A pulse oximeter has an integrated mode in which it operates as a plug-in module for a multiparameter patient monitoring system (MPMS). The pulse oximeter also has a portable mode in which operates separately from the MPMS as a battery-powered handheld or standalone instrument. The pulse oximeter has a sensor port that receives a photo-plethysmographic signal as input to an internal processor. The pulse oximeter processes this sensor signal to derive oxygen saturation and pulse rate measurements. In the portable mode, this information is provided on its display, and stored in memory for trend capability. A keypad provides a user interface for operational control in the portable mode. In the integrated mode, the pulse oximeter provides oxygen saturation and pulse rate measurements to the MPMS through a communications interface, along with previously stored trend data, and displayed on the MPMS monitor. The MPMS also provides external power and operational control of the pulse oximeter in the integrated mode. Alternatively, a docking station operates as a plug-in module that provides the mechanical and electrical interface between a portable pulse oximeter and MPMS instruments from a variety of manufacturers. In the integrated mode, the portable pulse oximeter docks to the docking station, which in turn is inserted in one or more MPMS slots. The docking station can function as a simple electrical pass-through device between the docked portable pulse oximeter and the MPMS or it can provide a MPMS communications interface.