Impact of femoral nerve block approach on anaesthetic drug requirements in dogs undergoing hindlimb orthopaedic surgery

This retrospective clinical audit aimed to determine which peripheral nerve block approach to the femoral nerve had lower intraoperative drug requirements. A total of 30 hospital records for client-owned dogs undergoing hindlimb orthopaedic surgery were reviewed, and 23 were included in statistical analysis. Dogs were grouped as follows: pre-iliac femoral approach (group PI, n=11); or femoral triangle (group FT, n=9). In group PI, the block was performed by drawing a line from the spinous process of the 6th lumbar vertebra, perpendicular to the spine in a drso-ventral direction. A second line parallel to the spine was drawn from the most cranial aspect of the iliac crest until the lines intersected. In the FT group, the femoral nerve was approached by finding the femoral pulse and inserting the needle slightly cranial to this landmark. Both groups used electrostimulation to confirm correct insertion. Dogs were monitored intraoperatively and received a fentanyl constant rate infusion. Analysed data included: the type of surgery, the execution time, the intraoperative fentanyl concentration, the intraoperative isoflurane concentration and any prolonged neurological complications. There was no statistically significant difference between the average use of intraoperative fentanyl (µg/kg/h) in dogs that received the FT approach (median, IQR) (3.25, 2.77–4.63) compared with those that received a PI approach (2.94, 2.55–3.43) (U=40.0, P=0.159). There was no statistically significant difference between the average percentage of intraoperative isoflurane used throughout the procedure in dogs that received the FT approach (1.8, 1.61–2.02) compared with those that received a PI approach (2.94, 2.55–3.43) (U=58.0, P=0.781). No proprioceptive deficits were noted. Neither femoral nerve block technique offered a superior approach to the patient's analgesic plan. Further research is needed to draw definitive conclusions.