Using an alternating pressure mattress to offload heels in ICU Sarah Masterson and Caroline Younger
The heel continues to be one of the most common sites of pressure damage. This article reviews the anatomy and physiology of the heel and explores significant risk factors, including those found in the critically ill patient. Interventions to prevent heel pressure ulceration by offloading the heel are explored. An evaluation of the Nimbus 4 alternating pressure mattress was undertaken within an intensive care unit (ICU) to consider the efficacy of its unique Wound Valve Technology, which is designed to help prevent heel pressure ulceration. During the evaluation period none of the patients using the Nimbus 4 developed a pressure ulcer. Staff observed that the Wound Valves provided effective pressure redistribution and, although the cells frequently needed to be adjusted, patient safety was maintained throughout. The Wound Valves were most effective on patients who were less prone to voluntary movement. Key words: Heel pressure ulcer ■ Heel anatomy ■ Heel physiology ■ Risk factors ■ Intensive care unit ■ Nimbus 4 ■ Wound Valve
P
revention of pressure ulcers within acute care settings remains a significant challenge, with reported heel ulceration accounting for 25-30% of all pressure ulcers (McGinnis et al, 2014). Heels are the secondmost common site of damage after the sacrum (Vanderwee et al, 2007). Pressure ulcer prevention is regarded as a multidisciplinary issue and as a quality indicator of harmfree care (European Pressure Ulcer Advisory Panel (EPUAP) and National Pressure Ulcer Advisory Panel (NPUAP), 2009; Department of Health (DH), 2010; 2012). This article focuses on the prevention of heel pressure ulcers within the intensive care unit (ICU) setting. The anatomy of the heel is described, and theories relating to the pathology of heel ulcer development are examined, together with specific risk factors affecting ICU patients. Use of an alternating pressure air-filled mattress, with unique Wound Valve Technology at the foot of the mattress, was assessed by nurses in a general intensive care/high dependency unit (ITU/HDU) with an additional two burns ICU beds. The process of the evaluation and feedback is provided, and the impact of this technology on clinical practice is considered. Sarah Masterson, Tissue Viability Clinical Nurse Specialist; Caroline Younger, ICU Sister, Chelsea and Westminster Hospital NHS Foundation Trust, London. Accepted for publication: July 2014
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Cost to health economies and individuals The cost of pressure ulcers is significant for both the individual and health economies. Bennett et al (2004) estimated the total cost to the NHS to be between £1.4 billion and £2.1 billion annually. More recent estimates indicate this cost is increasing (Dealey et al, 2012). For the individual patient, the impact can be considerable, leading to physical, psychological and social issues in addition to the financial impact (Gorecki et al, 2009). Pressure ulcers on the heel can result in increased length of hospital stay and even the loss of the limb due to infection, and potential development of osteomyelitis (Burdette-Taylor and Kass, 2002). There may also be life-threatening consequences such as sepsis and multi-organ failure (Sopher et al, 2011).
Heels: anatomy and physiology The heel is particularly at risk of developing ulceration due to its unique anatomy. The foot is designed to be loaded with significant stresses, such as pressure and shear, on mobilising (Salcido et al, 2011). The skin of the heel is generally thicker than other areas of the body, with dense connective tissue and good microcirculation. It lacks hair follicles and sebaceous glands, with a large number of (eccrine) sweat glands, and maintains good sensitivity and microcirculation (Thoolen et al, 2000). The lack of sebum contributes to the dry nature of the skin, reducing elasticity and resilience with dryness that is exacerbated by friction (Ousey, 2009). Cichowitz et al (2009) studied the heel’s structure, finding that the heel pad has a cup-like structure, made up of skin and connective tissue, with pockets of fat that are thought to offer shock absorbency. Unlike other areas of significant bony prominences, such as the ischial tuberosities where there are gluteal muscles, there are no large muscles to further minimise pressure (Sopher et al, 2011). The blood supply includes the medial calcaneal branch of the posterial tibial artery and the lateral and medial plantar arteries. However, the fat between the connective tissue is almost avascular, (Cichowitz et al, 2009) (Figure 1).
Pressure ulcers and the heel Pressure ulcers are localised areas of damage to the skin and underlying tissues caused by direct pressure and shear, friction and other factors yet to be fully determined (EPUAP and NPUAP, 2009) (Figure 2). Pressure ulcers usually develop over bony prominences of the body such as the sacrum and heel. The heels are particularly at risk due to the limited surface area and thin layer of tissues overlaying the calcaneus (Fowler et al, 2008; Gefen, 2010). Patients with
© 2014 MA Healthcare Ltd
Abstract
British Journal of Nursing, 2014 (Tissue Viability Supplement),Vol 23, No 15
British Journal of Nursing.Downloaded from magonlinelibrary.com by 130.113.086.233 on January 6, 2015. For personal use only. No other uses without permission. . All rights reserved.
Andrew Bezear
Box 1. Hyperaemia When pressure is applied, the microcirculation can be reduced or stopped. When pressure is removed or interrupted, blood flow returns and the vessels dilate to provide an increased blood flow to enable a return to normal perfusion as quickly as possible, this is called reactive hyperaemia
Achilles tendon
Sources: Hampton, 2003; Wong and Stotts, 2003
Bursa
Box 2. Risk factors affecting the critically ill Decreased tissue perfusion due to: mean arterial blood pressure ■■ Altered cardiac function ■■ Vasopressors, i.e. noradrenaline or adrenaline infusions ■■ Low circulating blood volume ■■ Low haemoglobin ■■ Low
Vulnerable zone
Immobility due to: required for mechanical ventilation ■■ Decreased level of consciousness and delirium ■■ Nurses unable to turn patient with severe cardio-respiratory instability ■■ Sedation
Calcaneus Heel fat pad
Malnutrition due to: metabolic requirement caused by critical illness ■■ Impaired gut motility and/or absorption caused by opiate use or gastrointestinal surgery/disease ■■ Increased
Andrew Bezear
Figure 1. Heel anatomy
Skin changes: maceration i.e. sweating and wound exudate ■■ Low serum albumin ■■ Generalised tissue oedema ■■ Faecal incontinence ■■ Skin
Other factors: of multiple co-morbidities ■■ Elderly patients. ■■ ICU length of stay >3 days ■■ Presence
Figure 2. Heel pressure point where ulcer occurs
co-morbidities such as diabetes, oedema and arterial disease are at increased risk of heel pressure ulcers. The diabetic heel is at risk of pressure ulceration because of peripheral neuropathy, where the protective sensation is lost, resulting in continued trauma or pressure to the skin. Hyperglycaemia over time causes linking of collagen fibres in the connective tissues, resulting in stiffer skin that is less able to diffuse pressure through tissue deformation (Gefen, 2010).
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The frequently dry epidermis is more susceptible to tearing and atrophy of the subcutaneous tissue, reducing its ability to assimilate shock during mobilisation (Hampton, 2003; Kim and Steinburg, 2013). Patients with arterial disease, either macrovascular or microvascular, are also at risk as adequate perfusion is required to maintain healthy tissues. In arteriosclerosis, the lumen of the blood vessel is narrowed reducing blood flow. With advancing arterial disease, blood vessels can become occluded leading to ischaemia. People with diabetes have an increased risk of arterial disease associated with calcification of the large arteries as well as microvascular disease due to thickening arterial and basement membranes (Ockenden, 2001). Impeded blood flow will also slow its hyperaemic response (Hampton, 2003; Kim and Steinberg, 2013) (see Box 1). Oedema affects the diffusion of oxygen and nutrients to the soft tissues by increasing the distance between blood plasma and the cells (Rutishauser, 1994). Oedema results from injury; limb dependency; renal, hepatic or cardiac
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Source: Theaker et al, 2000
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PRODUCT FOCUS failure; hypoalbuminaemia; post-thrombotic syndrome or secondary venous obstruction (Ockenden, 2001). Gefen’s (2010) work supported the argument that oedema is a risk factor in pressure ulcer development due to the increase in tissue thickness and stiffening, possibly due to accumulation of fluid causing swelling or potentially an increase in osmotic tissue pressures. However, Coleman et al (2013) undertook a systemic review of primary research to identify risk factors that can independently predict pressure ulcer development in adults. This identified that a complex interplay of factors can explain pressure ulcer risk, with perfusion, including in diabetes, being one of the three most frequently identified independent factors.
Risk factors affecting ICU patients A number of critically ill patients are subject to the risk factors already described, but there are many additional factors to consider (Box 2). Despite the use of risk assessments and adherence to a skin-care bundle, which requires regular assessments of pressure points, nursing interventions and the high nurse– patient ratio in ICU, pressure ulcers do occur. It is also important to take account of tissue damage that may have occurred prior to patient admission to ICU and to recognise that pressure ulcers are not always avoidable (Black et al, 2011). Nevertheless, reducing the incidence of pressure ulcers developing on the heels should be an achievable goal, as offloading the patient’s heels is usually possible even for the most unstable patients.
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Offloading the heels EPUAP and NPUAP (2009) advise that heel pressure ulcers can be prevented by completely removing contact with the mattress. This can be achieved by lifting the lower legs and heels using pillows. In this way, pressure can be redistributed along the calf and the heels are raised from the mattress. Hyperextension of the knee should be prevented by maintaining slight flexion to prevent reduction in blood flow to the popliteal vein (Wong and Stotts, 2003). However, the legs may slide off the pillows, as the patient slips down the bed due to gravitational forces, leaving the heels in contact with the mattress once more (Heyneman et al, 2009). Disposable foam, padded or air-filled ‘boots’ have also been used with varying results and more research is needed to confirm their effectiveness (Junkin and Gray, 2009). The boots usually have an opening over the heel zone to provide a zero-pressure area to achieve offloading. These boots can be effective (EPUAP and NPUAP, 2009) but they are not without their flaws. In some cases the amount of air in the boot is insufficient to lift the heel off the bed, while foam boots may become compressed by heavier patients, reducing their effectiveness (Campbell et al, 2010). Also the thicker padded boots tend to be hot and are disliked by patients who are not sedated (Donnelly et al, 2011). Some types of boots cover only the foot and ankle and do not support the calf; this may cause hyperextension of the knee (Gilcreast et al, 2005). ICU patients are often nursed on either continuous lowpressure air mattresses (CLPAMs) or alternating-pressure mattresses (APMs). However, Ousey (2009) found that the
British Journal of Nursing, 2014 (Tissue Viability Supplement),Vol 23, No 15
interface pressure between the heel and the air mattress remains too high to maintain tissue perfusion of the heel. In contrast, Goossens and Rithalia (2007) demonstrated that some APMs significantly improved tissue perfusion of the heel. Mayrovitz et al (2003) found that hyperaemia was greatest when complete offloading was provided, in comparison with partial offloading in healthy subjects. Further work (Mayrovitz and Sims, 2004) reviewed the effect of pressure loading on hyperaemia in diabetics and non diabetics. They found that ‘hyperaemia was significantly greater in full off loading in non-diabetics compared to partial offloading’, but that diabetics showed no significant increase in hyperaemia from partial to full offloading, though the hyperaemic affect was significantly diminished in comparison to the non-diabetic group. The authors stated that these results provide preliminary evidence that periodic total offloading should be offered to all at-risk patients and prolonged total offloading to patients with reduced capacity for vasodilation. Although APMs are widely used within the acute hospital setting, the National Institute for Health and Care Excellence (NICE) (2014) has called for more independent research to confirm the overall efficacy and cost/benefit of these pressure-redistributing devices (in comparison with more basic products such as high-specification foam mattresses) and does not specifically endorse them. However, the Nimbus 4 mattress replacement system is unique in providing a specific heel zone designed to help prevent heel pressure ulcers.
The Nimbus 4 The Nimbus 4 mattress replacement system provides active pressure redistribution through a system of ‘figure 8’ airfilled cells, which alternately (1 cell in 2) inflate and deflate, to enable tissue reperfusion during the deflation cycle (McGinnis et al, 2014). In addition, at the foot end of the mattress are five cells with Wound Valve Technology. These Valves can be operated by the nurse to deflate one or more cells to relieve pressure directly underneath the patient’s heels (Figures 3 and 4). This completely removes heel contact from the surface of the mattress, achieving complete offloading. Rithalia (2007) analysed the effectiveness of the Wound Valve Technology, demonstrating that a period of reactive hyperaemia followed by prompt return to baseline perfusion occurred when the cell was deflated under the heel.
The evaluation The purpose of the evaluation was to determine whether the Nimbus 4 with Wound Valve Technology in the heel section would effectively provide pressure relief by offloading the heels. It also set out to assess the ICU nurses’ opinions on its ease of use and to establish whether it would reduce the use of other pressure-relieving adjuncts such as foam boots and pillows. ArjoHuntleigh representatives demonstrated the key features of the Nimbus 4 and provided written information on how the Wound Valves should be used. Staff were also given user guides on the functions and settings of the mattress, and how to use its pump. The nurses were encouraged to use the Wound Valves to
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Box 3. Classification of critical care patients Level 2 Patients requiring more detailed observation or intervention, including support for a single, failing organ system, postoperative care or those stepping down from a higher level of support. Level 3 Patients requiring advanced respiratory support alone, or basic respiratory support, together with support for at least two other organs. This level includes all complex patients requiring support for multi-organ failure. Source: Department of Health, 2000
about their experience using the Nimbus 4. Of these, 30 replied, giving a response rate of 50%.
Efficacy None of the patients cared for on the Nimbus 4 mattresses developed heel ulcers during the evaluation period. Given that the level 3 patients’ typically had Waterlow Scores >20, this demonstrates that the mattress was tested on patients at a high risk of pressure ulceration.
Figure 3. Bed view
Figure 4. Wound valves
provide pressure relief on their patients’ heels and to continue using the ICU skin care bundle, which includes assessment of key pressure points every 2–4 hours; patient repositioning; and attending to factors such as nutrition, hydration, skin hygiene and continence (Intensive Care Unit, Chelsea and Westminster Hospital, 2013).The Waterlow risk assessment tool was used to assess the patients’ overall risk of pressure ulceration. The evaluation took place over a 10-week period. During this time, 82 patients were admitted: 24 level 3 patients and 58 level 2 (Box 3). A small minority of patients admitted as level 2 deteriorated and required level 3 care. Initially, only level 3 patients used the Nimbus 4 mattress but approximately twothirds of the way through the evaluation period, level 2 patients were also included in order to maximise the opportunity to evaluate the product. Waterlow scores ranged from 16 to 42, indicating that patients were at high or very high risk of pressure ulceration (Waterlow, 2005). During the evaluation, 60 registered ICU nurses were invited to fill in a questionnaire enquiring
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None of the nurses had used the Nimbus 4 mattress before, but all were familiar with the Nimbus 3 APM, which is similar to the Nimbus 4 but does not have Wound Valve Technology. All staff stated they found the Nimbus 4 easy to set up and use. The majority of staff had previously used foam boots or pillows to offload the heel. These had also been effective, with no incidence of heel pressure ulcers in the preceding 6 months. However, the key advantage of Nimbus 4 is that it provides immediate and integral offloading of the heel from the moment the patient is admitted into ICU, when the nurses will be focusing on the acute management of a clinically unstable patient. It also reduces the need for additional devices for heel offloading, which can take time to access. The absence of boots facilitated ease of skin assessment, and patients who were alert may have been more comfortable without foam boots, which some regard as hot and uncomfortable. Patient comfort was not specifically addressed, as the focus of this evaluation was prevention of heel ulcers. However, one patient who exceeded the unit’s average length of stay, and had a high Waterlow score, stated expressly that she found the ‘mattress very comfortable’. In the early stages of the evaluation, many of the nurses were cautious about switching over to the Wound Valves, but most became confident about using the Nimbus 4 as the evaluation progressed. A few minor limitations were reported. In general, only one cell adjacent to the heel was deflated to provide an area of complete offloading. Therefore, if a patient moved his or her foot voluntarily or as result of gravitational forces, the heel would invariably rest on an adjacent cell. While there was no risk to the patient, as the cell was still alternating, a quick manual action was required to deflate this new cell. As with any alternating surface, it was also necessary to ensure
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Ease of use and use of foam boots or pillows
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PRODUCT FOCUS the bedsheet was not stretched tightly over the mattress, to prevent hammocking over the vented heel cell. When the mattress was in static mode for patient-positioning purposes or to conduct a nursing procedure, a manual operation was required to resume alternating pressure. The intention is to ensure nurses have enough time to complete the procedure. However, as there is only a visual alarm to indicate that the device was in static mode, care was needed to ensure the device was not left in this mode for longer than was necessary. Finally, the authors note that care should be taken to ensure that the heel is monitored for shear and friction in an agitated patient with voluntary movement. These limitations could be minimised by providing staff with further training and support, and increasing their familiarity with the product. In addition, it would be helpful to include in the ICU skin bundle documentation a prompt for nurses to check the mattress settings. Despite these limitations, the product was found to be effective in preventing pressure ulcers. Nimbus 4 might be considered for future bed management projects within the trust.
Conclusion Overall, the absence of heel or sacral pressure ulcers may be regarded as a positive indicator associated with this product. However, it is important to acknowledge the limitations of this evaluation in terms of the small patient numbers and short timescale. Eliminating heel pressure ulcers remains a significant focus, particularly for critically ill patients, due to the anatomy and physiology of the heel, and underlying risk factors associated with ICU patients. While various devices are available to prevent pressure ulcers on the heels, the Nimbus 4 offers an integrated system of pressure redistribution for the body surface, while also providing an innovative method for offloading heel pressure. It also provides an additional option BJN to enhance care and comfort of vulnerable patients.
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Conflict of interest: This article was supported by ArjoHuntleigh Bennett G, Dealey C, Posnett J (2004) The cost of pressure ulcers in the UK. Age Ageing 33(3): 230-5 Black JM, Edsberg LE, Baharestani MM et al (2011) Pressure ulcers: avoidable or unavoidable? Results of the National Pressure Ulcer Advisory Panel Consensus Conference. Ostomy Wound Manage 57(2): 24-37. http://tinyurl. com/kddzlto (accessed 5 August 2014) Burdette-Taylor SR, Kass J (2002) Heel ulcers in critical care units: a major pressure problem. Crit Care Nurs Q 25(2): 41-53 Campbell KE, Woodbury MG, Houghton PE (2010) Implementation of best practice in the prevention of heel pressure ulcers in the acute orthopedic population. Int Wound J 7(1): 28-40 Cichowitz A, Pan WR, Ashton M (2009) The heel: anatomy, blood supply, and the pathophysiology of pressure ulcers. Ann Plast Surg 62(4): 423-9. doi: 10.1097/SAP.0b013e3181851b55. Coleman S, Gorecki C, Nelson A et al (2013) Patient risk factors for pressure ulcer development: systematic review. Int J Nurs Stud 50: 974-1003. doi: 10.1016/j.ijnurstu.2012.11.019 Dealey C, Posnett J, Walker A (2012) The cost of pressure ulcers in the United Kingdom. J Wound Care 24(6): 261-6 Department of Health (2000) Comprehensive Critical Care: A Review of Adult Critical Care Services. DH, London Department of Health (2010) Essence of Care 2010: Benchmarks for Prevention and Management of Pressure Ulcers. http://tinyurl.com/okvlhkt (accessed 5 August 2014) Department of Health (2012) Delivering the NHS Safety Thermometer CQUIN 2013/14. http://tinyurl.com/b7kptql (accessed 5 August 2014) Donnelly J, Winder J, Kernohan WG, Stevenson M (2011) An RCT to determine the effect of a heel elevation device in pressure ulcer prevention post hip fracture. J Wound Care 20(7): 309-18 European Pressure Ulcer Advisory Panel, National Pressure Ulcer Advisory
British Journal of Nursing, 2014 (Tissue Viability Supplement),Vol 23, No 15
KEY POINTS n The heel is particularly at risk of developing ulceration due to its unique anatomy n Reducing the incidence of heel pressure ulcers in the intensive care unit (ICU) should be an achievable goal, as offloading the patient’s heels is usually possible even for the most unstable patients n The Nimbus 4 replacement system is unique in providing a specific heel zone designed to help prevent heel pressure ulcers n None of the ICU patients cared for on the Nimbus 4 mattresses developed heel ulcers during the evaluation period. Panel (2009) Pressure Ulcer Prevention: Quick Reference Guide. http://tinyurl. com/378oexd (accessed 5 August 2014) Fowler E, Scott-Williams S, McGuire JB (2008) Practice recommendations for preventing heel pressure ulcers. Ostomy Wound Manage 54(10): 42-57 Gefen A (2010) The biomechanics of heel ulcers. J Tissue Viability 19:124-31. doi: 10.1016/j.jtv.2010.06.003 Gilcreast DM, Warren JB, Yoder LH, Clark JJ, Wilson JA, Mays MZ (2005) Research comparing three heel ulcer-prevention devices. J Wound Ostomy Continence Nurs 32(2): 112-20 Gorecki C, Brown J, Nelson A et al (2009) Impact of pressure ulcers on quality of life in older patients: A systematic review. J Am Geriatr Soc 57(7): 1175-83. doi: 10.1111/j.1532-5415.2009.02307.x. Goossens RH, Rithalia SV (2007) Physiological response to the heel tissue on pressure relief between three alternating pressure air mattresses. J Tissue Viability 17: 10-14 Hampton S (2003) The complexities of heel ulcers. Nurs Stand 17(31): 68-79 Heyneman A, Vanderwee K, Grypdonck M, Defloor T (2009) Effectiveness of two cushions in the prevention of heel pressure ulcers. Worldviews Evid Based Nurs 6(2): 114-20. doi: 10.1111/j.1741-6787.2009.00153.x Intensive Care Unit Chelsea and Westminster Hospital (2013) Skin Bundle; Version 1.1. Chelsea and Westminster Hospital, London Junkin J, Gray M (2009) Are pressure redistribution surfaces or heel protection devices effective for preventing heel ulcers? J Wound Ostomy Continence Nurs 36(6): 602-8. doi: 10.1097/WON.0b013e3181be282f. Kim P, Steinberg J (2013) Complications of the diabetic foot. Endocrinol Metab Clin North Am 42: 833-47. doi: 10.1016/j.ecl.2013.08.002. Mayrovitz H, Sims N (2004) Effects of support surface relief pressures on heel skin blood flow in persons with and without diabetesm. Adv Skin Wound Care 17(4): 197-201 Mayrovitz H, Sims N,Taylor M, Dribin L (2003) Effect of support surface relief pressures on heel skin blood perfusion. Adv Skin Wound Care 16(3): 141-5 McGinnis E, Greenwood D, Nelson E, Nixon J (2014) A prospective cohort study of prognostic factors for the heeling of heel pressure ulcers. Age Ageing 43: 267-71. doi: 10.1093/ageing/aft187. Epub 2013 National Institute for Health and Care Excellence (2014) Pressure ulcers: Prevention and Management of Pressure Ulcers. Clinical Guideline 179. http:// tinyurl.com/nu3lawr (accessed 5 August 2014) Ockenden L (2001) Aetiology and pathology of vascular disease. In: Murray S, ed, Vascular Disease: Nursing and Management. Whurr, London Ousey K (2009) Heel ulceration—An exploration of the issues. Journal of Orthopaedic Nursing 13: 97-104. doi: 10.1016/j.joon.2009.06.001 Rithalia S (2007) Using non-invasive measurement techniques to describe the technical and physiological performance of a unique alternating pressure redistributing mattress (APRM):Nimbus 3 professional; incorporating ‘wound valve’ technology. Clinical focus therapeutic surfaces. Arjo Huntleigh Getinge Group, UK Rutishauser S (1994) Physiology and Anatomy. A Basis for Nursing and Health Care. Churchill Livingstone, Edinburgh Salcido R, Lee A, Ahn C (2011) Heel pressure ulcers: purple heel and deep tissue injury. Adv Skin Wound Care 24(8): 374-80. doi: 10.1097/01. ASW.0000403250.85131.b9. Sopher R, Nixon J, McGinnis E, Gefen A (2011) The influence of foot posture, support stiffness, heel pad loading and tissue mechanical properties on biomechanical factors associated with a risk of heel ulceration. J Mech Behav Biomed Mater 4(4): 572-82. doi: 10.1016/j.jmbbm.2011.01.004 Theaker C, Mannan M, Ives N, Soni N, (2000) Risk factors for pressure sores in the critically ill. Anaesthesia 55(3): 221-4 Thoolen M, Ryan TJ, Bristow I (2000) A study of the sole of the foot using high frequency ultrasonography and histology. The Foot 10: 14-17. doi: 10.1054/ foot.1999.0568 Vanderwee K, Clark M, Dealey C, Gunningberg L, Defloor T (2007) Pressure ulcer prevalence in Europe: a pilot study. J Eval Clin Pract 13(2): 227-235 Waterlow J (2005) Waterlow Pressure Ulcer Prevention/Treatment policy card. Revised version. Revised 2005. http://tinyurl.com/63dj6c5 (accessed 5 August 2014) Wong VK, Stotts NA (2003) Physiology and prevention of heel ulcers.The state of the science. J Wound Ostomy Continence Nurs 30(4): 191-8
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British Journal of Nursing.Downloaded from magonlinelibrary.com by 130.113.086.233 on January 6, 2015. For personal use only. No other uses without permission. . All rights reserved.
The heel continues to be one of the most common sites of pressure damage. This article reviews the anatomy and physiology of the heel and explores significant risk factors, including those found in the critically ill patient. Interventions to prevent heel pressure ulceration by offloading the heel are explored. An evaluation of the Nimbus 4 alternating pressure mattress was undertaken within an intensive care unit (ICU) to consider the efficacy of its unique Wound Valve Technology, which is designed to help prevent heel pressure ulceration. During the evaluation period none of the patients using the Nimbus 4 developed a pressure ulcer. Staff observed that the Wound Valves provided effective pressure redistribution and, although the cells frequently needed to be adjusted, patient safety was maintained throughout. The Wound Valves were most effective on patients who were less prone to voluntary movement. Key words: Heel pressure ulcer ■ Heel anatomy ■ Heel physiology ■ Risk factors ■ Intensive care unit ■ Nimbus 4 ■ Wound Valve
P
revention of pressure ulcers within acute care settings remains a significant challenge, with reported heel ulceration accounting for 25-30% of all pressure ulcers (McGinnis et al, 2014). Heels are the secondmost common site of damage after the sacrum (Vanderwee et al, 2007). Pressure ulcer prevention is regarded as a multidisciplinary issue and as a quality indicator of harmfree care (European Pressure Ulcer Advisory Panel (EPUAP) and National Pressure Ulcer Advisory Panel (NPUAP), 2009; Department of Health (DH), 2010; 2012). This article focuses on the prevention of heel pressure ulcers within the intensive care unit (ICU) setting. The anatomy of the heel is described, and theories relating to the pathology of heel ulcer development are examined, together with specific risk factors affecting ICU patients. Use of an alternating pressure air-filled mattress, with unique Wound Valve Technology at the foot of the mattress, was assessed by nurses in a general intensive care/high dependency unit (ITU/HDU) with an additional two burns ICU beds. The process of the evaluation and feedback is provided, and the impact of this technology on clinical practice is considered. Sarah Masterson, Tissue Viability Clinical Nurse Specialist; Caroline Younger, ICU Sister, Chelsea and Westminster Hospital NHS Foundation Trust, London. Accepted for publication: July 2014
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Cost to health economies and individuals The cost of pressure ulcers is significant for both the individual and health economies. Bennett et al (2004) estimated the total cost to the NHS to be between £1.4 billion and £2.1 billion annually. More recent estimates indicate this cost is increasing (Dealey et al, 2012). For the individual patient, the impact can be considerable, leading to physical, psychological and social issues in addition to the financial impact (Gorecki et al, 2009). Pressure ulcers on the heel can result in increased length of hospital stay and even the loss of the limb due to infection, and potential development of osteomyelitis (Burdette-Taylor and Kass, 2002). There may also be life-threatening consequences such as sepsis and multi-organ failure (Sopher et al, 2011).
Heels: anatomy and physiology The heel is particularly at risk of developing ulceration due to its unique anatomy. The foot is designed to be loaded with significant stresses, such as pressure and shear, on mobilising (Salcido et al, 2011). The skin of the heel is generally thicker than other areas of the body, with dense connective tissue and good microcirculation. It lacks hair follicles and sebaceous glands, with a large number of (eccrine) sweat glands, and maintains good sensitivity and microcirculation (Thoolen et al, 2000). The lack of sebum contributes to the dry nature of the skin, reducing elasticity and resilience with dryness that is exacerbated by friction (Ousey, 2009). Cichowitz et al (2009) studied the heel’s structure, finding that the heel pad has a cup-like structure, made up of skin and connective tissue, with pockets of fat that are thought to offer shock absorbency. Unlike other areas of significant bony prominences, such as the ischial tuberosities where there are gluteal muscles, there are no large muscles to further minimise pressure (Sopher et al, 2011). The blood supply includes the medial calcaneal branch of the posterial tibial artery and the lateral and medial plantar arteries. However, the fat between the connective tissue is almost avascular, (Cichowitz et al, 2009) (Figure 1).
Pressure ulcers and the heel Pressure ulcers are localised areas of damage to the skin and underlying tissues caused by direct pressure and shear, friction and other factors yet to be fully determined (EPUAP and NPUAP, 2009) (Figure 2). Pressure ulcers usually develop over bony prominences of the body such as the sacrum and heel. The heels are particularly at risk due to the limited surface area and thin layer of tissues overlaying the calcaneus (Fowler et al, 2008; Gefen, 2010). Patients with
© 2014 MA Healthcare Ltd
Abstract
British Journal of Nursing, 2014 (Tissue Viability Supplement),Vol 23, No 15
British Journal of Nursing.Downloaded from magonlinelibrary.com by 130.113.086.233 on January 6, 2015. For personal use only. No other uses without permission. . All rights reserved.
Andrew Bezear
Box 1. Hyperaemia When pressure is applied, the microcirculation can be reduced or stopped. When pressure is removed or interrupted, blood flow returns and the vessels dilate to provide an increased blood flow to enable a return to normal perfusion as quickly as possible, this is called reactive hyperaemia
Achilles tendon
Sources: Hampton, 2003; Wong and Stotts, 2003
Bursa
Box 2. Risk factors affecting the critically ill Decreased tissue perfusion due to: mean arterial blood pressure ■■ Altered cardiac function ■■ Vasopressors, i.e. noradrenaline or adrenaline infusions ■■ Low circulating blood volume ■■ Low haemoglobin ■■ Low
Vulnerable zone
Immobility due to: required for mechanical ventilation ■■ Decreased level of consciousness and delirium ■■ Nurses unable to turn patient with severe cardio-respiratory instability ■■ Sedation
Calcaneus Heel fat pad
Malnutrition due to: metabolic requirement caused by critical illness ■■ Impaired gut motility and/or absorption caused by opiate use or gastrointestinal surgery/disease ■■ Increased
Andrew Bezear
Figure 1. Heel anatomy
Skin changes: maceration i.e. sweating and wound exudate ■■ Low serum albumin ■■ Generalised tissue oedema ■■ Faecal incontinence ■■ Skin
Other factors: of multiple co-morbidities ■■ Elderly patients. ■■ ICU length of stay >3 days ■■ Presence
Figure 2. Heel pressure point where ulcer occurs
co-morbidities such as diabetes, oedema and arterial disease are at increased risk of heel pressure ulcers. The diabetic heel is at risk of pressure ulceration because of peripheral neuropathy, where the protective sensation is lost, resulting in continued trauma or pressure to the skin. Hyperglycaemia over time causes linking of collagen fibres in the connective tissues, resulting in stiffer skin that is less able to diffuse pressure through tissue deformation (Gefen, 2010).
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The frequently dry epidermis is more susceptible to tearing and atrophy of the subcutaneous tissue, reducing its ability to assimilate shock during mobilisation (Hampton, 2003; Kim and Steinburg, 2013). Patients with arterial disease, either macrovascular or microvascular, are also at risk as adequate perfusion is required to maintain healthy tissues. In arteriosclerosis, the lumen of the blood vessel is narrowed reducing blood flow. With advancing arterial disease, blood vessels can become occluded leading to ischaemia. People with diabetes have an increased risk of arterial disease associated with calcification of the large arteries as well as microvascular disease due to thickening arterial and basement membranes (Ockenden, 2001). Impeded blood flow will also slow its hyperaemic response (Hampton, 2003; Kim and Steinberg, 2013) (see Box 1). Oedema affects the diffusion of oxygen and nutrients to the soft tissues by increasing the distance between blood plasma and the cells (Rutishauser, 1994). Oedema results from injury; limb dependency; renal, hepatic or cardiac
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Source: Theaker et al, 2000
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PRODUCT FOCUS failure; hypoalbuminaemia; post-thrombotic syndrome or secondary venous obstruction (Ockenden, 2001). Gefen’s (2010) work supported the argument that oedema is a risk factor in pressure ulcer development due to the increase in tissue thickness and stiffening, possibly due to accumulation of fluid causing swelling or potentially an increase in osmotic tissue pressures. However, Coleman et al (2013) undertook a systemic review of primary research to identify risk factors that can independently predict pressure ulcer development in adults. This identified that a complex interplay of factors can explain pressure ulcer risk, with perfusion, including in diabetes, being one of the three most frequently identified independent factors.
Risk factors affecting ICU patients A number of critically ill patients are subject to the risk factors already described, but there are many additional factors to consider (Box 2). Despite the use of risk assessments and adherence to a skin-care bundle, which requires regular assessments of pressure points, nursing interventions and the high nurse– patient ratio in ICU, pressure ulcers do occur. It is also important to take account of tissue damage that may have occurred prior to patient admission to ICU and to recognise that pressure ulcers are not always avoidable (Black et al, 2011). Nevertheless, reducing the incidence of pressure ulcers developing on the heels should be an achievable goal, as offloading the patient’s heels is usually possible even for the most unstable patients.
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Offloading the heels EPUAP and NPUAP (2009) advise that heel pressure ulcers can be prevented by completely removing contact with the mattress. This can be achieved by lifting the lower legs and heels using pillows. In this way, pressure can be redistributed along the calf and the heels are raised from the mattress. Hyperextension of the knee should be prevented by maintaining slight flexion to prevent reduction in blood flow to the popliteal vein (Wong and Stotts, 2003). However, the legs may slide off the pillows, as the patient slips down the bed due to gravitational forces, leaving the heels in contact with the mattress once more (Heyneman et al, 2009). Disposable foam, padded or air-filled ‘boots’ have also been used with varying results and more research is needed to confirm their effectiveness (Junkin and Gray, 2009). The boots usually have an opening over the heel zone to provide a zero-pressure area to achieve offloading. These boots can be effective (EPUAP and NPUAP, 2009) but they are not without their flaws. In some cases the amount of air in the boot is insufficient to lift the heel off the bed, while foam boots may become compressed by heavier patients, reducing their effectiveness (Campbell et al, 2010). Also the thicker padded boots tend to be hot and are disliked by patients who are not sedated (Donnelly et al, 2011). Some types of boots cover only the foot and ankle and do not support the calf; this may cause hyperextension of the knee (Gilcreast et al, 2005). ICU patients are often nursed on either continuous lowpressure air mattresses (CLPAMs) or alternating-pressure mattresses (APMs). However, Ousey (2009) found that the
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interface pressure between the heel and the air mattress remains too high to maintain tissue perfusion of the heel. In contrast, Goossens and Rithalia (2007) demonstrated that some APMs significantly improved tissue perfusion of the heel. Mayrovitz et al (2003) found that hyperaemia was greatest when complete offloading was provided, in comparison with partial offloading in healthy subjects. Further work (Mayrovitz and Sims, 2004) reviewed the effect of pressure loading on hyperaemia in diabetics and non diabetics. They found that ‘hyperaemia was significantly greater in full off loading in non-diabetics compared to partial offloading’, but that diabetics showed no significant increase in hyperaemia from partial to full offloading, though the hyperaemic affect was significantly diminished in comparison to the non-diabetic group. The authors stated that these results provide preliminary evidence that periodic total offloading should be offered to all at-risk patients and prolonged total offloading to patients with reduced capacity for vasodilation. Although APMs are widely used within the acute hospital setting, the National Institute for Health and Care Excellence (NICE) (2014) has called for more independent research to confirm the overall efficacy and cost/benefit of these pressure-redistributing devices (in comparison with more basic products such as high-specification foam mattresses) and does not specifically endorse them. However, the Nimbus 4 mattress replacement system is unique in providing a specific heel zone designed to help prevent heel pressure ulcers.
The Nimbus 4 The Nimbus 4 mattress replacement system provides active pressure redistribution through a system of ‘figure 8’ airfilled cells, which alternately (1 cell in 2) inflate and deflate, to enable tissue reperfusion during the deflation cycle (McGinnis et al, 2014). In addition, at the foot end of the mattress are five cells with Wound Valve Technology. These Valves can be operated by the nurse to deflate one or more cells to relieve pressure directly underneath the patient’s heels (Figures 3 and 4). This completely removes heel contact from the surface of the mattress, achieving complete offloading. Rithalia (2007) analysed the effectiveness of the Wound Valve Technology, demonstrating that a period of reactive hyperaemia followed by prompt return to baseline perfusion occurred when the cell was deflated under the heel.
The evaluation The purpose of the evaluation was to determine whether the Nimbus 4 with Wound Valve Technology in the heel section would effectively provide pressure relief by offloading the heels. It also set out to assess the ICU nurses’ opinions on its ease of use and to establish whether it would reduce the use of other pressure-relieving adjuncts such as foam boots and pillows. ArjoHuntleigh representatives demonstrated the key features of the Nimbus 4 and provided written information on how the Wound Valves should be used. Staff were also given user guides on the functions and settings of the mattress, and how to use its pump. The nurses were encouraged to use the Wound Valves to
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Box 3. Classification of critical care patients Level 2 Patients requiring more detailed observation or intervention, including support for a single, failing organ system, postoperative care or those stepping down from a higher level of support. Level 3 Patients requiring advanced respiratory support alone, or basic respiratory support, together with support for at least two other organs. This level includes all complex patients requiring support for multi-organ failure. Source: Department of Health, 2000
about their experience using the Nimbus 4. Of these, 30 replied, giving a response rate of 50%.
Efficacy None of the patients cared for on the Nimbus 4 mattresses developed heel ulcers during the evaluation period. Given that the level 3 patients’ typically had Waterlow Scores >20, this demonstrates that the mattress was tested on patients at a high risk of pressure ulceration.
Figure 3. Bed view
Figure 4. Wound valves
provide pressure relief on their patients’ heels and to continue using the ICU skin care bundle, which includes assessment of key pressure points every 2–4 hours; patient repositioning; and attending to factors such as nutrition, hydration, skin hygiene and continence (Intensive Care Unit, Chelsea and Westminster Hospital, 2013).The Waterlow risk assessment tool was used to assess the patients’ overall risk of pressure ulceration. The evaluation took place over a 10-week period. During this time, 82 patients were admitted: 24 level 3 patients and 58 level 2 (Box 3). A small minority of patients admitted as level 2 deteriorated and required level 3 care. Initially, only level 3 patients used the Nimbus 4 mattress but approximately twothirds of the way through the evaluation period, level 2 patients were also included in order to maximise the opportunity to evaluate the product. Waterlow scores ranged from 16 to 42, indicating that patients were at high or very high risk of pressure ulceration (Waterlow, 2005). During the evaluation, 60 registered ICU nurses were invited to fill in a questionnaire enquiring
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None of the nurses had used the Nimbus 4 mattress before, but all were familiar with the Nimbus 3 APM, which is similar to the Nimbus 4 but does not have Wound Valve Technology. All staff stated they found the Nimbus 4 easy to set up and use. The majority of staff had previously used foam boots or pillows to offload the heel. These had also been effective, with no incidence of heel pressure ulcers in the preceding 6 months. However, the key advantage of Nimbus 4 is that it provides immediate and integral offloading of the heel from the moment the patient is admitted into ICU, when the nurses will be focusing on the acute management of a clinically unstable patient. It also reduces the need for additional devices for heel offloading, which can take time to access. The absence of boots facilitated ease of skin assessment, and patients who were alert may have been more comfortable without foam boots, which some regard as hot and uncomfortable. Patient comfort was not specifically addressed, as the focus of this evaluation was prevention of heel ulcers. However, one patient who exceeded the unit’s average length of stay, and had a high Waterlow score, stated expressly that she found the ‘mattress very comfortable’. In the early stages of the evaluation, many of the nurses were cautious about switching over to the Wound Valves, but most became confident about using the Nimbus 4 as the evaluation progressed. A few minor limitations were reported. In general, only one cell adjacent to the heel was deflated to provide an area of complete offloading. Therefore, if a patient moved his or her foot voluntarily or as result of gravitational forces, the heel would invariably rest on an adjacent cell. While there was no risk to the patient, as the cell was still alternating, a quick manual action was required to deflate this new cell. As with any alternating surface, it was also necessary to ensure
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Ease of use and use of foam boots or pillows
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PRODUCT FOCUS the bedsheet was not stretched tightly over the mattress, to prevent hammocking over the vented heel cell. When the mattress was in static mode for patient-positioning purposes or to conduct a nursing procedure, a manual operation was required to resume alternating pressure. The intention is to ensure nurses have enough time to complete the procedure. However, as there is only a visual alarm to indicate that the device was in static mode, care was needed to ensure the device was not left in this mode for longer than was necessary. Finally, the authors note that care should be taken to ensure that the heel is monitored for shear and friction in an agitated patient with voluntary movement. These limitations could be minimised by providing staff with further training and support, and increasing their familiarity with the product. In addition, it would be helpful to include in the ICU skin bundle documentation a prompt for nurses to check the mattress settings. Despite these limitations, the product was found to be effective in preventing pressure ulcers. Nimbus 4 might be considered for future bed management projects within the trust.
Conclusion Overall, the absence of heel or sacral pressure ulcers may be regarded as a positive indicator associated with this product. However, it is important to acknowledge the limitations of this evaluation in terms of the small patient numbers and short timescale. Eliminating heel pressure ulcers remains a significant focus, particularly for critically ill patients, due to the anatomy and physiology of the heel, and underlying risk factors associated with ICU patients. While various devices are available to prevent pressure ulcers on the heels, the Nimbus 4 offers an integrated system of pressure redistribution for the body surface, while also providing an innovative method for offloading heel pressure. It also provides an additional option BJN to enhance care and comfort of vulnerable patients.
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Conflict of interest: This article was supported by ArjoHuntleigh Bennett G, Dealey C, Posnett J (2004) The cost of pressure ulcers in the UK. Age Ageing 33(3): 230-5 Black JM, Edsberg LE, Baharestani MM et al (2011) Pressure ulcers: avoidable or unavoidable? Results of the National Pressure Ulcer Advisory Panel Consensus Conference. Ostomy Wound Manage 57(2): 24-37. http://tinyurl. com/kddzlto (accessed 5 August 2014) Burdette-Taylor SR, Kass J (2002) Heel ulcers in critical care units: a major pressure problem. Crit Care Nurs Q 25(2): 41-53 Campbell KE, Woodbury MG, Houghton PE (2010) Implementation of best practice in the prevention of heel pressure ulcers in the acute orthopedic population. Int Wound J 7(1): 28-40 Cichowitz A, Pan WR, Ashton M (2009) The heel: anatomy, blood supply, and the pathophysiology of pressure ulcers. Ann Plast Surg 62(4): 423-9. doi: 10.1097/SAP.0b013e3181851b55. Coleman S, Gorecki C, Nelson A et al (2013) Patient risk factors for pressure ulcer development: systematic review. Int J Nurs Stud 50: 974-1003. doi: 10.1016/j.ijnurstu.2012.11.019 Dealey C, Posnett J, Walker A (2012) The cost of pressure ulcers in the United Kingdom. J Wound Care 24(6): 261-6 Department of Health (2000) Comprehensive Critical Care: A Review of Adult Critical Care Services. DH, London Department of Health (2010) Essence of Care 2010: Benchmarks for Prevention and Management of Pressure Ulcers. http://tinyurl.com/okvlhkt (accessed 5 August 2014) Department of Health (2012) Delivering the NHS Safety Thermometer CQUIN 2013/14. http://tinyurl.com/b7kptql (accessed 5 August 2014) Donnelly J, Winder J, Kernohan WG, Stevenson M (2011) An RCT to determine the effect of a heel elevation device in pressure ulcer prevention post hip fracture. J Wound Care 20(7): 309-18 European Pressure Ulcer Advisory Panel, National Pressure Ulcer Advisory
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KEY POINTS n The heel is particularly at risk of developing ulceration due to its unique anatomy n Reducing the incidence of heel pressure ulcers in the intensive care unit (ICU) should be an achievable goal, as offloading the patient’s heels is usually possible even for the most unstable patients n The Nimbus 4 replacement system is unique in providing a specific heel zone designed to help prevent heel pressure ulcers n None of the ICU patients cared for on the Nimbus 4 mattresses developed heel ulcers during the evaluation period. Panel (2009) Pressure Ulcer Prevention: Quick Reference Guide. http://tinyurl. com/378oexd (accessed 5 August 2014) Fowler E, Scott-Williams S, McGuire JB (2008) Practice recommendations for preventing heel pressure ulcers. Ostomy Wound Manage 54(10): 42-57 Gefen A (2010) The biomechanics of heel ulcers. J Tissue Viability 19:124-31. doi: 10.1016/j.jtv.2010.06.003 Gilcreast DM, Warren JB, Yoder LH, Clark JJ, Wilson JA, Mays MZ (2005) Research comparing three heel ulcer-prevention devices. J Wound Ostomy Continence Nurs 32(2): 112-20 Gorecki C, Brown J, Nelson A et al (2009) Impact of pressure ulcers on quality of life in older patients: A systematic review. J Am Geriatr Soc 57(7): 1175-83. doi: 10.1111/j.1532-5415.2009.02307.x. Goossens RH, Rithalia SV (2007) Physiological response to the heel tissue on pressure relief between three alternating pressure air mattresses. J Tissue Viability 17: 10-14 Hampton S (2003) The complexities of heel ulcers. Nurs Stand 17(31): 68-79 Heyneman A, Vanderwee K, Grypdonck M, Defloor T (2009) Effectiveness of two cushions in the prevention of heel pressure ulcers. Worldviews Evid Based Nurs 6(2): 114-20. doi: 10.1111/j.1741-6787.2009.00153.x Intensive Care Unit Chelsea and Westminster Hospital (2013) Skin Bundle; Version 1.1. Chelsea and Westminster Hospital, London Junkin J, Gray M (2009) Are pressure redistribution surfaces or heel protection devices effective for preventing heel ulcers? J Wound Ostomy Continence Nurs 36(6): 602-8. doi: 10.1097/WON.0b013e3181be282f. Kim P, Steinberg J (2013) Complications of the diabetic foot. Endocrinol Metab Clin North Am 42: 833-47. doi: 10.1016/j.ecl.2013.08.002. Mayrovitz H, Sims N (2004) Effects of support surface relief pressures on heel skin blood flow in persons with and without diabetesm. Adv Skin Wound Care 17(4): 197-201 Mayrovitz H, Sims N,Taylor M, Dribin L (2003) Effect of support surface relief pressures on heel skin blood perfusion. Adv Skin Wound Care 16(3): 141-5 McGinnis E, Greenwood D, Nelson E, Nixon J (2014) A prospective cohort study of prognostic factors for the heeling of heel pressure ulcers. Age Ageing 43: 267-71. doi: 10.1093/ageing/aft187. Epub 2013 National Institute for Health and Care Excellence (2014) Pressure ulcers: Prevention and Management of Pressure Ulcers. Clinical Guideline 179. http:// tinyurl.com/nu3lawr (accessed 5 August 2014) Ockenden L (2001) Aetiology and pathology of vascular disease. In: Murray S, ed, Vascular Disease: Nursing and Management. Whurr, London Ousey K (2009) Heel ulceration—An exploration of the issues. Journal of Orthopaedic Nursing 13: 97-104. doi: 10.1016/j.joon.2009.06.001 Rithalia S (2007) Using non-invasive measurement techniques to describe the technical and physiological performance of a unique alternating pressure redistributing mattress (APRM):Nimbus 3 professional; incorporating ‘wound valve’ technology. Clinical focus therapeutic surfaces. Arjo Huntleigh Getinge Group, UK Rutishauser S (1994) Physiology and Anatomy. A Basis for Nursing and Health Care. Churchill Livingstone, Edinburgh Salcido R, Lee A, Ahn C (2011) Heel pressure ulcers: purple heel and deep tissue injury. Adv Skin Wound Care 24(8): 374-80. doi: 10.1097/01. ASW.0000403250.85131.b9. Sopher R, Nixon J, McGinnis E, Gefen A (2011) The influence of foot posture, support stiffness, heel pad loading and tissue mechanical properties on biomechanical factors associated with a risk of heel ulceration. J Mech Behav Biomed Mater 4(4): 572-82. doi: 10.1016/j.jmbbm.2011.01.004 Theaker C, Mannan M, Ives N, Soni N, (2000) Risk factors for pressure sores in the critically ill. Anaesthesia 55(3): 221-4 Thoolen M, Ryan TJ, Bristow I (2000) A study of the sole of the foot using high frequency ultrasonography and histology. The Foot 10: 14-17. doi: 10.1054/ foot.1999.0568 Vanderwee K, Clark M, Dealey C, Gunningberg L, Defloor T (2007) Pressure ulcer prevalence in Europe: a pilot study. J Eval Clin Pract 13(2): 227-235 Waterlow J (2005) Waterlow Pressure Ulcer Prevention/Treatment policy card. Revised version. Revised 2005. http://tinyurl.com/63dj6c5 (accessed 5 August 2014) Wong VK, Stotts NA (2003) Physiology and prevention of heel ulcers.The state of the science. J Wound Ostomy Continence Nurs 30(4): 191-8
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