Cadaveric feasibility study on the use of ultrasound contrast to assess spread of injectate in the serratus anterior muscle plane

Abstract

Background:The Serratus anterior muscle plane (SAP) block has recently been described for the purpose of perioperative pain management following cases of trauma and breast surgery. It might prove a safer alternative to the other regional thoracic paravertebral and central neuraxial blockade techniques. There are no descriptive cadaveric studies in the pre-existing literature to delineate the anatomical plane for this novel technique. The main objectives for our study were to examine the location of the Serratus anterior muscle belly, assess the efficacy of achieving adequate delineation of the muscle plane utilising ultrasound imaging with agitated water as the contrast agent, and finally, to observe the extent of the cepahlo-caudal spread of the injectate in the SAP.Materials and Methods:Seven cadavers were studied. 20 mls of saline was injected into posterior axillary line (PAL) at the level of the 4-5th rib under ultrasound guidance. This was followed by injection of 10 mls of water with air (8 mls water and 2 mls of air). The presence of hyperechoic air bubbles in the fluid distended SAP (hypoechoic) area demonstrated the spread of water and air.Results:In 36% of cadavers, fully formed Serratus Anterior muscle belly was identified at the midaxillary line (MAL), 14% in PAL, and remaining 50% between PAL and MAL. The lower most limit of air-water spread was identified at the subcostal margin. Cephalad spread of contrast was noted in 2nd intercostal space ICS (7%), 3rd ICS (71%), and 4th ICS (22%).Conclusion:This study describes that the serratus anterior muscle is well-formed near the PAL and the injectate spread can be determined with the help of agitated water contrast on ultrasound. Furthermore, there was variability in the cephalad spread of the injectate.

Serratus anterior plane block for minimal invasive heart surgery

“…CWI in patients who underwent thoracotomy was also investigated in the literature, but does not lead to a decrease in morphine consumption compared to a PCA alone [ 18 ]. The metameric spread of SAPB was not evaluated in our study; usually SAPB covers dermatomes T2 to T6, with variable degrees of cephalad spread reported in cadaveric studies [ 19 , 20 ]. Nonetheless, the the surgical incision in MIHS, is systematically covered in the metameric spread of the block.…”

Serratus Plane Block

“…Daga et al, 9 Mayes et al, 10 and Torre et al 13 examined injectate spread following methylene blue dye or saline/air mixture injection deep to the SAM, whereas Varghese et al 12 injected superficial to SAM. All past anatomical studies evaluated the spread pattern of a 20-mL injection.…”

“…[9][10][11][12][13] However, the optimal plane and volume of injection for maximal spread in the anterior chest wall and axilla have not been evaluated. In this cadaveric study, our primary goal was to determine and compare the area of injectate spread between injections superficial and deep to SAM.…”

Interfascial block at the serratus muscle plane versus conventional analgesia in breast surgery: a randomized controlled trial

“…Anatomical studies conducted in cadavers show that an SPB performed with a volume of 20 mL of methylene blue and latex, spread across five to six dermatomes,23 with 30 mL of saline and air, could reach the second intercostal space 24. We used 30 mL volume to maximize spread and efficacy of the block, although we did not assess it anatomically.…”