1. How long does the compression anastomosis device have to stay in its place?
The first 2 to 3 days of healing involve an inflammatory response which clears the wound of debris. This period is followed by the laying down of granulation tissue, of which collagen fibrils are the load bearing components. In an experimental model, it has been shown that the maximal collagen deposition peaks at day 6, concurrent with maximal breaking strength of the anastomosis. The healing then continues to the remodeling or maturation phase. Thus, it would seem appropriate that the compression device is charged from the wound soon after day 6.
All anastomoses needs external devices (staplers, sutures or compression device) only for the first 6 days of healing. After this period the anastomosis will be strong enough to stand alone and any device will be foreign body and will interfere with the natural healing. The result will be extra scaring and inflammation.
2. How do we know that the anastomosis is strong enough at the time of the ring expulsion?
The strength of the anastomosis is usually measured by means of burst pressure. In a large animal trial, we have measured the burst pressure of the anastomosis on day 7. The results were never under 150mmHg, and always superior to stapler device.
3. How do we make sure that the compression device will not be expelled out of the body before day 6?
The principle of compression anastomosis consists of two rings that trap the cut ends of the transected bowel, bringing them into apposition. The trapped bowel is rendered ischemic and eventually sloughed, releasing the rings into the fecal stream.
The compression device will stay in the body as long as the necrotic process lasts. Thus, the secret is to control the ischemic process:
Stress (Force) vs. Strain (Extension) for Nitinol and for stainless steel
(click on image to enlarge)
The control is achieved by utilizing the Nitinol property – Constancy of Stress. We deform the Nitinol material between 1% - 6% of its deformation ability. Within these margins the pressure that the Nitinol applies on the tissue the same force range throughout the process, which means that the necrosis process will advance in a uniform rate.
The only question left is what pressure will verify that the duration of the necrosis will be no less than 6 days. This pressure was verified by tests on animal models and was set to approximately 1.5n/1cm.
4. What is the difference in wound healing process between sutures/staplers versus compression?
Compression Anastomosis, which is a sutureless anastomosis, differs from sutured anastomosis (both manual and stapled) in the absence of a great number of through-the-wall punctures in anastomosed organs. Therefore, the compression device practically eliminates pathogen infection in the tissue edges of the anastomosis.
A compression device mechanically squeezes the blood vessels creating an immediate and almost complete hemostasis, while in the case of suture anastomosis, platelets create hemostasis by the formation of a fibrin-based clot, thus lengthening the time to achieve hemostasis.
Compression Anastomosis eliminates the existence of any foreign bodies (sutures, staples) in the healing zone after 7-10 postoperative days as the clamping element is expelled and therefore eliminates foreign body reaction.
Given the aforementioned reasons, the use of a compression devise reduces or essentially eliminates, the first “lag” phase thereby facilitating the natural healing process. |
