Constant rate infusion of lidocaine, tumescent anesthesia and their combination in dogs undergoing unilateral mastectomy

Tumescent anaesthesia (TUM) is a technique for regional anaesthesia of the skin using direct infiltration of large volumes of diluted local anaesthetic combined with a vasoconstrictor. This technique has been applied in bitches and cats who underwent a unilateral mastectomy, demonstrating it facilitated the surgery procedure and assured satisfactory postoperative analgesia [1,2,3]. The aim of this study was to evaluate if the addition of TUM to lidocaine CRI modified intraoperative cardiopulmonary function in dogs undergoing unilateral mastectomy and provided adequate early postoperative analgesia. The study was approved by the Bioethics Committee of Messina. Twenty-four mixed-breed neutered dogs presented for unilateral mastectomy were included in the study. Dogs were premedicated with dexmedetomidine (3 g/kg) and methadone (0.2 mg/kg) intravenously. Induction of anaesthesia was produced by administration of propofol as required to enable endotracheal intubation. The animals were connected to a breathing circuit and isoflurane in 100% oxygen was delivered for maintenance of anaesthesia. Then, the dogs were randomly assigned to one of the three following groups: Group LID (n=8): an IV loading dose of lidocaine (2 mg/kg, Lidocaine 2%) followed by a CRI of 100g/kg/min; Group TUM (n=8): an IV loading dose of lactated Ringer’s solution followed by a CRI of Ringer’s solution in addition to local TUM applied immediately before mastectomy; Group LID/TUM (n=8): an IV loading dose of lidocaine (2 mg/kg followed by a CRI of 100 g/kg/min) in addition to local TUM. Group LID received an equivalent volume of lactated Ringer’s solution instead of local TUM. The ECG, invasive SAP, DAP and MAP, HR/min, RR/min, SpO2, T°C and EtCO2 mmHg were continuously recorded. Arterial blood pH, PaO2 and PaCO2 and HCO3- were recorded immediately after the introduction of the arterial catheter (T0), immediately after the start of the surgery (T1), and at 15 (T2), 30 (T3), 40 (T4) minutes following the start of the surgery. Subjective postoperative pain scores were evaluated using the Italian version of the Glasgow Composite Pain Scale-Short Form (ICMPS-SF). The scale was applied once the dogs had fully recovered from the sedative effects of the anaesthetic drugs (RT0), and following 15 (RT1), 30 (RT2), 45 (RT3), and 60 minutes (RT4). In the same time frame, considering postoperative pain scores exceeding level 6/24 as clinical decision-point for the requirement of rescue analgesia, IV administration of 0.2 mg/kg methadone was provided. For all dogs in the LID group (five at T0, two at T2 and one at T3) and five dogs in the TUM group (three at T0 and two at T1) rescue analgesia was required (LID vs TUM, p=0.2000). No dog in the LID/TUM group reached the threshold for rescue analgesia, hence showing a significant difference compared to both LID group (p=0.0002) and TUM group (p=0.0256).