The Immediate and Delayed Post-Debridement Effects on Tissue Bacterial Wound Counts of Hypochlorous Acid Versus Saline Irrigation in Chronic Wounds

METHODS

Seventeen consenting male and female adult patients with chronic stage 3 to 4 wounds of multiple etiologies were randomly selected for study. All patients were stable of metabolic and cardiovascular conditions and without clinical sepsis. All patients received appropriate perioperative antibiotics based on sensitivities and allergic status. All procedures were carried out by a wound surgeon. The patients were alternately divided into 2 groups. Group I patients received HA (Vashe Wound Solution; SteadMed Medical LLC, Fort Worth, Tex) as a wound irrigant with the ultrasonic debridement, and group II patients received saline as an irrigant with the ultrasonic debridement. Debridement was performed in both groups using Misonix low-frequency ultrasound (SonicOne OR, Ultrasonic Debridement System, Misonix Inc, Farmingdale, NY). All patients were anesthetized with general anesthesia or local anesthesia with monitored sedation for surgical procedures, depending on the patient's general condition.

Pre- and postdebridement tissue biopsies were obtained and immediately placed in liquid nitrogen for storage. Following debridement, all wounds were treated with silver-impregnated, time-release, custom-fit dressings, left in place undisturbed for 7 days. Drawtex hydroconductive wound dressings (SteadMed Medical LLC) were used as an outer dressing and held in place with an appropriate size foam dressing. The outer dressings were changed on alternate days or as needed, depending on the volume of wound exudate. All patients remained at bed rest using low-pressure mattresses throughout the study.

At 7 days following the initial debridement, all patients were returned to the operating room, where they were anesthetized, dressings removed, and the wounds biopsied for bacterial quantification. Samples were labeled and stored in liquid nitrogen. An additional biopsy sample was obtained for standard aerobic and anaerobic culture and sensitivities. All patients, following biopsy at 7 days, underwent selective wound closure at that time. The results of surgical closure were recorded at 7 to 10 days following wound closure.

Data were recorded pre- and postoperative debridement on day 1, at 7 days postdebridement prior to wound closure, and 7 to 10 days following wound closure. Clinical outcome data were compared 3 weeks after the definitive surgery. Mean bacterial counts for each patient group were determined at each time point and expressed as CFU (colony-forming unit) per gram of tissue. These values were compared at each time point using a 1-way analysis of variance. Post hoc analyses of differences between groups were carried out using Tukey's test, with P < .05 considered significant. Sigma Stat statistical software (Jandel Scientific, Corte Madera, Calif) was used for data analysis.

RESULTS

The results of this clinical study are demonstrated in Tables 1-4 and Figure 1. Tables 1 and 2 reflect the patient demographics and wound type. Tables 3 and 4 demonstrate comparable effective bacterial bioburden reduction in both groups I and II immediately after debridement. At 7 days after debridement, a significant difference (P < .05) was observed between the 2 groups. Group I treated with HA irrigation showed sustained suppression of bacterial growth. However, group II patients treated with saline irrigation showed growth of bacteria to near predebridement levels at 7 days.

Figure 1. Mean bacterial wound count log. Pseudomonas aeruginosa in wound debridement using hypochlorous acid versus saline irrigation.

The clinical outcomes of surgical wound closure demonstrated fewer postoperative complications in group I patients (25%) than in group II patients (>80%). The wounds in both groups were not clinically distinguishable one from the other group at 7 days postdebridement when the wounds were scheduled for closure. These observations were made by 1 experienced surgeon without knowledge of the bacterial quantification results. One patient with complication in group I died 7 days after sacral wound closure due to myocardial disease. The wound closure at that time, however, was intact and did not appear to contribute to the mortality.

DISCUSSION

To effect adequate debridement, nonviable tissue, debris, and bacteria must be removed from chronic wounds. A high tissue bacterial bioburden has been associated with a failure of wound healing.⁶ The level of tissue bacterial bioburden that inhibits healing has been shown in multiple studies to be greater than 10⁵ or at least 1 × 10⁶ bacteria per gram of tissue.^8,9 Such high levels of tissue bacteria can be present without clinical signs of infection and when present can deleteriously affect wound healing¹⁰ and prevent wound closure by wound approximation, skin graft, or pedicle flap.⁸

Low-energy ultrasonic mechanical debridement as used in this study has been reported to effectively debride wounds without causing excessive tissue trauma.⁹ Advantages of ultrasound to healing include release of nitrous oxide via fluid shear stress stimulation of cells resulting in resolution of vasospasm, thereby increasing blood flow around the wound.¹¹ In addition, fibroblasts, macrophages, and endothelial cells are stimulated.¹²

Wound antiseptics have been useful as wound irrigants, but some such as Dakin's solution and chlorhexidine have been reported to be cytotoxic.^13,14 Hypochlorous acid has been demonstrated to be noncytotoxic, so was chosen as an irrigant in this study.¹⁵ The antibacterial effects of HA maintained the debrided wounds in bacterial balance during the 7-day period until wound closure was performed. Despite the fact that clinically the wounds in both groups I and II patients appeared ready for closure, the wounds in group II patients that had been irrigated with saline had an increased bioburden and more than 80% of the wound closures were unsuccessful. This lack of correlation between clinical judgment and bacterial invasion of the tissue was as reported by Serena et al.¹⁰

CONCLUSIONS

This study demonstrates that ultrasound debridement is an effective method to lower tissue bacterial counts in chronic wounds. It also demonstrated that HA is more effective than saline as an irrigant with ultrasonic debridement for maintaining wounds post–initial debridement until wound closure can be performed. The results of surgical closure reconfirms that the bacterial load in wounds influences closure outcome when clinical judgment cannot discriminate between wounds with a high bioburden and those in bacterial balance. Using tissue bacterial levels can predict safe wound closure and reduce the need for repeated debridement or staging of wound closure. Finally, the clinical outcomes of surgical wound closure of chronic wounds 7 days after ultrasonic debridement were superior when HA was used as an irrigant in the ultrasonic debrider as compared with the more commonly used saline as an irrigant.