Effect of Nasogastric Tube Placement, Manipulation, and Fluid Administration on Transcutaneous Ultrasound Visualization and Assessment of Stomach Position in Healthy Unfed and Fed Horses

SIMPLE SUMMARY: In horses with colic (abdominal pain), it is vital to be able to identify and remove fluid building up in their stomachs. Ultrasound is a non-invasive diagnostic that is often used to estimate the size of the stomach in horses with colic, but our knowledge of ultrasound of the stomach in horses with colic is not complete. Because horses with colic may or may not be eating and a veterinarian often passes a stomach tube to help remove or give fluid, we need to know how feeding and the use of a stomach tube affects ultrasound of the stomach to help veterinarians interpret ultrasound of the stomach in horses with colic appropriately. In a group of healthy horses, ultrasonography revealed that feeding, stomach tube placement, and giving fluid, increased the size of the stomach. After fluid was given, it could be consistently identified within the stomach with ultrasound. Based on our findings, if a horse has been eating recently or had a stomach tube passed, the size of the stomach on ultrasound may be increased, unrelated to fluid buildup, and looking for fluid in the stomach may be a better method to diagnose fluid building up. ABSTRACT: Knowledge of the effects of feeding and nasogastric tube placement and manipulation on gastric ultrasound is limited. Given the variability in duration since feeding and the ubiquitous use of nasogastric tubes in horses with colic, the interpretation of gastric ultrasound in horses with colic requires an understanding of these effects. Cranial to caudal and dorsal to ventral ultrasonographic dimensions of the stomach were obtained in 10 unfed horses and five fed horses, before and after nasogastric tube placement, after checking for reflux and after administration of 6 L of water in unfed horses. Fed horses’ stomachs were larger in both cranial to caudal and dorsal to ventral dimension than unfed horses. Nasogastric intubation and the administration of water increased ultrasonographic gastric dimensions in fed and unfed horses. Checking for reflux did not consistently decrease ultrasonographic gastric dimension in fed or unfed horses. Fluid was consistently identified in the stomach with ultrasound after 6 L of water. Increases in gastric ultrasound dimensions found in horses that have been recently fed and/or had a nasogastric tube placed can occur without pathologic gastric distension related to colic and should be interpreted in this context. In contrast, the identification of fluid in the stomach on ultrasound occurs consistently with fluid administration and may be more useful than standard ultrasound parameters of gastric dimensions to identify horses with colic likely to have significant gastric reflux.