Abstract:
Materials and Methods Each dog underwent four treatments separated into two treatment blocks. All dogs received each treatment once in a balanced randomised order within each block. A three-week washout period between treatments within each block was observed. Initially, the dogs were exposed to the ropivacaine treatment block: RS (ropivacaine 0,5% plus saline 0.9%); RH (ropivacaine 0,5% plus hyaluronidase 100 IU ml-1); followed three weeks later by the bupivacaine treatment block: BS (bupivacaine 0,5% plus saline); BH (bupivacaine 0,5% plus hyaluronidase). The local anaesthetics were administered at 0.1 mL kg-1 per site. Hyaluronidase and saline were administered at 0.02 mL kg-1 per site. Femoral-ischiatic nerve blocks were performed using a combined ultrasound-guided/electrolocation technique. The mechanical nociceptive threshold was measured using an algometer to ascertain baseline, onset and offset of anaesthesia. Time 0 was deemed to be immediately after completion of both nerve blocks. Mechanical nociceptive threshold was measured at 3-minute intervals for the first 30 minutes (onset period), then at 30-minute intervals up to a maximum of 360 minutes (offset period). Onset and offset of regional anaesthesia were defined as a 25% increase above and as a return to <25% above baseline nociceptive threshold readings, respectively. Nociceptive thresholds were evaluated until offset or until 360 minutes post-block. The times to onset and offset were compared between treatments within a block using Mann-Whitney U test. Data were analysed using commercially available software and significance interpreted at p < 0.05.
Results There were no differences between treatments with regards to onset and offset times of regional anaesthesia. The median (range) onset of anaesthesia for RS and RH was 21 (3 to 60) and 12 (3 to 21) minutes, respectively (p = 0.141). The offset was 270 (90 to 360) and 180 (30 to 300) minutes for RS and RH, respectively (p = 0.361); while the onset was 24 (3 to 60) and 9 (3 to 27) minutes (p = 0.394), and offset was 360 (240 to 360) and 330 (210 to 360) minutes for BS and BH, respectively (p = 0.456).
Conclusion and clinical relevance Hyaluronidase had no effect on the onset and offset times of ropivacaine and bupivacaine femoral-ischiatic nerve blocks in dogs compared to saline. The onset and offset times were highly variable in all treatments. Clinically, the high variability of the onset and offset times of the regional anaesthesia of these local anaesthetic drugs mean that clinicians must monitor the patient’s response and, if required, provide additional analgesic drugs.
