Debriding Wounds Injured By High-velocity Projectiles With Bromelain

Objective:1. To establish an animal model for assessment on therapeutic effect of debriding medicine on firearm wound.2. To propose a new therapy using topical bromelain as a supplement to wound incision for the debridement of firearm wounds. We clarified the debriding effect of bromelain on firearm wounds in pigs.3. To investigate the effect of bromelain on the microenvironment of firearm wounds, and to understand how bromelain improves healing.Methods:1. 4 rabbits and 4 goats were group A and group B. 8 pigs were divided into group C and group D randomly. Hind limbs of animals in group A, B and C were wounded with spherical projectiles (velocity 850m/s, weight 0.375g) fired by a 53-type musket. Pigs in group D were wounded with cylindrical projectiles. Appearance of wound tracks, histopathologic zonation, bacterial content and cytokine levels of tissues around the wound tracks were measured. Constancy of model was evaluated using coefficient of variation (CV).2. In vitro, muscle tissues around the wound track and normal muscle were incubated in bromelain solutions of different concentrations. Tissue hydrolization was estimated by measuring tissue weight and the release of total amino acids. In vivo, the hind limbs of 15 pigs were wounded with high-velocity projectiles. Five groups were classified: wound excision (E), wound incision (I), bromelain (B), incision + bromelain (IB) and control (C). Debriding effectiveness was estimated using bacterial content, histopathologic examination, and wound healing time. 3. Twelve Chinese landrace pigs wounded by high-velocity projectiles were divided randomly into three groups: wound incision (group I), incision + bromelain (group IB) and control. Blood perfusion, oxygen partial pressure (pO2), and the content of tumor necrosis factor (TNF)-?and transforming growth factor (TGF)-?in wound-track tissue were measured. Wound healing was also noted.Results:1. All wound tracks were simple penetrating wounds. Size of wound track entrance and exit, volume of wound track in group B and group C were more consistent than in group A and group D. Under light microscope, typical histopathologic zonation of firearm wounds was observed, which revealed that the status of injuries in group C was more invariant than the other three groups. Bacterial count showed that contamination to the wound track was heavy, and there was no statistic difference among groups (p>0.05). TNF-?and IL-6 levels in tissues heightened gradually within 24 hours after wounding. The change of TNF-?and IL-6 levels showed a similar trend in the plasma, but the levels were lower relatively.2. In vitro, hydrolization of wound tissue was significantly more intensive than that of normal tissue (p<0.05). Bromelain solution (10 mg/mL) hydrolyzed wound tissue rapidly with minimal proteolysis of normal tissue. In vivo, the wound-track bacterial content of group IB was similar to that of group E, and was significantly lower than that of groups I, B and C. The wound healing time of group IB was also shorter.3. The recovery of blood perfusion in tissue and pO2 in wound tracks was significantly more rapid in group IB than in group I and control (p<0.05). The tissue level of TNF-?was significantly lower in group IB than in group I and control 48 h and 72 h post-wounding (p<0.05). The tissue level of TGF-?in group IB was sustained at a significantly higher level than in group I and control (p<0.05). Wound healing time was also shorter in group IB.Conclusions:Simple soft tissue penetrating wounds on hind limbs of pigs wounded with spherical projectiles (velocity 850m/s, weight 0.375g) possesses the histopathologic and bacterial characteristics of firearm wound. State of injuries is consistent. Approach to this model is simple. Bromelain is effective in the debridement of uncomplicated firearm wounds if used as a supplement to simple wound incision. This new therapy shows notable advantages over conventional surgical debridement as it greatly simplifies the procedures. Enzymatic debridement using topical bromelain in incised wound tracks ameliorates the wound microenvironment for tissue repair and improves the healing of firearm wounds.