Capnography

Original Editors - Charlotte Fastenaekels

Top Contributors - Admin, Charlotte Fastenaekels, Scott Cornish, Adam Vallely Farrell, Kim Jackson, Laura Ritchie, WikiSysop and Lucinda hampton  

Introduction

Capnography, a noninvasive diagnostic tool, is an essential component in the monitoring of ventilated patients in certain clinical settings.

Capnography provides real-time, ongoing monitoring of carbon dioxide (CO2) concentration in exhaled breath, providing valuable information pertaining to a patient’s ventilatory status, metabolic rate, and circulatory status.

The value of capnography is evident in various clinical settings, including anesthesia, emergency medicine, and critical care.

Capnogram

Capnography works on the principle of infrared absorption spectroscopy. Essentially it measures the concentration of carbon dioxide in exhaled air by detecting the amount of infrared radiation absorbed by the CO2 molecules. As the CO2 molecules in the exhaled air absorb the infrared light, the detector senses the changes in light intensity, these are then converted into electrical signals, which are processed and displayed as a waveform on a monitor, known as a capnogram.

Indications for Use

This technique allows insight into the alveolar ventilation, perfusion and metabolism of breathing. On top of the use of validity for the measured level of EtCO2, it gives us two main advantages.

1. The appropriate tracing/mark on a pulse oximeter guarantees that the recorded oxygen saturation provided is valid.
2. The evaluation of the provided waveform gives key information about latent, underlying physiologic conditions and the ongoing processes of diseases.
   

Capnometry is a non-invasive monitoring technique:

• Allows quick and reliable insight into aspects like: ventilation, circulation, and metabolism.
• In diagnosis, monitoring, and prediction of outcome capnometry is an important tool, especially in the pre-hospital setting.

Conditions such as pulmonary embolisms (PE's) and congenital heart disease, affecting perfusion of the lung do not affect the shape of the curve, but have an affect on the relationship between expired CO2 and arterial blood CO2.

Capnography can also be used to measure carbon dioxide production. Increased CO2 production is seen during fever and shivering. Reduced production is seen during anesthesia and hypothermia.

The Future of Capnography

Capnography and the measurement of PETCO2 will be augmented in the future by relatively new measurement methodology. Including the study of oxygen kinetics as a future direction.

Capnography is increasingly being used by Emergency medical personnel to assist in their assessment and treatment of patients prior to transportation to hospital. These uses include verifying and monitoring the position of an ETT (endotracheal tube) or a blind insertion airway device. A misplaced tube in the oesophagus will lead to a patient's death if it goes undetected.