Close inspection needed for foot ulcer control

Most diabetic patients get perfunctory exams

Determining which diabetic patients are at higher risk for foot ulcers is often a simple matter of inspection and a few direct questions that can be asked by a primary care provider. Often, however, foot examination is cursory and insufficient, experts say.

Inspection does not mean just a quick glance at the feet and palpation of pedal pulses, says David Armstrong, DPM, assistant professor, department of orthopedics at the University of Texas Health Science Center in San Antonio. Instead, the clinician should look closely at all areas of the foot and pay particular attention to the plantar aspect, the posterior heel, and the interdigital spaces. Armstrong laments that many diabetic patients in an outpatient setting are treated similarly to nondiabetics with respect to foot examinations. He adds that only 10% to 19% of diabetic patients receive even a cursory foot evaluation by their primary health care providers.

Patients who are at high risk for foot ulcers should carefully follow a plan of care outlined by their physician or podiatrist. At the Primary Foot Care Center in North Miami Beach, FL, Tamara Fishman, DPM, sends patients home with a list of dos and don'ts. (See list, p. 115.) Patients who are vigilant and who understand the potentially serious consequences of neglecting their health care can play a tremendous role in preventing diabetic foot wounds.

Such ulcers may go unnoticed because neither the patient nor the health care provider examines the feet regularly. This, stresses Armstrong, should be a routine part of patient care.

Armstrong and his colleagues at the University of Texas developed a simple matrix to help classify diabetic foot wounds. (See chart, below.) The matrix takes into consideration the presence or absence of infection, the depth of the wound, and the degree of epithelialization.

When a patient develops an ulcer, the first step should be a wound assessment that includes an evaluation of the lower-extremity vascular supply, says Jeffrey Jensen, DPM, clinic director at the Diabetic Foot and Wound Center in Denver. Vascular status can be measured using methods such as toe systolic pressure, pulse volume recordings, or transcutaneous oxygen pressure.

"These give an indication of whether the patient has the ability to heal a wound from a vascular point of view," says Jensen. If the tests show poor vascular supply, blockage at the macrovascular level is a likely cause. In severe cases, bypass surgery may be required to revascularize the leg. If the blocked vessel is large, it can be bypassed, Jensen explains. If the blocked vessel is small, then overall circulation will not be seriously compromised and proper wound care should result in healing.

Patients who are not candidates for revascularization, such as the very elderly or those who are undergoing dialysis, may suffer from foot wounds that are very difficult to heal. In this respect, says Jensen, the sometimes-controversial label of "nonhealing diabetic foot wound" may be an accurate descriptor.

X-rays of the ulcer can be used to rule out osteomyelitis, gas formation, the presence of foreign objects, and asymptomatic fractures.

If no vascular blockage is found, the clinician should look for signs of infection. Any infection must be treated aggressively with well-matched antibiotics. If left unchecked, an infection can lead to disastrous complications, such as microthrombi formation, further ischemia, necrosis, and progressive gangrene. Infection is the leading cause of amputation among patients with diabetic ulcers.

Aggressive antibiotic treatment is indicated for infected diabetic foot wounds, but proper culturing and identification of pathogens must be completed first. Pathogens that are common in diabetic wounds include aerobic gram-positive staphylococci and streptococci. Culturing technique is important, experts say. "Simply swabbing the ulcer is not satisfactory. Instead, curettage at the base of the ulcer after debridement is the method of choice. Anaerobe and aerobic cultures should be obtained," writes Marvin E. Levin, MD.1

When an infected wound does not respond to aggressive antibiotic treatment, debridement and reculturing should be repeated. A recurrent or resistant infection may be a sign of osteomyelitis, according to Jensen.

Appropriate debridement is an important step in the care of diabetic foot wounds. "The wound has to be debrided of all nonviable tissue, and its depth also needs to be determined. Not doing so is one of the biggest mistakes made with these wounds," says Jensen. "Often, the clinician doesn't take off enough tissue." He adds that healing also relies on proper blood glucose control. "If a patient has a hemoglobin A1C level of 20, that wound has a very difficult time healing," he adds.

Because of the extent of debridement needed for these wounds, a whirlpool is not the best choice because the water doesn't remove enough necrotic tissue. In addition, whirlpools can cause edema, may harbor Pseudomonas, and can lead to excessive hydration and maceration. For patients with poor vascularization, revascularization should be done before or at the same time as debridement.

Limited mechanical debridement can be undertaken without anesthesia for some patients with an insensate foot, but for more extensive debridement, the clinician should consider performing the procedure in the operating room with anesthesia. Debridement reportedly can result in long-term salvage of 75% of limbs among high-risk patients with diabetic ulcers.

The choice of wound dressings is dictated by the nature of the wound. Diabetic ulcers tend to produce a low amount of exudate, so a dressing with high absorption characteristics could absorb too much moisture and dry out the wound. Jensen often uses amorphous hydrogels, which keep the wound bed moist and require only daily dressing changes.

Offweighting of the foot becomes crucial once an ulcer has developed, Jensen adds. "Because patients have neuropathy, their motivation to stay off their feet is not as great as with someone who can feel pain. Sometimes it's a challenge to get patients to comply with these instructions. Asking them to use a wheelchair or crutches is often futile," he says.

One clinician calls the contact cast "the best method for achieving non-weight-bearing in the appropriately selected patient."1 The device allows patients to walk while still offweighting the ulcerated foot because it reduces pressure on the wound area.

Jensen emphasizes that appropriate care of patients with diabetic foot ulcers requires a multidisciplinary team. "If a patient with diabetes comes into the clinic with a foot ulcer, is on dialysis, has compromised lack of blood supply to the foot, and has an infection, it stands to reason they need an internal medicine specialist to treat them for their diabetes, a nephrologist for the dialysis, a vascular surgeon to restore blood supply, an infectious disease specialist to determine what antibiotics would work best, and a podiatrist to address the local problems of the foot wound - and of course you need the nursing staff and all of the other support," says Jensen.

"The term 'multidisciplinary' is used a lot, but it's not always followed. All it means is that a patient's needs are addressed by the people who know how best to address them," he says.

Reference

1. Levin M. Prevention and treatment of diabetic foot wounds. JWOCN 1998; 3:129-143.