Sheep (Ovis aries) as a Model for Cardiovascular Surgery and Management before,during, and after Cardiopulmonary Bypass

Because of its similarity to humans in important respects, sheep (Ovis aries) are a common animal model for translational research in cardiovascular surgery. However, some unique aspects of sheep anatomy and physiology present challenges to its use in these complicated experiments. In this review, we discuss relevant anatomy and physiology of sheep and discuss management before, during, and after procedures requiring cardiopulmonary bypass to provide a concise source of information for veterinarians, technicians, and researchers developing and implementing protocols with this model.Abbreviation: ACT, activated clotting time; CPB, cardiopulmonary bypass; CVP, central venous pressure; MAP, mean arterial pressure; RAP, retrograde autologous primingThe recent focus on rapidly translating findings in the laboratory to clinical applications has resulted in a shift to large animal models that closely correlate with human anatomy and physiology. The field of cardiac surgery is perhaps the most apparent beneficiary of animal research.⁶ Sheep (Ovis aries) have emerged as a widely used model for cardiovascular surgical device testing, especially that involving cardiac valves.^30,42,62 Despite the widespread use of sheep in the research setting, there are no comprehensive reviews of the relevant anatomy and surgical approaches, animal preparation, anesthetic protocols and monitoring, and postoperative care. The unique physiology of sheep coupled with the complexity of cardiovascular surgical research results in significant morbidity and mortality in this animal model.⁴²After IACUC approval, our institution undertook investigations of several novel cardiac devices and interventions in sheep, thus requiring the development of a conditioning and management protocol for animals before, during, and after major cardiac surgery involving cardiopulmonary bypass (CPB). Because neither a thorough review of sheep anatomy and physiology nor an adequate discussion of all the layers of anesthetic management during these complex procedures existed in the literature, our procedures were developed through a review of published literature, extrapolation from humans, clinical experience, and continued refinements as outcomes were evaluated. In this review, we aim to provide a comprehensive overview of relevant literature and share our experience from studies conducted in our AAALAC-accredited, NIH-assured institution to provide a concise source for researchers and veterinarians who are developing cardiovascular surgical protocols in sheep and to minimize adverse events during their implementation.