Evaluation of Capnography Sampling Line Compatibility and Accuracy when Used with a Portable Capnography Monitor

This bench test, performed in combination with a portable bedside capnography monitor allows us to determine the accuracy of match and crosspaired capnography sampling lines. The main advantage of this technique is that it can be used to directly compare the accuracy of multiply capnography sampling lines under consistent control testing condition. Capnography sampling line accuracy evaluation is essential for a variety of clinical settings in which accurate and reliable end tidal carbon dioxide measurements are vital to understanding a patient's ventilatory status.

To calibrate the tensile testing jig in the tensile testing jig software, set the load cell selection to 100 kilograms and the load parameter to 10 kilograms. Attach the sampling line components to the calibrated tensile testing jig and starting with a mass of zero kilograms initiate tension on the sampling line component while observing whether the sampling line connection remains intact. If the connection remains intact automatically and continuously increase the tension until the sub parts break or disconnect, recording the maximum tension exerted before the break occurred.

To calibrate the rise time measurement device first cut a standard 0.95 millimeter internal diameter carbon dioxide PVC tube into 10, 15 centimeter pieces. Next, turn on the air compressor jig controller and power supply and open the carbon dioxide gas flow. Attach one of the 15 centimeter pieces of PVC directly to the measurement chamber as a sampling channel and use a mass flow meter and a dedicated restrictor to calibrate the airflow to 10 liters per minute and the carbon dioxide sampling rate to 50 milliliters per minute.

In the jig software, set the air to carbon dioxide ratio to one to one the air time to three seconds, the carbon dioxide time to three seconds and 10 cycles and the rise time measurement length to none. Open the carbon dioxide valve and click finish calibration confirm that the button has turned green. Click measure and wait for the gas flow cycles to end before closing the carbon dioxide valve.

Record the background rise time and confirm that the result is less than 60 milliseconds. Open a new commercial sampling line and connect the sampling line to the rise time measurement device. Then click start, in the rise time measurement device software and wait for the device to measure the rise time.

To measure the end tidal carbon dioxide accuracy as a function of the respiratory rate. Place a mannequin in the supine position and connect the sampling line to the mannequin according to the manufacturer's instructions. To control the simulated respiratory rate, use a flow meter to measure the gas flow and calibrate the flow to 10 liters per minute as demonstrated.

In the breath simulator jigs software, set the duty cycle to 50%and use a leak testing jig to test for leaks in the system. When the patency of the sampling line has been confirmed, connect the breath simulator jig to the mannequin and use the simulator to increase the 5%carbon dioxide flow rate to 10 liters per minute and the nitrogen flow rate to 10 liters per minute. Wait 30 seconds to allow a steady capnography waveform to be established before recording the end tidal carbon dioxide value.

After measuring a total of 10 end tidal carbon dioxide values over 180 seconds. Use the breath simulator jig to change the respiration rate and allow the capnography waveform to normalize for 30 seconds before recording 10 additional entitled carbon dioxide readings over 180 seconds. To measure the end tidal carbon dioxide accuracy in the presence of supplemental oxygen.

Set the breathe simulator jig to 10 breaths per minute and connect the oxygen line to 100%oxygen and carbon dioxide output. Increase the carbon dioxide flow rate to six liters per minute and the oxygen flow rate to zero liters per minute for use as a reference measurement. Wait 30 seconds to allow the capnography waveform to stabilize before recording the end tidal carbon dioxide value 10 times over 180 seconds.

Then change the flow rate of the carbon dioxide and oxygen allow the capnography waveform to normalize for 30 seconds and repeat 10 additional end tidal carbon dioxide measurements over 180 seconds. While a majority of the sampling lines in this representative analysis exhibited accuracy at 150 breaths per minute for both breathing ratios, some lines failed to maintain accuracy, while others maintained accuracy under all of the tested conditions. Among the adults sampling lines tested at 10 breaths per minute sampling lines one, two, five, six, seven, eight and nine read end tidal carbon dioxide within an acceptable range at the lowest respiration rates.

In contrast, sampling lines three and four reported low end tidal carbon dioxide levels at the lowest respiration rate, which decrease to zero millimeters of mercury when the respiration rate increased to 80 breaths per minute or higher. Only sampling lines one, eight and nine continued to capture readings at very high respiration rates. In the presence of two, four or six liters per minute of supplemental oxygen, the expected end tidal carbon dioxide was 34 millimeters of mercury.

Upon the addition of two liters per minute of supplemental oxygen, a majority of the sampling lines exhibited a decrease in the observed end tidal carbon dioxide values. Similar decreases were also obtained in the presence of four or six liters per minute of supplemental oxygen. To improve clinical applicability similar end tidal carbon dioxide measurements should be performed in humans to evaluate the accuracy of capnography sampling lines in a clinical setting.

Our assessment of capnography sampling lines, highlights the need for an improved device accuracy evaluation particularly when using sampling lines and monitors from separate manufacturers.