Capnography

Hi friends!!!

In our previous blog we have seen about Computed Tomography.

Please check out for the link given below.

Generations of CT scanners

COMPUTED TOMOGRAPHY | TECHNOLOGY | ARTIFACTS

Today we are going to see about capnography.

Capnography is a important diagnostic and monitoring equipment used mainly during anesthesia procedure. Failure to used capnography in patients dependent on an artificial airway contributed to more than 70 percent of the ICU related airway deaths.

Therefore it is important for every healthcare professional to know in detail about capnography.

Let’s get into the topic.

WHAT IS CAPNOGRAPHY?

Capnography is used to measure the amount of carbon dioxide in exhaled air. It is also used in indirect monitoring of carbon dioxide in arterial blood. The capnography displays the waveform of expiratory carbon dioxide with time. The capnography waveform provides details about metabolism, circulation and ventilation of patients.  It has its contribution in the fields of anesthesia and intensive care.

Image courtesy: pxfuel.com

Licensed under: CC Share Alike 

NOTE: Normal value of expired carbon dioxide (Capnometer) is 35 mmHg to 45 mmHg.

WHAT IS CAPNOGRAPHY WAVEFORM?

The following is the normal capnogram waveform.

Image courtesy: Wikimedia commons

Licensed under: CC Share Alike 

The capnography has four phases. The 4 phases of capnography as follows

Phase 1: The phase 1 capnography is a inspiratory baseline, which is due to inspired gas with low levels of carbon dioxide.

Phase 2: Phase 2 is a expiratory upstroke which occurs during expiration of both dead space gas and alveolar gas (CO2 from alveoli reaches the upper airway and mix with the dead space air). Thus CO2 is detected in the exhaled air. The transition from phase 2 to phase 3 is called alpha angle capnography.

Phase 3: The phase 3 capnography is a alveolar plateau, where the last of alveolar gas is exhaled. The alveolar plateau has slightly upward tilt towards the end. The end of phase 3 is the end of exhalation which means end of exhalation has highest amount of CO2, thus it is called as etco2 (Entitled or Expired Carbon dioxide) and displayed in the monitor. The transition from phase 3 capnography to phase 0 is called beta angle. The beta angle is used to access the rebreathing. If the rebreathing occurs the angle is greater than 90 degrees.

Phase 0: Phase 0 is a inspiratory downstroke, that is the beginning of the next inspiration. Oxygen fills the airway and CO2 levels drop back to zero. The return to baseline is called phase 0.

There is a additional phase called Phase 4, which is a terminal upstroke (quick upstroke) which is seen during pregnancy.

WHAT ARE THE 

CHARACTERISTICS OF 

CAPNOGRAPHY 

WAVEFORM?

The capnography monitor (etco2 monitor) displays Capnography waveform which has five important characteristics to look out for.

1. Frequency.

2. Rhythm.

3. Height.

4. Baseline.

5. Shape.

The waveform should return to the baseline, the frequency should match the patient’s respiratory rate. The height of the capnography waveform should be between 35mmHg and 45mmHg, which is the normal etco2 reading.

WHAT ARE THE USES OF 

CAPNOGRAPHY?

1. Capnography is used to diagnose early respiratory depression and airway disorders during sedation, which results in reduction of unknown complications during sedation.

2. Capnography is useful in assessing tracheal tube and tracheostomy patency and position.

3. Capnography is useful in monitoring the adequacy of ventilator support. It provides important information about ventilation status.

4. Capnography provides indications about conditions like Apnea, Hypoventilation, Hyperventilation, asthma, laryngospasm, bronchospasm, rebreathing of CO2.

 

Now I hope you have acquired some knowledge about capnography. We will discuss in detail about interpretation of capnography waveform and its indications in our next blog.

NOTE: Dear friends!!! ...Please do comment a topic related to Biomedical, so that we can discuss it in future blogs.

Check out for my other blogs 

DON’T FORGET TO FOLLOW THIS BLOG PAGE

DROP YOUR MAIL ID TO GET IMMEDIATE UPDATES

If you find this blog post knowledgeable, comment & share it with a friend!