Using Electrical Bioimpedance Assessments to Estimate Perioperative Total Body Water and Postoperative Fluid Need

Being able to accurately monitor patient bodily fluid levels during and after surgery is very important, as there are a number of complications that can arise if a patient's fluid levels become unbalanced, such as swelling within or pressure on various bodily organ systems. There are several different ways that physicians can monitor a patient's fluid balance during and after surgery, such as measuring the amount of urine output or the use of central venous catheters which measure the pressure in the veins entering the heart. Most of these techniques are invasive since they require tubes to be inserted into the body. A potential alternative would be to use a noninvasive technique such as electrical bioimpedance (BIA). Bioimpedance assessments work by using small electrical currents that can accurately predict both the water surrounding the outside of cells in the body, as well as the total amount of water in the entire body. Electrical bioimpedance assessments have been used to estimate patient swelling following surgery (edema), to measure the volume of blood the heart is pumping out, as well as to calculate body fat percentages. The goal of this study is to relate this technology to fluid shifts within the body that occur as a result of surgery, in particular, major intra-abdominal surgeries. By using bioimpedance during and after surgery, the investigators will compare the data collected with that calculated by using traditional measures of body fluid status, such as urine output and intraoperative blood loss. During the study, the bioimpedance monitors will not replace the standard bodily fluid monitors and will not interfere with their readings. Additionally, the electrical current produced by the bioimpedance monitors is too small for patients to feel and will not interfere with medical devices such as pacemakers.