Identification of lung injury, in different positions, induced by general anesthesia in horses, using microbubble contrast echocardiography

Abstract

General anesthesia in horses allows the performance of many surgical procedures. However, it can promote complications by hampering gas exchange into the lungs by reducing the ventilation/perfusion ratio, pulmonary atelectasis, and reduction in blood pressure. The respiratory depressant effects promoted by inhalational anesthetics increase intrapulmonary shunt and contribute to pulmonary hypoperfusion. Furthermore, controlled ventilation can lead to lung injuries resulting from high inspiratory pressures and large alveolar distension. Due to the anatomy of horses, the quadrupedal position favors gas exchange and ideal pulmonary function; however, in the supine position (dorsal recumbency), the lungs are pressured by the abdominal compartment through the diaphragm, with direct negative consequences for gas exchange. In humans, portal hypertension in patients with chronic liver disease can lead to hepatopulmonary syndrome (HPS). Patients with HPS have changes in blood gases that reflect the presence of intrapulmonary shunt secondary to intrapulmonary vascular dilations. The diagnosis of SHP can be obtained by microbubble contrast-enhanced echocardiography. Transthoracic echocardiography contrasted with microbubbles was adapted for horses, in order to be used as a non-invasive diagnostic method for lung lesions in this species. In this context, we will seek to verify the potential use of the microbubble contrast echocardiography test in the diagnosis of pulmonary shunts possibly caused by inhalation anesthesia in horses. For this, between 10 to 15 animals in need of surgical treatment will be used, which will be submitted to the microbubble test as part of the admission examination protocols, and the test will be repeated during the anesthetic procedure, every 20 minutes, for the duration of the anesthesia and at the end of the procedure. For this, 60 m of contrast microbubble solution will be injected into the patients' external jugular vein. Concomitantly, through echocardiography, the passage of contrast in the heart from the right to the left heart chambers will be verified. (AU)