Evaluation of Postoperative Residual Analgesia of Two Solutions Used for Local Anesthesia By Tumescence In Bitches who Underwent a Unilateral Mastectomy

Resumo

Background: Breast tumors are common and require surgical treatment. A mastectomy causes edema, inflammation, and moderate to severe pain; therefore, analgesics should be used efficiently during the trans- and postoperative periods. Tumescence anesthesia has been studied in veterinary medicine; however, there is limited literature on the comparison of the constituents of the different solutions and the most suitable protocol. The objective of this study was to evaluate the residual postoperative analgesia of two solutions through the Melbourne, Modified Glasgow for dogs (EGM), and Visual Analogue (EVA) scales in bitches who underwent a unilateral mastectomy.

Materials, Methods & Results: Twelve bitches, weighing between 5 and 15 kilograms and aged between 5 and 13 years old, were included in the study. To determine if the animals were medically fit to undergo the procedure, they were evaluated by clinical examination, laboratory testing (complete blood count, serum biochemistry [urea, creatinine and alanine aminotransferase/ALT], and imaging (thorax x-ray and abdominal ultrasonography). Patients were randomly divided into two groups. One group received a lidocaine-containing tumescent solution (GTL) that consisted  of 210 mL of lactated Ringer's solution (at a temperature between 8 and 12°C), 40 mL of 2% lidocaine hydrochloride without vasoconstrictor, and 0.5 mL of adrenaline (1 mg/mL). The other group received ropivacaine (GTR) with 233.3 mL of lactated Ringer's solution (at the same temperature as the previous group’s), 16.7 mL of ropivacaine (7.5 mg/mL), and 0.5 mL of adrenaline (1 mg/mL). Both groups received a combination of acepromazine (0.04 mg/kg) and meperidine (2 mg/kg) as preanesthetic medication (MPA), followed by induction using propofol (to effect) and maintenance using isoflurane. The solutions were infused  subcutaneously (SC) 5 min after stabilization of the anesthetic plane. For the mastectomy, the solutions were distributed throughout the mammary chain to be withdrawn, starting at the thoracic and abdominal regions and ending in the inguinal region. In the postoperative period, the animals were evaluated using three different scales (Melbourne, Glasgow modified for dogs [EGM], and Visual Analogue [EVA] scales), at six time points: one, two, four, eight, 12 and 24 h after extubation, or until the time of analgesic rescue when the animal presented with a score higher than 3.33 on the EGM scale. There were no statistical differences between the groups (P > 0.05) in any of the scales evaluated; however, most of the animals demonstrated analgesic rescue in the first hour of evaluation. GTR showed an additional rescue compared to GTL.

Discussion: Analgesic rescue occurred in the first hour of the postoperative period. This differs from other studies that used morphine in MPA and observed higher analgesia. This occurred because meperidine, the drug used in the study, has a shorter duration and is a less potent analgesic than morphine. We opted for this opioid because of its minimal interaction with the drug used in MPA and to better identify the residual effect of the administered solution. In addition, it does not interact with the other drugs used in the anesthetic protocol. It is known that the tumescence technique prolongs the analgesic effect of MPA because of subcutaneous absorption of a portion of the injected solution adjacent to the area being operated on. However, this was not observed as 50% of the animals in each group were rescued during the first hour of the evaluation. From this study, it was concluded that the tumescent solutions used in the trans-operative period should not be expected to have analgesic effects during the postoperative period of mastectomies because of the short duration of action.