Epidural Volume of Injectate Using a Dose Regimen Based on Occipito-Coccygeal Spinal Length (OCL): Randomized Clinical Study Comparing Different Ropivacaine Concentrations, with or without Morphine, in Bitches Undergoing Total Unilateral Mastectomy

SIMPLE SUMMARY: Radical mastectomy involves the removal of mammary tissue and the surrounding lymph nodes. Inadequate perioperative analgesia for such extensive tissue resection may result in adaptive and maladaptive pain. The influence of anaesthetic/analgesic protocols on tumour progression and recurrence has been previously demonstrated, particularly the value of opioid-reduction strategies using locoregional and neuraxial anaesthesia has emerged. The aims of this study were (I) to evaluate the efficacy of lumbosacral epidural anaesthesia using a total volume of local anaesthetic tailored on individual spinal length; (II) to compare different concentrations of ropivacaine, with or without morphine, in terms of intraoperative inhalant anaesthetic and perioperative systemic opioids requirements; (III) to evaluate the incidence of intraoperative cardiorespiratory side effects, postoperative motor, and urinary functions impairments. The results of this study showed a significant reduction of perioperative opioid requirement and lower cardiorespiratory complications in dogs receiving epidural anaesthesia, with a volume injected based on the individual spinal length. Further studies comparing the volume of epidural injectate calculated based on bodyweight or on the individual spinal length are needed. ABSTRACT: A prospective, randomized clinical trial was designed to compare four epidural treatments in dogs undergoing total unilateral mastectomy. The epidural volume of injectate was based on the individual occipito-coccygeal length (OCL) aiming to reach the first thoracic vertebra (T(1)). The first ten dogs were allocated in a control group (C) and did not receive epidural treatment. Subsequently, forty dogs were randomly allocated in four groups of ten: epidural ropivacaine 0.5% (R(0.5%)); morphine 0.1 mg kg(−1) plus ropivacaine 0.5% (MR(0.5%)); morphine 0.1 mg kg(−1) plus ropivacaine 0.35% (MR(0.35%)); morphine 0.1 mg kg(−1) plus ropivacaine 0.25% (MR(0.25%)). Intraoperatively, isoflurane requirement (1.3% vs. <1.1% FE’Iso) and fentanyl requirement (9.8 vs. <1.1 µg kg(−1) h(−1)) were significantly higher in C group compared to all epidural groups. Postoperatively, methadone requirement was higher (1.8 mg kg(−1) vs. <0.8 mg kg(−1)) for C group compared to all epidural treatment groups. The ability to walk and to urinate returned 4 h earlier in MR(0.35%) and MR(0.25%). The mean epidural volume of ropivacaine, using a dose regimen based on OCL, to reach T(1) was about 0.15 mL cm(−1). The addition of morphine further reduced the methadone requirement, without affecting urinary and motor functions.