P ressure ulcers present a serious and common problem, especially in the elderly. More than 1 million individuals develop pressure ulcers annually.1 The prevalence of pressure ulcers has been reported as 11% in skilled-care and nursing homes,2 10% in the acute care setting,3 and 6.8% in the home care setting, with a range of 0.5% to 35.7% reported between agencies.4 In 2001, the National Pressure Ulcer Advisory Panel reported an incidence rate of pressure ulcers from 2.2% to 23.9% in long-term care settings.5
Pressure ulcers impair quality of life because of pain, stress, and loss of independence leading to grief reactions,6 depression, and social isolation.7-9 Furthermore, treatment of pressure ulcers is costly. In 1994, Miller and Delozier,10 in a publication sponsored by the Agency for Health Care Policy and Research (AHCPR), estimated that the total national cost of pressure ulcer treatment exceeded $1.35 billion annually. In 1999, Berkrich11 reported an estimated yearly cost to treat 1 to 1.7 million hospital-acquired pressure ulcers, limited to an acute care setting, at $5 billion to $8.5 billion. Reports of estimates of costs to treat pressure ulcers have ranged from $4,000 to $40,000, depending on the stage of the pressure ulcer.12
Cost estimates for treatment are related to pressure ulcer severity.13 Optimal care of more severe ulcers requires increased time and resources. In 1996, Xakellis and Frantz14 reported the average cost for treatment of Stage II ulcers as $1,119, versus $10,185 for Stage III and IV ulcers, across healthcare settings. Treatment costs escalate when patients require hospitalization for complications. Pompeo15 coined the term “wound burden” to classify wounds according to their stage and size as follows: Class 1 (Stage II: <5 cm2), Class 2 (Stage II: >5 cm2), Class 3 (multiple Stage II or single Stage III: <5 cm2), Class 4 (Stage IV: <5 cm2), and Class 5 (Stage III or Stage IV: >5 cm2 or multiple Stage III or Stage IV). Using this approach, Pompeo found a statistically significantly greater cost for wound care with an increasing wound burden. For example, total average costs per patient in a long-term acute care hospital with Class 4 pressure ulcers (N = 71) were $54,954 as compared to an average cost of $38,228 for those with Class 3 pressure ulcers (N = 89).
Pompeo further contends that these analyses grossly underestimate the true cost of wound care because most studies base cost estimates on acute care settings, while the majority of costs occur in long-term care. Additionally, while prevalence rates are generally estimated using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD 9-CM) codes such as 707.0 for decubitus, many ulcers are not coded.15 In fact, in the National Health and Nutrition Survey Examination Study follow-up (NHANES1), Guralnik16 reported that only 9 out of 54 pressure ulcers were reported in discharge summaries; in the other 45 cases, patients or their representatives subsequently identified pressure ulcers.
The impact of pressure ulcers is highlighted by a four-fold increased risk of death in geriatric patients who develop a pressure ulcer; this risk is increased to six times when the pressure ulcer does not heal.17 Furthermore, as pressure ulcers increase in severity, the probability of healing decreases, while morbidity and mortality increase. A marked risk of complications from pressure ulcers occurs in nursing home or home care settings; in one study, the cumulative incidence did not plateau after a 2-year follow-up period.18
Pressure reduction is a crucial component of pressure ulcer treatment; redistribution of the tissue load and improved circulation allow pressure ulcers to heal. Pressure reduction is provided by specialty beds, including air-fluidized therapy (Group 3); low-air-loss beds, powered, and non-powered overlays or mattresses (Group 2); and, to some extent, static overlays and replacement mattresses (Group 1). Air-fluidized therapy, initially developed in the 1960s, provides an effective treatment that not only reduces pressure, but also reduces friction and shear forces and decreases moisture.19,20 Support for improved healing with air-fluidized therapy has been reported in a variety of randomized trials and clinical reports.21-29 However, few large clinical outcomes studies have directly compared the relative effectiveness of air-fluidized therapy with that of other specialty support surfaces. This retrospective study was designed to compare the relative effectiveness of different support surface groups using existing data from the National Pressure Ulcer Long-Term Care Study (NPULS).
The primary objective of this study was to compare the healing rate of pressure ulcers in nursing home residents placed on air-fluidized therapy, designated as Group 3 support surfaces, with that of residents placed on Group 1 and Group 2 support surfaces. Changes in wound size, reported as cm2/week, represent the primary measure of healing rate. Support surfaces are grouped according to the description outlined by the Agency for Healthcare Research and Quality (AHRQ)1,30 and used by the Centers for Medicare and Medicaid Services (CMS).31
Secondary objectives included assessment of the residents’ rate of hospitalization and emergency room visits and evaluation of healing rates in pressure ulcers with a comparable baseline size. In addition, regression analyses were used to evaluate various parameters that affect healing, described in the section on the NPULS study (see below), obtained from the resident’s chart or from ICD-9-CM codes. Variables were not included in the analysis if data were missing for a substantial number of residents in the subset or if the data were ambiguous.
Use of pressure reducing surfaces. Pressure ulcers, or localized areas of damaged skin and underlying tissue, result from constant pressure (especially over an extended period of time) as well as from shear forces and friction.1,30,32-34 The pathogenesis of pressure ulcers involves initial ischemia leading to subsequent necrosis.35 Because pressure is a key determinant of pressure ulcer formation,36 pressure ulcers affect people unable to change position regularly.
Specialized support surfaces help relieve or reduce external pressure. The actual value of increased internal capillary pressure required to impair circulation and contribute to pressure ulcer formation is not firmly established in the literature; reports range from less than 20 mm Hg to greater to than 40 mm Hg. However, 32 mm Hg is an often reported average interface pressure that results in capillary closure and cellular compromise.37 Actually, the value varies between individuals because of the relationship between increased pressure and additional factors, unique to the individual, that lead to pressure ulcer formation, including location of the pressure, nutritional status, and comorbid illnesses. In a compromised individual, pressures as low as 12 mm Hg may result in a pressure ulcer.38 Following treatment with advanced support surfaces, pressure reduction allows blood vessels to dilate, with subsequent increased blood flow to deliver oxygen and nutrients to tissues and to remove carbon dioxide and metabolic by-products. Hargest and Artzc20 reported a decreased interface pressure of 10 mm Hg with air-fluidized therapy. Other reports of decreased pressure have ranged from 5 mm Hg to16 mm Hg for air-fluidized therapy, while low-air-loss beds reduced pressures to 12 mm Hg to 45 mm Hg.39 In one study, interface pressures on a standard hospital bed ranged from 44 mm Hg (sacrum) to 104 mm Hg (heel). Reported interface pressure measurements for static overlays vary from approximately 30 mm Hg (sacrum) to 90 mm Hg (heels).37
In addition to increased interface pressure, both intrinsic and extrinsic factors may contribute to pressure ulcer formation and maintenance. Extrinsic factors including pressure, shear, and friction are treated by vigilant positioning techniques and support surfaces. Intrinsic factors include impaired mobility, incontinence, impaired nutrition, and reduced levels of consciousness.40 Air-fluidized beds were developed to manage several factors, including shear, friction, and increased moisture.20 The literature to date supports the effectiveness of air-fluidized therapy in healing pressure ulcers, especially in patients with Stage III/IV pressure ulcers. Authors of the 2002 Cochrane Review, “An assessment of the effectiveness of pressure relieving beds, mattresses, and cushions (support surfaces) used to prevent and treat pressure ulcers,”41 identified six randomized clinical trials that provide good evidence that air-fluidized and low-air-loss beds improve pressure ulcer healing rates. However, they concluded that the data do not distinguish the best treatment from among these options.
Two prospective studies, which included a contemporaneous control population, support the use of air-fluidized therapy in patients with pressure ulcers. In the first study, Allman et al21 found a 5.6-fold improvement in healing with air-fluidized therapy as compared to the control group (an alternating air mattress covered with a foam pad). Patients with Stage III/IV ulcers treated with air-fluidized therapy showed a statistically significant decrease in pressure ulcer surface area, as compared to the control group; this finding was not replicated in patients with Stage I/II pressure ulcers.
In the second prospective controlled study, Strauss et al22 examined the cost-effectiveness of air-fluidized beds over a 36-week period and found that patients who received air-fluidized therapy required 55% fewer days in the hospital, with a shorter average period of hospitalization, as compared to the control group. Support surfaces used for the control group, chosen at the discretion of the treating physician, included alternating pressure pads, air support mattresses, water mattresses, and foam pads. The smaller sample size, selected to assess cost-effectiveness, was not sufficiently powered to demonstrate the efficacy of air-fluidized therapy to promote healing. Although controlled studies23,24 demonstrate the efficacy of air-fluidized therapy as compared to conventional therapy to treat pressure ulcers, these studies did not specifically compare air-fluidized therapy to Group 1 and Group 2 support surfaces.
Additionally, studies with historical controls25,26 and retrospective27,28 and uncontrolled29 studies have shown advantages of treatment with air-fluidized therapy as compared to conventional support surfaces. Although these study designs have distinct limitations, including the lack of randomization and the inability to control for multiple treatments that affect healing, they also offer advantages. For example, the importance of chart review data is discussed in a report of a large retrospective study by Berlowitz et al.42 The group reported results from Patient Assessment Files from 19,981 patients at a Veterans Administration hospital using a model developed to calculate expected pressure ulcer healing rates from chart data. Berlowitz et al stressed the high cost of prospective trials and highlighted the importance of retrospective analyses to identify effective treatment interventions. Thus, a retrospective chart review, as used in this study, provides a cost-effective opportunity to examine treatments in a typical community setting while incorporating larger numbers of patients than would be practical in a randomized controlled trial.
Comprehensive (or Computerized) Severity of Illness (CSI®). Severity scores, used to quantify hospitalized patients’ burden of illness, have been utilized for more than 25 years to assess mortality, length of hospital stay, and hospitalization costs.43 Although no gold standard exists among severity indexes, the Comprehensive Severity Index (CSI®) also known as the Computerized Severity Index, developed in 1982, provides a valid and reliable measure of illness severity.44 In a 1991 study evaluating six illness severity instruments, the CSI® compared favorably with the other systems, particularly in the area clinical acceptance by physicians.45
The CSI® has been validated and used in a variety of clinical settings, including determining illness severity and resource use differences among Caucasian and African American hospitalized patients,46 assessing illness severity in children hospitalized with bronchiolitis,47 evaluating quality of care,48 determining the relationship between hospital costs and the illness severity,49 and assessing quality of care in patients with cardiac conditions.50 The CSI® also has been modified to include separate components to measure severity of illness in ambulatory, long-term care, hospice, and rehabilitation settings.
An example of comprehensive CSI® scores is provided in a study of ambulatory care for 13,000 patients across the US. Patients older than 65 years had an average approximate CSI® severity score of 11 at each visit.51 In the NPULS study, the source of data for this paper, residents at risk for a pressure ulcer had an initial mean long-term care CSI® score (the CSI component most closely related to ambulatory CSI scores) of 63.2, while those with existing pressure ulcers had a mean long-term care CSI® score of 96.6, indicating a significantly greater level of illness in the NPULS residents with existing pressure ulcers. Frequent diagnoses included hypertension, dementia, urinary tract infection, diabetes mellitus, and congestive heart failure.52 Additional details of the CSI® system, including aspects of validation and reliability, have been discussed in great detail.46,53,54