Human life relies on respiration: the intake of oxygen and the release of carbon dioxide. Respiration provides a constant flow of oxygen molecules to our brain, organs and tissues while providing a way to remove the waste CO2 molecules that are created in the cells.
Without respiration, our bodies will shut down within seconds. For this reason, regardless of the procedure, wound, disease or illness, one of the first priorities of a physician is to insure continuous respiration.
In order to measure respiration, physicians and health care workers use several oxygen and carbon dioxide gas sensors. These gases are measured in 2 areas: the breath and the blood.
Breath Gas Monitoring and Analysis
Measuring the gases in a patient’s breath gives an indication of the effectiveness of the lungs to take in oxygen and expel CO2. Because breath gas analysis is non-evasive, it can be done safely and provides instant feedback about the effectiveness of respiration. For this reason, breath gas monitoring is one of the first procedures performed on a patient in an ambulance or hospital to verify their overall health in an emergency situation.
Fresh air contains approximately 21% oxygen by volume. During respiration, only a portion of the oxygen is used by the lungs. Exhaled breath still contains 13% to 16% oxygen, with the difference made up of an increase in water vapor and carbon dioxide.
To measure the change in oxygen during breathing oxygen sensors capable of taking a reading every second are used. For oxygen control, ventilator manufacturer’s typically use electro galvanic oxygen sensors capable of measuring up to 100% oxygen enriched air from compressed oxygen tanks.
Capnography is the monitoring of CO2 levels expelled from the lungs. Inhaled ambient air has about 400 parts per million (0.04%) by volume of CO2. Exhaled breath contains about 4% to 5% CO2.
A capnograph is a device that displays the CO2 levels in the expelled air in real-time, either as an End Tidal CO2 (ETCO2) graph or as a numerical readout. The advantage of capnography is that it is an indirect monitor of the CO2 levels in blood. Conversely, a difference between the CO2 levels in expired air and the blood is an indicator of lung disease.
To measure CO2 levels in expelled air, a capnograph relies on fast carbon dioxide sensors that can measure minute CO2 changes in real time.