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Stepping up care for diabetic foot ulcers

SIEGGREEN, MARY Y. RN, APRN,BC, CVN, MSN

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FOOT ULCERS MAY START small, but they're a significant cause of amputation and death for people with diabetes. Half of all patients with diabetes who lose one leg will lose the other within 5 years. Only about 40% of patients who've had a foot or leg amputated live for another 5 years.

Your nursing care and teaching can help a patient beat the odds. To help you intervene effectively, I'll discuss why foot ulcers develop, how to recognize them early and respond effectively, and what to teach your patient to help him avoid more problems.

Reviewing the risks

Although all patients with diabetes are at risk for foot ulcers, these factors put patients at higher risk for ulcers and amputation:

  • male sex
  • smoking
  • having diabetes for more than 10 years
  • poor blood glucose control
  • previous foot ulcer or amputation
  • other complications of diabetes, such as peripheral neuropathy.

Let's take a closer look at some key factors that increase the likelihood of diabetic foot ulcers.

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Peripheral neuropathy

About half of all patients with diabetes have damage to the peripheral nervous system, especially in the feet. Both small and large fibers are affected in diabetes-associated peripheral neuropathy.

Damage to small nerve fibers of the feet causes numbness, burning, tingling, itching, and pain. Large-fiber damage causes changes in vibratory perception, proprioception, and deep tendon reflexes.

Neuropathy also weakens foot muscles, leading to deformities and gait changes. Increased pressure or shear stress over deformed bony prominences sets the stage for ulceration.

Autonomic neuropathy in the skin affects the sweat glands, reducing or eliminating perspiration and leading to dry, cracked, atrophic skin and encouraging callus formation. Peripheral vascular disease, common in patients with diabetes, reduces blood flow to the feet and legs. All of these changes contribute to ulcer formation and compromise healing.

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Peripheral arterial disease

Arterial insufficiency is four times more prevalent in patients with diabetes than in those without diabetes. Nearly half of patients who've had diabetes for 20 years or more have peripheral arterial disease (PAD), usually below the knees. The reduced blood flow robs the feet of nutrients needed to maintain healthy tissue and to heal ulcers.

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Charcot's foot

Caused by neuropathy, this progressive and degenerative arthropathy of the foot joints is common in patients with long-standing diabetes. Charcot's foot typically starts with a traumatic injury to the neuropathic foot. Over time, chronic inflammation and bone remodeling cause the foot's arch to collapse. If the patient is unaware of the problem and continues to put weight on the foot, the damage is compounded (see photograph).

Figure. C

Figure. C

Renal disease of diabetes—which can be asymptomatic in the early stages—also contributes to the bony changes and deformities in the foot. Disorders of calcium and phosphate metabolism associated with renal disease cause bone disease that often results in skeletal abnormalities. The arch becomes inverted (convex), and the thin skin of the arch, which isn't meant to bear weight, is vulnerable to ulceration.

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Foot trauma

Repetitive stress is probably the most frequent cause of injury to the diabetic foot. Because of neuropathy, the patient can't feel foot pain and may not notice trauma occurring over time. After an injury, the patient may not understand the importance of staying off his feet during treatment because the injured foot doesn't hurt. This is why teaching him about daily foot inspections and other routine care is so important (more on this later).

The patient may inadvertently puncture or cut his foot by trimming his toenails incorrectly or attempting to remove calluses. He can sustain blunt injuries if a heavy object falls onto his foot or if he stubs his foot on furniture while walking barefoot. An injury that would be minor to someone without diabetes could fracture fragile bones or disrupt intact tissue in your patient's feet.

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Performing an initial assessment

To assess the peripheral arterial system in your patient's feet and legs, palpate his femoral, popliteal, dorsalis pedis, and posterior tibial pulses. Diminished or absent pulses usually indicate PAD.

Because a patient with diabetes and neuropathy may also have PAD, he can develop neuropathic and arterial ulcers. Here's a quick and easy way to tell them apart:

  • Diminished or absent dorsalis pedis and posterior tibial pulses may indicate PAD.
  • Absent sensation most likely indicates neuropathy.

Note, however, that the presence of pedal pulses doesn't rule out PAD. For more details, see Arterial or neuropathic?

Next, inspect the skin on the foot for cyanosis, dependent rubor, pallor, erythema, calluses, dryness, cracking, edema, and ulceration. Also assess skin temperature and capillary bed refill time. Note any changes associated with chronic PAD, such as cool skin, decreased pedal hair, and nail atrophy.

Assess for musculoskeletal abnormalities in the diabetic foot, such as limited joint mobility, prominent metatarsal heads, and Charcot's deformities. Move the patient's toe and ankle joints through their range of motion to assess for joint rigidity and crepitus.

Also examine the patient's footwear for signs of pressure and rubbing that could lead to ulceration. Compare the relationship of worn areas inside the shoes with the location of redness or calluses on the patient's feet.

Figure

Figure

Your neurologic assessment should include testing for changes in foot sensation and proprioception (position sense). The Semmes-Weinstein monofilament test is a simple, inexpensive, and reliable test for sensory neuropathy. To perform this test, the clinician places a 10-gram filament against the skin with just enough pressure to cause the filament to bend. A patient with normal sensation will feel the pressure; a patient with neuropathy won't.

An ankle/brachial index, a test that indicates whether arterial flow to the extremities is compromised, can be easily performed at the bedside or in outpatient settings, but it may be artificially high in a patient with diabetes because of vessel calcification. Refer patients with diabetes to an accredited vascular lab for a toe/brachial index (TBI). Because calcification is less common in toe arteries, this measurement is more reliable in patients with diabetes and PAD. A TBI greater than 0.9 indicates that arterial flow is sufficient to heal a foot ulcer.

Thoroughly document all your assessment findings.

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Assessing a diabetic foot ulcer

If you discover your patient has a foot ulcer, assess and document its location, dimensions, undermining (if any), a description of the ulcer base and the periwound skin, presence or absence of exudate, and whether or not bone is exposed. Use a sterile blunt instrument to determine wound depth and assess for bone exposure.

Heel ulcers in a patient with diabetes are difficult to manage and are more likely to result in limb amputation than ulcers on other areas of the foot. Pressure is the most common cause of heel ulcers, which can develop if the patient is confined to bed or a chair. You'll typically find these ulcers on the medial, lateral, or posterior aspect of the heel. For more on managing them, see “Treating Heel Pressure Ulcers” in the Wound and Skin Care department of the January issue of Nursing2005.

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Managing a diabetic foot ulcer

With the exception of stable eschar on an uninfected heel ulcer, necrotic tissue and calluses must be removed for a foot ulcer to heal. The patient may believe that a callus is the body's way of protecting an area from injury, so teach him that a callus is a warning sign of abnormal pressure. As it thickens, it can destroy deeper soft tissue beneath it as the damaged area is subjected to repetitive pressure.

Calluses are best removed by a specialist using sharp debridement techniques. Other necrotic tissue can be removed by sharp, enzymatic, or autolytic debridement, as chosen by the patient's primary wound care provider or specialist.

One method that's not recommended is wet-to-dry gauze dressings. Although dried gauze will debride the wound when it's removed, it isn't selective and the removal traumatizes healthy new tissue.

Once the ulcer has been debrided and cleaned, it can be graded using a classification system. Several systems are in use for neuropathic ulcers, but none are universally accepted. Choose one and use it consistently to track the ulcer's progress. (See Grading a diabetic foot ulcer.)

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Dressing for healing success

The type of dressing used for a diabetic foot ulcer depends on the wound's characteristics, but all dressings should protect the wound from trauma, prevent contamination, and maintain a moist wound bed. Here are some choices and when they're indicated.

  • Occlusive and semiocclusive dressings are suitable for clean, uninfected wounds with minimal or no drainage. These dressings promote moist wound healing and should be used in patients with adequate arterial perfusion.
  • Absorbent dressings, such as foams or alginates, are used for wounds with large amounts of exudate. Gauze also can be used to absorb fluid. A wound with copious drainage may benefit from negative-pressure wound therapy to contain the moisture, stimulate new tissue growth, and reduce the number of dressing changes needed.
  • Silver impregnated dressings are appropriate for infected or heavily colonized wounds.

Growth factors such as becaplermin have been shown to enhance granulation tissue formation and promote healing in diabetic foot ulcers. The gel, which can be applied to full-thickness wounds with adequate blood supply, is used as an adjunct to good wound care.

Because healing can be delayed in patients with diabetes, skin substitutes may be a cost-effective choice for a diabetic foot ulcer. Apligraf, a human skin substitute, is indicated for full-thickness neuropathic foot ulcers (without tendon, muscle capsule, or bone exposure) of more than 3 weeks duration that haven't responded to conventional therapy. Applied to a wound, the two-layered sheet of living skin cells promotes revascularization and healing. Consult a wound care specialist if the patient's wound requires specialized treatment.

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Grading a diabetic foot ulcer

The two systems below commonly are used to grade diabetic foot ulcers.

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Meggit-Wagner Ulcer Classification

These grades are based on ulcer depth, and don't consider infection or ischemia.

  • 0–preulceration lesions, healed ulcer, or bony deformity
  • 1–superficial ulcer; no subcutaneous tissue involvement
  • 2–full-thickness ulcer; may expose bone, tendon, ligament, or joint capsule
  • 3–osteitis, abscess, or osteomyelitis
  • 4–gangrene of toe
  • 5–gangrene of foot
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University of Texas Staging System

Under this system, a wound is assigned a stage based on the presence or absence of infection and ischemia, and a grade based on the depth of the wound. The higher the grade and stage, the greater the risk of amputation.

  • Stage A–clean wounds (lowest risk)
  • Stage B–nonischemic infected wounds
  • Stage C–ischemic noninfected wounds
  • Stage D–ischemic infected wounds
  • Grade 0–Preulcerative or postulcerative lesion, completely epithelialized
  • Grade I–Superficial wound, not involving tendon, capsule, or bone
  • Grade II–Wound penetrating to tendon or capsule
  • Grade III–Wound penetrating to bone or joint
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Keeping the pressure off

To promote healing in a diabetic foot ulcer, keep pressure off the injured area. Teach the patient to use crutches or a wheelchair, or keep him on complete bed rest (if indicated) with pressure relief. If the wound isn't infected, another effective option for off-loading pressure is the total contact cast. When applied properly, it distributes pressure over the entire surface of the foot and leg, easing pressure on the ulcer. Total contact casting contributes to healing in about 90% of ulcers, compared with 61% for the removable walking cast. The advantage of the removable walking cast is that it can be removed, and the disadvantage is…that it can be removed. Its removability may be partly responsible for its lower healing rate. To prevent the patient from removing a walking cast, it can be covered with stockinette gauze and a light plaster cast dressing. This solution is less costly than total contact casting, but it also makes the wound inaccessible for routine care, so like the total contact cast, it's not suitable for infected wounds.

Other pressure-relieving devices, such as removable walking braces with rocker bottom soles, half shoes or wedge shoes, and shoe cutouts, are less effective. The choice of device depends on the patient's ability to understand and cooperate with treatment regimen.

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Fighting back against infection

Patients with diabetes are more prone to soft tissue and bone infections than patients without diabetes. Notoriously difficult to treat, infected diabetic foot ulcers significantly raise the risk of amputation. So be alert for signs and symptoms of infection and intervene aggressively at the first sign of trouble.

Patients with diabetic foot ulcers are susceptible to fungal infections, soft tissue infections, deep space abscesses, and osteomyelitis. The infection may be caused by more than one pathogen. These infections can be difficult to recognize because of the patient's impaired immune responses and neuropathy. Watch for an unexplained rise in serum blood glucose and white blood cell count, which may be accompanied by fever.

Obtain wound culture specimens from the wound tissue after the surface is cleaned and debrided. Administer an antibiotic that targets the offending pathogens, as prescribed. Note that decreased blood supply to the diabetic foot may limit the delivery of systemic antibiotics to the site of infection.

A patient with a limb-threatening infection, especially an older patient, may not have the usual systemic symptoms of infection (fever, chills, loss of appetite, and leukocytosis). Assess for cellulitis greater than 2 cm, lymphangitis, soft tissue necrosis, fluctuance, odor and other signs of gangrene, osteomyelitis, and in older patients, confusion. If the patient has one or more of these signs, he'll be admitted to the hospital for aggressive intervention including intravenous antibiotics and debridement.

Antibiotic-loaded beads are a new method of antibiotic delivery for patients with infected diabetic foot ulcers. The beads, made of bone cement polymethyl methacrylate, provide high levels of antibiotics locally. Because serum concentration of the antibiotic is low, the patient is at less risk for systemic toxicity. However, he must remain immobile during therapy and the wound must be inspected regularly to ensure correct bead placement. Bead removal can be painful, so administer appropriate analgesia first.

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Turning to surgery

Surgical intervention for a diabetic foot ulcer may be indicated if the patient also has bone deformities. If he has PAD, treating him with an arterial bypass, balloon angioplasty, or stent procedure may improve circulation enough to heal the ulcer.

Orthopedic reconstructive surgery may be indicated if his foot deformity can't be accommodated by a custom shoe or orthosis (brace). Surgery is rarely performed on Charcot's deformities unless the bony structure of the foot must be stabilized.

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Getting your patient on the team

All patients with diabetes should have annual comprehensive foot examinations. A high-risk patient should be screened for PAD and referred to a specialist for treatment if necessary.

Getting a multidisciplinary foot care team involved in foot care reduces the risk of ulcers and amputation. Besides diabetes nurse-educators, the team may consist of infectious disease specialists; endocrinologists; orthopedic, vascular, and plastic surgeons; radiologists; podiatrists; and dietitians.

But the most important member of the foot care team is the patient. Teach him to practice morning and evening foot and shoe inspection, and to report changes in foot skin color, foot trauma, and inflammatory changes such as redness and swelling (which may indicate a fracture). If he has a foot ulcer, teach him how to recognize healthy, healing tissue and how to spot problems with healing, so he can monitor his own progress. Give him a copy of the accompanying patient-education guide, Foot care for patients with diabetes, to reinforce your teaching.

By teaching your patient how to prevent diabetic foot ulcers, you can help him stay on his feet.

Mary Y. Sieggreen is an advanced practice nurse in vascular surgery at the Detroit (Mich.) Medical Center's Harper University Hospital.

The author has disclosed that she has no significant relationship with or financial interest in any commercial companies that pertain to this educational activity.

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SELECTED WEB SITES

American Diabetes Association: Foot Complications http://www.diabetes.org/type-1-diabetes/foot-complications.jsp

MedlinePlus: Diabetic Foot http://www.nlm.nih.gov/medlineplus/diabeticfoot.html

Last accessed on September 7, 2005.

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SELECTED REFERENCES

Armstrong DG, Lipsky BA. Advances in the treatment of diabetic foot infections. Diabetes Technology and Therapeutics. 6(2):167–177, April 2004.
Baranoski S, Ayello E. Choosing a debridement method. Nursing2004. 34(5):26–27, May 2004.
    Frykberg RG. Diabetic foot ulcerations: Management and adjunctive therapy. Clinics in Podiatric Medicine and Surgery. 20(4):709–728, October 2003.
    Frykberg RG. A summary of guidelines for managing the diabetic foot. Advances in Skin & Wound Care. 18(4):209–214, May 2005.
    Frykberg RG, et al. American College of Foot and Ankle Surgeons. Diabetic foot disorders: A clinical practice guideline. Journal of Foot and Ankle Surgery. 39(5, Suppl.):S1-S60, September-October 2000.
      Kerstein MD. Heel ulcerations in the diabetic patient. Wounds. 14(6):212–216, August 2002.
      Macfarlane DJ, Jensen JL. Factors in diabetic footwear compliance. Journal of the American Podiatric Medicine Association. 93(6):489–491, November-December 2003.
        Mendez-Eastman S. Using negative-pressure wound therapy for positive results. Nursing2005. 35(5):48–50, May 2005.

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          Saltzman CL, et al. 4.5 gram monofilament sensation beneath both first metatarsal heads indicates protective foot sensation in diabetic patients. Journal of Bone and Joint Surgery. American volume, 86-A(4):717–723, April 2004.
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