Out outwards to inwards by positioning the cadaver in

Out of the 25 cadavers, obtained by the institute under legal rules and regulations, two of the cadaver will be used for dissectional study of the boundaries and adnexa of the TPVS. This will be done by placing the cadaver in supine position and the anterior thoracic wall, inner organs, major blood vessels, oesophagus and trachea will be removed. The stratification of layer from inside to outside will be dissected, studied and permissibly photographed in one of the specimens. In the other cadaver, the dissection will be done from outwards to inwards by positioning the cadaver in prone position. The superficial layers will be carefully dissected and the deep layers will be studied and then dissected. Care willbe taken to preserve the contents to the best. An attempt willbe made to preserve the endothoracic fascia and the contents piercing it. If the endothoracic fascia is identified, separate study of the subendothoracic TPVS and extraperitoneal TPVS will be conducted. Photographs will be taken as and when required and possible. The boundaries will be identified and their relations will be made clear. The next three procedures can be carried out simultaneously.  The remaining twenty three cadavers will be brought under the procedure one at a time. The procedure will be kept constant for all the remaining specimens. For the purpose of measuring the depth to which the needle is pierced or rather measuring the depth to which the needle should be inserted for a successful TPVB, the following methodology will be used. A syringe or needle of suitable type and dimensions will be used. The preferred needle will be 22-gauge, 8–10-cm short bevelled spinal needle, or a Tuohy needle 2. The conventional procedure of the TPVB will be followed. The needle will be inserted 2.5–3 cm lateral to the most cephalic aspect of the spinous process. It will then be advanced perpendicular to the skin in all planes to contact the transverseprocess of the vertebra below. The depth can be anywhere between 2 to 4 cm. The depth usually depends on the built of the person. If bone is not encountered at this depth, it is possible that the needle tip is lying between adjacent transverse processes. It is imperative to locate the transverse process before advancing the needle any further to prevent inadvertent deep insertion and possible pleural puncture 2.In case, the transverse process is not encountered, the needle will be advanced a further centimetre and the above process will be repeated until the transverse process is contacted.The needle will then be pushed above the transverse process and will be gradually advanced until a subtle “pop” is felt. This lessening of resistance against air or saline is called “loss of resistance” and thus, the method is called “Loss Of Resistance” (LOR) method 1,2. This is experienced as the needle pierces the superior costotransverse ligament. The length of the needle inserted will be measured using a marker or marking tape. This procedure will be repeated for all the cadavers and the measure of depths in each specimen will be analysed.During the above procedure, when the needle is inserted in the TPVS, a dye (possibly methylene blue MB will be used) will be injected. The dye injected in the TPVS will show the spread of anaesthetics or analgesics which are used in TPVB and post operative and miscellaneous pain relief respectively 4. The spread of the dye will be carefully and precisely observed and the path of spread will be noted. An estimation of the spread will be deduced. Any anomaly will be noted and compared to the needle depth so that a wrong injection could be eliminated. As the specimen is embalmed and dissected, the complications due to blood and other organs will be prevented. Dye (MB) will also be injected at the caudal and cranial ends of the TPVS i.e. at the level of T1 and T12 respectively. The spread of these injections in the cervical and lumbar PVS will be studied. This will help in the study of communications between the TPVS and cervical and lumbar PVS. This will also likely be useful in knowing the pathway of communication.  The lateral spread or transverse spread will also be analysed. The spreading of the dye into the intercostal spaces will also be evaluated. This will be helpful in studying the transverse communication. The spread of small amount of dye into adjacent TPVS can also be observed. All this intends to establish a better understanding of the notorious communications of the paravertebral spaces.Along with this, the failure rate and success statistics will also be noted. This will be useful in determining the accuracy of the experiments conducted and will also analyze the failure rate of TPVB which are important in surgeries like breast surgeries, cholecystectomy, etc.2, 4 The percentage of failure of spread of the dye will be evaluated and compared with the depth of needle measured earlier and cause for failure will be determined.

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