Is There A Role For HBO In Limb Salvage?
There are 15 million people in the United States with diabetes mellitus, half of whom are undiagnosed. Diabetic foot ulcers (DFUs) occur in 12 percent of these individuals, accounting for 60 percent of lower extremity amputations and costing more than $1 billion annually.1
Diabetic foot ulcers have various mechanisms including:
• microneurovascular dysfunction with loss of the nociceptive reflex and an exacerbated inflammatory response;
• vasomotor dysfunction with arteriovenous shunting;
• capillary basement membrane thickening with altered capillary exchange;
• foot deformities increasing the likelihood of pressure points;
• diminished sensation; and
• ischemia due to tibial peroneal occlusive disease.
In addition to neuropathy, patients with diabetes suffer from impaired resistance to infection. This has been partly explained by an impaired “respiratory burst.”2 There is also impaired microvascular perfusion due to changes in platelet aggregation and increased rigidity of red cells.
Diabetic foot ulcers are hard to heal. Margolis has demonstrated that even with adequate arterial inflow, diabetic foot ulcers have a 24 percent closure rate at 12 weeks and a 31 percent closure rate at 20 weeks.3 Other researchers have demonstrated that adherence to standardized protocols based on clinical guidelines reduces the amputation rate.4 For example, Margolis, et al., demonstrated a 68 percent healing rate at 20 weeks in lower complexity DFUs managed by protocol within a multicenter wound care network in comparison to a 44 percent healing rate prior to the standardization of care.5
Understanding The Impact Of Tissue Hypoxia
While it is possible that strict care protocols can overcome some impediments to healing, the final common denominator among most non-healing wounds is tissue hypoxia. It is well known that hypoxia inhibits healing. More than 30 articles since 1984 have demonstrated that tissues below 40 mmHg signify impaired healing.6 If the transcutaneous oximetry (TcPO2) value is less than 20 mmHg, then the risk of amputation is 161 times greater than in patients whose TcPO2 is at least 40 mmHg.
Furthermore, if the Doppler ankle-brachial index (ABI) is less than 0.45, the risk of amputation is 55 times greater than if the ABI is 0.7.7 Among chronic limb ischemia patients undergoing bypass for ischemic tissue loss, 63 percent required more than three months for complete healing with the mean time to healing being 86 days. Greater than 7 percent of these patients never healed.8
These data suggest there is significant room for improvement in the outcome of DFU healing in general and ischemic foot ulcers in particular. The focus of that effort should be on the correction of hypoxia and, clearly, current revascularization techniques are not the final answer.
A Closer Look At The Effects Of HBO
Hyperbaric oxygen (HBO) is a treatment in which the patient breathes oxygen intermittently while inside a chamber at a pressure greater than 1.4 ATA (atmospheres absolute), usually 2.0 to 2.4 ATA. Treatments usually last for 90 minutes per day and patients usually undergo between 20 and 60 treatments.9
While the oxygen carrying capacity of hemoglobin is fixed due to the structure of the molecule, an increase in atmospheric pressure allows additional oxygen to dissolve in the blood plasma. An additional 2 volumes percent of oxygen dissolve into the blood plasma for each additional atmosphere of pressure to which the body is exposed. In addition to the correction of hypoxia, HBO reportedly facilitates upregulation of growth factors and the activation of growth factor receptors, control of excess inflammation, better control of infection and increased angiogenesis.