Effects on wound healing of zinc oxide in a hydrocolloid dressing.

BACKGROUND: Zinc oxide incorporated in gauze enhances healing of chronic wounds in humans and experimental pig wounds. OBJECTIVE: The purpose of this study was to examine the effects of zinc oxide added to a hydrocolloid dressing on the healing of surgical wounds in domestic pigs. METHODS: Forty partial-thickness wounds (2.2 x 2.2 cm and 400 microns deep) were treated with different zinc oxide concentrations, and epithelialization was evaluated morphometrically in a total of 320 histologic sections. Wound closure, bacterial growth, and inflammation were studied in eight full-thickness wounds (2.5 x 4.5 cm). The level of serum zinc was determined before and after treatment. RESULTS: In partial-thickness wounds, concentrations of zinc oxide at or below 1.0% (wt/wt) inhibited epithelialization, whereas no effect was observed at zinc oxide concentrations from 2% to 6%. In full-thickness wounds, zinc oxide (6%) reduced bacterial growth by about 2 log units and increased the inflammatory response in the granulation tissue, but had no effect on healing when compared with control (hydrocolloid alone). Serum zinc levels remained unchanged throughout the treatment period. CONCLUSION: Apart from inhibiting bacterial growth, no additional beneficial effects on wound healing in nutritionally balanced pigs were found by supplementing a hydrocolloid dressing with zinc oxide.

The effect of single shock waves on the vascular system of artificially perfused rabbit kidneys.

Extracorporeally-perfused rabbit kidneys were exposed to five shock waves at 14 kV on the XL1 Dornier experimental lithotripter (Dornier Medical Systems, Inc., Germering, Germany). While the perfusion flow rate was kept constant, the arterial perfusion pressure was recorded to assess changes in vascular resistance. Immediately after shock wave application, perfusion pressure decreased by 20%-30%, followed by a short, relative pressure rise that did not reach pretreatment values. Fifteen-twenty minutes later, arterial perfusion pressure reattained pretreatment values. Subsequent to treatment, urine flow decreased by greater than 50%. The observed pressure rise was also induced in nontreated kidneys by perfusion with the effluent of treated kidneys indicating that this is based on a humoral mechanism. On the other hand, shock wave application to formalin fixed kidneys only caused a marked decrease in arterial perfusion pressure, suggesting that this effect is due to a pure mechanical interaction of the shock wave also found with denaturated kidneys. The observed decrease of urine flow is probably caused by a decreased filtration rate. Since this was not the case in nontreated kidneys being perfused with the effluent of treated kidneys, the reduction of urine flow after extracorporeal shock wave lithotripsy does not appear to be mediated by a humoral factor, but is more likely a result of the mechanically-induced vasodilation with consecutive decline of the glomerular filtration rate.

Collagen fibers as a temporary scaffold for replacement of ACL in goats.

ACL substitutes made of braided or plied purified collagen fibers and cross-linked with hexamethylenediisocyanate were implanted into a total of 14 adult goats to achieve resorption within 8 to 10 months. Two types of collagen fiber prostheses differing in degree of collagen purification were tested. The implants were harvested 2 to 11 months postimplantation, tested for mechanical strength, and evaluated by morphological methods. In the first group (n = 5), the less purified and less cross-linked collagen fiber ACL implant induced fast connective tissue ingrowth. At 6 months postimplantation, 40 to 60% of the collagen implant was resorbed. No studies on breaking strength were done in this group. In the second group, highly purified and more crosslinked ACL implants were less infiltrated by cells and were resorbed only by 10 to 20%. Still, the breaking strength was decreased to 10% of the original implant strength. In the second group, the fixation of the ACL implant in the bone tunnel with a bone wedge was insufficient (n = 6); however, additional fixation with metal screws was successful (n = 3). We conclude that cross-linked collagen fibers alone cannot be used as a safe ACL substitute as they quickly lose mechanical strength despite limited biodegradation.

Effect of surgical manipulation of polytetrafluoroethylene grafts on microstructural properties and healing characteristics.

The effects on graft healing of alterations in the microstructure of polytetrafluoroethylene (PTFE) grafts induced by surgical instruments have not been fully elucidated. This study evaluates changes in the structural and physical properties of PTFE grafts resulting from the intentional application of commonly used surgical instruments and the influence of these changes on cellular ingrowth. The extent of cellular ingrowth into intact (10, 30, and 60 microns unreinforced and 30 microns reinforced [R]) and structurally compromised PTFE grafts (30 reinforced and 60 microns nonreinforced) implanted subcutaneously in Sprague-Dawley (n = 14) rats was evaluated at 7 and 21 days. The thrombogenicity of 10-, 30-, 60-, and 80-microns intact graft segments was determined gravimetrically after suspension in the internal jugular vein of dogs for 90 minutes. Cellular ingrowth consisting of fibroblasts, macrophages, and microvessels was directly related to porosity and was most extensive in 60-microns uncompromised graft segments, being 7-, 17-, and 20-fold greater than was observed in 60- and 30R-microns compromised grafts and undamaged 10-microns grafts, respectively. There was a direct relationship between porosity and thrombogenicity of intact graft segments suspended in the jugular vein. The amount of thrombus adherent to 80-microns graft segments was eightfold greater compared with 10-microns grafts. Manipulation of PTFE with surgical instruments significantly impairs healing and may be a possible etiologic factor in the poor long-term performance of these grafts.

Use of an antibiotic-bonded graft for in situ reconstruction after prosthetic graft infections.

We have developed an infection resistant vascular prosthesis by bonding rifampin to Dacron grafts with the use of a collagen matrix release system. The purpose of this study was to determine the efficacy of this antibiotic-bonded graft in resisting infection after an in situ reconstruction of a previously infected prosthetic bypass. Eighty-three adult mongrel dogs underwent implantation of a 3 cm untreated Dacron graft into the infrarenal aorta. This initial graft was deliberately infected, at the time of operation, with 10(2) organisms of Staphylococcus aureus by direct inoculation. One week later, the dogs were reexplored, the retroperitoneum debrided, and the animals randomized to undergo an end-to-end in situ graft replacement with either one of two types of prosthetic grafts: group I (collagen, n = 36) received control collagen-impregnated knitted Dacron grafts; group II (rifampin, n = 47) received experimental collagen-rifampin-bonded Dacron grafts. Each group of animals was then subdivided to receive one of four treatment protocols: (a) no antibiotic therapy, (b) cephalosporin peritoneal irrigation solution (cefazolin 500 mg/1000 ml) during operation and two doses of cephalosporin (cefazolin, 500 mg intramuscularly) postoperatively, (c) treatment as in protocol group b plus 1 week of cephalosporin (cefazolin, 500 mg intramuscularly, twice daily), and (d) treatment as in protocol group b plus 2 weeks of cephalosporin (cefazolin, 500 mg intramuscularly, twice daily). All grafts were sterilely removed between 3 and 4 weeks after implantation. There were no anastomotic disruptions and all grafts were patent at the time of removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of shock waves on fracture healing.

During the last decades the influence of physical factors on fracture healing has been widely described. With the use of shock waves for the treatment of urolithiasis, a new mechanical medium has been introduced into medicine. For the first time the influence of shock waves on fracture healing was studied in rats. With fractioned shock-wave treatment (5 times 100 shock waves at 14 or 18 kV) an enhancement in healing could be achieved.

Effects of electrocautery on midline laparotomy wound infection.

This study compared the healing of midline fascial incisions made with either scalpel or electrocautery and inoculated with Escherichia coli in 57 Sprague-Dawley rats. At 7 days, tensile strength was significantly less when incisions were made with electrocautery than with a scalpel. Additionally, would strength was inversely related to the concentration of the inoculum of E coli. The use of electrocautery was also associated with more frequent bacteremia at 48 hours and higher mortality at 7 days. Our results suggest that the technique used to incise the abdominal fascia influences subsequent wound healing, particularly in contaminated wounds.

Prevention of graft infection by use of prostheses bonded with a rifampin/collagen release system.

The objective of this study was to test the efficacy of bonding rifampin to double-velour Dacron grafts with collagen to prevent graft sepsis. Fifty 6.0 mm Dacron grafts (length 5.0 cm) impregnated with either collagen (control) or collagen plus rifampin (experimental) were implanted in dogs end-to-end into the infrarenal aorta. The dogs were divided into four groups (each with an experimental and control subdivision) as a function of time between grafting and bacterial challenge. At 2, 7, 10, or 12 days after graft implantation, sequential groups were challenged with 1.2 x 10(8) colony forming units of Staphylococcus aureus (clinical isolate) intravenously suspended in 250 ml normal saline. Three weeks after hematogenous seeding, the grafts were sterilely harvested. One-tailed Fisher's exact test was used to compare the patency and culture-proven infection of control and antibiotic coated grafts as a function of implantation time before bacteremic challenge. In the 2-day group, four of six control grafts were infected compared with zero of six experimental grafts (p less than 0.030). In the 7-day group, five of six control grafts were infected with S. aureus versus zero of six in the experimental group (p less than 0.008). In the 10-day group, one of six experimental grafts was infected, but the control group had only two of six graft infections. In the 12-day group two of six experimental grafts and one of five control grafts were infected. These results indicate that rifampin bonded with collagen to knitted Dacron grafts will protect the graft from bacteremic infection for 7 days after implantation in a highly challenging model.(ABSTRACT TRUNCATED AT 250 WORDS)

Inert wound dressing is not desirable.

Four Yorkshire piglets were inflicted with a total of 92 split-thickness wounds 4.8 cm2 in area and 400 microns deep. The wounds were treated with eight dressing regimens under the same experimental design. The rate of reepithelialization of the wound was quantitated by a morphometric method. The magnitude of inflammatory reaction of the wound to the dressing was scored from histological slides. The results indicate a relationship between the rate of reepithelialization of split-thickness wounds and the inflammatory response of the wound to the dressing. Dressings, such as collagen sponge, polyethyleneglycol, Duoderm, and lanolin ointment, induce moderate to severe inflammatory changes when placed on the wounds. These wounds reepithelialize significantly faster than control, gauze-covered wounds. This contrasts with inert dressings, such as hydrated hydrogel membrane, Carbopol 934P, or Silvadene cream, which did not affect the rate of reepithelialization when compared with the healing of control wounds. Simultaneously, these dressings induced no or minimal inflammatory reaction in the wound tissue. Only when the inflammatory reaction to the wound dressing was excessive (methylcellulose) was the rate of reepithelialization of the wounds significantly inhibited in comparison with control wounds. We hypothesize that wound dressings, by inducing inflammatory reaction, enhance healing by activating cells, such as macrophages or fibroblasts, that produce growth factors and other mediators of the repair process.

Vitamin E reduction of lipid peroxidation products in rats fed cod liver oil and ethanol.

The purpose of this study was to investigate the effects of vitamin E supplementation on ethanol- and cod liver oil-induced lipid peroxidation. Adult male rats received diets containing ethanol, cod liver oil and supplemented with vitamin E for 28 days. Following treatment, hepatic conjugated dienes, lipid fluorescence, and exhalation of ethane were measured as indices of lipid peroxidation. Ethane expiration over a 3-hour period was reduced by 96% in rats fed ethanol supplemented with vitamin E. Exhalation of ethane was increased by CLO feeding but was reduced 89% in the CLO-fed rats supplemented with vitamin E. In addition, ethane production was elevated in rats fed ethanol plus CLO compared to rats fed diets containing CLO supplemented with vitamin E. Supplementation of the CLO diet with vitamin E also significantly decreased hepatic conjugated fatty acid dienes levels. Levels of hepatic conjugated fatty acid dienes from rats fed ethanol plus vitamin E were reduced 91% compared to rats fed ethanol diets. Additionally, hepatic lipid fluorescence expressed as per mg of hepatic phospholipid basis was also significantly increased in rat groups fed vitamin E, ethanol, and cod liver oil diets. Where vitamin E was added to these same diets a significant decrease of hepatic lipid peroxidation products occurred. The observed reduction in lipid peroxidation by vitamin E may be useful to retard lipid peroxides derived materials involved in the development of alcoholic liver diseases.

Efficacy and duration of antistaphylococcal activity comparing three antibiotics bonded to Dacron vascular grafts with a collagen release system.

Type 1 collagen, minimally cross-linked, was used to bind one of three antibiotics (amikacin, chloramphenicol, or rifampin) to double-velour Dacron grafts to develop a prosthesis resistant to infection. Six millimeter disks of graft were placed in separate flasks (specific for each antibiotic) containing albumin in saline and continuously agitated. At daily intervals the solution was changed, and paired graft samples were removed and placed on a blood agar plate confluently streaked with bacteria. The initial zone of inhibition (centimeters squared), the time to 50% reduction of initial inhibition zone, and the overall duration of antibacterial activity were recorded on an exponential model. Grafts bonded with amikacin and chloramphenicol had an overall duration of activity of only 2 and 1 day, respectively, against Staphylococcus aureus. The collagen bonded rifampin grafts had an initial zone of 14.76 cm,2 took 3.92 days to reach 50% of initial inhibition, and had an overall duration of activity of 22.4 days. This was significantly better than grafts preclotted with 1.0 ml of rifampin (60 mg/ml) and 9 ml of blood (10.92 cm,2 1.06 days, and 5.6 days). When tested against a slime-producing Staphylococcus epidermidis (American Type Culture Collection No. 35983), the graft bonded with rifampin had inhibitory activity of up to 27.77 days with a 50% of activity eluted at 4.78 days, significantly better than the preclotted rifampin graft without collagen bonding. These data suggest that rifampin bonded by collagen can protect a vascular graft against infection from S. aureus and S. epidermidis for up to 3 weeks after implantation.

Enhancement of re-epithelialization with topical zinc oxide in porcine partial-thickness wounds.

We investigated the effect of locally applied zinc on the healing of partial-thickness skin wounds in the domestic pig using two zinc compounds (zinc oxide and zinc sulfate) in two different vehicles (a gauze compress and a collagen sponge). The rate of re-epithelialization was determined morphometrically 48 and 64 hr after infliction of standardized square wounds (4.8 cm2 and 400-microns deep) with an electrokeratome. Zinc oxide in gauze significantly (P less than 0.05) increased re-epithelialization of the wounds (33% more epithelialized than control wounds after 64 hr) and in collagen sponge (76% more epithelialized than control wounds after 64 hr). Zinc sulfate had no such stimulatory effect at any dosage or vehicle used. Our results show that topical zinc oxide enhances re-epithelialization of partial-thickness wounds in nutritionally balanced pigs and that the mode of delivery of zinc is probably critical for achieving the beneficial healing effect of zinc.

The effect of vitamin E (alpha-tocopherol) supplementation on hepatic levels of vitamin A and E in ethanol and cod liver oil fed rats.

Eight groups of 5 rats were fed 8 differing liquid diets with and without ethanol, cod liver oil and/or increased levels of vitamin E. Hepatic levels of vitamins A and E were determined following the 28-day feeding time. Ethanol consumption decreased the levels of hepatic vitamin E (p less than 0.05), vitamin A (p less than 0.05) and the ratio of vitamin A/E (p less than 0.05). Hepatic levels of vitamins A and E were unaffected in rats fed cod liver oil. Supplementation of the normal dietary level of 30 IU of vitamin E per kg diet, with an additional 142 IU alpha tocopherol/kg diet, restored hepatic concentrations of vitamin E to normal levels in alcohol-fed rats. The hepatic levels of vitamin A in rats fed ethanol diets supplemented with vitamin E were less than that of control rats but were 4.3 times greater than that of rats on ethanol diets unsupplemented with vitamin E. However, the vitamin A and E ratio was equal to normal in this group of rats. The vitamin A/E ratio was reduced in liver of rats fed non-alcoholic diets supplemented with vitamin E due to increased levels of hepatic vitamin E. Additionally, rats fed cod liver oil diets containing ethanol also indicated decreased hepatic vitamin A and E levels. However, these levels were greater than that of rats fed only alcoholic diets suggesting that these vitamins are replaced by the vitamin A and E content in the cod liver oil.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of electrocautery on wound healing in midline laparotomy incisions.

The effect of electrocautery on midline fascial wound healing was studied in 108 Sprague-Dawley rats. Midline wound tensile strength was significantly reduced in fascia incised with the coagulation current compared with the cutting current or scalpel. In addition, tissue necrosis and inflammation as well as adhesion formation between the incision and abdominal viscera were more extensive in animals with incisions made using coagulation current. The results of the study indicate that the use of electrocautery coagulation current is associated with increased tissue damage and a significant reduction in the tensile strength of healing wounds. The contribution of electrocautery to wound complications in patients needs further evaluation.

A comparison of parallel versus perpendicular placement of retention sutures in abdominal wound closure.

A new technique for placement of retention sutures is described. Twenty-five rats underwent midline laparotomy incision. The control group was closed with traditional placement of through-and-through retention sutures placed in a perpendicular direction to the wound. The experimental group was closed with retention sutures placed in a parallel direction to the wound as described below. Wound bursting strength was significantly (P less than 0.001) greater at one to five days in the experimental group compared with the control animals. In addition, inflammatory reaction and pressure necrosis were greater in the control group. It appears that parallel placement of sutures has less of a tendency to cut through tissue when subjected to the distracting forces on a midline wound.

Occlusion of the vas deferens in dogs with a biocompatible hydrogel solution.

The surgically exposed vasa deferentia of 21 dogs were injected, under visual inspection, with Hypan N-90 acrylic hydrogel (50-150 microL). The hydrogel was deposited inside the vas lumen via a 22-gauge Teflon intercatheter. The solution gelled within 120 seconds. Semen was collected by manual collection and analyzed for volume, sperm count and viability. After occlusion with 150 microL of the polymer in the distal direction (direction of the testis), the volume of ejaculate (2.2 mL) did not change. Subsequent samples showed no viable or dead spermatozoa. The stained smears of the ejaculate showed the presence of cell debris, granulocytes and few epithelial cells. When the vas was injected with 50 microL of the polymer in either a distal or proximal direction, the occlusion effectiveness was 75% and 25%, respectively. In the proximal direction, granulomas were noticed in the vas wall where semen leaked through the injection port. Histology of successfully occluded vasa (with Hypan) showed no cellular reaction or fibrotic changes in the proximity of the polymer. For less than or equal to 20 weeks after vas occlusion, no evidence of abnormal morphology was found in the epididymal and testicular tissue. This highly biocompatible polymer solution, when gelled in contact with tissue fluid, offers safe and effective occlusion of the vas with the promise of reversibility.

Effect of shock waves on the healing of partial-thickness wounds in piglets.

During the last 20 years, the role of various physical factors in wound healing has been widely studied and recognized. With the use of shock waves for the treatment of urolithiasis, a new mechanical medium has been introduced into medicine. The influence of shock waves on the reepithelialization of partial-thickness wounds was studied in four Yorkshire piglets by a quantitative morphometric method. Wounds were inflicted either in intact skin (three pigs) or in skin irradiated with 1500 rads to achieve delayed healing. A significant enhancement in normal or delayed healing was found with low-dose treatment (10 SW at 14 kV). High-dose application of shock waves (100 SW at 18 kV) resulted in inhibition of the rate of reepithelialization of the wounds. Shock waves of intermediate energies were without effect. The stimulating effect of low-energy shock waves coincides with significantly increased vascularization of the upper dermis and thicker layer of the newly formed epithelial cells covering the wound.

Antibiotic irrigation and the formation of intraabdominal adhesions.

The efficacy of antibiotic peritoneal lavage in the prevention of postoperative infection is controversial. The role of intraperitoneally administered cefazolin and tetracycline in the formation of adhesions was studied in the rodent model. Thirty-two rats were divided into 3 groups. Group 1 underwent midline laparotomy with instillation of 10 ml of normal saline solution. Group 2 and Group 3 underwent the same procedure with instillation of 0.2 percent saline solutions of cefazolin or tetracycline, respectively. Animals were sacrificed after 2 weeks. Intraabdominal adhesions were graded and samples of parietal peritoneum were processed for histologic data. Group 2 and Group 3 had significantly higher adhesion scores compared with Group 1 (p less than 0.001). Histologic appearance of both antibiotic-irrigated groups showed mesothelial thickening with presence of fibroblasts and collagen. Cefazolin and tetracycline irrigation of the abdominal cavity contributes to the formation of peritoneal adhesions in the rat model.