Measurement of the distance of the thoracolumbar facial plane to the skin at different lumbar levels and in different positions under ultrasonography

Introduction and Purpose: With the widespread use of USG, applications of peripheral nerve blocks have begun to increase. With the use of USG, the application of TLIP block, one of the interfacial plane blocks, has also come to the fore. Facial plane block types can be used both for anesthetic purposes and in the treatment of acute and chronic pain. TLIP block; It has been successfully applied for analgesia in patients undergoing lumbar surgery and in patients suffering from chronic low back pain. TLIP block can be applied in different positions (sitting-lateral-prone) and at different lumbar levels. In our study, we aimed to calculate the most ideal measurement of the distance of the Thoracolumbar Interfacial Plane to the skin, accompanied by ultrasonography at different lumbar vertebral levels (L1-L3) and in different positions (lateral-sitting-prone) in order to increase the quality of the block in patients who will undergo Thoracolumbar Interfacial Plane block. Method: This study was conducted prospectively in the Department of Anesthesiology and Reanimation, Faculty of Medicine, Harran University. The approval of the Harran University Faculty of Medicine Clinical Research Ethics Committee (Decision dated 10.04.2023 and numbered 23.06.11) was obtained for the study. Patients in surgeries involving the upper-middle-lower lumbar region were included in the study. A total of 80 ASA I-II-III patients, 40 women and 40 men, aged 18-75 years participated in the study. The patients were first examined on their right sides in an upright sitting position with their hands tied in the umbilicus, secondly, lying on their left sides in the lateral decubitus position, with their hands at their sides on their right sides, and thirdly in the prone position with their hands extended to their sides, their heads turned to the left and their right sides were examined under ultrasound guidance. In the lateral and prone positions, the spinous processes of the related vertebrae (L1 and L3) are determined with a linear USG probe and moved 3 cm laterally until the transverse process is seen, and when the transverse process is detected, they are moved a little more laterally, and the plane between the multifidus and longissimus muscles and the plane between them can be displayed most clearly. The distance from the upper midpoint of the screen to the middle of the interfascial plane was measured and recorded by freezing the USG. Thus, these different measurements are compared among themselves. Findings: No relationship was found between age and the distance of the thoracolumbar interfacial plane to the skin. There is a strong correlation between the increase in BMI and the distance of the erector spina muscle to the skin (p<0.01). The distance from the skin to the skin of the cases whose stance position was prone in L1 was found to be significantly lower than the cases whose stance position was seated and lateral (p<0.01). In the sitting-lateral-prone positions, the distance from the skin of the cases with lumbar level L1 was found to be significantly lower than the cases with lumbar level L3 (p<0.01). Conclusion: The distance from the thoracolumbar interfacial plane to the skin varies with age, weight and BMI. The distance from the skin varies according to the difference in the applied lumbar level and the difference of the application position. As a result, the thoracolumbar interfacial plane was found closer to the skin when the patients were in the prone position. In terms of levels, at the L1 level, the thoracolumbar interfacial plane is located at the closest distance to the skin. However, when performing TLIP-B, we aimed to see which position would be more comfortable, in which positions the block success would be better and the risk of complications would be less. We also aimed to see at which lumbar level the thoracolumbar interfascial plane would be closer to the skin and clearer. Key words: Thoracolumbar interfacial plane block, multifidus muscle, longissimus muscle, peripheral nerve block, regional anesthesia, interfacial plane block.