The carbon dioxide concentration at the end of expiration is called the end-tidal carbon dioxide concentration (ETCO₂, normal range 35-40 mm Hg) which represents the alveolar carbon dioxide concentration.

The phases I, II, and III represent expiration and phase IV, inspiration.

The normal capnogram has four different phases.When the carbon dioxide concentration is displayed against time, a capnogram is obtained.This absorption is measured and the carbon dioxide concentration is displayed according to a nomogram.The carbon dioxide in the gases absorbs the infrared light in proportion to its concentration.The capnography passes infrared light through the gases to be analyzed.

The amount of carbon dioxide in the exhaled gases can be measured using a capnograph.Therefore, it provides a real-time monitor for apnea and an assessment of effectiveness of cardiopulmonary resuscitation. Quantitative waveform capnography, on the other hand, immediately responds to changes in the level of CO 2 in expired air. The detection system used in pulse oximetry is slow to respond to changes in the oxygen levels of blood.

Moreover, pulse oximetry is a delayed assessment of the patient’s oxygenation status. Quantitative waveform capnography provides many details about resuscitation efforts that pulse oximetry cannot. So, if during the course of advanced cardiovascular life support a patient’s ETCO 2 increases rather dramatically (e.g., from 15 to 35 mmHg) this is consistent with the return of spontaneous circulation. Even under the best circumstances, it will be rare for a person delivering CPR to achieve 35 to 45 mmHg of ETCO 2. A drop-in ETCO 2 may prompt rescuers to switch roles and give the person delivering chest compressions a chance to recover.Īnother use for quantitative waveform capnography is to identify patients who have achieved a return of spontaneous circulation or ROSC. If the rescuer began the intervention by delivering high-quality compressions and achieving satisfactory ETCO 2 but CO 2 levels dropped over time, it’s important to consider whether rescuer fatigue is setting in. Rescuers should strive to deliver high-quality chest compressions that keep ETCO 2 levels at least 10 mmHg and preferably 20 mmHg or higher. In an unconscious patient or in someone who is in cardiopulmonary arrest, ETCO 2 may be undetectable. Normal end-tidal carbon dioxide (ETCO 2) usually falls in the range of 35 to 45 mmHg in adults. Specifically, if the rescuer is delivering ventilations but the end-tidal carbon dioxide is too low, then ventilation is insufficient and these should not be considered actual ventilations. The capnography device can also provide the means of quantifying respiration rate that is more accurate than simply counting ventilations. If cardiac output is insufficient, carbon dioxide returning from the tissues through the veins is not reaching the lungs.

That we are creating some form of circulation.

That the ventilation is being delivered.

Therefore, if we can detect CO 2 in exhaled breath it provides us with some very important information about our life support efforts. As cells create energy, they consume oxygen and give off CO 2 as a waste product.

This is precisely why quantitative waveform capnography is useful in life support situations.ĬO 2 is a product of cellular respiration. Of course, when a patient is being ventilated either a rescuer or a ventilator machine is assisting those expirations. This device can be part of a nasal cannula filter line or be attached to a bag mask device or ET tube. The capnography device uses a sensor that detects CO 2 levels in expired air. Quantitative waveform capnography is the continuous measurement of carbon dioxide (CO 2), specifically end-tidal CO 2.

Normal range of capnography