This is the fifth article in the “DFA Guides You Through” series on Australian and International diabetic foot disease guidelines.
As discussed in our previous article, peripheral artery disease and infection were outside the scope of the Australian guidelines. For the Australian situation, a therapeutic guideline exists for antibiotic use, which can be applied to patients with diabetic foot disease. An international group is currently working on a vascular surgery guideline for the management of severe limb ischemia. With the multidisciplinary nature of diabetic foot disease, the specific focus of the IWGDF chapters on that population makes it a useful endeavor as an Australian clinician to familiarize with them. In this article, we will guide you through the IWGDF Guidance on these two topics.
Peripheral artery disease
Identifying PAD among patients with a diabetic foot ulcer is important because its presence is associated with worse outcomes. In a person with a foot ulcer, the following non-invasive bedside tests are recommended to exclude PAD: measuring ankle-brachial index (values 0.9-1.3 exclude PAD), measuring toe-brachial index (values ≥0.75 exclude PAD) and the presence of triphasic pedal Doppler arterial waveforms. All of these bedside techniques should be performed in a standardised manner by trained healthcare professionals. It should be noted that there is insufficient evidence to support selecting any one of the bedside non-invasive diagnostic modalities for the detection of PAD across a spectrum of patients with diabetes. Healthcare professionals should be aware of the limitations of each modality and must decide which, either singly or in combination, to use, given their local expertise and test availability.
The second step is the prognosis of the outcome of an ulcer. Unfortunately, in patients with a diabetic foot ulcer and PAD, no specific symptoms or signs of PAD reliably predict healing of the ulcer. However, one of the following simple bedside tests should be used to inform the patient and healthcare professional about the healing potential of the ulcer, as any of the following findings increases the pre-test probability of healing by at least 25%: a skin perfusion pressure ≥40mmHg; a toe pressure ≥30mmHg; or, a TcPO2 ≥25mmHg. When a toe pressure below 30mmHg, a TcPO2 value below 25mmHg, an ankle pressure <50mmHg or an ankle brachial index <0.5 is found, urgent vascular imaging revascularization should be considered. The same holds for any ulcer that does not improve within six weeks despite optimal management.
Treatment of PAD starts with vascular imaging to obtain anatomical information. Techniques to define the lower limb arterial system in patients with diabetes include duplex ultrasound, MR angiography, CT angiography and digital subtraction angiography, with each having its own (dis)advantages. Most important is visualization of the entire lower extremity arterial circulation, especially of below-the-knee and pedal arteries. The aim of revascularization should be to restore direct flow to at least one of the foot arteries. There is inadequate evidence to establish superiority of one revascularization technique over another. Decisions should be made in a multidisciplinary team, this team should have access to both endovascular techniques and bypass surgery, and follow-up care should be provided by this team after revascularization. When PAD and infection are both present, a patient requires emergency treatment. On the other hand, when the risk-benefit ratio for the probability of surgical success is unfavourable, revascularization should be avoided.
Diabetic foot infection
The chapter on the diagnosis and management of foot infection is the longest chapter of the IWGDF guidance, with 26 recommendations in six different areas.
Diabetic foot infection should be diagnosed clinically, using the IWGDF classification system (see here). Clinicians should evaluate a diabetic patient presenting with a foot wound at three levels: the patient as a whole (e.g., cognitive, metabolic, fluid status), the affected foot or limb (e.g., presence of neuropathy, vascular insufficiency), and the infected wound. Clinical diagnosis rests on the presence of at least two local ﬁndings of inﬂammation: redness (erythema or rubor), warmth (calor), pain or tenderness (dolour), induration (swelling or tumour) or purulent secretions.
Wound cultures serve to determine the causative organisms and their antibiotic sensitivities, to select the most appropriate antimicrobial therapy. A tissue specimen rather than a swab is recommended to obtain cultures. Cultures should not be repeated, unless the patient is not clinically responding to treatment, or occasionally for infection control surveillance of resistant pathogens.
Diabetic foot osteomyelitis can present the clinician with formidable diagnostic and therapeutic challenges. Clinicians should suspect osteomyelitis when an ulcer lies over a bony prominence, particularly when it fails to heal despite adequate off-loading, or when a toe is erythematous and indurated (the so-called “sausage toe’). For an infected open wound, perform a probe-to-bone test; in a patient at low risk for osteomyelitis a negative test largely rules out the diagnosis, while in a high risk patient a positive test is largely diagnostic. For blood tests, markedly elevated serum inflammatory markers, especially erythrocyte sedimentation rate, are suggestive of osteomyelitis in suspected cases. For imaging, obtain plain X-rays of the foot in all cases of non-superficial diabetic foot infection and use MRI when an advanced imaging test is needed to diagnose osteomyelitis.
Surgical treatment of diabetic foot infection should be discussed in selected moderate and all severe cases of infection. Urgent surgical intervention is necessary in most cases of deep abscesses, compartment syndrome and virtually all necrotizing soft tissue infections.
Antimicrobial therapy should only be given to infected ulcers; non-infected ulcers should not be treated with antimicrobials. In case of infection, the specific antibiotic agents for treatment should be selected based on the likely or proven causative pathogens, their antibiotic susceptibilities, the clinical severity of the infection, and evidence of efficacy for DFI and costs. A course of antibiotic therapy of 1-2 weeks is usually adequate for most soft tissue diabetic foot infections. Parenteral antibiotic therapy should be administered for most severe and some moderate infections, with a switch to oral therapy when the infection is responding. For diabetic foot osteomyelitis, 6 weeks of antibiotic therapy is recommended for patients who do not undergo resection of infected bone; no more than a week of antibiotic therapy is recommended if all infected bone is resected. IWGDF recommendations on selecting an empiric antibiotic regimen for diabetic foot infections can be found here.
All IWGDF recommendations on PAD and infection can be found in this table.
The final article focuses on where do we go from here?
Return to DFA guides you through series.