Non-gas analyzer monitor of inspired gas concentration

A system for monitoring an inspirable gas concentration for delivery to a patient, comprising:

• a pumpless branched breathing circuit comprising a first branch conduit and a second branch conduit, wherein the first branch conduit is fluidly connected to a first gas source having a first gas concentration and the second branch conduit is fluidly connected to a second gas source having a second gas concentration, wherein the first and second branch conduits merge directly into a patient delivery conduit without passing through a mixing chamber or a mixed gas control valve, wherein the patient delivery conduit downstream of the merge does not comprise a pressure sensor, and wherein the pumpless branched breathing circuit does not comprise an exhalation valve;
• a first flow sensor in the first branch conduit configured to generate a first flow measurement, a second flow sensor in the second branch conduit configured to generate a second flow measurement, and a third flow sensor in the patient delivery conduit configured to generate a third flow measurement;
• and
• a control unit electrically coupled to the first, second and third flow sensors;
• wherein the control unit is configured to:
• determine a blended gas concentration comprising the second gas in a blend of gas in the patient delivery circuit based on the third flow measurement and at least one of the first and second flow measurements, and
• monitor in parallel, first and second comparisons, triggering an alarm or a safety feature when the first or second comparisons fail, the first comparison based on comparing a sum of the first and second flow measurement to the third flow measurement, and the second comparison based on comparing the blended gas concentration in the patient delivery conduit to a preset target patient gas concentration.