Negative Pressure Wound Therapy on Diabetic Foot Ulcers

Reconstruction of diabetic foot ulcers is often a challenging problem. The impairments involved with the healing process, along with the lack of resistance against infection in patients with diabetes, represent a familiar clinical problem.¹ High treatment costs and unsatisfactory results are common.

The surgical treatment of the diabetic wounds with loss of soft tissue continuity usually consists of closure using a split-thickness skin graft or transposition flap. However, immediate surgical closure often fails because surgical closure is not always appropriate given the general condition of the patient and the wound.Therefore, initial treatment begins with open wound care.

The NPWT wound dressing (V.A.C.^® GranuFoam^™, KCI, San Antonio,Tex), developed by Argenta and Morykwas,² assists in healing open wounds. In clinical and experimental studies, the effects of NPWT that accelerate wound healing are reported as increased local blood flow, formation of granulation tissue, and decreased bacterial colonization.^2,3 Faster wound healing results in an overall decrease in hospitalization and avoids the additionalmorbidity of chronic wounds.^4–6 Successful results with the NPWT system are reported in other studies.^7–9

The study aim was to promote healing through the use of NPWT on problematic diabetic foot ulcers and to compare the results with use of conventional moist gauze dressings.

Methods

Twenty-four patients with diabetes and nonhealing, lower-extremity wounds were included in the study. Patients were prospectively randomized to the NPWT group or control group. To avoid bias, all patients were prospectively randomized into groups according to the last digit of the hospital protocol numbers that a blinded official had assigned. Odd numbers were assigned to the NPWT group, even numbers to the control group. All patients were properly informed and gave written consent. The Medical Park Hospital Ethics Committee approved the study.

Seventeen of 24 patients (71%) had insulin dependent diabetes and 7 patients (29%) had noninsulin dependent diabetes. Fifteen of 24 patients (62.5%) had peripheral neuropathy of varying intensity. Five patients (21%) had peripheral vascular dysfunction and were revascularized. The patients with vascular dysfunction who lacked pedal pulses were not enrolled in the study. One patient was undergoing treatment for chronic renal failure but was included in the study.

The diabetic foot ulcers were surgically debrided of nonviable tissue prior to application of NPWT or moist gauze dressing. In the control group, traditional moist gauze dressings were used and were changed twice a day. After debridement, the surface area of the wound was measured in the operating room and at the bedside using sterilized millimetric paper and a disposable pen. Since the paper was cut to fit the wound, the template was useful for measuring the surface area of the wounds and for cutting the NPWT wound dressing to facilitate optimal wound coverage.

In the NPWT group, the wounds were covered with the polyurethane ether dressing and a tube was placed underneath the dressing. The tube and dressing were covered with a clean, nonsterile, adhesive drape to create an airtight seal.The tube was then connected to an aspirator pump to create negative pressure. In this group, -125 mmHg continuous negative pressure was used. The NPWT dressing and tube were changed every 48 h in correlation with other studies.^2,3,7,8,10

Intravenous analgesic agents were given to all patients in the NPWT group before dressing changes because the polyurethane dressings were sticking to the wounds and were causing pain at removal. In the control group (standard saline moist gauze dressings) the dressings were changed twice daily and were less painful to change.Oral analgesics were used in the control group when required. Systemic antibiotherapy was given to all patients for prophylaxis after the surgical debridement. There was no sign of wound infection that would require antibiotherapy for the remainder of the treatment period. Multivitamins and nutritional supplements, including zinc, were given to all patients. The wound surface areas were measured every 48 h in both groups. Open wound care therapy was continued until the wound bed was almost completely granulated and there was no sign of inflammation.

All data were collected prospectively. Treatment groups were compared via the Wilcoxon Signed Ranks and Mann-Whitney tests for homogeneity. Data was tested for significance using SPSS 10.0 for Microsoft^® Windows statistical software. Significance was determined at P < 0.05 for all tests.

Results

The mean age of the patients in the NPWT group was 66.2 years (range, 54–77) and 64.7 years (range, 56–74) in the control group (P = 0.506). Before treatment, the mean wound surface area was 109 cm² in the NPWT group and 94.8 cm² in control group (P = 0.729). There was no significant difference in groups regarding initial wound surface area and patient age (P > 0.05).

In the first week of the NPWT therapy, an increased amount of granulation tissue formation and a decreasing amount of nonviable tissue was seen in the NPWT group. Edema of the extremities diminished in all patients and the surface area of wounds also decreased. The mean length of open wound care was 11.25 days in the NPWT group and 15.75 days in control group (P = 0.05).

Following therapy, the mean wound surface area decreased 20.4 cm² (109 cm² to 88.6 cm²) in the NPWT group, and decreased 9.5 cm² (94.8 cm² to 85.3 cm²) in the control group (P = 0.032). The difference in the rate of surface area decrease between the groups was significant. The surface area of wounds in the NPWT group was reduced more effectively than control group wounds (P < 0.05).

Nineteen of 24 wounds underwent split-thickness skin grafting—4 of 24 wounds underwent regional fasciocutaneous flap transposition to facilitate wound closure. One patient in the NPWT group required wound closure using a distal pedicled fasciocutaneous flap based on the sural vein and its concomitant arterial vessels. However, in the control group,3 patients underwent wound closure by using regional distal pedicled fasciocutaneous flaps—2 sural flaps and 1 saphenous flap.The flap donor sites were covered with split-thickness skin grafts. All of the operations were carried out under regional (spinal) anesthesia.

After NPWT, 1 patient’s wound bed granulated rapidly and became too narrow for surgical closure.Therefore, it was left to be closed by secondary intention. All skin grafts covered the wounds satisfactorily and there were no significant complications with the transpositioned fasciocutaneous flaps except for 1 in the control group, which had partial necrosis distally; however, it was repaired with local debridement and a split-thickness skin graft. All data from the NPWT group and control group, including wound records and closure techniques, are shown in Table 1 and Table 2.

Wound infection was not a problem and there were no local or systemic signs of infection. No negative impact was seen on extremity function or on the psychology of patients.Wound bleeding was seen in some patients from both groups during dressing changes because of excessive growth of granulation tissue into the dressing; however, simple hand pressure applied to the dressing was usually enough to stop the bleeding.

Discussion

It has been reported that NPWT decreases bacterial colonization and interstitial edema and increases capillary blood flow.^2,3 Localized negative pressure removes fluid from the wound and promotes the formation of granulation tissue, which is required for wound closure.^2,3 Furthermore, it reduces wound surface area by the traction force of negative pressure, which increases mitosis of tissue around the wound.^11,12

A moist wound environment heals wounds faster by increasing epithelial migration and by decreasing the infection rates.² Negative pressure wound therapy provides a moist wound bed, which is required for faster healing of chronic open wounds.^2,3,11,12 Faster wound healing during the treatment of diabetic foot ulcers may decrease hospital stays and avoid extensive surgery for wound closure, therefore, possibly lowering the cost of treatment and the additional morbidity of infection and pain.⁴

Wound debridement is essential before applying NPWT to promote healing of diabetic wounds because nonviable tissue has been shown to retard healing.^2,3 In the present study, all of the diabetic ulcers were debrided and surface areas were measured after debridement. Prior to treatment,the mean wound surface area was 109 cm² in the NPWT group and 94.8 cm² in control group (P = 0.729). There was a difference in groups regarding initial wound surface areas and ages, but neither was statistically significant (P > 0.05). The randomization of a small number of patients may cause this nonsignificant difference. However, a significant difference was observed in the surface area decrease in the NPWT group over the control group (P < 0.05). These results correlate with other reports.^9,10 Clare et al,¹⁰ successfully healed 6 of 17 diabetic, dysvascular wounds with serial NPWT dressing changes, brief growth factor use, and split-thickness skin grafting. In a study by DeFranzo et al,⁷ 71 of 75 lower extremity wounds with exposed bone were healed using NPWT. Twelve of the healed wounds were treated by delayed primary closure. de Lange et al⁸ studied 100 patients, including multiple regional wounds, and treated 29 wounds without surgical intervention. In this study, no growth factors were used, but multivitamins and nutritional supplements, including zinc,were given to all of the patients.

In a study on degloving injuries by Josty et al,¹³ the length of therapy ranged from 4 to 8 days. Clare et al¹⁰ applied NPWT for an average length of 8.2 weeks (1 to 20 weeks). The mean duration in the present study was 11.25 days in the NPWT group, and 15.75 days in the control group (P = 0.05). The wounds in the NPWT group were quicker to granulate (ie, ready for surgicalclosure) than the control group wounds. The duration of therapy was shorter because the open wound care therapy was ended when the wound bed tissue was almost completely granulated and had no signs of inflammation.^4,10 In correlation with Armstrong et al,⁶ NPWT (as a prior therapy) was used for a shorter time before surgical wound closure.

The NPWT system was used to drain the wounds with -125 mmHg continuous pressure. The NPWT dressings were changed every 48 h as in other reports.2,3,7,8,10 Polyurethane ether dressings were not used in the control group in order to compare the NPWT dressing with the moist gauze dressing.The difference in dressing techniques limits the experimental design of the study.

The patients in the NPWT group were given intravenous analgesics before dressing changes because the polyurethane dressings were sticking to the wounds and were causing pain. In the control group, the moist gauze dressings were changed twice daily and were easier and less painful to change. Oral analgesics were administered for control group patients when required.

In the treatment of diabetic ulcers, the NPWT wound dressing provides a faster wound resolution compared to saline-moistened gauze. Negative pressure wound therapy may be beneficial in treating nonhealing, lowerextremity diabetic wounds.^4–6

Conclusion

Appropriate use of NPWT may be an effective alternative therapy to achieve faster granulation of the wound bed in diabetic foot ulcers prior to surgical closure. Negative pressure therapy can be accepted as an initial therapy before surgical closure of problematic wounds. The results of this small study using NPWT are hopeful. In the future, the authors hope to report on a larger cohort of patients in order to compare the effects of NPWT to moist gauze in treating nonhealing, diabetic wounds. Further studies are needed to clarify the effects and indications and to modify the technique of this alternative treatment for nonhealing wounds.