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.

Linshom Medical (Linshom) has developed the FDA-cleared Continuous Predictive Respiratory Monitor (CPRM) a small and inexpensive sensor and monitor that provides continuous real-time tracking of these critical indicators of RDE. Linshom technology is based on our novel Linshom thermal sensor which is regulated by a thermoelectric cooler utilizing a proprietary control loop process. Respiration state is measured via temperature change throughout a patient's inspiratory/expiratory cycle. This delivers a respiratory signature allowing for continuous measurement of RR, relative Tidal Volume (rTV), relative Minute Ventilation (rMV), seconds since last breath (SSLB), and inspiratoryexpiratory (I/E) ratio. The CPRM solves existing unmet needs mentioned above with a small, portable, and inexpensive sensor and monitor that tracks RR, rTV, rMV (calculation of RR x rTV), seconds since last breath (SSLB), and I:E ratio in real time and continuously. These parameters are crucial in monitoring of patients suffering from both acute and chronic respiratory illness. Linshom offers an OR-quality respiratory profile at the patient bedside, which allows health care providers to promptly diagnose emerging respiratory decline and intervene with appropriate medical care.

In Phase I, investigators will conduct a clinical study in 145 post-operative patients comparing Linshom's CPRM to current SOC (clinical attention + pulse oximetry) and capnography. We will collect SOC, CPRM and capnography data simultaneously from each patient to demonstrate the ability of Linshom CPRM to identify Respiratory Depression Episodes in advance of SOC and/or capnography.

In Phase II, investigators will conduct a continuation of the phase I clinical study until the enrollment for this phase (175 patients) is reached, which would give an adequate statistical power for development of the Linshom CPRM alarm function.

Specific aims:

Aim 1: Demonstrate that Linshom CPRM is able to identify RDE earlier than pulse oximetry and capnography.

o Outcome: Investigators expect to successfully demonstrate that Linshom CPRM is capable of identifying RDE in advance of pulse oximetry and capnography by performing statistical analyses (non-inferiority and superiority hypothesis tests).

Aim 2: Identify parameters and threshold values for the alarm function of Linshom CPRM for RR, rTV percent change, rMV percent change, I:E ratio and SSLB.

Outcome: Investigators will identify Linshom CPRM parameters and threshold values with high predictive abilities for RDE. These parameters and threshold values will be incorporated into future product to alert for clinicians and allow them to provide timely interventions to patients.

Inclusion Criteria:

• ≥18 years old undergoing non-cardiac surgery
• Post-operative patients admitted to the PACU and expected to stay in the hospital for at least overnight
• Receiving supplemental oxygen via face mask in the PACU
• On continuous SpO2 saturation monitoring
• Receiving standard postoperative of care

Exclusion Criteria:

• Requirement for any form of postoperative invasive ventilatory support
• Patients receiving only local or topical anesthesia
• Day/outpatient surgery
• Unable to cooperate with the application of the study device
• Surgical/nursing/anesthesia staff suggest no study-related monitoring because of medical situation

This study will be conducted at The University of Maryland Medical Center (UMMC) where about 9% of the surgical procedures will go to the ICU or other non-PACU location and 20% will go home same day (within 24 hours). Based on previous trial data from UMMC, investigators expect gender to be ~50% male, 76% white and 23% non-white with an age distribution of 1/3 < 60 years of age and 2/3 > 60 years of age. This enrollment criteria makes the study results generalizable; population balanced and supports enrollment.

Data and specimens will only be shared with individuals who are members of the IRB approved research team or approved for sharing as described in this IRB protocol.