The finding that the most important single factor in the prevention or treatment of pressure ulcers is frequent movement of the patient so that pressure at any one point is not permitted to exists for too long has been known since mid-16th century. In a case report Ambroise Pare (1510-1590), an influential French surgeon, reported a successful treatment of a pressure ulcer with nutritional support and pressure relief [21]. In 1853 Brown Secquard, from paraplegic animal experiments, proved that pressure ulcers can be prevented and cured by avoiding prolonged pressure [22].

In 1940 Munro described the prevention of pressure ulcers in paraplegic patients by systematic hourly turning of patients on a Sorbo mattress. By 1945 he had found that two-hourly turning was adequate in acute paraplegic patients. In 1944 Stoke Mandeville Spinal Centre was established under the management of Guttmann who introduced the Lifting and Turning Team. While Guttmann was turning his patients half hourly, two and three hourly repositioning regimes remained the standard treatment for paraplegia [22].

Since then it has been widely accepted that the cornerstone of pressure ulcer therapy was to reduce or eliminate pressure through the use of pressure redistributing devices (support surfaces) and mobilisation of the patient (repositioning of the patient) [18].

The concept of active mattresses was first conceptualized by Gardner in 1947 with the primary objective of enhancing skin health and reducing the incidence of pressure ulcers, a health concern particularly prevalent among the elderly or those with reduced mobility, and to save the nurses’ time normally spent in turning patients [22, 32]. Dr Gardner have been using this type of mattress in his Cleveland Clinic since July 1947 and was first to report promising results of use of this technology. In his 1948 article Dr Gardner described 16 paraplegic or quadriplegic patients that were considered to be likely candidates for bedsores and were treated on the mattress for periods from 5 to 63 days. Nine of 16 patients showed improvement of complete healing of their bedsores after 5 – 34 days on the mattress. The study conclusion was that the principle of alternating pressure mattress appears to be beneficial in the prevention and treatment of bedsores in some bedridden patients. It adds to the comfort of the patient and decreases the amount of nursing care required [32].

Based on the foundational research of F.X. Keane, many active mattresses, such as the Arjo Nimbus 4 and Auto-logic, Hill Rom P280 and Squirrel Medical Active Mattress Systems fulfil the minimum physiological mobility requirement for individuals on a soft surface. Keane's landmark paper presented in 1978 highlighted the importance of 'muscle care' as opposed to 'skin care' alone, calling for more frequent postural changes to relieve pressure on muscle tissues. He proposed that humans sleeping on a natural hard surface change position, on average, every 11.6 minutes. This frequency of postural changes is reflected in the design of the forementioned active mattresses and has been shown to effectively increase resting blood flow to skin tissues, thus reducing pressure-induced ischemia and contributing to improved skin health and function [22].

Frequency of postural changes has been shown to be affected by age, gender and mobility status. Indeed, a prospective observational study in 241 hospitalised patients demonstrated that patients were repositioning on once every 1.7 hours over 24-hour period instead of 11.6 minutes. This figure was found to be higher in the morning shift (7am – 3pm) – once every 1.4 hours and lower during the night shifts (11pm to 7am) – once every 2 hours. The evening shift (3pm to 11pm) had the frequency of once every 1.7 hour, significantly lower than the frequency of repositioning of 11.6min necessary for maintaining a healthy balance in skin. The study results also demonstrate that with the increase in participant’s age the frequency of repositioning decreased making the older patients more susceptible to development of pressure injuries [33].

Nowadays, active mattresses are recommended as a prevention and treatment option for both healthcare and home facilities [19].

Active mattresses (also referred to as alternating pressure mattresses) are designed to provide an effective pressure redistribution. The pressure is redistributed several times each hour even if the patient cannot or does not move, this is typically achieved though the inflation and deflation of a series of air cells activated and controlled by a specialist mains-powered pump unit. The active mattresses mimic natural spontaneous movement, which is a protective mechanism that ensures effective tissue off-loading (up to six times each hour), this continues even in the absence of patient movement.

The first step in pressure ulcer prevention is to reduce the patient’s exposure to prolonged pressure and shear. Mild pressure applied intermittently, such as during a massage or natural repositioning during sleep, stimulates a cycle of hyperaemia, promoting endothelial function and increased blood flow [1].

Healthy blood flow, in turn, plays a vital role in facilitating homeostatic balance. It empowers the skin to effectively regulate temperature, maintain an immune response and fortify itself against the development of pressure injuries.

Active support mattresses are associated with the following physical and physiological benefits:

• Enhanced tissue perfusion and rapid removal of toxic metabolites through the stimulation of reactive hyperaemia (increased blood flow)
• Increases skin blood flow
• Enhanced lymphatic drainage
• Pressure off-loading, comfort and support

Active mattresses are Class IIa under Rule 9 of the Medical Device Directive 93/42/EEC. Squirrel Medical commenced UKCA class lla accredition under the supervision of SGS UK Ltd in May 2022 and has completed the stage 1 combined UKCA / ISO13485 audit.

The Squirrel Medical Active Mattress Systems are intended to be used as an aid to assist in the managed treatment and prevention of pressure ulcers when used in conjunction with a patient care plan and/or pressure ulcer prevention program and must not be considered or relied upon as an independent curative device.

All patients must be clinically risk assessed before being prescribed any Squirrel Medical Active Mattress Systems and used with clinical guidance.

The Care Provider is responsible for ensuring that the person(s) setting up and using any Squirrel Medical Active Mattress Systems are trained and competent in its use.

Caution

Support surfaces alone neither prevent nor heal pressure ulcers. They are to be used as part of a total management plan for the prevention and treatment of pressure ulcers (NPUAP, EPUAP & PPPIA 2014)

Squirrel Medical Active Mattress Systems provide alternating therapy and should not be used with patients that have spinal injuries and/or unstable fractures of the spine.

Patients with other fractures and burns should undergo a thorough medical examination/risk assessment before being prescribed its use.

An active alternating air mattress is designed to provide pressure relief and promote better circulation for individuals who are at risk for developing pressure ulcers (also known as bedsores) or who already have pressure ulcers. The target population for an active alternating air mattress includes:

• Patients at risk of developing pressure ulcers
• Patients that are acutely ill and/or in critical care
• Patients with neurological conditions
• Patients with diabetes mellitus
• Patients who are elderly / infirm.
• Patients who are in the long-term care or community care
• Patients who have experience trauma and/or prolonged surgery
• Patients presenting cardiovascular risks

Those with limited mobility or paralysis, including individuals with spinal cord injuries, multiple sclerosis, or stroke, may be at risk for developing pressure ulcers and can benefit from this type of mattress.

Patients with chronic illnesses, such as diabetes or peripheral vascular disease, may have compromised circulation, putting them at a higher risk for developing pressure ulcers.

Older adults are more prone to developing pressure ulcers due to factors like decreased mobility, thinner skin, and reduced circulation. An alternating air mattress can help prevent pressure ulcers in this population.

Patients recovering from surgery, especially those who have undergone procedures that limit mobility or result in extended periods of bed rest, may benefit from an alternating air mattress.

Recent scientific findings suggest that active alternating air mattresses may also be beneficial for individuals seeking improved cardiovascular health. The use of these mattresses has been associated with enhancements in endothelial function and resting blood flow, which can contribute to better overall cardiovascular health.

It's important to note that while active alternating air mattresses can be highly beneficial for these target populations, they may not be suitable for all individuals. It is essential to consult with a healthcare professional to determine the appropriate type of mattress for a specific patient's needs.

Active alternating air mattresses are designed to benefit a wide range of users, including those in private households and caregivers with varying levels of knowledge. In this context, the intended users of an active alternating air mattress include:

• Individuals at home: People who are bedridden, have limited mobility, or are recovering from surgery or illness can use active alternating air mattresses in their homes to prevent pressure ulcers and promote better circulation.
• Family caregivers: Family members who provide care for a loved one with limited mobility or a higher risk of developing pressure ulcers can benefit from using an active alternating air mattress to ensure their loved one's comfort and well-being.
• Informal caregivers: Friends, neighbours, or community members who assist with caregiving duties for individuals at risk of developing pressure ulcers can use these mattresses to provide better support and care.
• Home healthcare professionals: Nurses, therapists, and other healthcare providers who offer home-based services can recommend and utilize active alternating air mattresses for their patients who need pressure relief and better circulation.
• Professional caregivers: Caregivers working in assisted living facilities, nursing homes, or other long-term care settings can use active alternating air mattresses to provide proper pressure relief and support for their residents.

The intended use environments for an active alternating air mattress include:

• Hospitals: Active alternating air mattresses may be used in various hospital units, such as intensive care units (ICUs), general wards, and post-operative recovery rooms. In these settings, the mattresses can help prevent and manage pressure ulcers for bedridden patients or those with limited mobility.
• Long-term care facilities: These mattresses can be used in nursing homes and assisted living facilities to provide pressure relief and support for residents who are at risk for developing pressure ulcers or have limited mobility.
• Home healthcare settings: Active alternating air mattresses can be used in private households for individuals receiving home-based care from healthcare professionals, family caregivers, or other informal caregivers. In these settings, the mattresses can help manage pressure ulcers for bedridden individuals or those with limited mobility.
• Palliative care and hospice settings: Patients receiving end-of-life care can benefit from the comfort and pressure relief provided by active alternating air mattresses, helping to improve their overall quality of life.

The Squirrel active mattress does not directly or indirectly contact the patient's body. Traditional bedlinen, particularly fitted sheets, act as an interface between the mattress and the patients skin. These sheets ensure hygiene by enabling regular laundering, reducing the risk of dirt and bacterial build-up. They also provide absorbency to manage sweating or fluid excretions, helping maintain a dry and comfortable sleeping environment. Furthermore, the sheets contribute to overall patient comfort due to their soft texture and conformability. Active mattresses must not be used without bed linen as an interface.

Squirrel active mattresses are specifically designed to support patients suffering from age-related endothelial dysfunction, a condition that perpetually predisposes them to pressure ulcers. The intended use of the Squirrel range of active mattresses is not only to prevent the onset of pressure ulcers but also to aid in the treatment of existing ones. By stimulating endothelial function and promoting blood circulation, the mattress aims to maintain overall skin health. Given the nature of this condition, these mattresses are typically prescribed for prolonged, if not indefinite, use.

In many cases, due to the chronic nature of the underlying health conditions of the patients, the Active Mattress may be prescribed in end-of-life situations. In these instances, the duration of use extends until the end-of-life care period. However, the duration of use can also extend indefinitely for other patients who, despite not being in end-of-life care, will continue to benefit from the support offered by the Active Mattress due to their constant susceptibility to pressure ulcers.

In summary, the duration of use of the Active Mattress is patient-specific and will generally span a long-term, often indefinite, period due to the chronic nature of the conditions it is designed to manage.

Elderly and infirm individuals who suffer from age-related endothelial dysfunction and immobility face a heightened risk of developing pressure ulcers. Their compromised skin health, diminished thermoregulation, and reduced resilience to pressure necessitate the continuous support provided by active mattresses throughout bed rest. These mattresses are designed to be used on a semi-perpetual and repeated basis to mitigate the risk of pressure ulcers and maintain skin health.

The alternating air chamber technology of Squirrel Medical active mattresses promotes endothelial function and blood flow by relieving pressure on vulnerable areas of the skin. This cyclic inflation and deflation mechanism mimics natural repositioning, which stimulates blood circulation and helps prevent pressure ulcers. By using active mattresses on a repeated basis, the continuous stimulation of blood flow and pressure relief contributes to enhanced endothelial function and increased skin resilience.

Active mattresses are a practical solution for these individuals as they provide continuous support, alleviate pressure, and stimulate blood flow, reducing the risk of pressure ulcers.

The technology behind active mattresses is mature as the product has existed on the market for over 50 years. During this time a series of standards, including a product-specific standard ISO 20342-1, were developed. ISO 20342-1 specifies general requirements and test methods relevant to assistive products for tissue integrity in the lying position (mattresses, mattress overlays and mattress coverings) in different application environments, such as hospitals, home care and institutions.

A number of generic standards applicable to all medical devices, such as ISO 14971, ISO 13485, ISO 10993, IEC 60601-1, IEC 60601-1-2, IEC 60601-1-11 and others apply to the product.

These standards are considered a State-of-the-Art and, although compliance with the standards may be voluntary, it provides a presumption of conformity with the UK regulatory requirements.

Active mattresses are recognised method of treatment and prevention of pressure injuries since its introduction into clinical practice in 1947, during this time it has developed into a mature technology that forms part of the clinical care protocol in different jurisdictions. There is a number of established practice guidelines available from professional organisations, such as European Pressure Ulcer Advisory Panel or the National Institute for Health and Care Excellence. All clinical practice guidance reviewed in this section are based on a large number of randomised controlled clinical studies, systematic reviews and meta-analysis, and, as such, represent high quality clinical evidence.

A NICE clinical guideline CG179 on pressure ulcer prevention and management published in 2014 lists a high-specification foam or equivalent mattress for adults as a device for pressure ulcer prevention. The mattress is indicated for adults who are admitted to secondary care and assessed as being at high risk of developing a pressure ulcer in primary and community care settings. The same guideline advises on using high-specification foam or equivalent pressure redistributing surfaces for all adults undergoing surgery and using a high-specification foam or equivalent pressure redistributing cushion for adults who use a wheelchair or who sit for prolonged periods. With regards to the equivalent pressure redistributing surfaces the guidance advises to use dynamic support surface as active mattresses are references as one of the pressure redistributing devices [9]. A 2018 update to the CG179 included information form the several additional studies and maintained advice given in the 2014 version of the guidance [10].

A quality standard QS89 that cover prevention, assessment and management of pressure ulcer produced by the National Institute for Health and Care Excellence instruct the clinical user to use the pressure redistributing devices for people at high risk of developing pressure ulcers in the Quality Statement 8. The pressure redistributing equipment is understood as any item, such as mattress or an overlay that either spread out the pressure or removes pressure from different parts of the body. For people spending long time in a wheelchair cushions are offered as a pressure redistributing device [11].

With regards to guidance on wound dressings and antimicrobial dressings (alternative management option) for chronic wounds, a NICE evidence summary ESMPB2 found that overall, the quality of clinical evidence for wound dressings for pressure ulcer prevention and management was low to very low. Based on this, NICE does not make any recommendations about specific types of dressings, except that the gauze dressings should not be used for pressure ulcers. It is advisable to use a dressing that promotes a warm, moist wound healing environment for grade 2, 3 and 4 pressure ulcers [12] .

The international clinical practice guideline on prevention and treatment of pressure ulcers/injuries published by the European Pressure Ulcer Advisory panel, National Pressure Injury Advisory Panel and Pan Pacific Pressure Injury Alliance recommends alternating pressure support surfaces with strength of evidence B1 (level1 studies of moderate to low quality providing direct evidence or level 2 studies of high or moderate quality providing direct evidence with consistent outcomes) and weak positive recommendation [13]. The evidence on alternating pressure mattresses is mixed but could be explained by the range of different mattresses and the different concurrent interventions implemented in the studies analysed in the guidance. Majority of the studies indicated beneficial effect of the device. Evaluations from individuals using alternating pressure mattresses and overlays generally indicate satisfaction [13].

Overall, current clinical guidelines from international and UK professional organisations indicate that active mattresses are safe and effective prevention/ treatment option for pressure ulcers and represent a standard of care in many countries. The limitations of the technology are typically minor (nausea, affected sleep), but the benefits of preventing development of new pressure ulcers or treatment of already existing greatly outweigh the risks.

The endothelium, a unique layer of cells that line the interior of blood vessels, is integral to skin health, performing various regulatory functions beyond merely serving as a barrier. These include the regulation of vascular tone, blood coagulation, immune responses, and inflammation. The endothelium's role is particularly crucial in the maintenance of skin hydration, nutrient distribution, and temperature regulation. Through the release of vasodilators like nitric oxide, the endothelium enables blood flow to the skin, which supports thermoregulation and nutrient distribution. Additionally, endothelial cells aid in maintaining skin hydration by managing fluid and electrolyte balance [14, 15].

Endothelial dysfunction, on the other hand, is characterized by an imbalance between the substances that the endothelium produces to dilate and constrict blood vessels and can adversely impact multiple physiological processes including skin health. A large number of clinical studies have assessed arterial endothelial function in health and disease, particularly for cardio-vascular disorders. Most of these studies tested the ability of normal endothelium to release the vasorelaxing factor in response to pharmacological or physiological stimuli [15]. The studies to date found that endothelial dysfunction can disrupt microcirculation, leading to inadequate nutrient delivery and insufficient waste removal from tissues. It has been shown to be a key pathological condition which is associated with most, if not all, cardiovascular risk factors [14, 16]. There is extensive scientific evidence correlating endothelial dysfunction to cardiovascular risk, in particular, endothelial dysfunction was observed in patients with arterial hypertension, in normotensive subjects with a family history of hypertension, in smokers including passive smokers, in dyslipidaemia, in ageing, diabetes mellitus, in obesity, in hyperhomocysteinaemia, in humans with low intracellular magnesium levels and in patients with inflammatory of infectious diseases [14, 16].

On a cellular and tissue level, the consequences of endothelial damage include increased adherence of monocytes, increased permeability to monocyte/ macrophages and lipoproteins, increased platelet adherence, increase smooth muscle cell migration and proliferation leading to obstructive coronary stenoses. The clinical correlate of impaired endothelial function in the coronary arteries may be episodic myocardial ischemia [15]. Endothelial injury, either physical trauma or more subtle cellular damage, is now regarded as an important initial event in atherogenesis. In the coronary arteries impairment of endothelial function occurs early in the course of atherosclerosis in relations to systemic risk factors and abnormal haemodynamic shear stresses [14].

Endothelial dysfunction is a systemic condition and is the reason why endothelial function in coronary arteries correlates to peripheral endothelial function. It has been shown that endothelial dysfunction in the periphery and in the coronary arteries is not only a market for cardiovascular risk, but is also a contributor to the progression of atherosclerosis and cardiovascular events [14]. Peripheral endothelial dysfunction is found in up to 75% of patients presenting with acute coronary syndrome and undergoing percutaneous coronary intervention [17].

While endothelial dysfunction is mostly studied in the cardiovascular conditions, it is implicated in the development of pressure ulcers. Endothelial dysfunction is through to be one of the internal factors that contribute to the development of pressure ulcers [18, 19] and has been proposed as a risk factor for the disease [16]. It has been further suggested that perfusion problems commonly associated with endothelial dysfunction contribute to pathophysiology of pressure ulcer development [16]. Further confirming this suggestion is a nested case-control study undertaken within a longitudinal cohort study of endothelial function in ambulatory community of cognitively intact subjects age 60 and older [20].

The incidence of endothelial dysfunction was 100% with patients

Endothelial function was measured using peripheral arterial tonometry and found to be significantly worse in persons with a history of pressure ulcers in the last 5 years compared to controls (1.32 vs 1.76, P = 0.04). The prevalence of endothelial dysfunction was higher in patients with pressure ulcers compared to controls (100% vs 43%, P = 0.04) [20].

Pressure ulcers (also known as pressure injuries, pressure sores, decubitus ulcers and bed sores) are localised injuries to the skin or underlying soft tissue or both, caused by unrelieved pressure, shear or friction as defined by NPIAP. The first description of this condition dates back to Hippocrates in 400 BC, however, the problem of pressure ulcers is possibly much older as they have been documented in autopsy reports on 5000-year old Egyptian mummies [21]. In mid-16th century when French physician Ambroise Pare noted that “the bedsore on the buttock has come from having been too long a time lying on it, without moving himself” [16].

It is postulated that in the presence of prolonged pressure and shear forces, there are four mechanisms (local ischaemia, reperfusion injury, impaired interstitial fluid flow and lymphatic drainage, and sustained deformity of cells) within three functional units (capillaries, the interstitial spaces and the cells) that lead to pressure ulcer development. The mechanisms, alone or combined, reduce the oxygen and nutrient supply to cells, impair removal of waste products of cell metabolism leading to cell damage and inevitable tissue destruction. It is worth mentioning that most individuals do not develop pressure ulcers due to the relative health and resilience of their skin, as it is a major organ capable of withstanding pressure. Additionally, many people possess an innate discomfort response that prompts them to reposition themselves approximately every 11.6 minutes during sleep, serving as a natural and gentle form of massage that stimulates endothelial function and improves blood flow to the skin [22]. However, certain individuals may lack the ability to perceive discomfort or have difficulty repositioning themselves as frequently as necessary, which can lead to skin tissue damage within as little as 60 minutes, potentially progressing to the development of pressure ulcers [23]. Pressure ulcers are not inherently fatal, but they can become a pathway for dangerous infections, and even the smallest pressure ulcer can have fatal consequences [13].

Susceptibility to pressure ulcers comes from a combination of external factors (pressure, friction, shear force and moisture) and internal factors (fever, malnutrition, anaemia and endothelial disfunction). Dysfunction of autonomic regulatory mechanisms of local blood flow may increase susceptibility to pressure ulcers. Any agents that created immobility may contribute to the development of pressure ulcers. In patients with normal sensitivity, mobility and mental faculty, conscious and unconscious feedback leads to position shifts before irreversible tissue damage occurs, therefore, pressure ulcers occur most often in aged, incontinent, debilitated, paralysed and unconscious patients [18, 19, 23].

According to NICE, all people are potentially at risk of developing a pressure ulcer. However, they are more likely to occur in people what are seriously ill, have a neurological condition, impaired mobility, poor posture or a deformity, compromised skin or who are malnourished. The use of equipment that is not specifically designed to provide pressure relief can also contribute to the development of pressure ulcers. As pressure ulcers can arise in a number of ways, it requires a complex prevention and treatment interventions that need to be applied across a wide range of settings, including the community, care homes and hospitals [11].

Quality of Life

Impact of pressure ulcers on quality of life is well documented. The condition can be debilitating for the patient, with the most vulnerable people being those aged over 75. Pressure ulcers can be serious and lead to life-threatening complications such as blood poisoning or gangrene [11].

A systematic review of 31 studies including 2,463 participants with pressure ulcers identified 11 themes that were impacted by pressure ulcers: physical impact, social impact, physiological effect, pressure ulcer symptoms, general health, healthcare professional – client relationship, need to versus effect of interventions, impact on others, financial impact, perceived aetiology and need for knowledge, indicating strong evidence that pressure ulcers and pressure ulcer interventions have a significant impact of health-related quality of life and cause substantial burden to patients [30].

Financial Impact on Healthcare System

Pressure ulcers confer a heavy burden in terms of personal impact and health service resource use. Ulceration was found to impair physical, social and phycological activities, health-related quality of life and result in long hospital stays, therefore impacting health systems. Pressure ulcers are costly to healthcare services with costs ranging from € 121.44 million to € 2.59 billion annually depending on the country and setting [25].

A systematic survey across a range of care settings in Europe and North America showed that pressure ulcer-related treatment costs ranges between € 1.71 and € 470.49 per person per day. In the Netherlands pressure ulcers were reported the third most costly issue for healthcare services [31], mainly due to prolonged hospitalisation and the intensive nursing care required rather than costs of medication or surgical intervention. In the USA hospital costs for adults with a diagnosis of pressure ulcers totalled $ 11.0 billion in 2006 [18, 31].

In the UK service attributable managing one person with pressure ulcer is estimated to be £ 1400 for a grade 1 pressure ulcer and £ 8500 for more severe stages up to £ 10,551 for grade 4 and the total annual cost for pressure ulcer management in the UK is £ 1.4 to 2.1 billion, or 4% of the total UK healthcare expenditure [29, 31].

In the UK more than 90% of the cost of treatment is the cost of nurse time [29].

In Australia, the annual cost of treating pressure ulcers was estimated to be AUD 983 million [24].

Clinical evidence of active mattress performance is supported by a high-quality research, mostly systematic reviews, meta-analysis and randomised clinical trials.

An earlier systematic review of Shi et al found moderate-certainty evidence that the active air surfaces probably reduce the risk of pressure ulcer incidence compared with standard hospital surfaces. The study did not make any conclusions about what class of the support surfaces was the most effective. Evidence presented in the review is generally applicable for the older adult population regardless of settings (primary care vs home) and baseline skin status [34].

A 2021 publication by the same group (overview of Cochrane reviews and a meta-analysis of 68 studies involving 18,174 participants) found low-certainty evidence of pressure ulcer prevention while using alternating pressure mattresses as compared to the foam surfaces (RR 0.63, 95% CI 0.42 to 0.93). The study found that for preventing pressure ulcers alternating pressure air surfaces are probably more cost-effective than the foam surfaces [35]. In a further analysis focusing specifically on the effect of alternating pressure air surfaces (mattresses, overlays and beds) versus any support surfaces on incidence of pressure ulcers in any population in any settings the group found evidence that alternating pressure mattresses reduce the risk of pressure ulcer incidence in different settings and populations [24]. The review included 32 studies with 9,058 participants and found that, overall, alternating pressure air surfaces may reduce the proportion of participants developing new pressure ulcers compared with foam surfaces in general settings (RR 0.63, 95% CI 0.34 to 1.17). Alternating pressure air surfaces applied on both operating tables and hospital beds may reduce the proportion of people developing new pressure ulcers compared with reactive gel surfaces used on operating tables followed by foam surfaces applied to hospital beds (RR 0.22, 95% CI 0.06 to 0.76). Another systematic review of 8 studies (randomised controlled trials, cohort studies and quasi-experimental studies) also confirmed the efficacy of active and reactive support surfaces in reducing the pressure ulcer incidence [28].

A multicentre, phase III, open, prospective, parallel group, randomised controlled trial PRESSURE II in 42 UK secondary/community in-patient facilities comparing safety and effectiveness of high specification foal mattresses with alternating pressure mattresses found a statistically significant difference between the treatment groups in the treatment phase sensitivity analysis [36]. The trial was the largest pragmatic RCT of pressure relieving mattresses undertaken world-wide and was performed in 2029 high risk (acutely ill, bedfast/chairfast and/or category 1 pressure ulcer pain at pressure ulcer site) elderly patients (medial 81 years). While there was no statistically significant difference between mattress groups for the primary endpoint (time to first new PU category  2; 18 days for alternating pressure mattresses and 12 days for high specification foam mattresses) in the adjusted analysis, the treatment phase sensitivity analysis (between randomisation and end of treatment phase) demonstrated a statistically significant difference in time to development of PU category  2 (5.2% for alternating pressure mattresses vs 7.8% for high specification foam mattresses, P=0.0176. Both high specification foam mattresses and alternating pressure mattresses were similar in terms of incidence of pressure ulcers  category 1 (6.9% for active mattresses vs 8.9% for high specification foam mattresses, NS) [36].

Importantly, meta-analysis of Shi and colleagues found that there was little or no difference between different types of alternating pressure air surfaces (multiple active mattress systems were reviewed) in the pressure ulcer incidence indicating that clinical performance of different active mattresses is very similar [24]. This finding was further confirmed in the systematic comparative effectiveness review of Shou et al. The authors’ conclusion based on 5 clinical trials was that there was no difference among various alternating pressure mattresses or overlays in pressure ulcer incidence and severity [37]. The difference, however, may exist between different designs of the mattresses (single cell vs double cell). Efficacy evaluation of different designs of the active overlay (single-layer air-cell vs double-layer air-cell overlay) in terms of pressure ulcer prevention has been conducted by Sanada et al in a randomised controlled trials involving 82 elderly patients [38]. The study found that a significantly lower percentage of patients who used double-layer air-cell overlays developed pressure ulcers (3.4%) compared to patients in the single-layer air-cell overlay (19.2%) or standard mattress (37.0%, p < 0.01 amongst three groups). The relative risk reduction for the double-cell and single-cell overlays compared to the standard hospital mattress was 90.8% and 48.1% respectively, while the absolute risk reduction was 33.6% and 17.8%, respectively [38].

With regards to the secondary outcomes, these mostly include patient comfort, adverse events, health-related quality of life and cost-effectiveness. Shi et al found no difference in the support-surface associated patient comfort in meta-analysis of 32 studies involving 9058 participants as only one study out of 32 reported this outcome and there was no significant difference found in the study. Regarding the adverse events, three analysed studies reported this outcome, but no difference was found between the active mattresses and foam surfaces [39].

Health-related quality of life was reported only in one study analysed by the meta-analysis, no statistically significant difference was found [39]. Similarly, a large multicentre, Phase III, open, prospective, parallel group, randomised controlled trial PRESSURE II found that the mean estimated quality adjusted life years were higher for the alternating pressure mattresses than for the high specification foam mattresses, however, the difference was not statistically significant (0.128; 95% CI 0.126 – 0.130 vs 0.127; 95% CI 0.124 – 0.129, P=0.47) [36].

Although there was only a small difference in quality adjusted life years between active mattresses and high specification foam mattresses, the difference in costs between the two options drives the cost-effectiveness towards alternating pressure mattresses.

The results of probabilistic sensitivity analysis further confirm this finding as in 99% of Monte Carlo simulations the alternating pressure mattresses were cost-saving, while in 77% alternating pressure mattresses produce more quality adjusted life years than high specification foam mattresses. The analysis indicate that alternating pressure mattresses have a 99% probability of being cost effective at a threshold of £20,000. The same study found that the mean total healthcare costs of using alternating pressure mattresses was lower than that for high specification foam mattresses (£4482 vs £4621, respectively, P < 0.000), this despite the alternating pressure mattress being more costly as the biggest proportion of the costs (around 60%) correspond to in-patient care [36]. This is further confirmed by a systematic review and meta-analysis of 32 clinical studies with 9,058 participants with moderate-certainty evidence that alternating pressure mattresses have a 99% probability of being cost-effective compared to foam surfaces [24].

With regards to the wheelchair cushions, a systematic comparative effectiveness review of Chou et al reported four fair quality trials investigating effect of a wheelchair cushion on the incidence of pressure ulcer.

Two trials did not find a difference in risk of pressure ulcer, while two other trials (n=141 and n=232) found a reduction in a risk of pressure ulcer development compared to standard foam cushions (8.8% vs 26% for stage 2 or 3 ulcers; RR 0.36, 95% CI 0.15 to 0.85 and 9.9% vs 6.7%; RR 0.13, 95% CI 0.02 to 1.0) [37].

A systematic review of 65 randomised clinical trials involving 14,332 participants to assess pressure ulcer incidence found moderate-certainty evidence that the powered active air surfaces and powered hybrid air surfaces probably reduce pressure ulcer incidence compared to standard hospital surfaces (risk ratio 0.42, 95% confidence interval 0.29 to 0.63). The following surfaces were assessed in the review: static air mattress overlays, dry floatation mattresses, static air mattresses, low air loss hydrotherapy, air-fluidised beds, convoluted foam overlays, gel mattresses, water mattresses, alternating pressure-relieving mattresses, foam mattresses with dynamic and static modes, standard hospital (foam) mattresses. The network for comfort suggested that powered active air surfaces are probably slightly less comfortable than standard hospital mattresses (RR 0.80), again, moderate-certainty evidence. Importantly, the analysed studies included a range of settings: accident and emergency departments, acute care, intensive care units, general medical wards, orthopaedic centres, operating theatres and long-term care settings (nursing homes, extended care facilities, rehabilitation wards, long-term units) [34].

Another systematic review of 68 studies with 18,174 participants found low-certainty evidence that, compared to foam mattresses, reactive air surfaces may reduce pressure ulcer incidence with a RR of 0.46 (95% CI 0.29 to 0.75). The reactive air surfaces were found to reduce the hazard of developing new pressure ulcers (HR 0.20, 95% CI 0.04 to 1.05) [35].

A systematic review of meta-analysis of Shi et al comparing alternating pressure mattresses to other surfaces for preventing pressure ulcers found no difference in the primary endpoint (pressure ulcer incidence) between the active mattresses and reactive air surfaces (RR 1.61 95% CI 0.90 to 2.88), water-filled surface (RR 1.21 95% CI 0.52 to 2.83) or reactive fibre surface (RR0.90 95% CI 0.68 to 1.19). In terms of another primary endpoint (time to pressure ulcer development) the study found a higher risk of developing a pressure ulcer in people treated with alternating pressure mattress compared to a reactive air surface within 14 days of follow-up (HR 2.25 95% CI 1.05 to 4.83). The same effect, however, was not found for water-filled or fibre reactive surfaces within 14 days follow-up or any reactive surface during 60-day follow up. There was no difference in any of the secondary endpoints analysed in the study (patient comfort, reported adverse events, health-related quality of life, cost effectiveness) between any of the reactive surfaces and the active mattress group [24].

In a systematic review and meta-analysis of Shi et al reactive beds, mattresses and overlays (non-foam and non-air-filled) found that reactive gel surfaces used on operating tables followed by a foam mattress applied to hospital beds may increase the proportion of people developing a new pressure ulcer compared with alternating pressure air surface applied on both operating tables and hospital beds (RR 4.52, 95% CI 1.31 to 15.65). There was no certainty in any other comparisons made in the study. In terms of secondary outcomes, no difference was found in patient comfort between alternating pressure air surface and reactive fibre surface or in adverse events between reactive gel surfaces followed by the foam surfaces and alternating pressure air surfaces applied both on operating tables and hospital beds [39].

Specifically for the reactive air mattresses, a systematic review and meta-analysis of 17 studies involving 2,604 participants demonstrated that reactive air surfaces may reduce the proportion of participants developing a new pressure ulcer compared with foam surfaces (RR 0.42, 95% CI 0.18 to 0.96) [42]. The same study did not find evidence that reactive air surfaces are more efficacious compared to active air surfaces (RR 0.62, 95% CI 0.35 to 1.11), reactive water surfaces (RR 0.43, 95% CI 0.04 to 4.29) or reactive gel surfaces (RR1.25, 95% CI 0.56 to 2.77). Low-certainty evidence suggest that patients in nursing home settings using reactive mattresses may be less likely to develop a new pressure ulcer over 14 days follow-up than people on active air surfaces (HR 0.44, 95% CI 0.21 to 0.96). There was no evidence that support surface-associated patient comfort differed between the groups (secondary outcome), nor reported adverse events or cost-effectiveness [42].

A systematic literature review of 24 randomised controlled trials and 9 systematic/literature reviews concluded that, based on 7 moderate quality studies, viscoelastic foam mattresses are more effective than standard of care, however, these results were inconclusive when comparing viscoelastic mattresses with other PU care mattresses. Similar results were reported for continuous low-pressure support surfaces [25]. Overall, evidence suggests that the benefit-risk ratio for reactive surfaces is equivalent to that of active mattresses in terms of pressure ulcer prevention, however, it is higher compared to standard foam mattresses.

Repositioning is one of the main pressure ulcer preventive measures. It is a current practice in the intensive care units to turn the patient every 2h, however, this frequency was reduced to 4h schedule as a standard protocol. A single-site open label, parallel group randomised control trial involving 330 patients assessed efficacy of each turning regime (2-h against 4-h) for the prevention of pressure ulcer incidence (at least grade 2) in critical patients under invasive mechanical ventilation. Active mattresses were used as a concomitant intervention in both groups. All repositioning was performed manually by the nursing stuff. The pressure ulcer incidence was 10.3% in the 3-h group and 13.4% in the 4-h group (P=0.73). There were no differences in the ICU mortality, hospital mortality, median mechanical ventilation duration or length of ICU. Significantly different was found a daily nursing workload, 21min/patient in the 2-h group versus 11min/ patient in the 4-h group (P<0.001) [45].

Assessment of safety endpoints in the same study indicated that there was a significant difference between 2 regimes with 47.9% for 2-h vs 36.6% for 4-h, P=0.02, for the composite end point of device-related adverse events (all adverse events combined). Out of all adverse events assessed, only endotracheal tube obstruction was different between the groups, 36.4% vs 30.5% for 2-h and 4-h regimes respectively, P=0.065. All other adverse events (unplanned extubation, loss of medical device, reintubation, cardiac arrest of any cause, atelectasis, respiratory instability, clinical ventilator-associated pneumonia) did not differ significantly between the groups [45].

A systematic comparative effectiveness review of Chou et al describes 6 trials investigating the effect of repositioning on pressure ulcer incidence. One fair-quality cluster randomised trial with 213 participants found that repositioning at a 30-degree tilt every 3 hours was associated with lower risk for pressure ulcer incidence after 28 days compared to the standard of care (3% vs 11%; RR 0.27, 95% CI 0.08 to 0.93). Another fair quality trial with 235 patients found no difference in risk of pressure ulcer development between different repositioning intervals. Four other trials either found no effect of repositioning on the pressure ulcer incidence or were susceptible to confounding due to differential use of support surfaces [37].

A clinical trial involving 838 geriatric patients in nursing homes investigating four different repositioning schemes in combination with pressure reducing mattresses (viscoelastic foam) or standard institutional mattress followed up for 28 days found no difference in the incidence of stage 1 pressure ulcers at 34.8 to 38.1% (all NS). The following repositioning regimes and mattress combinations were evaluated: turning every 2h in combination with standard institutional mattress, turning every 3h in combination with standard institutional mattress, turning every 4h in combination with viscoelastic foam mattress and turning every 6h in combination with viscoelastic foam mattresses.

While the difference in the incidence of stage 1 pressure ulcers was not significant, development of the stage 2 and higher pressure ulcers was significantly reduced in the group of 4h repositioning + viscoelastic foam mattress (3.0% vs 14.3% - 24.1% for other groups) [46].