This is the only animal model that is available to study the mechanisms responsible for dialysis access-related hand ischemia. The model provides a robust platform to examine the complex interplay between uremia and neuromuscular perturbations that result from hemodynamic changes resulting from arterial venous fistula surgery. Access-related hand dysfunction affects up to 60%of hemodialysis patients and can severely impact patient quality of life.
This model helps us understand the disability and test novel therapies. Demonstrating the procedure will be Dr.Raymond Kim, a post-doctoral researcher from our laboratory. To begin, place the anesthetized mouse in the supine position on a surgery table covered by a sterile drape, and apply the ocular lubricant to protect the eyes from drying during surgery.
Using a pen trimmer, shave the abdominal hair for the operation and the leg hair for the postoperative perfusion measurements, then clear the hair off the surgical field. Next, fixate the upper and lower extremities with rubber bands and tacks. Check the depth of anesthesia by monitoring the toe pinch reflex and titrate anesthesia as necessary.
Perform the respiratory pattern evaluation every three to five minutes throughout the surgical procedure to calibrate the level of anesthesia. Make a midline laparotomy from the lower edge of the sternal margin to the pubis symphysis, and dissect out the pubis fat pad to obtain a wider operative field. Open the celiotomy to access the peritoneal contents and cover the bowels with a saline soaked, non-woven sponge.
Next, carefully dissect out the perivascular fascia and adipose tissue from approximately one centimeter proximal to the aortic bifurcation, extending to the level of the left iliac bifurcation using straight Dumont forceps and small double-ended hard sharp-pointed cotton swabs. Then pass the tip of the angled forceps under the left common iliac vascular bundle and gently spread multiple times to mobilize the vessels from the underlying retroperitoneal musculature. Place two 4-0 silk sutures around the isolated left common iliac arterio venous bundle and use them as ligatures to the vascular bundle.
Then create a single knot with each 4-0 silk tie and apply them sequentially, proximally, and then distally. Next, using the 4-0 silk suture strings as handles, rotate the left iliac arterial venous vascular bundle clockwise, and fine tune the position to temporarily locate the vein anterior to the artery. Make a longitudinal venotomy of approximately one millimeter with a straight Vannas spring scissors, and gently flush out residual blood from the venous lumen with 0.9%saline.
Then, place an implicating 10-0 nylon suture through the posterior wall of the vein. Afterward, grab the implicated suture ends and place them under gentle tension to displace the anterior wall from the posterior wall of the iliac artery. Next, make an elliptical incision of a size of approximately 1.0 by 0.3 millimeters using curved Vannas spring scissors, removing the adherent walls of both the iliac artery and vein.
Gently flush out residual blood of the exposed arterial lumen with 0.9%saline and heparinized saline. Following the creation of the arterial venous fistula, repair the initial anterior wall venotomy using two to three 10-0 nylon sutures in an interrupted fashion. Afterward, restore the vascular bundle to its original anatomic orientation and place a small piece of saline soaked absorbable gelatin sponge adjacent to the repaired venotomy to facilitate hemostasis.
Then, loosen the 4-0 single knot cross clamp ligatures sequentially from distal to proximal, while monitoring the venotomy site closely for excessive bleeding. Gently rub the vascular bundle with small double-ended, hard sharp-pointed cotton swabs which further facilitate the restoration of blood flow. Next, confirm the technical success of the operation using visualization of pulsatile bright red oxygenated blood entering the iliac vein and mixing with dark venous blood returning from the hindlimb.
Inject heparinized saline into the inferior vena cava for systemic anticoagulation to improve arterial venous fistula patency outcomes, and reinspect the surgical site for hemostasis after the injection of heparinized saline. If there are no bleeding concerns, close the midline fascia and then the skin incision with absorbable 5-0 PGA sutures in a running fashion. Doppler ultrasound was used to validate the patency of the arterial venous fistula.
Color Doppler revealed turbulent flow at the site of the fistula, and pulsatile spectral broadening was visualized on pulse wave Doppler assessment. If the fistula is patent, the aorta has elevated peak systolic and end diastolic velocity, whereas the inferior vena cava develops pulsatility with elevated peak velocity. The vessel dilation in both the aorta and inferior vena cava is apparent with serial pre and postoperative measurements.
The B-mode and pulse wave Doppler ultrasound measurements after surgery revealed inflow and outflow vessel dilation and increases in peak systolic velocity compared to the sham animals. Laser doppler assessment of the hindlimbs showed left POD perfusion deficits to be approximately 20%of the contralateral limb after surgery, with gradual recovery over time. The perfusion deficit of the tibialis anterior muscle was approximately 60%after surgery, with similar recovery.
Hindlimb neuromotor function was quantified via grip strength testing and treadmill gait pattern analysis, which were performed sequentially throughout the recovery period. Expected unilateral grip strength is approximately 50%of the contralateral limb on postoperative day four with gradual recovery. Each microsurgery step should be performed with extra care to avoid potential nerve or vascular trauma which can cause substantial changes in both hemodynamics and limb pathology.
After model characterization, a multitude of studies examining biologic drivers of neuromuscular dysfunction resulting from arteriovenous fistula placement were able to be explored.
