Comparative study of two incisional infiltration techniques in dogs undergoing ovariectomy

Incisional infiltration of local anaesthetic is a technique in support of multimodal analgesia. Usually, this technique is performed by injection of local anaesthetic directly into the incision site using a syringe. Comfort-in™ is a needle-free injection system that works by forcing the liquid medication at an elevated speed without piercing the skin; high pressure allows a wider diffusion of drugs. The aim of the study is to compare the analgesic effects of pre-operative incisional skin infiltration of lidocaine using the traditional technique and the Comfort-in™ in dogs undergoing ovariectomy. The study was approved by University of Messina Review Board for Animal Care (No. 021/2018). Twenty-two ASA 1 cross-breed dogs were randomly divided into two groups: - S group (11 subjects): was infiltrated with 2% lidocaine (4 mgkg-1) using an insulin syringe; - C group (11 subjects): was infiltrated with 2% lidocaine (4 mgkg-1) using the Comfort-in™ Technology. The dogs were premedicated with medetomidine (5 mcgkg-1) and tramadol (4 mgkg-1) intramuscularly. General anaesthesia was induced with tiletamine and zolazepam (5 mgkg-1) intravenously and maintained with isoflurane in oxygen diluted. After, the infiltration of the midline incision was performed depositing lidocaine in equal quantity in six injections that were made on each side of the incision, from the caudal to the cranial ends. During the procedure, heart rate, respiratory rate, systolic blood pressure, diastolic blood pressure, mean blood pressure, peripheral capillary oxygen saturation and end-tidal carbon dioxide were recorded after premedication, after incisional block, at skin incision, at muscular incision, at removal of an ovary and at suture. The evaluation of intra-operative analgesia was performed with a cumulative pain scale. The surgery was completed in all the animals, and there were no anaesthetic or surgical complications. The results of this study showed that the analgesia obtained at the skin incision was more satisfactory in C group than in S group, confirming that a better analgesia is provided from the better diffusion of drug and, also, from the absence of the needle trauma. Advantages of the Comfort-in™ use for incisional lidocaine block consist of lower quantity of local anaesthetics requirement, elimination of needle stick injuries and needle disposal, time saving and decrease of costs. Further studies are needed in order to demonstrate whether this technique can be a reliable alternative method to perform incisional infiltration.