Diabetic Lower Extremity Wounds, the Prototype Hypoxic Wound
Lower extremity ulcers and amputations are an increasing problem for people with diabetes. Up to 6 per cent of all hospitalizations for diabetics include a lower extremity ulcer as a discharge diagnosis. When present, an ulcer increased hospital length of stay by an average of 59% compared to diabetics admitted without lower extremity ulcers. Finally, once an amputation occurs, nine to 20% of diabetic patients will experience an ipsilateral or contralateral amputation within 12 months and 28-52% within five years. The cost of care for a new diabetic foot ulcer has been calculated to be $27,987 in the two years following diagnosis.
The pathophysiology of diabetic foot ulceration, faulty healing, and lower extremity limb loss has been well described. It involves the progressive development of a sensory, motor, and autonomic neuropathy leading to loss of protective sensation, deformity increasing plantar foot pressures, and alternations in autoregulation of dermal blood flow. Diabetics show earlier development and progression of lower extremity peripheral arterial occlusive disease with a predilection for the trifurcation level vessels just distal to the knee. Impaired host immune response to infection and possible cellular dysfunction all contribute to the clinical outcomes described above.
Management, likewise, has been extensively described and includes careful attention to identification and management of infection, aggressive surgical debridement, evaluation and correction of vascular insufficiency ambulatory off-loading, and glycemic control. While a full discussion of these interventions is beyond the scope of this review, they form the basis of effective diabetic foot ulcer management and must be applied consistently if adjunctive interventions are to provide an additive value. Other interventions have recently been advocated including topical application of a recombinant human platelet derived growth factor (PDGF-BB, becaplermin), bioengineered human monolayer fibroblast grafts and bilayer fibroblast and keratinocyte grafts, and negative pressure wound therapy (wound vac). Clearly, regardless of the interventions applied, limb salvage rates improve when care is applied in a multidisciplinary setting using comprehensive protocols for care.
Local wound hypoxia plays a pivotal role in diabetic wound healing failure and limb loss as evidence by the report by Pecoraro that when periwound PtcO2 values were below 20 mmHg they were associated with a 39 fold increased risk of primary healing failure. While aggressive distal lower extremity bypass grafting and lower extremity angioplasty have contributed to increased wound healing and limb salvage rates, technical grafting success does not necessarily equate with limb salvage. Hyperbaric oxygen treatment offers an intriguing opportunity to maximize oxygen delivery in the setting of minimal or insufficiently corrected blood flow.1
1 Hyperbaric Oxygen 2003: Indications and Results, The Hyperbaric Oxygen Therapy Committee Report by John J. Feldmeier, D.O., Chairman and Editor. Copyright 2003, Undersea and Hyperbaric Medical Society, Inc., Kensington, MD.