Methods of non-invasively determining blood oxygen level and related pulmonary gas exchange information

A method of non-invasively using breathing metrics to determine an oxygen status of a patient, comprising:

• obtaining a first oxygen measurement comprising an alveolar oxygen partial pressure (PAO2) from exhaled breath of the patient using a gas analyzer;
• obtaining a second oxygen measurement of the patient from other than breath sampling using a blood oxygen saturation monitor;
• obtaining a CO2 measurement comprising an end-tidal carbon dioxide partial pressure (PetCO2) from the patient using the gas analyzer;
• continuously determining partial pressure of oxygen in arterial blood (PaO2) based on the first oxygen measurement, the second oxygen measurement, and the CO2 measurement using a microprocessor;
• detecting a steady-state breathing condition of the patient based on a degree of change in the PAO2 and the PetCO2 and at least one additional physiological parameter across a plurality of consecutive breath cycles;
• in response to detecting the steady-state breathing condition, generating and outputting a stable PaO2 value for clinical use;
• and
• determining, using the microprocessor, an oxygen deficit of the patient based on a difference between the PAO2 and the determined PaO2.