylvania. Mr. Hargest is Director of the Engineering Development Section, Deaartment of Surnerv. Medical Colleee of South Carolina, Charleston, South Carolina. Curtis P. Artz, M.D., is a graduate of Ohio State University School of Medicine, Columbus, Ohio. Dr. Artz is Professor of Sureerv and Chairman of the Department, Medical College of South Carolina, Charleston, South Carolina. His article, “Surgical Aspects of the Management of Severe Bums,” coauthored with Dabney R. Yarbrough, 111, M.D., a p peared in the February issue of the Journal. _
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similar principle, the density of the supporting medium is increased by the addition of the ceramic spheres. (Figure 1.) This system requires only five per cent of the air volume of the Hover bed; thus all the undesirable features of high-volume air flow are eliminated. In the air-fluidized bed, billions of spheres of extremely small size are suspended in jets of air, all spheres being isolated from one another by a thin air space. The medical-grade ceramic spheres are the heart of the system. (Figure 2.) Their controlled size and density are critical to its operation. To achieve the best fluidization, spheres of crown optical glass in the range of 75 to 125 microns are utilized. Since no free silica is present, danger from silicosis does not exist.“ The specific gravity of the glass is 2.5. The weight of the media is 82.4 pounds per cubic foot. When fluidized, an average void volume of about 37 per cent is provided. This means that 37 per cent of the bed volume is air under a pressure Of less than One pound per inch. The ceramic spheres are isolated from direct contact with the patient by a sheet of square weave, mOnofilament Polyester closely knit to a controlled porosity of 37 microns, and providing 23 per cent pore space. This weave adequately retains all the spheres
AORN Journal
DIAGRAM OF AIR BED
M[D,A
DIFFU5tR
U
I
L
y
AIR INPUT
Figure 1. Diagram of air-fluidized bed showing position of the patient.
within the bed, but permits free passage of the air through the sheet and around the patient. A 12-inch depth of ceramic spheres will increase in volume by less than one-half inch when fluidized. In this state, the bed has a specific gravity of 1.3. Thus having a density somewhat greater than tap water, it can provide a bit more buoyancy without the instability and shifting normally associated with liquids. It is the factor of buoyancy, then, that is so unique to this device, separating it from all other types of beds in its method of support. The substitution of the large, thin filter sheet for the impervious rubber sheet of the water bed permits true floating of the body, thus reducing the pressures to those relating to the depth of penetration into the fluidized mass. Therefore, the maximum pressure at a four-inch depth, normal penetration, is actually less than 10 mm Hg. This means that in the air-fluidized bed when penetration is normal, the maximum pressure exerted cannot exceed the mean capillary blood pressure on any part of the body.4 Since decubitus ulcers are caused by three factors, compression, shearing force and moisture, acting either independently or together, the elimination of all those factors should end the problem. The air-fluidized bed accomplishes this result. Since temperature and humidity are controlled, moisture cannot accumulate. Because the fluidization of the bed removes all compression and shear forces, patients with decubitus ulcers actually heal
September 1969
while lying upon the damaged t i s ~ u e .In ~ the treatment of deep, second-degree burns, this factor might be of singular importance in the prevention of further deterioration of affected areas. Since the phenomenon of floating is the most gentle type of support that can be created, the patient will experience the least amount of discomfort while resting or being turned in the course of normal care, treatment or examination. Subjective tests indicate that many people troubled by insomnia sleep without drugs, and all patients find the bed comfortable and relaxing. It is a combination of these beneficial factors which suggests that the air-fluidized bed will be readily accepted by nursing personnel. Care of the difficult patient is reduced to simple procedures; the troublesome and demanding patient frequently becomes quiet and well-behaved. Turning is not necessary for the patient suffering from decubitus ulcers. The patient with skin grafts or flaps may lie upon those areas without the danger of pulling them loose. Several patients have remained in one position for periods of two to three weeks without developing any symptoms of respiratory difficulty. Changing the undersheet can be accomplished in less than a minute. Bed pans are placed by floating them under the patient, rather than having to lift him. They may be easily forgotten, however, because their presence is not obvious to the patient. Both general attitude and comfort are so substantially improved that few demands are made of the nurse. In some cases, the patient actually becomes “hooked” on the bed rather than drugs. Studies are underway to determine the effects of this fixation. Operation of the bed is simple and stable. (Figure 3.) The bed temperature can be controlled to one-half of one degree. Should the power fail, the patient is supported upon a contoured couch which will lose heat at the rate of only about 2°F. per hour.
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Figure 2. ( T o p ) Ceramic Spheres beside a human hair. Note the uniform size and shape. (Bottom) Spheres at high magnification showing stained bacteria at point of contact.
Humidity can also be controlled, but since this is really a function of pore space rather than the inert glass bead, it can be changed rapidly. (Figure 4.) One of the most interesting aspects of this bed is its continued sterility. Originally, it was believed that cleaning the bed and keeping the media from becoming contaminated would be our greatest problem. After ten months of examining weekly cultures, each of which has been negative, a study was made to determine the reasons for this bactericidal effect. It was learned that the high pH of the spheres is not conducive to growth, and that rapid desiccation and mechanical trauma are additional factors which are highly deleterious to bacterial survivaL6 The clumping that occurs when any liquid enters the bed isolates that contamination from the rest of the media. The cluster sinks to the diffuser and, there, is dried by the air entering the bed. These three factors-high pH, desiccation
52
Figure 3. Air-fluidized bed with control panel visible.
and trituration-are so effective that the possibility of infection or reinfection of the patient from the media practically does not exist. Maintenance of the equipment is quite simple. Changing the filter sheet and screening the media should be done at weekly intervals and can be accomplished in ten minutes or less. The only moving parts are two heavy duty motors, one of which drives the blower, the other, a simple electric fan. Both the blower and fan are of industrial quality. Replacement parts for the sensing system and heater elements are available at any electrical supplier. Thus, the development of the air-fluidized bed provides the physician with the ultimate in patient support; the patient with the most comfortable situation possible, and the nurse with a system that requires a minimum of physical effort in patient care. All this is accomplished by one hundred billion ceramic spheres and the continuous flow of warm air.
AORN Journal
Figure 4. Alternate control panel. REFERENCES
1. Hargest, Thomas S., “A Ceramic Application in Patient Care,” Hulbert, S. F., and Young, F. A., Eds., Use of Ceramics in Surgical Implants, Gorden and Breach, New York, 1969. 2. Medical World News, October 13, 1967, pp. 34-35. 3. “For Abrasive Glass Beads,” Military Specification MILA-9954 (R.S.A.F.) 25 May 1962, Para. 3.2. 4. Pfandler, M., “Flotation, Displacement and Decu-
bitus Ulcers,” American Journal of Nursing, 68:2351, 1968.
nomas
5. ~ ~J. Shad, ~ and~ H~~~~~~ i ~ s., , “The Air-Fluidized Bed: A New Concept in the Treatment of Decubitus Ulcers,” Plastic and Reconstructive Surgery (at press).
6. Unpublished Data.
“Stress is by no means always harmful. I t accompanies dl activity, and it suppresses disease much more often than it produces it. Besides, activity is the spice of life; stress cannot and should not be avoided. I t is absent only in the dead. The lesson here is certainly not to avoid stress and sink into passivity, but on the contrary to learn to live with stress and enjoy an active life.” (The Picomeao, Pinellas Co., Flu.)
September 1969
53
The air-fluidized bed brings to the nurse a totally new concept in patient support and care. In the past, the patient has been supported by various types of mattresses. In an air-fluidized bed, the patient floats within the bed itself on a fluid which is composed of air and ceramic t3pheres.l This fluid is not to be confused with liquid which is wet. While an air-fluidized bed is difficult to describe, the principle behind it is reasonably simple: a particle of any size or shape can be suspended in an air stream when the volume and pressure are adequate to support it. The British Hover bed makes use of this principle in the actual suspension of burned patients in air to form eschar; however, it is not utilized in a continuous mode because of excessive air requirements and the drying effect.2 While the air-fluidized bed operates on a Thomas S. Hargest obtained his B.A. degree from Lafayette College, Easton, Pennsylvania. Mr. Hargest is Director of the Engineering Development Section, Deaartment of Surnerv. Medical Colleee of South Carolina, Charleston, South Carolina. Curtis P. Artz, M.D., is a graduate of Ohio State University School of Medicine, Columbus, Ohio. Dr. Artz is Professor of Sureerv and Chairman of the Department, Medical College of South Carolina, Charleston, South Carolina. His article, “Surgical Aspects of the Management of Severe Bums,” coauthored with Dabney R. Yarbrough, 111, M.D., a p peared in the February issue of the Journal. _
I
I
I
50
.
similar principle, the density of the supporting medium is increased by the addition of the ceramic spheres. (Figure 1.) This system requires only five per cent of the air volume of the Hover bed; thus all the undesirable features of high-volume air flow are eliminated. In the air-fluidized bed, billions of spheres of extremely small size are suspended in jets of air, all spheres being isolated from one another by a thin air space. The medical-grade ceramic spheres are the heart of the system. (Figure 2.) Their controlled size and density are critical to its operation. To achieve the best fluidization, spheres of crown optical glass in the range of 75 to 125 microns are utilized. Since no free silica is present, danger from silicosis does not exist.“ The specific gravity of the glass is 2.5. The weight of the media is 82.4 pounds per cubic foot. When fluidized, an average void volume of about 37 per cent is provided. This means that 37 per cent of the bed volume is air under a pressure Of less than One pound per inch. The ceramic spheres are isolated from direct contact with the patient by a sheet of square weave, mOnofilament Polyester closely knit to a controlled porosity of 37 microns, and providing 23 per cent pore space. This weave adequately retains all the spheres
AORN Journal
DIAGRAM OF AIR BED
M[D,A
DIFFU5tR
U
I
L
y
AIR INPUT
Figure 1. Diagram of air-fluidized bed showing position of the patient.
within the bed, but permits free passage of the air through the sheet and around the patient. A 12-inch depth of ceramic spheres will increase in volume by less than one-half inch when fluidized. In this state, the bed has a specific gravity of 1.3. Thus having a density somewhat greater than tap water, it can provide a bit more buoyancy without the instability and shifting normally associated with liquids. It is the factor of buoyancy, then, that is so unique to this device, separating it from all other types of beds in its method of support. The substitution of the large, thin filter sheet for the impervious rubber sheet of the water bed permits true floating of the body, thus reducing the pressures to those relating to the depth of penetration into the fluidized mass. Therefore, the maximum pressure at a four-inch depth, normal penetration, is actually less than 10 mm Hg. This means that in the air-fluidized bed when penetration is normal, the maximum pressure exerted cannot exceed the mean capillary blood pressure on any part of the body.4 Since decubitus ulcers are caused by three factors, compression, shearing force and moisture, acting either independently or together, the elimination of all those factors should end the problem. The air-fluidized bed accomplishes this result. Since temperature and humidity are controlled, moisture cannot accumulate. Because the fluidization of the bed removes all compression and shear forces, patients with decubitus ulcers actually heal
September 1969
while lying upon the damaged t i s ~ u e .In ~ the treatment of deep, second-degree burns, this factor might be of singular importance in the prevention of further deterioration of affected areas. Since the phenomenon of floating is the most gentle type of support that can be created, the patient will experience the least amount of discomfort while resting or being turned in the course of normal care, treatment or examination. Subjective tests indicate that many people troubled by insomnia sleep without drugs, and all patients find the bed comfortable and relaxing. It is a combination of these beneficial factors which suggests that the air-fluidized bed will be readily accepted by nursing personnel. Care of the difficult patient is reduced to simple procedures; the troublesome and demanding patient frequently becomes quiet and well-behaved. Turning is not necessary for the patient suffering from decubitus ulcers. The patient with skin grafts or flaps may lie upon those areas without the danger of pulling them loose. Several patients have remained in one position for periods of two to three weeks without developing any symptoms of respiratory difficulty. Changing the undersheet can be accomplished in less than a minute. Bed pans are placed by floating them under the patient, rather than having to lift him. They may be easily forgotten, however, because their presence is not obvious to the patient. Both general attitude and comfort are so substantially improved that few demands are made of the nurse. In some cases, the patient actually becomes “hooked” on the bed rather than drugs. Studies are underway to determine the effects of this fixation. Operation of the bed is simple and stable. (Figure 3.) The bed temperature can be controlled to one-half of one degree. Should the power fail, the patient is supported upon a contoured couch which will lose heat at the rate of only about 2°F. per hour.
51
Figure 2. ( T o p ) Ceramic Spheres beside a human hair. Note the uniform size and shape. (Bottom) Spheres at high magnification showing stained bacteria at point of contact.
Humidity can also be controlled, but since this is really a function of pore space rather than the inert glass bead, it can be changed rapidly. (Figure 4.) One of the most interesting aspects of this bed is its continued sterility. Originally, it was believed that cleaning the bed and keeping the media from becoming contaminated would be our greatest problem. After ten months of examining weekly cultures, each of which has been negative, a study was made to determine the reasons for this bactericidal effect. It was learned that the high pH of the spheres is not conducive to growth, and that rapid desiccation and mechanical trauma are additional factors which are highly deleterious to bacterial survivaL6 The clumping that occurs when any liquid enters the bed isolates that contamination from the rest of the media. The cluster sinks to the diffuser and, there, is dried by the air entering the bed. These three factors-high pH, desiccation
52
Figure 3. Air-fluidized bed with control panel visible.
and trituration-are so effective that the possibility of infection or reinfection of the patient from the media practically does not exist. Maintenance of the equipment is quite simple. Changing the filter sheet and screening the media should be done at weekly intervals and can be accomplished in ten minutes or less. The only moving parts are two heavy duty motors, one of which drives the blower, the other, a simple electric fan. Both the blower and fan are of industrial quality. Replacement parts for the sensing system and heater elements are available at any electrical supplier. Thus, the development of the air-fluidized bed provides the physician with the ultimate in patient support; the patient with the most comfortable situation possible, and the nurse with a system that requires a minimum of physical effort in patient care. All this is accomplished by one hundred billion ceramic spheres and the continuous flow of warm air.
AORN Journal
Figure 4. Alternate control panel. REFERENCES
1. Hargest, Thomas S., “A Ceramic Application in Patient Care,” Hulbert, S. F., and Young, F. A., Eds., Use of Ceramics in Surgical Implants, Gorden and Breach, New York, 1969. 2. Medical World News, October 13, 1967, pp. 34-35. 3. “For Abrasive Glass Beads,” Military Specification MILA-9954 (R.S.A.F.) 25 May 1962, Para. 3.2. 4. Pfandler, M., “Flotation, Displacement and Decu-
bitus Ulcers,” American Journal of Nursing, 68:2351, 1968.
nomas
5. ~ ~J. Shad, ~ and~ H~~~~~~ i ~ s., , “The Air-Fluidized Bed: A New Concept in the Treatment of Decubitus Ulcers,” Plastic and Reconstructive Surgery (at press).
6. Unpublished Data.
“Stress is by no means always harmful. I t accompanies dl activity, and it suppresses disease much more often than it produces it. Besides, activity is the spice of life; stress cannot and should not be avoided. I t is absent only in the dead. The lesson here is certainly not to avoid stress and sink into passivity, but on the contrary to learn to live with stress and enjoy an active life.” (The Picomeao, Pinellas Co., Flu.)
September 1969
53