List of abbreviations
NPIAP
National pressure injury advisory panel
PI
Pressure injury
SCI
Spinal cord injury
Introduction
After a spinal cord injury (SCI), individuals often remain with limitations that will impede mobility and functional independence. Presence and severity of the neurological deficits associated with SCI represent important risks for developing pressure injuries (PI). During hospitalization, pain, associated injuries, medical complications, spasticity, joint contractures, and surgical interventions may further lead to prolonged bed rest and contribute to increased occurrence of PI. Achieving an optimal plan for preventing PI can be difficult in practice, particularly for individuals requiring total assistance for mobilization and repositioning in bed. The selection of a specialized support surface is thus a critical component of a comprehensive plan for PI prevention and treatment. Support surface refers to “a specialized device for pressure redistribution designed for management of tissue loads, micro-climate, and/or other therapeutic functions” as defined by the National Pressure Injury Advisory Panel ( ). In this document, support surface pertains to bed, mattress, overlay, and integrated bed system. At the end of this chapter, the reader will be able to:
- (1)
Describe the different forces that are involved in the pathogenesis of PI in the SCI population.
- (2)
Provide an overview of the main types and features of support surfaces to prevent and/or treat PI.
- (3)
Propose a simple decision table for guiding healthcare providers to select a support surface for the prevention and treatment of PI in hospitalized SCI patients.
Pressure injuries (PI): Definition, epidemiology and impacts
Defined by the National Pressure Injury Advisory Panel (NPIAP) as a “localized damage to the skin and/or underlying tissue over a bony prominence,” pressure injuries (PI) (also called bedsores, decubitus ulcers, pressure sores) represent one of the most common medical complications experienced by hospitalized patients ( ). No other preventable event occurs as frequently as PI, occurring at a rate of 2%–40% of all acute care hospitalization in the United States and Canada ( ; ). PI can occur throughout the continuum of care, with a prevalence of 9.7%, 11.8%, and 12.0% for all patients hospitalized in acute care, in patient rehabilitation, and long-term care (nursing home), respectively ( ).
In the lying position, PIs usually develop at the sacrum (17%–27%), heel (9%–18%), malleoli (4.6%), trochanters (1.4%), and scapulae or occiput (< 5%) areas ( ; ; ). It is however proposed that prevention and management of heel PIs may be best managed independently from the bed support surface ( ). The occurrence of PI is particularly concerning for individuals with SCI as it interferes with rehabilitative care, community reintegration, and quality of life ( ; ; ). PIs are associated with higher morbidity and mortality and represent an enormous growing financial burden for healthcare systems, with a patient care cost per PI of 20,900 US$ to 151,700 US$, totalizing 26.8 billion US$ in 2019 ( ; ). Individuals with SCI are among the most vulnerable populations for PI, occurring in more than 95% of them during their lifetime ( ). Recent literature estimates that hospital-acquired PI among SCI patients ranges from 29.7% to 49.2% ( ). According to , the risk to develop PI is higher for individuals with severe spinal cord injury.
Pathogenesis of pressure injuries following spinal cord injury
The pathophysiology of PI involves different extrinsic factors, paralleling the severity of the neurological impairments related to the SCI. Pressure is acknowledged to be the main factor and is defined as the amount of force applied perpendicular to a surface per unit area of application ( ). In addition, shearing and friction represent stresses that are exerted parallel to the area of application and significantly contribute to the capillary damage ( ; ) ( Fig. 1 ). The resultant reduction in blood flow reduces the oxygen and nutrients being delivered to the tissues, while simultaneously limiting the removal of metabolic waste products ( ). Neurological impairments associated with severe SCI also lead to difficulties in identifying painful stimulus associated with prolonged and/or excessive compression, to which must be added the difficulty to make independent postural adjustments necessary to restore tissue perfusion ( ). Without the relief of compression on soft tissues, ischemia persisting for more than 2 hours may lead to necrosis of subcutaneous tissues ( ). Inadequate maneuvers while transferring, repositioning, and positioning in bed may also lead to excessive shearing and friction stresses to the skin, further contributing to the development of PI ( ). Immobility is also associated with the build-up of temperature at the interface, increasing local inflammation biomarkers, associated with PI occurrence ( ).
Dysfunction of the autonomic nervous system may also contribute the pathophysiology of PI following SCI, by altering the micro-vascular response below the level of the injury. Blood flow regulation relies on the rhythmic alteration of blood vessels constriction controlled by central neurogenic, local myogenic and metabolic mechanisms, which can be altered following SCI ( ). Impaired myogenic and neurogenic responses of the vascular smooth muscle due to chronic denervation also lead to an inappropriate local blood flow and metabolic responses to pressure load and unload. This phenomenon may be exacerbated in individuals with endothelial dysfunction (for instance, caused by smoking) and in the elderly, for which the loss of elastin and degradation of the collagen matrix put the skin at further risk of deformation of the blood vessels under loading pressure ( ).
Moreover, 70%–84% of individuals with SCI experience sphincter dysfunction (neurogenic bladder & bowel), which may lead to higher moisture and irritation of the skin, fostering the development of PI ( ). Nutrition status, comorbidities and body weight should also be assessed following SCI. Obesity and diabetes may reduce the skin ability to dissipate local heat and cutaneous temperature regulation under loading. On the other hand, muscle atrophy associated with SCI may make bony prominences to emerge, leading to increased local pressure and friction/shear in bed. Spasms and joint contractures associated with SCI should also be assessed, as a potential cause of excessive friction and shear and hindrance for proper positioning and repositioning in bed (increased pressure).
Support surfaces: An approach for prevention and treatment of pressure injuries
Biomechanical properties of support surfaces during loading
Support surfaces use three main mechanisms to prevent PI during loading: (1) pressure redistribution; (2) micro-climate, and (3) horizontal stiffness management. Their performance levels on these important features allow differentiating between the variety of available products and help in selecting a proper support surface that matches patient’s needs. During loading, the pressure at a specific location will decrease as the contact area increases. Based on this concept, support surfaces aim to redistribute the pressure by using two basic principles ( ; ; ; ) ( Fig. 2 ):
- (1)
Envelopment , referring to the ability of a support surface to conform, so to fit and mold around irregularities in the body. It is generally measured in laboratories by indenter tests providing average pressures on each depth level (mm Hg).
- (2)
Immersion , referring to the penetration (sinking) of the body into a support surface, measured by the depth of penetration (mm).
A higher envelopment and immersion performance of a support surface is associated with greater pressure redistribution, but at the expense of higher instability of the surface making it more difficult for a patient to reposition and/or get out of bed ( ).
The micro-climate is defined as the temperature and humidity at the body interface with the support surface and plays an important role in the development of PI, independently of the average peak pressure ( ). High skin temperature leads to an increased cutaneous stiffness under loading, higher inflammation, and metabolic activity, further leading to tissue damage ( ). Moisture can accumulate on the skin increasing the coefficient of friction at the interface while diluting the skin acidity, which was shown to reduce its antibacterial properties ( ; ). Micro-climate is measured in laboratories using the local temperature, relative humidity, evaporative capacity and/or dissipating properties of the support surface. However, support surfaces that provide great micro-climate management may also cause patients to feel cold or dehydrate.
The horizontal stiffness refers to shear and friction stresses that are generated when the gravity pulls the body down on a support surface, which reacts by pushing back. Horizontal stiffness is measured and reported in Newtons of force. A stiff support surface exerts high resisting forces on the tissues in response to a given amount of displacement, while this force is lower for softer support surfaces. However, the latter can contribute to sliding down in the bed and even to falls ( ).
Main configurations and classification of support surfaces
Support surfaces are commercially available in three main configurations: (1) mattress, (2) mattress overlay (on top of the patient’s mattress), and (3) integrated bed system (combining bed frame and a support surface into a single unit). Individuals with SCI with limited mobility may particularly benefit from specialized bedframes (manual, semi-electric, and electric), which allow adjustments of height and head/foot elevation. These adjustments may promote functional independence, enhance sleep quality, and manage different medical conditions associated with SCI (e.g., autonomic dysreflexia, orthostatic hypotension, and/or spasticity).
Support surfaces can be classified into two main groups (reactive or active) based on the technology used ( ; ). Costs related to the different types of support surface technologies are important to consider, as the most expensive does not necessarily signify the “best” mattress for a given patient. Specific properties and performances should be analyzed based on a holistic assessment of the patient’s characteristics.
Reactive support surfaces
Reactive support surfaces are powered or non-powered surfaces with the ability to adjust its load distribution properties solely in response to an applied load ( ; ). Thus, reactive support surfaces do not independently change its load distribution. Consequently, reactive support surfaces provide a constant pressure at the interface, unless the patient actually moves. Different types of reactive support surfaces are available, differing by their structure and material used, providing different properties.
Non-powered reactive support surface
Foam
In its simplest form, a non-powered reactive support surface consists of a single block of foam covered by a plastic or nylon cover. Foam has a flexible, cellular material structure, which may be available in different densities. Foam mattress work reactively to provide pressure redistribution by spreading the load across the whole interface surface area ( ). However, their capacity to immerse and envelop the body is limited by their stiffness and density ( ). Due to its low cost, foam mattresses are widely used in hospitals ( ). Within this type of support surface, high specification foam may incorporate multiple constructs and/or be compartmentalized into different sections with distinct properties ( ; ; ). Softer foam mattresses will provide higher level of immersion as compared to stiffer foams, but necessarily need to be thick enough to avoid “bottoming out,” referring to the deformation beyond critical immersion whereby the effective pressure redistribution is lost ( ; ). Foam mattresses can progressively degrade and lose their capability of returning to its original forms or thickness, typically wearing out after 3 years ( ; ). suggested that high specification foam mattresses were more effective than “standard” hospital foam mattresses in moderate to high-risk patients in terms of pressure relief. suggested that the use of a viscoelastic support surface reduced the incidence of PI (stage 2) in critically ill patients when compared to standard mattress. Moreover, when non-air reactive mattresses are used, the use of contoured postural management components may enhance its pressure redistribution properties ( ).
Gel
Gel mattresses consist of a semi-solid system of solid aggregates, colloidal dispersion or polymers exhibiting elastic properties ( ). Gel mattresses can range from hard to soft, providing distinctive immersion, envelopment, and horizontal properties. Gel mattresses are generally easy to clean up; however, they may be heavy. Temperature and moisture control may be challenging with the use of non-air non-powered reactive support surfaces, due to their lack of aeration and poor heat conduction properties ( ). Tomova-Simitcheva et al. showed in 2017 that a reactive gel support surface (featuring a breathable cover and an open gel column) may exhibit similar effectiveness with an alternating pressure mattress (with low-air-loss function) on the transepidermal water loss, temperature, and erythema at the sacral and heel skin, both being superior as compared to a basic foam mattress.
Air-filled
The use of reactive air-filled mattress overlay is an alternative in patients at some risk of PI development. Indeed, suggested that air mattress overlay plus three-inch foam increases its area of contact and reduced tissue shear when compared with foam overlays, using in vivo measurements derived from pelvic CT scans. demonstrated that in air support surfaces, the internal pressure adjustment (inflation level) significantly influenced pressure redistribution properties, with a lower internal pressure resulting in greater immersion and contact area, resulting in a decreased maximum interface pressure. Similarly, demonstrated that the reactive air support surface was the most effective pressure-redistributing material for pediatric occipital pressure, displaying the lowest interface pressure and the most homogeneous pressure distribution compared to foam, fluidized and gel surfaces.
Powered reactive support surface
In a more complex form, reactive support surfaces use a powered flow of air to assist in the management of temperature and humidity of the skin ( ). Low-air-loss support surfaces are composed of multiple air chambers throughout. However, in contrast to alternating air pressure support (discussed below), low-air-loss surface displays tiny holes at its top surface continually blowing air out, while maintaining a specific inflation level in the chambers ( Fig. 3 ) ( ; ; ; ). The pressure at which the support surface must be inflated, and the rate for blowing out the air, is based on the individual’s height and weight ( ), and is adjusted to provide the desired level of immersion/envelopment. Temperature and moisture control at the skin surface is also improved, as compared to alternating air pressure system and non-powered support surfaces, most likely due to the evaporation effect caused by air circulating from the permeable cover ( ; ). However, the optimal skin temperature and moisture level for PI prevention is still unknown, and this technology represents higher costs compared to non-powered systems ( ).
A comparison cohort study by Black et al. in 2012 has suggested that critically ill patients placed on low-air-loss mattresses with micro-climate management in surgical intensive care unit had lower PI (stage 2) incidence than those placed on an integrated power air pressure redistribution beds (air alternating pressure) ( ). Lippodolt et al. in 2014 showed that low-air-loss technology significantly reduced the interface pressure at 0, 10, 30, and 45 degrees of backrest elevation in comparison with foam and air suspension support surfaces (air fluidized). It was thus suggested that low-air-loss technology could be an additional useful tool to help prevent skin breakdown at the sacrum as a compromise between seemingly incompatible demands of skin integrity and prevention of ventilator-associated pneumonia ( ). However, this study did not assess horizontal stiffness.
Reger et al. also suggested in 2001 that measurements of support interface climate change might allow for selective grouping of low-air-loss surfaces according to their rate of moisture evaporation and resulting temperature reduction. Combined, these characteristics can effectively describe the performance of any low-air-loss support system and may be used to define standards of performance ( ). A meta-analysis completed by suggested that hybrid low-air-loss air surfaces may have the highest probability of being the most effective intervention for PI prevention. However, the authors remain uncertain as to the true ranking of the different support surfaces because the certainty of evidence was very low ( ). It was also suggested that the performance of low-air-loss support surfaces may also be influenced by their age and should thus be assessed in the quality assessment of these technologies ( ).
Active support surfaces
In opposition to reactive support surfaces, active support surfaces are powered support surface that have the ability to periodically change the load distribution regardless of the applied load (individual’s position or movement) ( ). This technology mostly rely on its ability to provide pressure redistribution via cyclic changes in loading and unloading as characterized by frequency, duration, amplitude and rate of change parameters ( ; ; ). Because of this feature, powered support surfaces are generally beneficial to individuals with low mobility. Furthermore, the inflation level can be adjusted to provide the desired level of immersion/envelopment and horizontal stiffness with the body. As illustrated in Fig. 3 , active support surfaces can be stratified into two groups according to their mechanism of action (alternating air pressure and air fluidized).
Alternating air pressure
Alternating air pressure support surfaces are composed of multiple air chambers throughout, in which the air is pumped alternately to inflate and deflate the chambers ( Fig. 3 ) ( ; ; ; ). As a result, the pressure is periodically relieved and redistributed by changing the location of the contact areas between the individual’s body and the support surface ( ; ; ). Cyclic redistribution of loading helps to restore blood flow and re-establish blood supply to the soft tissues ( ). However, it was recently hypothesized that unloading may be associated with reperfusion-induced inflammatory process ( ). Accordingly, the main limitation of air alternating support surfaces remain the lack of evidence pertaining to the ideal frequency, duration and amplitude of cell’s inflation/deflation for preventing and treating ( ; ). However, a study by showed that the maximum contact pressure on the sacrum were significantly lower on devices for which inflation pressure was adjusted according to the body mass of the subject.
investigated the pressure-relieving ability of three specialized support surfaces (low-air-loss, air fluidized, pegasus airwave (air alternating pressure)) compared to a standard foam hospital mattress, by measuring the total body tissue interface pressure. The air alternating pressure surface outperformed the other tested support surfaces by decreasing the overall pressure ( ). A meta-analysis completed by Shi et al. in 2018 suggested a moderate certainty evidence that powered active (alternating) air surfaces and powered hybrid air surfaces (offering both reactive and active pressure redistribution modes) probably reduce PI incidence compared with standard hospital surfaces by 58% and 78% on average, respectively.
An interesting study was completed by , aiming to guide the selection of parameters of commercial alternating pressure support surfaces for the prevention of PI in the SCI population. In this study, sacral skin response (using laser Doppler flowmetry) was compared for different pressure interface in alternating air pressure and continuous (reactive) air systems. Results showed that alternating pressure (at a low-interface pressure at 0 mmHg and high-interface pressure at 60 mmHg with a cycle time of 5 min) enhanced skin perfusion of weight bearing tissues as compared with constant pressure (with an interface pressure of 30 mmHg) in people with SCI.
Air fluidized
Air fluidized is a feature of a support surface that provides pressure redistribution by forcing air through a granular medium (e.g., beads) producing a fluid state ( ; ). This high-technology (also called high-air-loss) may provide the greatest level of immersion and envelopment of any support surfaces ( ; ; ). According to , almost two-third of the body is immersed using this type of support surface, which represents a large contact surface distribution ( ). In addition to its high-pressure redistribution quality, air fluidized support surfaces also provide an effective micro-climate management, by letting warm air escape from the top surface ( ; ). the heel blood flow between standard hospital foam mattress bed, viscoelastic foam mattress and an air-fluidized bed. Authors reported that only the air-fluidized bed resulted in a maintained blood circulation ( ). Previous randomized controlled studies have shown the benefit of this system for individuals with stage III and IV PI in comparison with other non-fluidized support surfaces ( ). However, it also showed its risk of dehydration and dry skin (also indirectly associated with PI). One systematic review reported significant reductions in PI size (of any stage and any setting) with air-fluidized devices ( ). Authors however concluded that there was a limited evidence for the effectiveness of air-fluidized as opposed to “low-tech” devices in the treatment of existing PI. While the body of evidence was qualified as “good” by , it was deemed as low quality by McInnes ( ). Air fluidized technology is also one of the most expensive support surface system.
Emerging technologies
Adjustable rotational beds consist in integrated bed systems featuring computerized lateral rotation (tilting) of the support surface for assisting patients for periodical repositioning in bed. In addition to promoting functional independence, these systems may also facilitate caregiver interventions (e.g., turning and transferring individuals, examining the skin, assisting in bedding equipment changes, and providing physical/respiratory therapies). Different tilting options can be provided, such as rotational beds and lateral rotating beds. On the other hand, these systems are expensive. Moreover, while pressure redistribution in this system mainly relies on the repositioning of the patient, these systems may potentially generate higher shear and friction stresses than conventional technologies. However, this remains to be defined in the clinical and laboratory settings.
Positioning, surface material and bed making
Positioning of the bed and surface materials are important factors to consider as they influence support surfaces performance during loading. A recent study by identified, using a computational model of the weight-bearing pelvis that applying a sufficient supporting lateral pressure may counteract the under-body pressure. Although this study was completed in seated individuals, this strategy is yet to be determined in the lying position (support surfaces) ( ). Tran et al. in 2016 investigated the impact of the repositioning frequency on shear stress and overall healthcare cost by decreased utilization of medical personnel. The authors concluded that the traditional repositioning frequency of every 2 hours may be equal in effectiveness to a frequency of 4 hours, and it was suggested that the frequency of repositioning be individualized based on the patient’s risk factors, needs and support surface utilized ( ). Current literature doesn’t show that any method of positioning is preferred, and therefore, 30-degree tilted side-lying position, the prone position, and the 30-degree semi-Fowler position, are all considered acceptable ( ).
Current evidence suggests that surface material impacts on micro-climate, temperature, and humidity at the interface. observed that temperatures were lower in all risk areas that had no support surface protector and were greater when the surfaces were in contact with protector material, with increases up to 2.13°C. Recent studies suggest that silk-like fabrics may be effective in reducing shear and subsequent PI when compared with cotton or cotton-blend fabrics ( ). showed that friction and bed making method do not significantly reduce maximum interface pressure, although the hammock effect (forces generated by tension along the loaded interface) can be reduced through the use of stretchable bed sheets on the support surface ( ). Another study proposed by concluded that putting additional linens or underpads on low-air-loss surfaces may adversely affect skin temperature and moisture, thereby reducing the PI prevention potential of these surfaces.
Global evidence on the effectiveness of support surfaces
Globally, studies assessing support surfaces are heterogeneous in terms of settings, participants’ baseline skin status, and follow-up durations. Moreover, over half of the studies have serious or very serious study limitations, reflecting the global uncertainty of evidence pertaining to the efficacy of support surfaces technologies to prevent and treat PI. It was also reported that most studies assessing support surfaces in PI prevention mostly involved participants aged over 55 years old, suggesting that the current evidence may generally apply for the older population ( ). Overall, with the current state of evidence, it is thus impossible to determine the most effective support surface for either prevention or treatment. Thorough assessment of the patient’s characteristics is required for selecting a support surface that will best serve the patient’s needs.
Decision-making for selecting proper support surfaces
Proper risk assessment and implementation of prevention strategies for PI are crucial to providing comprehensive care in the SCI population while reducing healthcare costs ( ). The following section aims to propose a simple algorithm to identify an appropriate support surface for patients with SCI in hospital settings. This section considers recommendations of the S31 NPIAP committee for “using standards to choose wisely” ( ), suggesting these important steps:
- •
Carefully consider the patient population and needs
SCI individuals may be highly vulnerable to PI occurrence, according to their level and severity of the injury, which is particularly true in hospitals setting. Accordingly, particular attention should be given to the following characteristics at admission: presence and severity of motor and sensory function, risk of sphincter incontinence, current or past PI, presence of obesity or bony prominence(s), comorbidities, age, smoking status, and nutritional status. The current mobility (transfer and repositioning) and functional status are also crucial to assess. Secondary conditions related to the SCI and medical complications should also be identified, as they may limit proper positioning and/or repositioning of the patient in bed (orthostatic hypotension, dysphagia, mechanical ventilation, spasticity, joint contractures, etc.).
Individuals with severe (motor-complete) tetraplegia (or high paraplegia) may be at risk of autonomic dysreflexia and poikilothermia (defined as the ability to regulate core body temperature due to the SCI), leading to variability of the body temperature and higher risk of elevated temperature/moisture. The authors thus recommend that the temperature of low-air-loss and air fluidized support surfaces be carefully monitored in individuals with SCI at risk of poikilothermia. Finally, as suggested by , heels will be excluded of the proposed decision table, as the prevention and management of PI at this location may be best managed independently from the support surface.
- •
Determine the type of support surface that will be evaluated and request relevant testing data for the chosen surface from manufacturers
After determining the patient’s profile and needs, selection of the support surface’s type can be completed by matching their specific properties (ability of immersion, envelopment, horizontal stiffness, and to manage micro-climate) during loading. Table 1 (adapted from ) provides a simple decision table to guide the multi-disciplinary team to select a support surface’s type based on relevant characteristics of the SCI population in a hospital context (for prevention or treatment of PI). One can also refer to the manufacturer’s data and current literature to compile support surface’s performance characteristics on pressure redistribution and micro-climate properties to provide an overall ranking for the most appropriate support surface type, considering costs and hospital resources. Finally, collaborate with the hospital’s administration regarding procurement of recommended support surface, keeping in mind that PIs are a common and resource-intensive challenge for hospitals worldwide and prevention strategies are significantly less costly than treatment regimen.
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