Melbourne Veterinary School - Theses
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ItemAssessment of a ropivacaine ultrasound-guided Transversus Abdominis Plane (TAP) block for peri-operative analgesia in the dog undergoing ovariohysterectomy surgery( 2019)Advances in veterinary medicine have led to the development of further techniques to provide analgesia for our patients. Ovariohysterectomy is a commonly performed surgery in female dogs which causes significant pain. Multimodal analgesia often combining opioids, non-steroidal anti-inflammatories and local anaesthetic techniques is implemented to treat this type of pain. The transversus abdominis plane (TAP) block is a local anaesthetic technique that provides analgesia to the afferent nerves supplying the parietal peritoneum, muscles and skin of the anterior abdominal wall. The TAP block is utilized in human anaesthesia and has been shown to reduce post-operative pain scores and opioid consumption. The TAP block has potential to provide local anaesthesia to the mid-caudal abdomen for dogs undergoing ovariohysterectomy. The initial pilot study was a cadaveric study carried out in 5 dogs with an ultrasound guided two-point TAP injection performed in each hemiabdomen. The study identified that a two-point TAP injection delivered consistent dye dispersion to adequately stain branches of thoracic nerve T13 and lumbar nerves L1, L2 and L3. It concluded that this technique should be assessed in vivo to evaluate the analgesic efficacy in mid to caudal abdominal surgeries. A subsequent randomized controlled trial assessed the two-point ultrasound-guided ropivacaine TAP block for dogs undergoing ovariohysterectomy, with the hypothesis that dogs receiving the ropivacaine TAP block would have a lower minimum alveolar concentration (MAC) isoflurane at skin incision and a lower opioid rescue analgesic requirement post-operatively. The results concluded that the estimated population MACiso for the treatment group was lower than the control group but that this was not significant. There was also no significant difference in pain scores between the groups as measured by the Glasgow composite pain scale short form and mechanical nociceptive threshold testing. The proportion of subjects receiving rescue analgesia in the treatment group was lower than the control group, but this was not significant. The study concluded that the two-point TAP block did not provide significant MAC reduction or additional intra-operative or post-operative analgesia compared with the control for dogs undergoing ovariohysterectomy. Multiple confounding factors such as the administration of morphine as premedication and the low concentration of local anaesthetic used, ropivacaine 0.2%, could have contributed to these findings. Although the cadaver study identified that a two-point TAP injection delivered consistent dye dispersion to thoracic nerve T13 and lumbar nerves L1, L2 and L3, the technique when performed with 0.2% ropivacaine in dogs undergoing ovariohysterectomy did not provide significant additional MACiso reduction or intra-operative or post-operative analgesia compared with the control for dogs. Further assessment of the toxic dose of ropivacaine in dogs and the minimum effective concentration of ropivacaine for TAP blocks in dogs needs to be evaluated in order to further develop and assess this technique.
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ItemInfluence of retractor type and position on thoracoscopic-assisted pulmonary surgery in dogs( 2018)Thoracotomy is performed frequently in dogs for the purposes of exploration of the thorax, lung lobectomy, correction of vascular ring anomalies and patent ductus arteriosus, pericardiectomy, thoracic duct ligation, biopsy and resection of mediastinal and pleural masses and removal of foreign bodies from within the pleural space, intrathoracic oesophagus and the lower respiratory tract. Persistent post-thoracotomy pain is reported frequently by human patients characterised by discomfort and altered sensation in the skin adjacent to the surgical site. Multiple surgical techniques have been developed in an attempt to reduce the morbidity of these procedures. Minimally invasive surgical techniques have been a significant step towards this goal. A significant limitation of minimally invasive surgery is the loss of tactile feedback and video-assisted techniques which utilise smaller incision, permitting the introduction of the surgeon’s hand or fingers to the thorax have been developed to overcome these limitations. These techniques have recently been introduced for veterinary patients (Chambers and others 2012, Gower and Mayhew 2011a, Laksito and others 2010b, 2011, Wormser and others 2014). Both traditional and video or thoracoscopic-assisted techniques require the use of tissue retractors, typically placed in an intercostal position. Access is afforded by the forceful retraction of soft tissues such as the intercostal muscles and ribs. Studies in both animals and humans have demonstrated detrimental soft tissue changes associated with such retraction including direct and ischaemic damage to the soft tissues adjacent to the retraction device. The present study examines several aspects of thoracoscopic-assisted pulmonary surgery in dogs including the effect on blood flow in the intercostal musculature and nerve conduction in the intercostal nerves associated with two different retraction modalities. Additionally, the influence of assisted port location and thoracic conformation on access to and delivery of pulmonary tissues for the purposes of complete or partial lung lobectomy was assessed. Force, contact area and pressure were compared and related to intramuscular pressure, perfusion, oxygen indices, nerve conduction and histologic change in dogs undergoing simultaneous controlled thoracotomy incisions. The novel retractor resulted in lower pressure and improved oxygenation in adjacent tissues compared to mechanical retraction which may translate clinically into reduced post-operative morbidity. For all lobes except the accessory lung lobe, the exposure provided by the reported thoracoscopic-assisted approach was considered adequate for complete or partial lung lobectomy. The cranial and caudal portions of the left cranial lung lobe and the right middle lung lobe were best exposed with the assisted portal in the middle dorso-ventral third of the thoracic wall at the fourth intercostal space of the ipsilateral side in both breeds. The right cranial lung lobe was best exposed with the assisted portal positioned in the middle third of the fourth intercostal space in kelpies but the sixth intercostal space in greyhounds. The right caudal lung lobe was best exposed when the assisted portal was positioned in the ventral third of the fourth intercostal space in the kelpie but in the middle third of the sixth intercostal space in the greyhound. The described thoracoscopic-assisted technique is a practical method for exposure of the lobes of the lung, other than the accessory lobe, for partial lung lobectomy in the dog. The portals described also allow the introduction of a linear stapler for the purpose of complete lung lobectomy.