Introduction In the past during the era of paraesthesia, blind and anatomical landmark related blocks the success of the block entirely was dependant on a three-dimensional view of the related plexus/nerve and its related structures. a well developed eye hand coordination, in order to place a needle accurately into the proximity of unseen (blind blocks) nerves or nerve plexuses was mandatory.

Brachial Plexus The traditional methods achieved more than 90% success rate for supraclavicular brachial plexus blocks. With appearance of isolated case reports of pneumothorax, modified plumb bob¹ techniques was introduced based on cadaveric study.

The traditional interscalene² technique was associated with numerous isolated case reports of total spinal anesthesia³ and hemidiaphgramatic paresis⁴ (HDP). Large volumes of local anesthetic (LA) was placed close to the tubercle.

Proficiency in regional anesthesia rests thus firmly on a foundation of the understanding of anatomy⁵.

It is an extremely important to understand the anatomic outlay of brachial plexus and the vital structures its closely related to.

The neck is a compact structure packed with aerodigestive and neurovascular structures. Blind needling in this area requires tremendous confidence and thorough knowledge of the related anatomy.

Placing a 22g blunt stimulating needle in the subclavian perivascular area close to the pleura or in the interscalene groove close to the central neuraxis require enormous dexterity.

The cadavers which are either formalin based or thiel based offer lots of potential to understand the brachial anatomy.

The brachial anatomy depicts the closeness of phrenic nerve to the interscalene brachial plexus and offers options under ultrasound for a superior trunk block – Proximal Humerus Surgery – decreasing the incidence of HDP and central neuraxial spread.

In the supraclavicular area the needle can be demonstrated close to the pleura and the options for the commonly missed inferior trunk can be blocked with a corner pocket injections⁶.

Figure 1: Right Brachial Plexus exposed after opening up the deep cervical fascia; Dissection by Georg Feigl

With the advent of ultrasound, the LA is deposited to surround the nerves and plexuses. the volume has drastically reduced 1/3 of the traditional volumes.

Ultrasound has revolutionized the brachial plexus blocks in the following aspects.

Localization of target

Reduced Volumes of LA

Decreased incidence of complications

Three Dimensional Cadaveric Specimen

Regional anaesthesia techniques can be further optimized by returning to the cadaveric lab and understanding anatomic relationships. the three dimensional arrangements of the nerves can be best visualized by handling the particular specimen and closely inspecting the vital structures around it⁷.

In the feedbacks of the cadaveric courses conducted by this author, 95% of the attending anaesthesiologists appreciate the brachial anatomy to be the most important session. the delegates revealed that the best part of the brachial anatomy course was the needle tip closeness to the pleura in supraclavicular and central neuraxis during the interscalene approaches.

Figure 2: the Three dimensional specimen depicting the transition from supraclavicular – costoclavicular brachial plexus

Look on to the specimen from the topand laterally

Ventilating Cads The ventilating theil based cadavers, offers an important knowledge about the proximity of the pleura during an interscalene and supraclavicular brachial plexus blocks. the thiel cadavers are so supple, that, the lungs can be ventilated, and, demonstrated not only how close the pleura is to the supraclavicular brachial plexus but also the during an interscalene block.

There is also an attempt of providing pulsating cadavers⁸ for simulation purposes in trauma.

Conclusion This cadlab exercise of several hours confirm that an actual dissection is superior to viewing of prosected specimens and anatomic models.

Thoracic and Lumbar Paravertebral

With the advent of newer fascial plane blocks, the landmark guided thoracic paravertebral block is falling into disrepute. To revive the technique this authors offers hands on thoracic paravertebral blocks (TPVB) for delegates. the performer sits behind an open eviscerated thorax with intact endothoracic fascia. the needle penetrates the back muscles until the costotransverse junction (CTJ) is identified. the needle tip is place 1.5cm beyond the CTJ, and, methylene blue is injected as the second performer identifies the spread from within.

Figure 3 Delegates practising landmark guided thoracic paravertebral and lumbar plexus block

Lumbar Plexus A similar exercise of hands on is carried out for anatomical landmark guided lumbar plexus block.

The performer sits behind eviscerated abdomen and identifies the anatomical landmarks for lumbar plexus (LP). Needles are introduced to encounter the transverse process (TP) and tip is placed 1.5–2cm beyond the TP.

The second performer assess the tip placement as to how close is it to LP.

The feedback mentions more than 60–75% had increased level of confidence in performing TPVBs and LPBs respectively. More than 50–65% first timers were ready to perform these blocks under supervision.

Cross sections At this point cross sections at the level of T4 and L4 are displayed on same tables. the cross sections provide ample information regarding the anatomical boundaries, limitations of needle tip placements, possible spread of the LA and occurrence of complications.

Figure 4: the cross section at L 4

Ventral Rami – Yellow

Psoas Major – Light brown

The formalin based cross sections provide important information about the anatomy of the fascia, whereas, the theil based cross sections illustrate the ventral and the dorsal nerves as they proceed through their respective fascias.

The cross sections also form an important aspect of novel blocks. Again the needle tip placement, LA spread and associated complications can be anticipated.

Latex Injection The high viscosity of latex provides a stable spread after ultrasound injections. In the theme ‘Dissect as you Inject’ in the anatomy department of Graz, Proff George Feigl and Sandeep Diwan injected colored latex under high resolution ultrasound. the cadavers were dissected the next day and injections were graded according the placements of the latex.

It was observed that the fascial planes were more missed than the single targets like the interscalene.

The injection pressures were high with smaller guage than the larger needles.

The blue and yellow latex were better visualised than the green and red was the worst.

Probably a mix of dye solution and a latex would be a better combination for future studies.

Figure 5: Red latex in adductor canal

The mid adductor injections spreads more cephalad.

Ultrasound in Theil based cadavers To gain experience into ultrasound guided perineural injections the regional anaesthetists have looked for a suitable model to simulate the passive and dynamic components of nerve block.

Simulator for learning UGRA include phantoms, cadavers, animal models, computer-based methods, and virtual reality models⁹.

There is insufficient evidence¹⁰ regarding task fidelity, skill transfer, validity, and reliability for most of these tools.

The perineural anatomy, needle tip movements, perineural fluid injection and inadvertent intraneural injection can be gauged by applying techniques on cadaveric models.

The formalin embalmed cadavers are not ideal for upper and lower limb¹¹. Some block locations like axillary and subgluteal sciatic do not possess ideal imaging characteristics¹².

In unembalmed cadavers¹³ realistic imaging and provide good tactile feedback was observed during teaching UGRA.

Professor Thiel^{14 15} of the University of Graz, Austria, employed a novel preservation technique that retains full flexibility of the limbs.

A pilot project compared the ultrasound scan of the theil brachial plexus and sciatic nerves with those of volunteers and mimic nerve blocks.

The study revealed several advantages of thiel cadavers like easy to scan, position the arms for axillary blocks and the feel of the fascia.

The old age cadaveric images corelated well with the young volunteer sonoimages.

The intraneural injections were well simulated in theil cadavers.

Age and BMI of the cadaver also influence the quality of imaging due to poor reflection from tissues in the elderly¹⁵.

Fresh cadavers and Thiel cadavers for UGRA were compared in cervical region¹⁶. the Thiel cadavers offer safer and more realistic conditions than fresh cadavers.

In Graz, we performed a variety of plexus and interfascial plane blocks with colored latex injected under high resolution ultrasound in theil based cadavers. the block were graded from 1 to 3, with 1 closest to the nerve and 3 further away from nerve. Catheters were placed under ultrasound, on dissection the catheter was visualised under the sheath and injections were performed to understand its dynamic spread.

Cadaveric simulation¹⁷ has high validity and is accepted by both candidates and faculty. For many surgical programs, it is now considered to be the ‘gold standard’ for simulation. Then why not for a regional anesthesiologist?

References

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