Complete analysis of exhaled carbon dioxide monitoring instrument

1、Definition

Capnograph is a device that monitors the concentration of carbon dioxide in human breath in real time, and is widely used in anesthesia ICU、 The fields of first aid, respiratory therapy, sleep medicine, etc. are key tools for reflecting lung ventilation function and circulatory status.

2、 Working principle

Capnograph uses infrared spectroscopy to measure the concentration of CO ₂ in exhaled breath, draws a CO ₂ waveform (Capnogram), and displays the end tidal carbon dioxide partial pressure (EtCO ₂) value in real time.

EtCO ₂ (mmHg): End tidal carbon dioxide partial pressure, normal range 35-45 mmHg.

The waveform of Capnogram: CO ₂ concentration over time can intuitively reflect respiratory patterns.

Respiratory rate (RR): automatically calculated by the system.

3、 Main types

Mainstream

The sensor is directly placed at the airway interface, with excellent real-time performance.

Commonly used in anesthesia scenarios, it can provide timely feedback on ventilation status.

Sidestream

Extract gas through pipelines and send it to the analyzer.

Suitable for bedside ventilation assessment, with relatively flexible operation.

Transcutaneous monitoring (TcCO ₂)

Monitor CO ₂ concentration through skin.

Especially suitable for newborn or sleep monitoring, reducing interference with patients.

Portable Capnometer

Compact in size and easy to carry.

Suitable for transportation, first aid, or home respiratory management, meeting the needs of different scenarios.

4、 Clinical application scenarios

Anesthesia and surgical monitoring

Accurately assess the adequacy of ventilation to ensure normal breathing for patients; Quickly confirm the correctness of intubation to avoid danger caused by accidental insertion.

Adjust mechanical ventilation parameters based on monitoring data to ensure surgical safety.

Emergency and ICU

During CPR, the EtCO ₂ value is used to assess the effectiveness of resuscitation, providing key evidence for rescue efforts.

Monitor issues such as pulmonary embolism and hypoperfusion to promptly detect changes in the condition.

Respiratory system diseases

For patients with COPD and asthma, monitor the gas retention and assist in formulating treatment plans.

Evaluate the effectiveness of oxygen therapy and ventilator therapy, and adjust treatment parameters.

Sleep Medicine and Home Care

Used for assessing central/mixed sleep apnea and understanding the patient's sleep and breathing status.

Joint assessment of blood oxygen saturation for chronic respiratory diseases to achieve comprehensive monitoring.

5、 Advantages and limitations

Advantage:

Real time continuous and non-invasive monitoring to reduce patient pain.

Can quickly reflect respiratory ventilation status and provide timely information for medical staff.

Easy to integrate with other devices, facilitating the construction of a comprehensive monitoring system.

Suitable for various clinical scenarios, with a wide range of applications.

Limitations:

Easy to be affected by factors such as gas leakage and pipe detachment, resulting in inaccurate monitoring data.

EtCO ₂ is not exactly equal to arterial PaCO ₂, and there is a certain difference.

Operators need to have certain experience in operation and interpretation in order to accurately determine the condition.

The mainstream model has a larger volume and is not suitable for use by pediatric patients.

6、 Summary

As an important component of modern monitoring systems, Capnograph plays a crucial role in assessing respiratory status, ensuring anesthesia ventilation safety, ICU monitoring, and sleep management. With the development of technology, portable and intelligent Capnographs will be more widely used in home and chronic disease management in the future, providing patients with more convenient and efficient medical services.