Effect of photodynamic therapy on the critical primary ischemic time of fasciocutaneous flaps

A Model to Study Wound Healing Over Exposed Avascular Structures in Rodents With a 3D-Printed Wound Frame

BACKGROUND

Soft tissue defects with exposed avascular structures require reconstruction with well-vascularized tissues. Extensive research is ongoing to explore tissue engineered products that provide durable coverage. However, there is a lack of controlled and affordable testbeds in the preclinical setting to reflect this challenging clinical scenario. We aimed to address this gap in the literature and develop a feasible and easily reproducible model in rodents that reflects an avascular structure in the wound bed.

METHODS

We created 20 × 20 mm full thickness wounds on the dorsal skin of Lewis rats and secured 0.5-mm-thick silicone sheets of varying sizes to the wound bed. A 3D-printed wound frame was designed to isolate the wound environment. Skin graft and free flap survival along with exposure of the underlying silicone was assessed. Rats were followed for 4 weeks with weekly dressing changes and photography. Samples were retrieved at the endpoint for tissue viability and histologic analysis.

RESULTS

The total wound surface area was constant throughout the duration of the experiment in all groups and the wound frames were well tolerated. The portion of the skin graft without underlying silicone demonstrated integration with the underlying fascia and a histologically intact epidermis. Gradual necrosis of the portion of the skin graft overlying the silicone sheet was observed with varying sizes of the silicone sheet. When the size of the silicone sheet was reduced from 50% of the wound surface area, the portion surviving over the silicone sheet increased at the 4-week timepoint. The free flap provided complete coverage over the silicone sheet.

CONCLUSION

We developed a novel model of rodent wound healing to maintain the same wound size and isolate the wound environment for up to 4 weeks. This model is clinically relevant to a complex wound with an avascular structure in the wound bed. Skin grafts failed to completely cover increasing sizes of the avascular structure, whereas the free flap was able to provide viable coverage. This cost-effective model will establish an easily reproducible platform to evaluate more complex bioengineered wound coverage solutions.

Effect of Celecoxib on Fasciocutaneous Flap Survival and Revascularization

OBJECTIVES

To study the effect of celecoxib (Celebrex; Pfizer, Cambridge, Mass) on (1) primary ischemic time and (2) revascularization of fasciocutaneous free flaps in a rat model.

METHODS

In the ischemia study, 50 male Sprague-Dawley rats were divided into 2 groups of 25 rats each, a control group and a celecoxib group. Five rats in each treatment group were exposed to ischemic times of 4, 6, 8, 10, and 12 hours. Survival of the flap was assessed 7 days after reversal of the ischemia. Probit curves and the critical ischemic time were calculated. In the revascularization study, 30 male Sprague-Dawley rats were divided into 2 groups of 15 rats each. One group was fed celecoxib, while the other was fed a normal diet. All rats had a 3 x 6-cm fasciocutaneous flap based on the inferior epigastric artery elevated and exposed to 2 hours of primary ischemia. The flap was then sutured back into the wound bed. Each of these groups was then divided into 3 groups of 5 rats whose pedicles were divided on postoperative day 5, 6, or 7. Percentage survival of the flap was measured 7 days later. In both parts of the study, the experimental group was fed celecoxib, 1500 ppm, throughout the interoperative period. In each animal, a 3 x 6-cm ventral fasciocutaneous groin flap based on the left superficial epigastric artery was elevated.

RESULTS

In the ischemia study, respective flap survival rates from the control and celecoxib groups at the various ischemic times were as follows: 4 hours, 100% and 100%; 6 hours, 80% and 100%; 8 hours, 80% and 80%; 10 hours, 60% and 60%; and 12 hours, 20% and 10%. The median lethal ischemic times were 9.7 and 9.6 hours, respectively. There was no statistical difference in flap survival between the celecoxib and control groups. In the revascularization study, ligation of the flap pedicle on day 5, 6, or 7 did not result in any difference in the percentage of flap survival among the 3 groups.

CONCLUSION

Celecoxib appears to have no deleterious effect on free tissue transfer survival or healing, as evidenced by revascularization in a fasciocutaneous free flap model.

Ischemia-reperfusion injury of adipofascial tissue: an experimental study evaluating early histologic and biochemical alterations in rats

Fat necrosis remains a serious complication in reconstructive flaps. In clinical setting, it is well known that fat tissue is more susceptible to ischemic events. We aimed to evaluate early histological and biochemical changes of adipofascial tissue in an experimental model. An epigastric flap model in rats was used to evaluate the effect of ischemia-reperfusion (I-R) injury on adipofascial tissue. Two groups of animals (one with ischemia alone and other ischemia-reperfusion group) were used to evaluate the degree of histological edema, congestion and extravascular bleeding, and early biochemical alterations within the adipofascial flaps. The biochemical parameters included glutathione (GSH) and malondialdehyde (MDA). In each group, contralateral groin subcutaneous adipose tissue served as control. These evaluations were compared to normal unmanipulated, contralateral abdominal subcutaneous adipose tissue. The ischemia-reperfused flap group showed histologically significantly much edema congestion and bleeding than the control groups (P<.0001). The control group showed less edema in fat tissue than the ischemia-alone group (P<.05). All of the flaps in the ischemia-only group showed significantly less bleeding and edema than I-R group (P<.001). The ratio of MDA/GSH was 33 in control, 37 in ischemia alone, and 82 in ischemia-reperfusion groups, respectively. This study confirms that significant histologic and biochemical alteration occurs after ischemia and ischemia-reperfusion events in adipose tissue. Marked drop in adipose tissue antioxidant levels after I-R suggested that preemptive measures to this decrease should be undertaken in clinical settings.

Effects of Tisseel and FloSeal on Primary Ischemic Time in a Rat Fasciocutaneous Free Flap Model

OBJECTIVES

Free flaps are the technique of choice for reconstruction of defects resulting from extirpation of tumors of the head and neck. Advances in microsurgical technique have resulted in success rates of greater than 95%. Numerous intraoperative factors, ranging from technical issues to topically applied agents, can complicate the outcome of microsurgical free tissue transfer. Synthetic tissue adhesives and hemostatic agents are playing an ever-increasing role in reconstructive surgery. The safety of these factors in free flap surgery has not been ascertained.

STUDY DESIGN

Animal Care Committee live rat model.

METHODS

Male Sprague-Dawley rats were divided into three groups: group I, Control; group 2, FloSeal; group 3, Tisseel. In each group, a 3 x 6 cm ventral fasciocutaneous groin flap based on the left superficial epigastric artery was elevated and the experimental material applied beneath the flap and around the flap pedicle prior to suturing of the flap back to the wound bed. The experimental materials consisted of 0.2 mL saline in the control group, 0.5 mL FloSeal, and 0.2 mL Tisseel. In phase I of this study, the effect of each treatment on flap survival was assessed by survival at postoperative day 4. In phase II of the study, the effects of these agents on ischemic tolerance was investigated. Five rats in each treatment group were exposed to ischemic times of 6, 8, 10, and 12 hours. Survival of the flap was assessed 7 days after reversal of the ischemia. Probit curves and the critical ischemic time (CIT50) were calculated.

RESULTS

All flaps survived the 2-hour period of ischemia and were viable at postoperative day 4. Flap survival from group 1 (Control), group 2 (FloSeal), and group 3 (Tisseel) at the various ischemic times was as follows: at 6 hours, 80%, 80%, and 80%, respectively; at 8 hours, 80%, 80%, 60%; at 10 hours, 60%, 33%, 40%; at 12 hours, 20%, 20%, 0%. The CIT50 for the Control, FloSeal, and Tisseel groups was 9.4, 9.0, and 7.0 hours, respectively.CONCLUSIONS FloSeal, a thrombin-based hemostatic agent, and Tisseel, a fibrin glue, displayed no adverse effect on flap survival in this model.

Effect of photodynamic therapy on revascularization of fasciocutaneous flaps

OBJECTIVE

Photodynamic therapy (PDT) may be used as an adjuvant intraoperative treatment to improve locoregional control. PDT has been shown both to delay wound healing and to have a deleterious effect on flap survival after a primary ischemic insult. This delay in wound healing may make the flap dependent on its pedicled blood supply for a prolonged period. Long-term flap loss may be experienced. The effect of PDT on flap revascularization, with subsequent dependence on its vascular pedicle, is evaluated.

STUDY DESIGN

Randomized controlled trial using a rodent model.

METHODS

A rat fasciocutaneous flap was used. Study groups were as follows: group I received no treatment; group II received treatment with 630-nm light; groups IH and IV were given Photofrin (in group III, loupes without a fiberoptic light source were used for flap elevation, and in group IV, light source was employed); and group V was given Photofrin and 630-nm light. Primary ischemic times of 2 or 4 hours were used. Vascular pedicles were ligated on postoperative day (POD) 5, 6, or 7, and percentage of flap survival was evaluated 7 days later.

RESULTS

With 2 hours of ischemia, revascularization was decreased in the PDT group on POD 6 (P < .05) and on day 7 (P < .005) when compared with the other groups. With 4 hours of ischemia, revascularization was decreased in the PDT group on PODs 5 (P < .001), 6 (P < .01), and 7 (P < .005).

CONCLUSION

Intraoperative PDT decreases revascularization of a rat fasciocutaneous flap.