B40/B20 Patient Monitor17-16Basics of airway gases measurementAirway gases measurement description, CARESCAPE respiratory modules andAirway Gas OptionWith CARESCAPE Respiratory Modules and Airway Gas Option, you can measure and monitorgases being delivered to the patient and exhaled by the patient through the breathing circuit.The modules consist of an infrared sensor for measuring CO 2 and N 2O, and paramagnetic O2sensor. The E-sCAiO, N-CAiO modules also include anesthetic agents measurement.The gas sampling system samples the measured air to the module, and removes water andimpurities from it. The pump of the gas sampling system draws gas at a fixed rate through thesampling line into the gas measuring units. The side flow creates a slight sub-atmosphericpressure within the water trap, which causes fluid removed by the hydrophobic filter to collectin the bottle. After the measurement, gas is exhausted through the sample gas out connector.Airway gases measurement description, E-miniCThe E-miniC is designed for critical care environment to measure and monitor the expired andinspired CO2 concentration (EtCO2, FiCO 2) as well as the respiration rate (RR) up to 80 breathsper minute. E-miniC has a sample flow of 150 ml/min.Respiration rate from the CO2 parameter is counted from the frequency of end-tidal (peak) CO2measurements per minute. A sufficient respiration is defined as a difference of at least 1% (atleast 7 mmHg) between the measured inspired fraction and end-tidal CO2.Total sample size volume during one respiratory cycle depends on the respiration rate. Thefollowing table shows different sample size volumes with a 150 ml/min sample flow and I:Eratio of 1:2.Sidestream gas samplingThe gas modules use a sidestream gas sampling method. It means that a sample of patient’srespired gases from the sampling site is transported through a sampling line to the module foranalysis.A sidestream gas analyzer takes a constant sample from the patient airway adapter at thefollowing sample rates:• CARESCAPE respiratory modules: 120 ml/min• E-miniC: 150 ml/minTotal sample size volume during one respiratory cycle depends on the respiration rate.Respiration rate 10 20 30 40Duration of inspiration 2.0 seconds 1.0 seconds 0.7 seconds 0.5 secondsDuration of expiration 4.0 seconds 2.0 seconds 1.3 seconds 1.0 secondsVolume sampled duringinspiration5 ml 2.5 ml 1.67 ml 1.25 mlVolume sampled duringinspiration10 ml 5 ml 3.33 ml 2.5 mlTotal volume sampled 15 ml 7.5 ml 5 ml 3.75 ml
