The Relationship Between Cardiac Output and Microvascular Visceral Blood Flow

Although major surgery is often required to treat abdominal problems, there is a significant risk of death or complication following these operations. By using ultrasound the amount and timing of fluid patients receive during operations can be optimised and the risk of surgery reduced. However, little is known about the exact changes in blood flow in the small vessels of the body in response to fluid. A greater understanding of this may allow for more appropriate care of patients undergoing this type of surgery in the future. In this study of healthy volunteers we will attempt to better understand how fluid administration guided by ultrasound effects blood flow in large and small vessels, by using two different techniques of ultrasound imaging. A narrow bore (approximately 4-5mm diameter) ultrasound probe will be passed through the nostril and mouth to rest within the oesophagus allowing measurement of blood flow in the main artery, while a second probe will be rested on the volunteer's abdomen and used to record changes in blood flow in small liver blood vessels. Comparison of these two techniques during the administration of fluid will allow us to better understand the relationship between large and small vessel blood flow. Because different types of fluid may behave in different ways, we will test the effect of two types of fluid commonly used in clinical practice; 'normal' saline solution and gelofusine.