• ultrasound-assisted
• loco-regional anaesthesia
• horse
• dog
• ultrasound-guided

INTRODUCTION Perioperative analgesic management is mandatory in anaesthesia; the possibility to provide analgesia at the site of pain, with minimal impairment of other functions, is the rationale behind loco-regional anaesthetic (LRa) techniques. Loco-regional anaesthesia success is connected to optimal local anaesthetic distribution around the nerves; the real time sonographic visualization of the technique enhances the possibilities to make a more efficacious and safer block. Furthermore post-operative pain assessment in a patient where we are unable to communicate verbally is particularly difficult and an effective post-operative analgesia is essential.
OBJECTIVES To design and test with a clinical trial, efficacy, safety and duration of three new different ultrasound-guided loco-regional techniques in dogs and one ultrasound-assisted neuraxial technique in the equine specie.
LIST OF THE STUDIES
STUDY n°1: Comparison between three different ultrasound-guided for radial, ulnar, medial, musculocutaneous (RUMM) nerves block approaches in dogs undergoing thoracic limb surgery.
STUDY n°2: Ultrasound-guided femoral-obturator nerve in dogs undergoing TPLO surgery.
STUDY n°3: A new approach to transversus abdominis plane (TAP) block in dogs undergoing mastectomy.
STUDY n° 4: Ultrasound-assisted extradural technique in horse.
STUDY DESIGN All the studies started from a prospective anatomical research. Randomized and prospective single blinded clinical trials (study 1 and 2). Prospective clinical trials (study 3-4).
ANIMALS
1. Study n°1: 5 dog cadavers and 30 owner’s client dogs.
2. Study n°2: 6 dog cadavers and 20 owner’s client dogs.
3. Study n°3: 10 dog cadavers and 10 owner’s client dogs.
4. Study n°4: two horse’s tails obtained from the slaughterhouse, 15 experimental Standard bred horses, 20 owner’s client Warmblood horses.
METHODOLOGY All the studies were divided in one or more anatomical studies and one clinical study.
Anatomical study: dissections and ultrasound (US) scanning to gain three-dimensional and bi-dimensional anatomical knowledge of the interested region in order to find a target ultrasound window and to design an US-guided LRa needling technique. For the studies 1,2,3 a comparison between the sonoanatomy and the real anatomy was performed by evaluation of the spread after injection of new methylene blue solution around the nerves visualized by US.
Clinical study: US-guided techniques developed during the anatomical studies were applied in order to evaluate the intra operative and post-operative analgesia provided from the LR anaesthesia. Intra-operative monitoring and post-operative pain were evaluated by a blind operator (study 1-2-3).
RESULTS
Study n°1
Anatomical phase: opening the arm in the medial face, at gleno-humeral joint level, the four nerves appeared at the same deepness and held in the same intermuscular fascia; descending toward the elbow the radial nerve enters the intermuscular fascia and goes towards the lateral portion of the arm. The ultrasound images confirm the presence of the nerves around the axillary artery in the proximal approach called axillary approach (AGR). In the medial and lateral midhumeral approaches the radial nerve appeared at a different depth, in comparison to the other three nerves and near to the humerus.
Clinical phase: intra operative fentanyl infusion resulted necessary in 5/10 dogs LGR, 0/9 MGR dogs and 0/10 dogs AGR belonging the respectively groups. Post-operative first rescue analgesia performed 2.07 ± 1.98 LGR, 4.25 ±1.25 in MGR and 8.6 ± 1.15 hours after extubation for AGR. The execution of the block resulted easier in the AGR respect to the other groups.
Study n°2
Anatomical phase: femoral nerve (FN) and obturator nerve (ON) are present together at the level of L6th vertebral body and L7th transvers process. From the ultrasound study the two nerves appeared as two holes inside the iliopsoas muscle that diverge, moving the probe caudally. Both nerves were stained for more than 4 cm with a 0.1 mL kg-1 of new methylene blue solution injection.
Clinical phase: intraoperative fentanyl infusion resulted necessary in 1/10 dogs belonging R3 (ropivacaine 0.3%) and 3/10 dogs belonging R5 (ropivacaine 0.5%). Post-operative first rescue analgesia performed 550.9 ± 58.52 minutes R3, 664.2 ± 151.4 minutes R5 from the end of the surgery (p=0.06).
Study n°3
Anatomical phase: the abdominal nerves (T12-T13-L1-L2-L3- l4) appear to be very close dorsally, where they pass the aponeurosis of the transversus muscle in order to run over it and enter the fascia between the internal oblique and transversus muscle. The separation between the 2 muscle was identifiable in a US-window nominated as ‘target US pocket’. T13, L1, L2, L3, L4 nerves resulted stained with 0.2 mL kg-1 of new methylene blue solution.
Clinical phase: in 3/10 dogs where TAP block was performed at the ‘target US pocket’ with 0.2 mL kg-1 ropivacaine 0.25% 2μ kg-1 of fentanyl at T1 was administered. Post operative pain score < 3 for the first 4 hours after the surgery in 10/10 dogs.
Study n°4
Anatomical phase: two peculiar US images were detected for last sacral bone and first intercoccygeal spaces. First intercoccygeal gave a peculiar image named ‘cat face’ and it was used as US target window to design a US-assisted epidural technique. The mean ± SD depths detected at the level of first and second intercoccygeal spaces were respectively 2.79 ± 0.27 cm and 2.85 ± 0.18. Clinical study n°5: In 100% of the horses the ‘cat face’ was detected and in 20/20 horses epidural performed wit US-assisted technique result efficacy during laparoscopic surgery. The mean ± SD between the trained operator and untrained operator Δ (TO-UO) was 1.08 ± 1.06 cm. The mean ± SD between Δ (UO-US) was 2.55 ± 1.73 and the Δ(TO-US) was 1.86 ± 1.24.
DISCUSSIONS The axillary approach resulted in an easier and more effective block compared to the other two and it was superior in terms of duration for the post-operative analgesia.
The femoral-obturator approach provided an effective analgesia in dog undergoing TPLO surgery with both the ropivacaine concentration used. The block resulted capable to post pone a first rescue analgesia at least 5 hours after the end of the surgery.
The new approach to transversus abdominis plane block in dogs undergoing mastectomy resulted efficacious and it might be a routinely analgesia technique in a dog with a history of mammary tumour.
Ultrasound-assisted extradural technique in horse resulted feasible and it might increase the rate of success of neuroaxial anaesthesia in this species.