”Geometry-based cannulation technique” for cannulation of great saphenous vein during radiofrequency ablation of varicose veins at a university hospital of Nepal

Background: Radiofrequency ablation is an established minimal invasive treatment modality of varicose veins. This technique involves accessing the great saphenous vein (GSV) through which radiofrequency ablation catheter is inserted. Some established puncture techniques like in-plane and out-plane techniques are also not devoid of limitations. Aims and Objectives: To know the applicability of “Geometry based cannulation technique” in terms of mean cannulation attempts and percentage of successful cannulation. Materials and Methods: We are doing “Geometry based cannulation technique” for the cannulation of GSV. For cannulation 18G needle of length 3 cm attached with 10 ml syringe (cannulating needle) partly filled with normal saline is used. Doppler ultrasonography is done with Siemen's Acuson P300 machine with linear probe of frequency 7.5–12 MHz. The depth from the skin to the upper part of vein is measured in cm and is termed as distance “A.” The tip of the cannulating needle is positioned on the middle of the probe and gently pressed down the skin to form the shadow in the Doppler. The needle is readjusted such that the shadow corresponds to the GSV. Then, the needle is moved distally to A distance. Then the needle is made rotated 45° and skin is punctured to the length (distance B) calculated from the Pythagoras theorem as square root of 2A2. Then the angle is decreased to about 30° and further 2–3 mm advancement of the cannulating needle is done such that it lies inside the target GSV. Results: From 459 cannulations in the time frame of August 2013–December 2018, we found that mean cannulation attempts were 1.4 (standard deviation 0.72, 1–3 attempts). In 429 GSVs (95.5%), there were successful cannulations, whereas in 20 GSVs (4.5%), there was failure in cannulation. The cannulation of GSV has higher success if the diameter of GSV is more than 5 mm and the depth is less than 10mm. Conclusion: “Geometry based cannulation technique” for cannulation of GSV is a novel technique and can be used with high success.