Management of the Diabetic Foot: Preventing Amputation

Marvin E. Levin, MD

Disclosures

South Med J. 2002;95(1) 

In This Article

Infection

Infection is a common and serious complication of diabetic foot wounds.[26] Infection leads to formation of microthrombi, causing further ischemia, necrosis, and progressive gangrene.[27] Massive infection is the most common factor leading to amputation. Because infection in the diabetic foot can be complex, consultation with an expert in infectious disease may be beneficial.

Response to infection is often altered in the patient with diabetes. Infection-fighting capability is often diminished because of impaired leukocyte function. Impaired leukocyte function is significantly influenced by the degree of hyperglycemia; therefore, tight blood glucose control is extremely important when infection is present. In addition, patients with diabetes and severe foot infection often do not respond to the infection with elevation of body temperature and/or white blood cell (WBC) count. Leichter et al[28] have reviewed laboratory data in a large series of diabetic patients with serious pedal infections. Despite significantly elevated sedimentation rates, the mean WBC count was 9,700/102/mm3. Gibbons and Eliopoulos[29] have also documented the absence of temperature elevation, chills, or leukocytosis in two thirds of the patients with limb-threatening infection, including abscesses and extensive soft tissue infection. Similarly, Eneroth et al[30] found that approximately 50% of patients with foot infection had temperatures under 37.8°C and WBC counts under 10,000/102/mm3.[30] Given these findings, the clinician should not depend on elevated WBC counts and/or temperature elevation alone as indications of the severity of a diabetic foot infection.

Wound Debridement Problems With Conservative Treatment
All necrotic tissue is not excised
Sinus tracts -- > necrotic tissue
-- > anaerobic environment
Infected bone and tendon remain -- > reinfection
Bacteria produce glycocalyx

Aerobic gram-positive staphylococci and streptococci usually are the cause of infection; however, gram-negative organisms are frequently present as well. Anaerobic infection is common. Leichter et al[28] found that the serious infections in their series were polymicrobial; 72% of organisms cultured were gram-positive and 49% were gram-negative.

Culturing technique is extremely important in cases of diabetic foot infection. Simply swabbing the ulcer is not satisfactory and frequently produces inaccurate results. Specimens for culture should be obtained from tissue deep in the wound after debridement.[31] Cultures should be obtained anaerobically as well as aerobically.

Antibiotic therapy with a broad spectrum antibiotic should begin immediately after cultures have been obtained; the antibiotic can then be adjusted based upon the sensitivities of the causative organisms. Many diabetic foot infections contain gram-negative organisms; therefore, the initial antibiotic chosen should be effective against gram-negative as well as gram-positive organisms. Selection of an oral or a parenteral antibiotic for treatment of a diabetic foot infection must be based upon medical judgment.

If an oral antibiotic is selected, it is not advisable to simply instruct the patient to take the medication and return in a week. In the diabetic patient, infection can progress significantly in just 24 to 48 hours.The diabetic patient taking oral antibiotic therapy should therefore be seen within a few days after initiation of therapy. In addition, the patient must be instructed to notify the physician at once if any increase in redness or drainage or any evidence of lymphangitis is noted. While many of these patients have insensate feet, the development of pain is indicative of deep infection and requires immediate attention. The development of a foul odor also indicates worsening infection and may indicate the presence of anaerobes. It is important that diabetic patients with infection monitor their blood glucose levels closely, since rising blood glucose levels strongly suggest worsening infection, even when other signs and symptoms are absent.

The criteria for hospitalization and treatment with parenteral antibiotics include sepsis, leukocytosis, PAD, and uncontrolled diabetes. Another indication for immediate hospitalization is when what appears to be a minor infection on the plantar surface of the foot is accompanied by erythema and edema of the dorsum of the foot. When such signs are present even though the patient is not septic, there is a high probability that the infection has penetrated deep into the tissues and has spread to the dorsum of the foot. Such infections require incision, drainage of probable abscess, debridement, administration of parenteral antibiotics, and tight blood sugar control.

When infection fails to respond to aggressive treatment, the wound should be debrided and recultured, since the flora may have changed. Chronic, recurrent, or treatment-resistant infection suggests the presence of osteomyelitis.

Osteomyelitis is a frequent complication of diabetic foot ulcers and infection, but it may be difficult to detect on a clinical basis. In fact, Newman et al[32] found that only one third of biopsy-proven cases of osteomyelitis had been clinically suspected. If bone is visible or if the ulcer can be probed to the bone, the probability of osteomyelitis is high.[33] Scanning techniques for osteomyelitis are not always successful. The triple-phase scan with technetium lacks specificity,[34] but scanning with indium 111 is highly specific.[35] Magnetic resonance imaging (MRI) is a helpful technique.[36,37]

Debridement Effects
  • Removes foreign bodies, necrotic tissue

  • Decreases bacterial load

  • Cleans ulcer bed

  • Increases platelets/growth factors at ulcer site

  • Allows better visual assessment of ulcer area

Adapted from Steed et al, 1998.

Although soaking of the feet has been a traditional approach to treatment, it is of no benefit; in fact, it can lead to maceration and worsening infection. Because the foot is insensitive, soaking may take place in water that is too hot, resulting in severe burns. Chemical soaks can result in chemical burns. Soaking the feet or using the whirlpool delays appropriate and aggressive therapy.[38]

Edema is frequently present and can contribute to vascular insufficiency by compressing the capillaries. Elevation of the feet to the thickness of one pillow can be beneficial, but higher elevation may impede circulation. Careful compression may be helpful.

Avoidance of weight bearing is essential. These patients have insensate feet and, because the ulcers are not painful, they continue to walk. The result is an increase in pressure necrosis that not only delays healing, but also can result in enlargement of the ulcer. How can non-weight-bearing status best be achieved? Prolonged bed rest is impractical and potentially dangerous because of the risk of venous thrombosis and pulmonary emboli. The use of crutches is difficult and can be dangerous, since many of these patients have some degree of ataxia due to neuropathy. A wheelchair is seldom successful in achieving total avoidance of weight bearing. For consistent weight-bearing avoidance, in the appropriately selected patient the best choice is the contact cast. A contact cast is contraindicated in patients who have severe PAD or are ataxic, blind, or pathologically obese.[39] By decreasing pressure on the ulcerated area, the contact cast allows the patient to be ambulatory but essentially non-weight bearing.[39] A recent article has reported the improved effectiveness and safety of a nonremovable fiberglass off-weight-bearing cast.[40] In that study of the treatment of neuropathic foot ulcers, there was 50% healing in 30 days in patients using the fiberglass cast, compared with 20% healing in 30 days in those using a therapeutic shoe. There was a high rate of patient compliance in the study.

The incidence of immunosuppresion is increasing in patients with diabetes because of the increasing frequency of kidney and pancreas transplants. Immunosuppression markedly impairs healing of foot ulcers and eradication of infection, and immunosuppressed patients have a higher amputation rate.[41] Limb amputation occurs in the short term for at least 15% of diabetic patients who have had kidney transplants, and it becomes necessary for approximately 33% of 10-year survivors.[42]

The worst impediment to wound healing or clearing of infection in the diabetic patient is vascular insufficiency. When an ulcer does not heal despite good metabolic control, adequate debridement, parenteral antibiotic therapy, and avoidance of weight bearing, vascular insufficiency should be suspected as the reason. In a study conducted by Mills et al,[43] all appropriately treated neuropathic ulcers and forefoot infections healed in patients with palpable pedal pulses. When foot pulses were absent and arteriography confirmed significant stenosis, foot lesions and infections healed with revascularization. Ankle/brachial indices of less than 0.50 and transcutaneous oxygen pressures of less than 30 mm Hg are highly predictive of infections that will not resolve and ulcers that will not heal. Vascular surgery should be considered in these cases. LoGerfo et al[44] illustrated the importance of peripheral arterial reconstruction. In 2,883 cases of extreme-distal arterial reconstruction, they found a statistically significant decrease in every category of amputation, and that decrease correlated precisely with an increasing rate of dorsalis pedis artery bypass.

Patients with diabetes who have limb-threatening wounds may have normal temperature and blood studies.

Finally, managed care can be an impediment to wound healing. Managed care limits the time the clinician can spend with the patient, making it impossible to take a comprehensive history, perform a thorough examination, adequately treat the wound, and instruct the patient in wound care. The clinician who must see another patient every 15 minutes cannot adhere to standards of care; furthermore, in some situations managed care delays appropriate consultations and hospitalization.[45]

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