Capnography is a non-invasive method that measures the concentration of carbon dioxide during expiration (EtCO₂). Initially used in hospital surveillance and emergency care, capnography is rapidly becoming popular in medical practices and homecare medicine. The trend to miniaturize such modules emphasizes the advantages of the Axetris MEMS-based broadband infrared (IR) sources for NDIR gas detection. Axetris offers solutions by providing a portfolio of IR Sources with adapted reflectors and optionally mounted optical windows. Axetris' newly released qualified EMRIS50 is specifically made for compact NDIR capnography sensors for high-quality CO2 monitoring.

Axetris' EMRIS50 specifically made for compact NDIR capnography sensors

Ensuring Patients' Safety through CO₂ Monitoring

Main stream vs. side stream

A measurement module can either be placed in the direct path of the CO2 exhaled by the patient (main stream) or in a peripheral, indirectly fed system (side stream). When employing the main stream configuration, all the CO₂ exhaled by the patient is analyzed. Side stream analyzers use only a small sample of the respiratory gases.

A lightweight solution is especially important for main stream analyzers, as the sensor is inserted directly into the patient’s airway. Reducing the additional weight at the airway connection improves patient comfort. The EMIRS50 features a particularly small size, low power consumption and high modulation depth especially designed for this purpose. Since these properties are generally advantageous for capnography, the EMIRS50 can be used for side stream as well.

How does it work?

Non-Dispersive Infrared spectroscopy (NDIR) utilizes a broadband infrared source covering the entire wavelength spectrum needed to measure a large variety of gases and primarily CO2. Axetris EMRIS50 stands out through high emission efficiency of 4.26μm, close to a blackbody characteristic. The specific wavelengths desired to measure the gas(es) of interest are selected with narrow band pass filters. The radiation is absorbed by the gas, resulting in a signal decrease which is proportional to the concentration of gas inside the sample volume.

Advantages of Axetris‘ Infrared Source EMRIS50 with Reflector

9 Miniaturized size for integration in light weight mainstream analyzers

9 High modulation depth over a wide frequency range for time resolved measurements

9 Optimized reflector for an easy integration with maximum efficiency

9 Low power consumption allows the de-sign of a cost-optimized electronics

Patient monitored by intensive care unit

Infrared SourceApplication Note: Capnography

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Main stream analyzer (intubated): Sample cell or cuvette (airway adapter) is inserted in the airway. The sensor is placed directly on this adapter and CO₂ is detected between endotracheal tube and breathing circuit.

Side stream analyzer (intubated): Adapter between endotracheal tube and breathing circuit transports CO₂ via a sampling tube to main unit. CO₂ is measured in the main unit, away from patient‘s airway.

1. Infrared Source EMIRS50 2. Sapphire Window3. Sample Cell4. Detector5. Monitor with Capnogram

1. Infrared Source EMIRS502. Water Trap3. Sample Cell4. Detector5. Monitor with Capnogram6. Sampling Tube7. Main Unit

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CO₂ concentration in the analyzed sample is different during inspiration and expiration. The capnography curve shows this difference over time. A monitor displays the capnogram with the amplified detected signal of the proportional CO₂ pressure. This can be plotted against time over a respiratory cycle as well as against volume.

The amount of CO₂ during a respiratory cycle provides important information about the patient’s health condition. EtCO₂, the level of carbon dioxide released at the end of expiration, reveals the respiratory effort.

Capnogram: CO₂ waveform shows different phases of the respiratory cycle.

Phase 1: Airway deadspace (no CO₂)Phase 2: Mixed bronchus and alveolar air (expiratory upstroke)Phase 3: Alveolar volume (expiratory plateau)

Possible causes include a decrease in metabolic rate, a fall in body temperature and others. Moreover, using the EtCO₂ waveform, technical issues such as circuit breaks or leakage in the overall system can also be detected.

In order to draw useful data from a capnogram, it is vital to acquire 30 to 100 measurement points per second. For this reason, an emitter operating reliably at high sample rate is necessary. With the EMIRS50, Axetris provides an infrared source capable of emitting at remarkably fast electrical modulation rates and high modulation depth exceeding 60% at 100Hz.

The waveform can shed light on possible medical issues such as airway obstruction, partial rebreathing and hypo- or hyperventilation. The latter, for example, is characterized by a decrease in the EtCO₂ level in comparison to previously measured levels.

Phase 1 shows the CO₂ free anatomic deadspace. The mixture of gas from the anatomic deadspace and CO₂ containing alveoli in phase 2 causes an expiratory upstroke. The alveolar plateau of phase 3 represents the exhalation of mostly alveolar gas. At the end of exhalation the peak CO₂ concentration, the end-tidal value, is measured. As soon as the inhalation begins, a rapid and sharp inspiratory downstroke follows.

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Switzerland

Axetris AG (Headquarters)6056 Kaegiswilphone +41 41 662 76 76axetris@axetris.comwww.axetris.com

USA

Leister Technologies LLCItasca, IL 60143phone +1 844 293 8747axetris.usa@axetris.comwww.axetris.com

China

Leister Technologies Ltd.Shanghai 201 109 phone +86 21 6442 2398axetris@axetris.cnwww.axetris.cn

Japan

Leister Technologies KKShin-Yokohama 222-0033 phone +81 45 477 36 37 axetris@axetris.jpwww.axetris.jp

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About Axetris Infrared Sources

Axetris infrared sources are micro-machined, electrically modulated thermal infrared emitters.The unique design is based on a resistive heating element integrated onto a thin dielectric membrane, which is suspended on a micro-machined silicon structure.

Infrared sources from Axetris are used in a number of gas detection applications in medical, industrial, environmental and automotive industries.

Conclusion

The shape of the capnography waveform provides valuable information that facilitates better diagnostics. Fast and accurate measurements are therefore essential to capturing the instantaneous change of CO₂ concentration during each breath.

The high resolution measurement of the CO₂ concentration requires a high sampling rate, and for this purpose, the emitter should be able to operate at high modulation frequency with a minimal loss of amplitude.

A rapid response CO₂ sensor improves patients' safety and requires reliable components including infrared sources. Axetris‘ EMIRS50 is designed for medical applications such as capnography. Its characteristics meet the demands of medical device manufactures.

Partners who integrate the EMIRS50 as a component into NDIR modules such as CO₂ sensors benefit from the comprehensive qualification checks Axetris‘ IR sources undergo.

In addition, Axetris' integrated beam shaping improves the efficiency significantly. The combination of EMIRS50 and optimized reflector provides producers with equipment of the highest reliability. Axetris supports healthcare industry OEM customers with technological expertise, practical application knowledge and experience.

EMIRS50‘s high emission at 4.26μm makes this infrared source the first choice when it comes to integrating it in main- or sidestream devices. Its compact size and low weight are particularly advantageous in mainstream analyzers.

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