Safety of vessel ligation in laparoscopic surgery

Laparoscopic ligaturing entails the use of the Roeder knot which is fashioned outside the abdomen, slipped along the ligature to the intended site and locked in place. The safety of the one-way Roeder slip knot in securing blood vessels and the tension a vessel ligature has to withstand were investigated ex vivo. Ligature tension was measured using perfused blood vessels in a test rig. From these data the ligature tension exerted by vessels up to 3 mm diameter at 150 mm Hg pressure was observed to be less than 5 grams. The relationship between ligature tension (T) and intravascular pressure (p), radius of the vessel (r) and radius of the vessel at the point of ligature (delta) is expressed by the formula: T = 3/2 pr delta. A good correlation between values for ligature tension derived from this formula and those observed in the test rig confirmed the validity of this equation for the calculation of approximate ligature tension. Catgut sutures tied with Roeder knots were subjected to strain gauge distraction under different conditions. The tension required to induce reverse slipping of the Roeder knot fashioned from 0/chromic catgut had a median value of 1125 (225-2700) grams weight. Thus in laparoscopic surgery the Roeder knot with dry chromic catgut has a substantial safety factor ratio of 55:1 in ligation of vessels up to 3 mm diameter.