Abstract: Intravenous sensor systems and methods for determining in vivo characteristics are disclosed, as well as systems for cooling bags of intravenous fluid. The intravenous sensor systems include a probe configured for placement in a peripheral vein. The probe includes one or more sensors for obtaining sensed information, such as body temperature, blood oxygen saturation level and blood pressure. An interface unit determines the in vivo characteristics based upon sensed information received from the one or more sensors. The determined in vivo characteristics may be displayed on the interface unit and/or transmitted to a remote computer.