What is Capnography or ETCO2 Monitoring ?

Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO.2) in the respiratory gases. The Capnograph is the waveform that shows how much CO2 is present at each phase of the respiratory cycle, and it normally has a rectangular shape.

ETCO2 ( End-tidal CO2) and Capnography both names indicating the same process. Standard Multipara Patient Monitors or Portable EtCo2 Monitors with EtCO2 sensors are used in this monitoring. Cost of these Monitors range from 1 to 2 L(INR)

Its main development has been as a monitoring tool for use during anesthesia and intensive care.Commonly used during anesthesia procedures, capnography is increasingly being used by paramedics in the field for a variety of purposes, including the evaluation of the success of resuscitative efforts, the confirmation of clinical death, and the analysis of the causes of respiratory distress.

ICU patients require frequent changes in position. Capnography will help to monitor the integrity of the patient’s airway during changes in position. Partial endotracheal tube obstruction resulting from either kinking of endotracheal tube, or by secretions can be detected via continuous monitoring of CO2waveforms. Prolongation of phase II and sloping phase III suggest obstruction of the endotracheal tube. (See Phase I & Phase II in graph)

How does capnography work?

One of carbon dioxide (CO2 )’s properties is that it absorbs infrared radiation. When the patient exhales, a beam of infrared light is passed over the gas sample on a sensor. The presence or lack of CO2 , is inversely indicated by the amount of light that passes through the sensor. High CO2  levels are indicated by low intensity of infrared, whereas low CO2 levels result in high Intensity of Infrared. 

Sensor Placement :

There are Types of ETCo2 Sensors based on the Application/Placement

1. Main Stream ETCo2

2. Side Stream ETCO2

1) Main Stream ETCo2

In main-stream capnographs, a sample cell or cuvette, usually in the form of an airway adapter, is inserted directly in the airway between the breathing circuit and the endotracheal tube, or airway device.  A lightweight infrared sensor is attached to the airway adapter and emitted light is detected by a photo detector located on the opposite side of the airway adapter. This sensor type mainly used along with Ventilator Breathing circuit.

2) Side Stream ETCO2

With side-stream capnography, the CO2sensor is located in the main unit itself, away from the patient, and a pump aspirates gas samples from the patient’s airway through a 6 foot capillary tube into the main processing unit.  One advantage of side-stream capnography is that expiratory gases can be obtained from the nasal cavity using nasal adaptors or with a simple modification of the standard nasal cannula.  These devices are easy to connect, do not require sterilisation as they are disposable. This sensor type generally used with Nasal cannula and patient may not be connected with ventilators.

Sensor Images :

1) Main Stream directly Placed in Y Piece of Ventilation circuit and Cable connected to Monitor. This include Infrared Diodes in Device at Y Piece. Some cases this device also comes with a disposable Adapter.

2) Nasal cannula will be attached to this Main Devices and connected to monitor.

In this case, Infrared Sensor Located in EtCO2 Module(Device in image) which should be placed safely near to the Monitor . This device also contains a Micro Suction Motor which helps device in collection of breath air from patient.

Wave Shape Indicates the Inhalation and Exhalation phases(Phase I & II).

Note the high CO2 Partial Pressure during Exhalation.

What is measured by the capnograph is known as the End Tidal CO2(ETCO2) or the amount of (or partial pressure of) the carbon dioxide released at the end of expiration. Normal Range is .35-45 mm Hg

1. Multipara Monitor or Specialised EtcO2 Monitor

2. Portal Device directly placed in Ventilation Circuit

Note : Capnography can be performed in Patient Connected to Ventilator(Main Stream) or not connected (using Nasal cannula through side stream device)

Importance :

CO2  levels in the blood are incredibly important for proper oxygenation and metabolism, which is why capnography is so useful. An irregular amount of CO2  in a patient’s breath and the degree of that irregularity can tell health care providers a great deal about the condition and treatment required. In hospitals, capnography is traditionally used during anesthesia, where it monitors metabolic processes through CO2  levels, both expired and arterial.

In an EMS setting, capnography has a multitude of uses. ETCO2  levels are highly indicative of the effectiveness of chest compressions during CPR, and can be the first indicator of a return of spontaneous circulation. Furthermore, capnography can be used to analyze the causes for respiratory distress in patients, including asthma, chronic obstructive pulmonary disease, or bronchitis. It can also provide early warning signs of hypoventilation or airway obstruction before any changes are seen in a heart rate or blood pressure monitor.

Capnography is an incredibly effective way to identify reduced perfusion, since ETCO2 levels can also provide early warning signs of shock. And finally, capnography can also provide a way to decide when resuscitation efforts can reasonably stopped – in other words, certain ETCO2 activity levels can serve as a confirmation of clinical death.

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