A NEW FEMORAL BLOCK: LATERAL LOWER-ILIAC APPROACH IN THE PSOAS COMPARTMENT WITH ULTRASOUND TECHNIQUE IN DOGS; PRELIMINARY STUDY.

The aim of the study was to describe a new ultrasound-guided approach to the femoral nerve in the psoas compartment and to evaluate the clinical efficacy when combined with a parasacral sciatic nerve block in dogs undergoing surgery of the pelvic limb. Stage 1- Four cadaver dogs were used to investigate the ultrasound anatomy details of the femoral nerve within the psoas compartment and to describe the approach to the nerve. To obtain a good image of the femoral nerve the ultrasound probe was positioned in the middle of the angle created by a tangent line drawn to the cranial margin of the iliac wing and a tangent line drawn to the ventral angle of the iliac wing. After localization of the femoral nerve, 0.1 mL/kg of a methylene blue solution were injected. Then dissections were performed to determine the dyeing of the nerve. Stage 2- Seven client-owned dogs anaesthetized for elective pelvic limb surgery (TPLO and TTA), were enrolled in the study. Dogs were premedicated with acepromazine (0.01 mg/kg IM) and after 20 minutes fentanyl (5 mcg/kg IV) was given as a bolus. Anaesthesia was induced with propofol IV titrated to effect and maintained with isoflurane. Nerve blocks were performed with 0.5%, ropicavaine, 0.2 mL/kg each nerve (femoral and sciatic). The new femoral block approach was achieved by the use of the ultrasound and the nerve stimulator. The sciatic nerve block was done using only the nerve stimulator as described by Portela et al. During surgery heart rate (HR), respiratory rate (RR), mean blood pressure (MAP) with invasive technique, end-tidal carbon dioxide (EtCO2), end-tidal isoflurane percentage (Fe%Iso) were recorded every five minutes and during specific time points until the end of anaesthesia. Increase of more than twenty per cent of the HR, RR and MAP values was considered nociception and rescue analgesia was provided with fentanyl 2 mcg/kg IV. If more than 2 boluses of fentanyl were required to re-establish normal cardiorespiratory parameters a variable rate fentanyl infusion (5-20 mcg/kg/h) was started. After extubation, carprofen 2 mg/kg IV was administered. Post-operative pain assessment was measured with the Glasgow pain scale, until the first injection of rescue analgesia, using methadone 0.2 mg/kg IV. Stage 1: The femoral nerve was visible as a hypoechoic round structure in the middle of the ileopsoas compartment Anatomical dissection showed the right positioned of the methylene blue (dyeing of the entire circumference of the nerve) in all the 4 cases. Stage 2: the femoral nerve was localised in all dogs. During surgery four dogs received one or two boluses of fentanyl, but any of them required an infusion. Nociceptive stimulation were recorded during capsular, muscular and skin suture. Mean values of HR, RR and MAP were 109 ± 18 bpm, 11 ± 2 bpm and 78 ± 16 mmHg respectively. Mean FeIso was 1.06 ± 0.09 %. In the postoperative period mean time to first rescue analgesic treatment was 10 ± 2 hours after the execution of the block. The ultrasound-guided lateral lower-iliac femoral nerve block is a feasible technique to perform with the dog in lateral recumbency. The use of 0.2 mL/kg of 0.5% ropivacaine provided adequate intra-and postoperative pain relief for about 10 hours in dogs undergoing surgery of the pelvic limb