Topical Wound Oxygen Therapy in the Treatment of Severe Diabetic Foot Ulcers: A Prospective Controlled Study

Eric Blackman, MD, FRCS(C), FAADEP; Candice Moore, RN; John Hyatt, MD, FRCS(C); Richard Railton, MD, FRCS(C), FAGS; and Christian Frye, MD, MPH

Abstract

Diabetic foot ulcers (DFU) are common, difficult-to-treat, and prone to complications. A prospective, controlled study was conducted to: 1) examine the clinical efficacy of a pressurized topical oxygen therapy (TWO₂) device in outpatients (N = 28) with severe DFU referred for care to a community wound care clinic and 2) assess ulcer reoccurrence rates after 24 months. Seventeen (17) patients received TWO₂ five times per week (60-minute treatment, pressure cycles between 5 and 50 mb) and 11 selected a silver-containing dressing changed at least twice per week (control). Patient demographics did not differ between treatment groups but wounds in the treatment group were more severe, perhaps as a result of selection bias. Ulcer duration was longer in the treatment (mean 6.1 months, SD 5.8) than in the control group (mean 3.2 months, SD 0.4) and mean baseline wound area was 4.1 cm2 (SD 4.3) in the treatment and 1.4 cm2 (SD 0.6) in the control group (P = 0.02). Fourteen (14) of 17 ulcers (82.4%) in the treatment group and five of 11 ulcers (45.5%) in the control group healed after a median of 56 and 93 days, respectively (P = 0.04). No adverse events were observed and there was no reoccurrence at the ulcer site after 24 months’ follow-up in either group. Although the absence of randomization and blinding may have under- or overestimated the treatment effect of either group, the significant differences in treatment outcomes confirm the potential benefits of TWO₂ in the management of difficult-to-heal DFUs. Clinical efficacy and cost-effectiveness studies as well as studies to elucidate the mechanisms of action of TWO₂ are warranted.

Key Words: controlled prospective study, outpatients, diabetic foot ulcer, topical oxygen therapy, silver dressing Index: Ostomy Wound Management 2010;56(6):24-31

Foot disorders such as ulceration, infection, and gan­ grene, along with subsequent amputation, are signifi­ cant complications of diabetes, the leading causes for diabetes-related hospitalization, and estimated to cost bil­ lions of dollars each year.1•2 Diabetic peripheral wounds are a major risk factor for lower extremity amputation.3 Ap­ proximately 40% to 70% of all lower extremity amputations are performed in patients with diabetes; approximately 100,000 nontraumatic lower-limb amputations were per­ formed in the US among persons with diabetes in 2008.4 Even superficial diabetic wounds are often difficult to treat and show high rates of complications.5

Oxygen (0₂) is essential to wound healing. Local tissue hy­ poxia, caused by disrupted or compromised vasculature, is a key factor that limits wound healing.6•7 It is well established that 0₂ is vital in the synthesis of collagen, enhancement of fibroblasts, angiogenesis, and leukocyte function.8-10 02 also has key functions in energy metabolism 11•12 and in the inhibi­ tion of microbial growth.13

Clinical use of 0₂ to promote wound healing began in the 1960s with the administration of systemic full body hyper­ baric oxygen therapy (HBO) to treat wounds.13 Today, HBO is usually administered in single- or multiplace chambers uti­ lizing pressures of 2,500 mb and higher. HBO is reimbursed by the Center for Medicare and Medicaid Services in the US to treat certain wounds, including diabetic foot ulcers (DFUs) that have failed to heal using standard care. A Cochrane review by Kranke et al14 demonstrated that in people with foot ulcers due to diabetes, HBO significantly reduced the risk of major amputation and may improve the chance of healing at 1 year. The availability of HBO facilities, contraindications, the need to transfer the patients to the HBO facilities, and the risks of undesired systemic side effects such as barotraumas of the ear or confinement anxiety limit the widespread use of HBO to treat diabetic ulcers on a global basis.15

In an effort to address some of these drawbacks, the prin­ ciple of topical pressurized oxygen administration or topical wound oxygen therapy (TWOz) was introduced in the late 1960s.16 The approach of topically oxygenating the wound is quite different from HBO. TWOz does not involve pressures as high as in HBO. Additionally, TWOz is portable and can be administered in varied care sites, including in the patient’s home. A number of published studies,16-21 including smaller random controlled trials (RCTs) and case series involving pa­ tients with diabetic ulcers, venous ulcers, pressure ulcers, and other wounds demonstrates positive outcomes with TWOz, but the medical community is not commonly familiar with the principle.

The purpose of this prospective, controlled study was to:

• compare healing rates of chronic DFUs treated with TWO₂ versus DFUs treated with advanced moist dressing therapy and 2) compare DFU recurrence rates after 24 months in both treatment groups.

Methods

Study design, setting, and population. A prospective, con­ trolled study was conducted at a single center, St. Catharines Wound Clinic, St. Catharines, Ontario, Canada. One trained research nurse in this outpatient wound care center screened patients referred for wound care for study eligibility. Because all devices and dressings are registered products in Canada, no IRB approval was obtained. Informed consent of the par­ ticipating patients was obtained, including the option to opt out at any time. Patients were considered eligible for partici­ pation if they met the following criteria: provision of in­ formed consent, at least 18 years of age, an ankle-brachia! index (ABI) of at least 0.5 in the affected limb, and diagnosis of a DFU with a grade 2-A or worse according to the Univer­ sity of Texas (UT) Wound Classification System.22 Patients were ineligible to participate if they had a chronic wound of nondiabetic origin, deep vein thrombosis (DVT), were preg­ nant or lactating, were receiving palliative care, were known to be nonadherent with therapy, or had a HbAlc above 10%.

The manufacturer of the topical wound oxygen devices, AOTI Ltd (Galway, Ireland), supported the study by providing the medical devices and the oxygen for use during the study. Study protocol. After obtaining informed consent, a pa­ tient history and baseline assessment were obtained by the study nurse. Variables assessed included: ABI; wound duration and location, and size; loss of protective sensation (deter­ mined by 10-g monofilament); and HbAlc. All wounds were classified according to the UT classification for diabetic wounds by an advanced wound specialist based on clinical and laboratory data. All wounds were surgically debrided to a bleeding base; the number of debridements was not limited but usually debridements were performed once a week before treatment commenced. All wounds were offloaded with the Active Offloading Walker (Royce Medical, Camarillo, CA).

Key Points

• A prospective controlled study involving 28 outpatients was conducted to compare outcomes of diabetic foot ulcer treatments.
• The proportion of wounds healed and time to healing was good in both treatment groups but significantly better in the topical oxygen (TWO₂) than in the silver dressing group.
• Research to elucidate the mechanisms of action of TWO₂ and randomized controlled clinical efficacy and cost-effectiveness studies are warranted.

 

If a TWOz device was available after the initial assessment (there were a total of four devices), the patient was asked to be in the TWO₂ arm. If all TWO₂ devices were occupied at the first visit of the study participant, or the patient refused daily TWOz therapies, the patient was assigned to the control group (see Figure 1) and provided an advanced moist wound ther­ apy (AMWT) using a silver-based dressing (Silvercel'”, John­ son and Johnson Inc., Somerville, NJ), which is licensed for the treatment of DFUs by Health Canada.

Hyper-Box Topical Wound Oxygen Therapy Systems (AOTI Ltd., Galway, Ireland) were provided by the Canadian distributor (Therapeutic Surface Solutions Inc., Hamilton, Ontario, Canada) for use in the trial. This system is a class II medical device licensed for the treatment of DFUs as well as other wound types by Health Canada. The device also has US Food and Drug Administration (FDA) 510(k) clearance and CE-Mark approval for the same indications. It delivers hu­ midified medical grade Oz into an extremity chamber in a cyclical manner. This cycle consists of pressurizing the cham- her to 50 mb and then venting the Oz out of the chamber, al­ lowing pressure to reduce toward ambient pressure (5 mb) before re-pressurizing. Treatment consisted of daily 60-minute TWO₂ treatments, conducted Monday through Friday. Saline­ soaked gauze dressings, applied following treatment, remained in place until the next scheduled treatment. Both groups re­ ceived treatment based on current best practice guidelines, as decided in consultation with three participating surgeons. Dressing changes in the control group also were performed in the study center according to the physicians’ recommendation at a minimum of twice a week. Each participant’s wound was assessed weekly and debrided if necessary. All patients were followed for 90 days in the active treatment phase (ATP) until the wound healed; all patients were monitored monthly for 24 months in the follow-up phases (PUP) to determine if the wound recurred.

The primary study outcome was wound closure, defined as complete epithelialization of the wound with the absence of drainage. The secondary endpoint was reoccurrence rate after 24 months.

Statistical analysis. Data entry was performed twice and computations were performed using the statistical package SAS for Windows version 9.1 (SAS Institute, Cary, NC). Wound area was calculated using length and width measured with a digital caliper. Data from all patients enrolled in the study were analyzed (intent to treat) mainly using a time-to­ event strategy with Kaplan-Meier estimates, followed by a log rank test. This statistical procedure provides a comparison of the distribution of events between the two treatment groups. In addition to the event rates, mean and median time to 100% closure were calculated, as well as the proportion of patients with healed ulcers within the active treat­ ment phase. Continuous demographic variables, such as the patient’s age at en­ rollment, were summarized using de­ scriptive statistics and between-group differences were compared with a two­ sample t-test. Categorical demographic variables such as gender were summa­ rized and compared using a two-tailed chi-square statistic. Comorbidity risk factors were summarized by treatment assignment and according to the type of variable (categorical, continuous) and compared between groups.

Results

In the first week ofJanuary 2007, 33 el­ igible patients were asked to participate in the trial; of these, 30 agreed. Two patients had to be excluded after signing informed consent because they had nondiabetic ar­ terial neuropathic ulcers, leaving a total sample size of 28 patients for follow-up and data analysis. Of those, 27 were fol­ lowed-up until December 31, 2008 to doc­ ument DFU reoccurrence in healed wounds. One patient in the TWO₂ group withdrew from the study after 81 days and missing >50% of treatments (see Figure 1). The TWO₂ and AMWT groups were similar with respect to age, gender distri­ bution, HbAlc, and ABI. Baseline wound area was significantly larger in the TWO₂ than in the control group (mean 4.1 cm2 [SD 4.3] versus 1.4 cm2 [SD 0.6]; P = 0.02). Wound duration was longer in the TWO₂ group (6.1 months [SD 5.8] versus 3.2 months [SD 0.4] for control) but the difference was not statistically significant. All patients had plantar wounds and peripheral neuropathy as indicated by a loss of protective sensation. No toe or heel ulcers were noted in the study population. Except for one mid­ foot ulcer in the TWO₂ group, all ulcers were located at the first, third, and fifth metatarsal (see Table 1).

The proportion of ulcers with complete healing was signif­ icantly greater in the TWO₂ than in the AMWT group (P = 0.013) (see Figure 2). Fourteen (14) out of 17 (82.4%) versus five (5) out of 11 (45.5%), respectively, showed complete ep­ ithelialization of the wound (P = 0.04). Median time to closure was 56 days (interquartile range [IQR] 39-81 days) in the TWO₂ group and 93 days [IQR: 62-127]) in the control group. In the follow-up phase of up to 24 months, there were no reoccurrences at the healed ulcer site in either the TWO₂ therapy or control group.

No treatment-related adverse events were documented in either group.

Discussion

Overall study results. Wounds in patients treated with TWO₂ in this study were significantly more likely to heal and during a shorter period of time than wounds in patients re­ ceiving AMWT. These results must be interpreted within the context of the study design. There was no formal randomiza­ tion and in the vast majority of cases the secretary of the wound care center assigned the groups based on equipment availability and patient preference without knowledge about wound severity. Nevertheless, all staff members were aware of group assignments and it seems likely that more serious wounds were assigned to the TWO₂ group after noting posi­ tive results in a pre-study phase before this study commenced in January 2007. This selection bias helps explain why wounds in the TWO₂ group had a larger surface area, UT classification as more severe, and longer wound duration before enrolling into the study than wounds in the control group. In this re­ spect, the results of this trial may underestimate the potential benefits of TWO₂ compared to AMWT.

On the other hand, it is also possible that a “self-selection” of patients took place in favor of AMWT treatment for per­ sons with less interest in following the protocol of care and visiting the center five times a week. According to the study protocol, patients were given the option not to go into the treatment group but no patient “randomized” by the secretary refused to go into the treatment group.

Patient adherence to protocol (particularly with offload­ ing) in a study of neuropathic DFU is an important factor in healing. All patients received offloading but it is possible that poor adherence is at least partly responsible for the outcome differences observed. An additional potential bias is the posi­ tive reinforcement of daily 1- to 2-hour visits for the treatment group versus twice-per-week visits for the control group. Pos­ itive reinforcement of weight-bearing limitation is likely to occur during these visits. However, the magnitude of the dif­ ferences observed is unlikely to have occurred as a result of these potential differences only.

Previous studies23-27 conducted on DFUs that compare AMWT to other adjunctive modalities have shown propor­ tions of wounds healed ranging from 26% to 46.2% following 12 weeks of care in their control groups. The best results (46.2% healed after 12 weeks) were reported in a prospective, randomized, multicenter study27 of UT grade 1 or 2 DFUs (n = 86) that investigated healing time between patients receiving a cellular matrix and standard care. The high proportion of wounds healed in the more severe wounds enrolled in the con­ trol group of the current study, 45.5% of UT grade 2 and 3 wounds, suggests that the standard of care provided in control group in this wound clinic was good.

The role of oxygen. Although questions about the mecha­ nism of action ofTWO₂ remain, evidence suggests that TWO₂ plays a key role in achieving the needed oxygen balance in the wound bed required for wound healing to progress, as sug­ gested by Sibbald and Woo.28 It is well established that oxygen is vital in collagen syn­ thesis, fibroblast enhancement, angiogenesis and leukocyte function.8-10 Hypoxia caused by disrupted vasculature is a key factor that has been found to limit wound healing.6•7 The partial pressure of oxygen (pO₂) in the wound is lower than in healthy tissue; in dermal wounds, pO₂ ranges from 0 to 10 mm Hg in the center of the wound to 60 mm Hg at the periphery.6 In contrast, the pO₂ in arterial blood is ap­ proximately 100 mm Hg.

Oxygen needed for collagen synthesis proceeds in direct proportion to pO₂ across the entire physiologic range, from 0 to hundreds of mm Hg. Collagen synthesis requires several enzymes. A measure to characterize an enzyme is the substrate concentration at which the reaction rate reaches half of its maximum value (Vmax/2). This concentration can be shown to be equal to the Michaelis constant (KM). The KM of 0₂ in collagen synthesis has been determined to occur at a pO₂ of 20 to 25 mm Hg. Vmax is approximately 250 mm Hg, sug­ gesting that new vessels cannot approach their greatest possi­ ble rate of growth unless the wound tissue pO₂ is as high as 66.29 Consequently, in vivo and human studies have shown that hypoxic wounds deposit collagen poorly and are more likely to become infected.30 Recent research has focused on oxygen and infection. In a wound bed, large amounts of molecular oxygen are partially reduced to form reactive oxygen species (ROS). Leading re­ searchers view the NADP(H)-linked oxygenase as a key factor. In vitro studies have shown that this enzyme increases leuko­ cytic oxygen consumption by as much as SO-fold and subse­ quently uses most of the oxygen delivered to wounds.31 The NADPH oxidase catalyzes the production of ROS by phago­ cyte cells such as neutrophilic and eosinophilic granulocytes, monocytes, and macrophages. Exposing these phagocytes to an infectious stimulus activates a “respiratory burst” caused by activation of the plasma membrane-bound NADPH oxi­ dase. Research presented by Hunt13 has shown that approxi­ mately 98% of the oxygen consumed by wound neutrophils is utilized for respiratory burst. In simpler terms, the majority of oxygen in infected chronic wounds is probably used to fight infection via the ROS-system, leaving almost no oxygen for wound healing.

The ROS includes oxygen-free radicals such as the super­ oxide anion (O2-)as well as hydrogen peroxide (H2O2). The superoxide anion also drives endothelial cell signaling re­ quired during angiogenesis. Endogenous hydrogen peroxide drives redox signaling, a molecular network of signal propa­gation that supports key aspects of wound healing such as cell migration, proliferation, and angiogenesis.32 In summary, the dilemma in wound healing is that the oxygen supply is limited while oxygen demand increases significantly. Three major factors are responsible for wound tissue hypoxia: peripheral vascular diseases (PVDs) limiting the blood supply and thus the needed oxygen; in­ creased oxygen demand of the healing tissue needed for collagen synthesis and angiogenesis; and the generation of ROS needed for infection control (respiratory burst) and redox signaling

Topical oxygen therapy. The big question is whether topical oxygen can penetrate the wound sur­ face to increase the pO₂ in the wound tissue. Fries et al18 studied the efficacy of topical oxygen in an exper­ imental setting using a pre-clinical model involving excisional dermal wounds in pigs. Exposing open der­ mal wounds to topical oxygen treatment increased su­ perficial wound tissue pO₂. Fries et al used a probe designed to measure superficial pO₂ at 2 mm depth at the center of the wound bed and saw an increase of pO₂ from the baseline of 5 to 7 mm Hg to 40 mm Hg in as little as 4 minutes. More indirect evidence of the oxygen penetration into the tissue with topical oxygen devices comes from Scott and Reeves’33 un­ controlled experiments on three patients with plan­ tar diabetic wounds. Using multiplex ELISA assays of growth factor cytokines, the authors quantified levels of total proteins detectable in fluids collected twice weekly from wounds after exposure to topical oxygen. TWO₂ was shown to increase the levels of a variety of angiogenesis-related growth factors (BFGF, HB-EGF, KGF and VEG-F) in chronic wounds. In chronic DFUs treated with TWO₂, the most crucial angiogenesis-related growth factor, VEG-F, increased as much as 20-fold.34

Characteristics Control group TWO2group   Age (years) N = 11 63.4 (9.6) N =17 62.4 (9.7) Gender (male) 8 (72.7%) 12 (70.6%) HbA1c (%) 7.4% (1.2%) 7.3 (1.2) Current smoker 0(0%) 2 (11.8%) Ankle-brachia! systolic pressure 1 (0.18) 0.9 (0.21)

Wound area (cm2) 1.4 (0.6)a 4.1 (4.3)a Wound stage     CII 0(0%) 0(0%) GIii 0 (0%) 1 (5.9%) D11 7 (63.6%) 5 (29.4%) DIii 4 (36.4%) 11 (64.7%) Received offloading therapy 11 (100%) 17 (100%) Plantar location of wound 11 (100%) 17 (100%) 1st metatarsal 10 (91%) 4 (22%) 3rd metatarsal 1 (10%) 1 (6%) 5th metatarsal   11 (61%) Midfoot   1 (5%) Loss of protective sensation 11 (100%) 17 (100%) History of plantar ulceration 10 (90%) 15 (88%) Charcot foot   1 (5.9%)

Gordillo et al32 analyzed data from two simultane­ ous nonrandomized studies to test the effects of HBO and topical oxygen therapy. In total, 1,854 patients were screened in outpatient wound clinics for non-randomized enrollments into the HBO (n = 32; 31% were persons with diabetes) and TWO₂ (n = 25; 52% were persons with diabetes) studies. HBO did not result in sta­ tistically significant improvements in wound size or signifi­ cant changes in the expression levels of any of the genes studied. Topical oxygen treatment significantly reduced wound size and was associated with higher VEGF165 expres­ sion in healing wounds.

After an initial prospective case series study by Fisher16 in 1969, only in the last 5 to 10 years has there been new interest in topical approaches to oxygenate cutaneous wounds.18-21,28-36 The results obtained in this trial confirm previously published results of using TWO₂ in chronic wounds. In a prospective case series, Fisher16 treated 52 patients with venous ulcers (n = 16), pressure ulcers (n = 26), and DFUs (n = 2) with topical oxygen that had failed to heal from several months to several years without improvement. The diabetic ulcers were super­ ficial and had been present for 4 and 5 months. With topical oxygen treatment, the two diabetic ulcers healed within 6 and 9 days, failing in six of the 52 cases. In four of these failures, an underlying osteomyelitic process, unknown at the start of therapy, was noted. In the same study, six patients had almost identical lesions on both lower extremities and hips. One le­ sion was treated conventionally and the contralateral lesion was treated with topical oxygen. Two of six control-treated wounds showed mild improvement; all TWO₂ treated wounds healed within 7 weeks.

Heng et al2° conducted a prospective randomized con­ trolled study utilizing TWO₂. Participants included 40 inpa­ tients with 79 necrotic/gangrenous ulcers assigned to TWO₂ or control treatment. The ulcers were of mixed etiology- 39 were diabetic ulcers, 23 of which were located on the foot. Control group patients received standard wound care includ­ ing sharp debridement as needed and wet-to-dry or hydro­ colloid dressings were changed one to three times daily. TWO₂ consisted of topical oxygen delivered at 1.03 to 1.04 atmos­ pheres, with treatment set at 4 hours per day, 4 days per week, for a maximum treatment time of 4 weeks. In the TWO₂ group, 90% of ulcers healed compared with 22% in the con­ trol group.

Heng et al21 also conducted a 3-month prospective cohort study to assess the healing rate and cost-effectiveness of TWO₂ in healing necrotic/gangrenous wounds in patients with and without diabetes. Necrotic tissue was debrided by sharp de­ bridement and infected ulcers were treated with oral or intra­ venous antibiotics. Gangrenous digits or forefeet were treated by partial amputation with subsequent treatment of the skin defect with TWO₂. Fifteen (15) patients had 24 wounds, out of which 22 healed in 24 weeks.

Tawfick et al36 recently published the results of an 83-pa­ tient parallel observational study comparing TWO₂ and con­ ventional compression therapy used in venous ulcer management. After 12 weeks, 80% of TWO₂-managed ulcers were completely healed (median 45 days) compared to 35% of the control group ulcers (median 182 days) (P <0.0001). Pain scores in TWOrmanaged patients improved and nine of the 19 methicillin-resistant Staphylococcus aureus (MRSA)­ positive ulcers in the TWO₂ group were MRSA-negative after 5 weeks of treatment regardless of ulcer closure compared to none of the 17 MRSA-positive ulcers in the control group.

Implications for practice. The diabetes epidemic is a worldwide problem. In the most recent national cross-sec­ tional study37 from the year 2000 of coronary risk factors in Saudi Arabia (the CADIS study), 23.7% of adults over 40 years of age had diabetes. The sample included 16,806 adults and the final response rate was 93%. In 2007, more than 100,000 patients with diabetes in the US had a foot amputation.4 The mortality rate after a diabetes-related lower leg amputation is high. A retrospective database query and medical record re­ view for January 1, 1990, to December 31, 2001 by Aulivola et al38 reported survival rates after major amputation of patients with diabetes of 69.7% and 34.7% at 1 and 5 years, respec­ tively. In the current study, the attending orthopedic and vas­ cular surgeons estimated that 25% of the TWO₂ group patients faced imminent risk of amputation had the treatment regimen not been successful.

The financial burden of DFUs is also considerable. An un­ complicated DFU is estimated to cost $8,000 to treat, an in­ fected ulcer can cost $17,000 and the cost of amputation can reach $45,000.39A°Considering the results obtained in this and other studies, TWO₂ has the potential to provide substantial cost savings.

Conclusion

A significant difference in the proportion of DFUs healed was observed between daily TWO₂– treated wounds and those managed with advanced wound dressings. TWO₂ is a simple­ to-apply, noninvasive therapy. No adverse events were ob­ served in this or previously published studies. During the 24-month follow-up, no reoccurrence of healed ulcers was ob­ served in either treatment group. Well-designed RCTs to con­ firm the efficacy and evaluate the cost-effectiveness of TWO₂ are needed.

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