Description of Ultrasound-Guided Lumbar Erector Spinae Plane (ESP) Block and Comparison of the Spread of Two Volumes of Dye in Cat Cadavers

Abstract

The erector spinae plane (ESP) block is a widely used technique for perioperative analgesia. It involves the infiltration of anesthetics into the interfacial plane between the erector spinae muscle and the transverse processes of the vertebrae. In veterinary medicine, this technique has been adapted for different species, but there are no cadaveric studies in cats. This study describes the ultrasound-guided lumbar ESP-block technique and evaluates the spread of two volumes of dye in feline cadavers. Injections were performed at the second lumbar vertebra (L2) level using 0.6 mL/kg (high volume [HV]) and 0.4 mL/kg (low volume [LV]) of methylene blue bilaterally. After anatomical dissection, the distribution of the dye, the staining of the spinal nerve branches, and the presence of dye in the epidural space were recorded. The results demonstrated that the HV treatment provided wider longitudinal distribution, staining the dorsal branch of the spinal nerves in an average of five segments per injection, without extravasation into the epidural space. It is concluded that the HV treatment promotes efficient multisegmental spread in feline cadavers.

Keywords: ESP block; felines; regional anesthesia; ultrasonography.

Figure 1

Schematic representation of the lumbar spine region at the level of the second lumbar vertebra (L2). The different layers of the thoracolumbar fascia (TLF) are represented in light blue. The spinal nerve and its dorsal, ventral, lateral, and medial branches are represented in purple. The yellow circle shows the final injection point of the erector spinae plane (ESP) block. Ic: m. iliocostalis lumborum; L: m. longissimus lumborum; M: m. multifidi; AO: aorta; VC: vena cava; Lt: left; Rt: right. Source: personal archive.

Figure 2

Sonoanatomy of the epaxial muscles and landmarks for injecting the erector spinae plane (ESP) in the lumbar region in a feline cadaver. The injection target was the ESP at the level of the transverse process of L2, with the target point centered in the image. The cat is positioned in sternal recumbency with the ultrasound transducer longitudinally in a parasagittal orientation. The dotted lines identify the needle beam. ESP: erector spine plane; L3 TP: transverse process of the third lumbar vertebra; L1 TP: transverse process of the first lumbar vertebra; L and Ic: m. longissimus lumborum and m. iliocostalis lumborum; M: m. multifidi; Cd: caudal; Cr: cranial; D: dorsal and V: ventral.

Figure 3

Anatomical dissection of the spine comparing dye distribution and range of stained vertebrae after ultrasound-guided injection into the erector spinae plane (ESP) at L2 level in the two treatment volumes: high volume (HV) and low volume (LV). In blue, lateral aspect of the vertebral bodies. Cd: caudal; Cr: cranial; D: dorsal and V: ventral.

Figure 4

Number and level of dorsal and ventral branch stained with dye solution after erector spinae plane (ESP) injections at L2 using two injection volumes in eight cat cadavers. High volume: 0.6 mL/kg; low volume: 0.4 mL/kg. L, lumbar vertebra; T, thoracic vertebra.

Figure 5

Cross-section of the second lumbar vertebra (L2) showing the distribution after an ultrasound-guided injection into the erector spinae plane (ESP) in both volumes; LV on the left (Lt) and HV on the right (Rt). In blue, the dye staining the m. iliocostalis lumborum (Ic) and m. longissimus lumborum (L) muscles. There was no dye migration into the epidural space (white arrow). M: m. multifidi.