Systems and methods for determining a physiological parameter in a patient are provided. In certain embodiments, a system can include an analyte detection system configured to measure first analyte data in a fluid sample received from a patient, a medical sensor configured to measure second analyte data in the patient, and a processor configured to receive the first analyte data and the second analyte data and to determine a physiological parameter based at least in part on the first analyte data and the second analyte data. In certain such embodiments, the medical sensor may be a pulse oximeter, and the physiological parameter may include a cardiovascular parameter including, for example, cardiac output.