In our protocol we will test the hypothesis that closed-loop fluid administration can maintain higher cardiac stroke volume (shown to improve patient outcomes after surgery) than anesthesiologist management. We have shown this to be the case in multiple simulation studies and in-vivo animal studies, but not yet experimentally in a clinical setting. Investigators will recruit their patients from the surgical record that that require cardiac output monitoring undergoing surgery and require mechanical ventilation and consent to participate in the study will be included in the study. They will receive standard patient care in that in no way will their anesthetic or surgical procedure will be altered as part of the study, with the exception of fluid administration. Fluids are usually given to a patient based on the physician's discretion. As part of the study patients will receive fluid management via a closed loop (automated) system that will use an infusion pump (Q-Core) and a controller (a computer run index and algorithm developed by Sironis) to make frequent, regular and accurate adjustments to the amount of fluid the patient receives using feedback from standard operating room monitors at UCI). Data from this study will be retrospectively compared to subjects case matched to evaluate differences in cardiac output, total fluid given, and patient outcomes.