From the Guidelines
Capnography is the preferred method for measuring EtCO2 due to its ability to provide real-time information about a patient's ventilation status and detect respiratory depression earlier than pulse oximetry. This vital monitoring tool uses infrared technology to analyze the CO2 concentration in exhaled gas, displaying the results as both a numerical value and a waveform (capnogram) 1. The normal EtCO2 value ranges between 35-45 mmHg in healthy individuals. Capnography is widely used during procedural sedation, mechanical ventilation, cardiopulmonary resuscitation, and for monitoring patients with respiratory conditions, as it helps clinicians quickly identify and address ventilation problems before they become critical.
Some of the key benefits of capnography include:
- Providing immediate feedback on ventilation adequacy, airway patency, and metabolic status
- Detecting respiratory depression, bronchospasm, or airway obstruction before oxygen saturation levels drop
- Allowing for earlier intervention and potentially improving patient outcomes
- Being a non-invasive and relatively low-cost monitoring technique
According to the 2015 American Heart Association guidelines, continuous waveform capnography is recommended in addition to clinical assessment as the most reliable method of confirming and monitoring correct placement of an endotracheal tube (ETT) 1. The guidelines also note that colorimetric and nonwaveform CO2 detectors can identify the presence of exhaled CO2, but are not accurate for continued monitoring of ETT placement 1.
In terms of the evidence, a study published in Circulation in 2015 found that waveform capnography had a specificity of 100% for correct tube placement, although the sensitivity decreased after a prolonged cardiac arrest 1. Another study published in the same journal found that ultrasound transducer placement on the anterior neck could identify endotracheal or esophageal intubation with a positive predictive value of 98.8% and negative predictive value of 100% 1. However, the use of capnography remains the most widely accepted and recommended method for measuring EtCO2.
From the Research
Capnography and EtCO2 Measures
- Capnography is a standard practice in anaesthesia for monitoring respiratory and metabolic function by measuring end tidal carbon dioxide (EtCO2) 2.
- EtCO2 monitoring can also be used to assess the effectiveness of cardiopulmonary resuscitation and is becoming more common in intensive care units and during procedural sedation 2.
- Capnography is increasingly favoured over pulse oximetry for monitoring respiratory function due to its ability to accurately and rapidly detect respiratory, circulatory, and metabolic derangements 3.
- The use of capnography has been recognized as an indispensable patient safety monitor, with evidence suggesting it improves outcomes in various healthcare settings, including operating rooms, intensive care units, and emergency departments 3.
Benefits and Applications
- Capnography offers many benefits over pulse oximetry, including its ability to monitor respiratory depression in patients using opioid analgesics 2.
- It is essential to understand the differences between capnography and pulse oximetry, as well as the physiological processes involved in CO2 excretion, to use capnography safely and effectively 2.
- Capnography is useful for diagnosing and managing esophageal intubation, monitoring airway patency, and detecting hypoventilation in patients without instrumented airways 3.
Limitations and Future Directions
- Despite its widespread use in high-income countries, capnography remains largely unavailable in low- and middle-income countries, contributing to more frequent and serious airway events and higher rates of perioperative mortality 3.
- New capnography equipment has been developed to overcome cost and context barriers, and increasing access to capnography in low- and middle-income countries is necessary to improve patient outcomes and expand universal healthcare 3. Note: The study 4 is not relevant to the topic of capnography or EtCO2 measures.