Investigators will enroll 320 patients who will undergo non-cardiac surgery, receive supplemental oxygen via face mask, and will be on a continuous pulse oximetry monitor in the Post Anesthesia Care Unit (PACU). The enrollment criteria were adapted from a previous study that showed SpO2 values seriously underestimated the severity of post-operative hypoxemia in patients with and without specific risk factors for hypoxemia. Research personnel will screen and ensure that each subject meets the enrollment criteria, and the informed consent is properly executed. Upon arrival to the PACU, each subject will be fitted with oxygen mask containing the Linshom sensor, which will be connected to a Linshom monitor for data collection. A side stream capnography line will be connected to the same face mask and the capnography data will be collected on the Zoe Medical 740 SELECT™ monitor. Additionally, two pulse oximeters will be applied to the same hand (non- NIBP arm), one of which will be connected to a hospital monitor (SoC) and the other to a Zoe Medical 740 SELECT™ monitor. The Linshom and 740 SELECT™ monitors will collect data once every second. Research personnel will then initiate the Linshom CPRM baseline mode and begin recording any clinical intervention (e.g., medications, oxygen delivery change, and stimulation upon detection of changes in patient's condition) that is performed by the PACU staff, paying close attention to, and recording of time at which those interventions occurred. Data collection will be performed throughout the subject's entire PACU stay. The CPRM data collection will be performed passively while the patient is monitored via SoC and will not interfere with clinical interventions that may take place during the data collection. Clinical staff in the PACU will be blinded to the Linshom CPRM data as well as pulse oximetry (non-SOC monitor) and capnography data collected.