• anestesia loco-regionale
• blocco eco-guidato
• cane
• ropivacaina

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


AIM OF THE 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 arthroplasty surgery of the pelvic limb.

MATERIAL AND METHODS:

Stage 1- Four dog cadavers were used to study the ultrasound anatomy details of the femoral nerve within the psoas compartment and to characterize the approach to the nerve. 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 arthroplasty 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 administered. Anaesthesia was induced with propofol IV titrated to effect and maintained with isoflurane. The nerve blocks were performed with ropicavaine 0.5%, 0.2 mL/kg per point (femoral and sciatic). The femoral block was done with the new approach using the ultrasonography and the nerve stimulator. The sciatic block was done only with the nerve stimulator as described by Portela et al. During the 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 a rescue analgesia was performed with a bolus of fentanyl 2 mcg/kg IV. If more than 2 boluses 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 done with the Glasgow pain scale, until the first rescue analgesia requirement, done with methadone 0.2 mg/kg IV.

RESULTS:
Stage 1: to obtain a good transverse ultrasound images of the femoral nerve the probe was positioned with a 45°angle respect to a line tangent to the cranial margin of the iliac wing. The femoral nerve was visible as a hypoechoic round structure in the middle of the ileopsoas muscle. 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 found in all dogs. During the surgery 4 dogs received one or two boluses of fentanyl, but none required an infusion. Nociceptive stimulations were signaled 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 the mean time to the first rescue analgesic treatment was 10 ± 2 hours after the execution of the block.



CONCLUSION:

The lateral lower-iliac femoral nerve block by ultrasound technique is feasible and it allows to visualize the femoral nerve inside the ileopsoas compartment with the dog in lateral recumbency. This technique, done with 0.2 mL/kg of ropivacaine 0.5%, provided adequate intra-and post-operative pain relief for about 10 hours in dogs undergoing arthroplasty surgery.