Responses to Colloid Infusions

In situations such as dehydration, illness and surgery, fluid 'drips' are given to patients to keep them hydrated. Different fluids stay in the circulation for different lengths of time. For example, some types of fluid remain in the circulation for a short time which means patients would need to be given more fluid to achieve the desired effects. Giving a lot of fluid to sick patients can in itself cause problems, for example, it can affect the way the bowels work and delay the patient's recovery from illness. In these situations the investigators use specialized fluids called colloids, that are designed to stay in the circulation for longer. This means a smaller amount of fluid needs to be used and less problems are likely to occur. There are two different types of colloids that are commonly used, but the investigators do not know which of them is better. The purpose of this study is to investigate which of the two different colloids (one is called Gelofusin and the other is called Voluven) works better in patients who undergo surgery. Knowing which of the two fluids works best in patients will help us improve the care of surgical patients. The investigators hypothesis is that the fluid that has the larger size of molecules as part of the solution will work better during surgery.