Regarding the paper published “Serratus anterior plane block: Anatomical landmark-guided technique”

Sir,

We read with great interest the article by Vadera et al. titled “ Serratus anterior plane block: Anatomical landmark-guided technique”.[1] Authors have explained the administration of serratus anterior plane block (SAPB) with the help of anatomical landmarks. The novel ultrasound-guided regional anesthetic technique, originally explained by Blanco et al. achieved complete paresthesia of the hemithorax[2] performed the serratus block at two different levels, i.e., one superficial and other deep to serratus anterior muscle in the midaxillary line on four female volunteers. The block achieved complete paresthesia of the hemithorax by block primarily the lateral cutaneous branches of the thoracic intercostal nerves (T2–T12). Hence, the block was found useful for surgeries involving incision on the anterolateral chest wall like chest drain insertion, breast surgery[3], and anterior thoracotomy.[4] With the help of ultrasound, three muscles namely latissimus dorsi, teres major, and serratus anterior were identified at the level of the fifth rib. The block needle was then introduced in-plane with respect to the ultrasound probe from supero-anterior to postero-inferior direction and the desired plane for injection of local anesthetic (LA) was targeted. However, in the landmark-guided technique for administration of deep SAPB, Vadera et al. have described the point of intersection of the fifth rib and midaxillary line as the needle insertion point. The blind insertion of the needle can lead to injury to the thoracodorsal artery that lies in the plane superficial to the serratus anterior muscle. As ultrasound helps in visualization of the thoracodorsal artery, it prevents both vascular injury and inadvertent injection of LA into the vessel. Furthermore, authors have described blind insertion and advancement of needle perpendicular to the skin in all planes to contact the fifth rib. Nevertheless, as the depth of rib from the skin is variable and depends upon the build of the individual, there is a high risk of occurrence of both pleural puncture and failure of block. Next, the authors have described withdrawing the needle tip by 1–2 mm after hitting the rib to reach fascial plane deep to serratus anterior muscle. But clinically it is difficult to accurately withdraw such a short length of needle, further increasing the risk of failure of localization of correct interfascial plane resulting in block failure. Moreover, the authors have explained LA dripping from needle hub upon disconnection of the syringe as an indicator of deposition of drug in correct plane and the absence of backflow of injected LA as an indicator of intramuscular injection. The presence or absence of backflow itself depends on a multitude of factors including volume of LA given, the speed with which LA is given, and the built of the patient. Backflow may be present in a muscular patient with a tight plane and absent in an elderly frail patient. The safety and efficacy of SAPB with easily recognizable sonoanatomy is lost if the block is performed without using ultrasound. To conclude, the interfascial SAPB should be preferably performed under ultrasound guidance. The correct administration of block provides adequate analgesia and prevents inadvertent catastrophic complications like pneumothorax.

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