FROM RECUMBENCY TO STANDING: IMPROVING DIAGNOSTIC IMAGING QUALITY TROUGH THE EVOLUTION OF EQUINE ANAESTHETIC PROTOCOLS

Magnetic resonance (MRI), computed tomography (CT) and bone scintigraphy have, nowadays, a central role in the diagnosis of equine patient disorders and moreover, appropriate treatment plans for rehabilitation and recovery from musculoskeletal injuries are built on the foundations of an accurate diagnosis and detailed characterization of the pathology. The evolution in the last decades, both in anaesthesia and diagnostic imaging machines has lead clinicians to investigate more deeply on advantages and disadvantages of performing these examination in standing patients. General anaesthesia in this species is well known to be associated with higher risks due to body mass and anatomical conformation. Thus it is mandatory to evaluate risks, costs and benefits of the diagnostic examination under consideration. The decision of performing second level diagnostic imaging in standing or in general anaesthesia must to be based also considering the ultimate aim of these examinations that is to achieve a correct and accurate diagnosis. Motion artefacts can nullify the diagnostic quality and moreover, even if great improvements have been made in machines and techniques, not all anatomic regions of the horse can be investigated a the standing patient. Motion-correction software are nowadays available for MRI and bone scintigraphy in the face of mild to moderate swaying motion while for CT examination improvements are still necessary. Clinicians must be aware of these limitations to correctly plan a diagnostic approach to the pathology under investigation. In the present thesis, the focus moved to improve standing sedation to avoid patient motions and in cases where standing sedation is not possible, improve balanced anaesthesia in second level diagnostic examinations. Three studies have been included in this doctorate thesis. The first study evaluates, during bone scintigraphy, two different sedative opioids combined with detomidine. In this study not only the sedation score was evaluated but also patient immobility; bone scintigraphy is a very sensitive examination but with inherent poor spatial resolution, and thus anatomic detail is lost. Also time needed for acquisition is long with acquisition time for each image of 2 minutes. Therefore, immobility in this diagnostic imaging technique is mandatory. No studies in literature evaluate sedative protocols including immobility evaluation, thus drugs combination choice is limited to the anaesthesiologist preference and not on evidence based medicine The second study focused on balanced anaesthesia in horses undergoing MRI in general anaesthesia, also in this case time acquisition is long with examination time balanced between 1 and 3 hours. Anaesthesia in order to diminish the patient risks should be always considered. Two routes of dexmedetomidine administration, continuous rate infusion (CRI) and subcutaneous, were evaluated during isofluorane general anaesthesia. Cardiopulmonary stability and recovery quality, that have been described to be one of the most problematic and unpredictable phases of an anaesthetic plan for quine patients, were compared. Subcutaneous administration of Dexmedetomidine has not been reported in veterinary medicine, while in human patients this route has begun to be investigated only in the last few years therefore this study represents a scientific novelty regarding this topic. In the third study an alternative approach to retrobulbar local-anaesthesia was evaluated. Retrobulbar block is widely used in veterinary and human medicine to perform ophthalmic surgeries in general anaesthesia and in the standing horse. For this technique many possible complications and risks have been described, therefore in human and small animals an alternative loco-regional anaesthesia with minimal complications has been described, the peribulbar block. The aim of the work was to evaluate this alternative approach in equine cadavers. Peribulbar blocks were performed by injecting contrast medium and the likelihood of achieving anaesthesia was evaluated thought CT examination. This approach not only could be used as a safer alternative and as a part of balanced general anaesthesia but could also permit surgeons to perform ophthalmic surgeries in the standing horses, reducing costs and eliminating general anaesthesia related risks. This doctorate thesis consists of studies on different topics but, all aiming to increase safety in equine patients. The purpose of the study were to ameliorate standing sedation in order to achieve high quality images fundamental for a correct diagnosis and moreover an appropriate treatment plan for rehabilitation and recovery. To describe a locoregional technique with fewer and minimal possible complications that could permit avoiding general anaesthesia and in cases in which general anaesthesia is required, the aim was to improve balanced anaesthesia in order to reduce the associated risks, bringing new information into the field of veterinary medicine for an alternative route of administration of dexmedetomidine in equines.