Body Composition Monitoring for Determination of the Fluid Status in Patients Undergoing General Anesthesia

Patients undergoing anesthesia and surgery receive intravenous fluids during the procedure. The amount of administered fluid depends on the type of surgery, cardiovascular stability and intraoperative losses like hemorrhage. Fluid overload as well as hypohydration might be detrimental and might adversely effect outcome after surgery. Specifically overhydration results in significant weight gain, tissue edema and increased morbidity. Technically assisted assessment of volume status before surgery may be useful to direct intraoperative fluid administration and to prevent postoperative volume overload. As a prerequisite the investigators will test a recently developed whole-body bioimpedance spectroscopy device to determine the pre-to postoperative fluid distribution. This body composition monitor (BCM, Fresenius Medical Care, Germany) separates between extracellular and intracellular fluid volume non-invasively by applying a frequency sweep from 3-1000 kilohertz through the entire patient via electrodes placed on the wrist and ankle.

The investigators will test the hypothesis that

1. the amount of administered fluid correlates with the amount of overhydration measured postoperatively.
2. that preoperative BCM measurements and thus information about the preoperative hydration state might help to guide fluidmanagement and to reduce the amount of over/ hypohydration postoperatively.