title: Ultrasound-guided femoral and sciatic nerve blocks in dogs
Creators: name: Trimble, Toby
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: Femoral, sciatic, nerve block, locoregional anaesthesia, canine, dog.

description: Femoral and sciatic nerve blocks are an effective method to provide analgesia to the stifle of dogs undergoing orthopaedic surgery. Different modalities can be used to guide location of needle placement at the target nerve such as blind technique, electrolocation and ultrasound-guidance. The method that has demonstrated the most accuracy, speed of block performance and lowest required local anaesthetic volume of injection to achieve a successful nerve block is ultrasound-guidance. Anatomical studies in dog cadavers have investigated several approaches to the femoral and sciatic nerves; such as the lateral distal iliac approach to the sciatic nerve and ventral suprainguinal approach to the femoral nerve within the iliopsoas muscle. Previous studies have reported injection volumes as low as 0.1 mL kg-1 for the femoral, and 0.05 mL kg-1 for the sciatic nerve. A cadaver study was undertaken with injection of new methylene blue using the ventral suprainguinal block of the femoral nerve, and the lateral distal iliac approach to the sciatic nerve in six dogs. This preliminary investigation found injection volumes of less than 0.1 mL kg-1 at the femoral nerve could provide successful coverage of dye at this location. The volume of injectate at the sciatic nerve could not be reduced below those values previously recommended. To assess if this finding was replicated in living dogs a clinical trial was undertaken. Healthy dogs scheduled to undergo orthopaedic surgery of the stifle under general anaesthesia were randomised into two treatment groups to receive levobupivacaine; low dose group (LD) of 0.05 mL kg-1 for femoral nerve and 0.05 mL kg-1 for sciatic nerves and high dose (HD) group 0.1mL kg-1 for the femoral and 0.05 mL kg-1 for the sciatic nerve. Intraoperative cardiovascular parameters were monitored during surgery, if more than 25 % increase from pre-surgical values was seen rescue analgesia was administered. During the postoperative period dogs were pain scored at regular intervals. After statistical analysis, groups were found to be similar for preoperative and intraoperative factors, and postoperative pain scores. In both the LD and HD groups it was not possible to completely prevent the noxious response to surgery. In the postoperative period dogs appeared to have good pain relief, with low rescue analgesic requirements. In cases where an intraoperative cardiovascular response had been observed and treated, dogs still had good pain relief up to 10 hours in the postoperative period. In conclusion, this is the first clinical trial of the ventral suprainguinal femoral nerve block, in combination with the sciatic nerve block. This technique can provide intraoperative analgesia for dogs undergoing orthopaedic surgery of the stifle, but complete sensory blockade was not consistently achieved. However, in cases where an intraoperative cardiovascular response is seen, dogs may still have good pain relief for up to 10 hours in the postoperative period without requirement for further opioid analgesia. Our cadaver study showed volumes less than those previously reported should provide anaesthesia of the femoral nerve, but this was not borne out completely in a clinical trial where several elements of block success (duration and completeness) were tested. We recommend that cadaver studies be followed up by clinical trials to accurately assess the clinical benefit of locoregional techniques. Due to the inconsistent intraoperative affect we observed, in a clinical setting we recommend using a local anaesthetic injection volume higher than those used in this study, such as 0.2 ml kg-1, when using the ventral suprainguinal approach to the femoral nerve, as per the original reporting of this block, because a higher dose may provide a more consistent affect. Finally, we recommend a clinical trial comparing the ventral suprainguinal approach to the femoral nerve, to other techniques used to block this nerve. This would establish the most effective method to provide sensory blockade at the femoral nerve.