The spread of injectate after deep serratus anterior plane and superficial parasternal intercostal plane blocks: a cadaveric dye study

We investigated the distribution of injected dye after deep serratus anterior plane and superficial parasternal intercostal plane blocks in 15 Thiel embalmed cadavers. We injected 0.4 ml.kg of 0.25% aqueous methylene blue solution into the deep serratus anterior and superficial parasternal intercostal planes using real-time ultrasound needle visualisation followed by posterior dissection to observe the distribution of the injected dye in the chest wall. The two blocks were performed bilaterally in 15 cadavers at the T5/T6 level, comprising 60 blocks in 30 hemithoraces in total. At dissection, the intercostal nerve territories were observed to be dyed completely from T2 to T6 in 28 of 30 hemithoraces, and extending caudal to T6 in 10 hemithoraces. Following the deep serratus anterior plane blocks in all cadavers, the dye was found to have spread to the axillae. Following the superficial parasternal intercostal plane blocks, the dye reached T7 in four cadaver dissections. We concluded that the territories innervated by the intercostal nerves (T2-T6 dermatomes) are dyed following the combination of the two blocks when performed at the T5-T6 intercostal space level. These techniques might provide an effective option for anaesthesia in breast surgery.