Immobility, shear and friction

Patients who spend significant periods of time in a supine position, for example those on extended bedrest, may find that their feet tend to abduct (rotate externally). This rotation causes pressure to pass through the lateral (outer) aspect of the heel to the calcaneus, where the fat pad is thin and irregularly shaped (Tenenbaum et al 2013). Patients who have undergone surgery are at increased risk of heel pressure ulcers because analgesia and anaesthesia reduce their pain responses to pressure and because they are immobilised for prolonged periods (Edwards et al 2006). Orthopaedic and vascular surgical interventions may require postoperative immobilisation of the lower limb.

Shear and friction are common extrinsic factors increasing the risk of heel pressure ulcers. Shear occurs when the bones and the skin move in opposite directions – for example during suboptimal repositioning where the patient is pulled along the bed – and is a common issue in patients with suboptimal mobility (Davies 2018). Shear affecting the heels can occur if the patient slides downwards due to inadequate positioning in a chair or bed, or if the patient uses their heels as a pivot point when repositioning themselves. Friction can be described as the mechanical force exerted when a patient is moved across a coarse surface such as bed sheets, which prevents the skin from sliding along smoothly (Gleeson 2016). Friction to the heel can be caused by a suboptimal moving and handling technique or by frequent foot movements, for example in patients experiencing tremors or agitation.

Skin status and presence of pressure ulcers

The presence of a category 1 pressure ulcer is correlated with a two-to-threefold increase in a patient’s risk of developing a more severe pressure ulcer (Nixon et al 2007). The presence of scar tissue and the presence of dry, thin or oedematous skin also increase the pressure ulcer risk. Ageing has been found to increase the risk of pressure ulcers due to the thinning of the epidermis (outer layer of the skin) as part of the normal ageing process (Baumgarten et al 2006). Ageing also causes the skin to become dehydrated and lacking in sebum (Tong et al 2016), connective tissue to lose its elasticity and strength, and blood vessels to become increasingly fragile (Defloor 1999). Furthermore, subcutaneous tissues become thinner with age, which reduces the already minimal padding over the calcaneus and reduces the heel’s capacity to absorb shock (Alcántara et al 2002).

Suboptimal tissue perfusion

The lower limbs are particularly vulnerable to reduced perfusion, which causes a reduction in the supply of oxygen and nutrients to the tissues in the foot. Suboptimal lower limb perfusion has been estimated to affect 50-62% of patients with a heel pressure ulcer (Meaume and Faucher 2008, McGinnis et al 2014b). Examples of conditions that can cause suboptimal tissue perfusion include cardiovascular disease or coronary artery disease, diabetes, infections, peripheral vascular disease, stroke and renal disease. Suboptimal tissue perfusion can also be caused by the effects of cigarette smoking, hypotension, hypoalbuminaemia and the use of inotropes (medicines that affect the strength of heart contractions) to support cardiac function (Coleman et al 2014, EPUAP et al 2019).

When a patient is acutely unwell, their sympathetic nervous system preserves their vital organs – notably the heart and brain – by increasing circulation to these organs, which in turn results in decreased circulation to the peripheries. Vasopressors (medicines that induce vasoconstriction and raise blood pressure) work in a similar way. Therefore, acutely unwell patients such as those in intensive care settings are at higher risk than others of developing heel pressure ulcers (Coleman et al 2014, EPUAP et al 2019).

Peripheral vascular disease refers to any disease or disorder of the circulatory system outside the brain and heart. Peripheral vascular disease frequently affects the lower limbs and is caused by arteries becoming narrowed, weakened or blocked, resulting in reduced circulation to the feet. Peripheral vascular disease is commonly associated with older age but can also affect younger people who smoke or those with diabetes or hypertension (Tendera et al 2011).

Circulatory conditions such as peripheral vascular disease can lead to an increase in pedal (foot and ankle) oedema, which impairs the delivery of oxygen and nutrients to the tissues as well as the disposal of metabolic waste. Oedema can cause stiffening of the tissues, which affects pressure distribution, leading to greater stress during loading (when force and/or pressure is exerted through the tissues) (Gefen 2010). Oedematous lower limbs are also heavier, which can increase the pressure exerted on the heels.

Diabetes mellitus

Extended periods of hyperglycaemia as a result of diabetes can cause a thickening and interlinking of collagen fibres in the connective tissues, leading to progressive tissue stiffening (Gefen 2010). Diabetes can also cause foot ulceration, primarily over pressure points such as the toes and the plantar foot, often caused by accidental trauma, ill-fitting footwear and/or peripheral neuropathy (Jeffcoate and Harding 2003). Peripheral neuropathy involves nerve damage to the peripheral nervous system and can cause numbness as well as pain and weakness (Howarth 2019). Patients with peripheral neuropathy therefore become unaware of pain and pressure sensations that would normally indicate the need to reposition the foot and avoid trauma. As well as diabetes, peripheral neuropathy can also be caused by stroke, alcoholism, demyelinating diseases such as multiple sclerosis, and Guillain-Barré syndrome, a rare and serious condition that affects the nerves in the hands and feet (White et al 2004).

In patients with diabetes, it can be challenging for the nurse to differentiate between a diabetic foot ulcer located on the heel and a heel pressure ulcer. In this situation, the nurse needs to carefully consider the cause of the ulcer. For example, if the patient is immobile or bedbound and the ulcer affects the posterior aspect of the heel, it is likely to have been caused by pressure. Conversely, in a mobile patient or one whose ulcer is located on the plantar aspect of the heel, ill-fitting footwear may need to be considered as a potential cause. Regardless of the cause, any patient with diabetes and signs of foot ulceration should be referred to a multidisciplinary foot care service (National Institute for Health and Care Excellence (NICE) 2019).

Prevention of heel pressure ulcers

Because the development of a pressure ulcer is rarely due to a single causative factor, prevention strategies involve the nurse identifying each patient’s individual risk factors, as described previously – for example, immobility, skin status, presence of pressure ulcers and/or scar tissue, and suboptimal tissue perfusion. This should involve a holistic risk assessment along with a thorough skin assessment. The signs of pressure damage that the nurse should look for when examining a patient’s heels include any signs of redness, and whether the skin blanches (turns white when pressure is applied). It is not always possible to identify redness on darkly pigmented skin, so the nurse should assess for other signs of pressure damage including localised heat, oedema, blistering and induration (hardness) (Mitchell 2018).

In the UK, NICE states that patients in NHS secondary or long-term care must undergo a pressure ulcer risk assessment within six hours of admission (NICE 2014). If a patient is found to be at risk of pressure ulcers, a preventive care plan should be initiated.

An optimal moving and handling technique is crucial to prevent the development of pressure ulcers – but its description is beyond the scope of this article. Another crucial component of any pressure ulcer preventive care plan is reducing the duration of pressure to the heels through regular repositioning. In some patients, however, regular repositioning may not be possible or may be insufficient to prevent the development of heel pressure ulcers. This is the case, for example, in some patients with peripheral arterial disease or those with immobilised limbs such as in lower limb fractures or those who may have been sedated in critical care. In these cases, the nurse may use their clinical judgement to decide that medical devices – such as support surfaces, heel-specific devices, pillows, wedges and prophylactic dressings – can be used to minimise the risk of heel pressure damage.

Support surfaces

The term support surface refers to mattresses, overlays and cushions. Support surfaces are generally divided into two categories: alternating pressure surfaces and constant low-pressure surfaces.

Alternating pressure devices work by reducing the duration of pressure exerted at the body’s points of contact with the device. For example, alternating pressure mattresses use air-filled cells that inflate and deflate alternately during a set cyclical time period (usually every 5-10 minutes). Some alternating pressure mattresses contain specific ‘heel zones’ that feature an area of air-filled cells designed to reduce pressures at the heel.

Constant low-pressure devices distribute the body’s weight over a larger surface area, reducing the pressure exerted on all body parts (McInnes et al 2015). They include foam mattresses, low air-loss mattresses and overlays.

There is little evidence regarding the effectiveness of support surfaces in preventing heel pressure ulcers specifically, but they are frequently used as part of a multifaceted care plan (Greenwood 2020).

Heel-specific devices

Any heel-specific device should increase blood flow to the heel area, reduce pressure and prevent shear. The device should be comfortable, practical – in that it can be used in all positions and during mobilisation – and cost-effective (Huber et al 2008). It should also minimise hyperextension of the knee, because this can compress the popliteal vein and contribute to the development of deep vein thrombosis (Huber and Huber 2009). There are several types of heel-specific devices, which can generally be categorised as:

Pillows and wedges

In clinical practice, pillows and wedges are commonly used to offload pressure. Pillows and wedges are practical short-term methods that can be used in patients who are alert and co-operative and can maintain the same position (EPUAP et al 2019). They are less suited for more mobile patients, patients demonstrating signs of agitation and patients who frequently move the lower limb. They do not assist in preventing footdrop.

Pillows and wedges should be placed under the full length of the patient’s calf, avoiding hyperextension of the knee, with the heel suspended above the mattress. If the pillow or wedge is placed inappropriately, the heel may still be in contact with a hard surface area of the bed. The thickness of pillows and wedges varies. If they are too thin or if the limb is too heavy, the heel may not be fully offloaded. Figure 2 shows the appropriate heel elevation using a pillow.

Figure 2.

Appropriate heel elevation using a pillow

Prophylactic dressings

Studies have demonstrated that foam dressings can reduce pressure as well as shear and friction (Levy et al 2015, Levy and Gefen 2016). Nakagami et al (2006) found that simple film dressings could limit the effects of shear, while according to a systematic review by Moore and Webster (2018) that investigated dressings and topical agents for preventing pressure ulcers, the incidence of pressure ulcers in all body areas was reduced with the use of silicone foam dressings. However, further evidence is required due to the suboptimal quality of some of the trials. In terms of the heel area specifically, there is no direct evidence of the effectiveness of any of these dressings (Greenwood et al 2020b).

Homemade devices

Historically, nurses have found resourceful solutions when seeking to relieve pressure on their patients’ heels, often using homemade devices to prevent the development of pressure ulcers. These homemade solutions include using water-filled latex gloves to cushion the heel and intravenous fluid bags placed under the heel to increase elevation. However, it has been known for some time that water-filled gloves can lead to higher pressures at the heel, while intravenous fluid bags can increase the pressure at the Achilles tendon (Lockyer-Stevens 1993, Williams 1993). Therefore, while resourceful, these methods are not recommended.