A Novel Surgical Technique in a Sheep Model for Suburethral Graft Implantation

[Narrator] Stress urinary continence affects 26% of women.

[Narrator] Tension-free vaginal tape evolved as a lesser morbid surgical treatment. However, suburethral polypropylene mesh tapes were introduced without testing in a relevant animal model, leading to adverse responses. A sheep model based on the anatomical parallels between ewes and women tested new implanted materials for pelvic organ prolapse surgery, placing the graft between the rectum and vagina.

[Narrator] Lacking an animal model to mimic the suburethral implantation of a graft, exploring the possibility of using the ewes in experimental surgery.

[Narrator] In this model, we test a novel electrospun polyurethane graft that will likely have less tissue reaction than polypropylene mesh. Ensure that qualified veterinarians always conduct medical management and anesthesia. In the preoperative room, give the sheep atropine sulfate 0.02 milligrams per kilogram intramuscularly once for induction of anesthesia. Administer the analgesic carprofen at a dosage of two milligrams per kilogram subcutaneously.

[Narrator] Shave the skin around the lower abdomen and inner thighs using a hair clipper.

[Narrator] Induce anesthesia using propofol two milligrams per kilogram IV as needed and ketamine 10 milligrams per kilogram intramuscularly once. Insert a seven-millimeter diameter endotracheal tube under direct vision using a laryngoscope and connect the tube to a mechanical ventilator. Use oxygen and isofluorine inhalation anesthesia, 5% for induction and 2% for maintenance throughout the procedure.

[Narrator] Check the endotracheal tube's proper placement, ausculate the chest and abdomen during inhalation, and observe the chest wall movement.

[Narrator] Place a pulse oximeter under the tongue surface and fix it with adhesive tape. Observe the jaw tone for flaccidity to monitor the depth of anesthesia.

[Narrator] Complete flaccidity means deep anesthesia, and jaw spasticity means the animal is waking up.

[Narrator] Monitor the anesthesia machine for pulse rate and oxygen saturation changes from baseline. A 10% increased pulse rate or a drop in oxygen saturation suggests the animal is reviving from deep anesthesia, requiring an adjustment in anesthetic dosage. Check deep reflexes every 15 minutes with ear pinching. Increase anesthetic dose upon recovery from deep anesthesia. Carry out surgical procedure under sterile conditions. Place the animal supine.

[Narrator] Scrub the skin of the low abdominal wall, the perineum, and the vagina with a 7.5% solution of povidone iodine.

[Narrator] Then dry the skin with a sterile absorbent towel.

[Narrator] Administer cefazolin sodium 25 milligrams per kilogram intravenously at the induction of anesthesia.

[Narrator] Next, drape the animal with sterile surgical drapes, exposing the perineum. Insert a 12 French urethral Foley catheter for bladder drainage. Incise the ventral vaginal wall longitudinally. Develop the space between the vaginal wall and the urethra with lateral dissection using Metzenbaum scissors. Insert the scissor blades closed, direct them to the pelvic sidewall on one side. Open the blades and then withdraw them out. Repeat the procedure several times till the created space can admit the index finger into the retropubic space. Repeat the dissection on the opposite side. Use the electrospun polyurethane implant in five healthy adult multiparous ewes. Thread a polypropylene 1 monofilament suture on a 36-millimeter rounded needle through the lateral suture holes of the implant.

[Narrator] Pass the sutures cranially via the retropubic tissue using a needle introducer.

[Narrator] Identify the tip of the introducer at the anterior abdominal wall. Bring it out through a five-millimeter transverse anterior abdominal wall incision and bring the suture out. Place two additional absorbable sutures through the implants to side holes to fix it in position. Pull the implant cranially with the polypropylene sutures. Seat it underneath the urethra and tie the sutures. Tie the abdominal ends of the polypropylene sutures together and close the skin over the ends using 3-0 absorbable sutures. Close the anterior vaginal wall with absorbable 2-0 sutures. Utilize interrupted sutures and the surgical knot technique. Remove the catheter. Place a Betadine vaginal pack and remove it after 24 hours. Use a polypropylene transvaginal tape implant in the second group of animals consisting of two healthy adult multiparous ewes. Incise the ventral vaginal wall longitudinally. Develop the space between the vaginal wall and the urethra with lateral dissection retropubically. Attach the tape and its protector sheath to the product-dedicated introducer. Pass the introducer cranially by the retropubic tissues. Identify the tip of the introducer at the anterior abdominal wall and bring it out through a five-millimeter transverse anterior abdominal wall incision. Deliver the polypropylene tape. Pull the tape cranially and seat it underneath the urethra. Cut the central marker of the tape to release the protective sheaths. Pull the protective sheaths from the abdominal end out and discard them. Do not fix the tape with sutures, as it is self-fixing. Trim the abdominal ends of the tape and cover them with skin closure. Close the anterior vaginal wall with absorbable 2-0 sutures. Utilize interrupted sutures and the surgical knot technique. Postoperatively, observe the animal for pain and complications and allow them access to water and food ad libitum.

[Narrator] Administer analgesics starting eight hours after the preoperative dose, carprofen two milligrams per kilogram subcutaneously every eight hours as needed for three days postoperatively.

[Narrator] After full recovery, house the sheep together and allow them to move freely. Observe the animals daily and treat any signs of pain or distress or carry out euthanasia. Follow the animals for three months and perform tissue harvesting under general anesthesia for histopathological analysis. Examine the vagina under general anesthesia using a self-retraining retractor to look for evidence of erosion or gross anatomical deformity. Identify and excise the graft with the surrounding tissues and preserve it in 10% formalin for histopathological examination.

[Narrator] While under general anesthesia, administer sufficient dose of intravenous anesthetic for euthanasia or follow the euthanasia method approved in the animal protocol by the institution.

[Narrator] Seven ewes with a mean weight of 27.7 kilograms underwent surgery. There were no complications or morbidity directly attributable to the surgical procedure. All animals tolerated the surgery and exhibited normal eating behavior, bowel movement, and micturition in the next postoperative days.

[Narrator] There was no vaginal bleeding after removal of the pack.

[Narrator] All the animals survived to the endpoint. Examination of the vagina at harvest time showed good healing of the vaginal incision. There was no erosion or palpable mesh. A specimen excised three months post-surgery shows the polyurethane mesh between the intact vaginal wall and urethra.

[Narrator] This novel animal model describes a technique of graft implantation between the vagina and bladder neck in a large animal that may reproduce the surgical technique in women.

[Narrator] It renders itself to the resurgence of evaluation of new synthetic materials that may treat female stress incontinence, testing their tissue reaction in vivo.