Overview of Carbon Dioxide Detector
In the early 1900s, scientists first started measuring carbon dioxide (CO2), but it was a complicated process with limited use in treating patients. In simple terms, end-tidal CO2 (ETCO2) detectors track how much CO2 is in a patient’s breath. This can give a pretty accurate picture of how much CO2 is in a patient’s arteries. However, there are several factors that can affect this relationship. Thanks to advancements in technology, these CO2 measurements have become widely used in healthcare for different purposes.
Though various types of CO2 detectors essentially measure the same thing—that is, how much CO2 a patient breathes out—there are some key differences in design. Detectors fall into two categories: qualitative and quantitative. Qualitative detectors simply show whether CO2 is present or not. The easiest type to understand is the colorimetric detector. It changes color as the gas flows through a special film in the patient’s airway tube. Qualitative detectors are mainly used to verify correct placement of a patient’s breathing tube by detecting whether there is or isn’t any exhaled CO2. These types of detectors are generally straightforward, lightweight, portable, and don’t need a power source.
On the other hand, quantitative detectors measure the actual level of CO2 a patient exhales, so they can provide more detailed information. They are broken down into capnography and capnometry. Capnography produces a graph of CO2 levels, while capnometry displays the CO2 concentration as a number. A graph can give healthcare providers even more insight into a patient’s health.
Detectors can also be categorized based on where they’re placed in a patient’s airway. Mainstream detectors are directly in the patient’s gas flow path and use a special sensor to produce real-time CO2 graphs. These are usually more expensive and are mainly used for patients who are intubated (have a breathing tube). Sidestream detectors are set up off to the side of the main gas flow. They often use a small tube to sample the gas. This type of setup is typically used for monitoring CO2 from a patient’s nose.
It’s important to note that there are some potential drawbacks and considerations when using CO2 detectors. Substances like vomit, frothy secretions from a condition called acute pulmonary edema, mucus from pneumonia, or even moisture can make CO2 detectors stop working. The special paper used in colorimetric units is especially sensitive to fluids. Mainstream detectors can increase the amount of undesirable dead space due to their direct placement in the patient’s airway. And because the sensor in sidestream detectors isn’t located directly in the airway, there can be a slight delay in measurement compared to mainstream detectors.
Anatomy and Physiology of Carbon Dioxide Detector
The image shows a typical CO2 (carbon dioxide) graph that you might see from a device called a mainstream capnograph. A capnograph is a medical device that measures the amount of carbon dioxide in the lungs. The graph has different paragraphs labelled A – E, each representing different steps of breathing.
Firstly, Phase A illustrates the first stage of exhaling, where breath from the ‘dead space’ (parts of the lungs where no gas exchange takes place) reaches the detector of the device. This breath doesn’t contain any CO2, so the graph part is flat.
Phase B shows a rapid increase in CO2 as the exhalation continues, reflecting a mix of the ’dead space’ breath, which has no CO2, and the breath from the air-exchanging part of the lungs.
Phase C shows a more constant CO2 level over time, representing the breathing out of air from the lungs. Point D shows the highest level of CO2 (end-tidal CO2) during the breathing cycle, which happens at the end of breathing out.
Phase E represents the quick drop in CO2 levels that happens when you start to breathe in again. This fresh air doesn’t have much CO2, so the line on the graph drops to the bottom (baseline).
Changes in this standard graph can be hints to the doctor that the patient’s health is changing. Faster breathing (hyperventilation) usually shows on the graph as more frequent waves in a short time, along with a depressed wave. Slower breathing (hypoventilation) can occur in at least 2 common forms. One is bradypnea hypoventilation, where the slower breathing rate leads to a graph with fewer waves and a higher ETCO2 level. The other instance, hypopneic hypoventilation, shows a lower ETCO2 level, due to the patient taking less deep breaths than normal. Even though these are both forms of slower breathing, one results in a higher ETCO2 level, and the other results in a lower ETCO2 level.
What Else Should I Know About Carbon Dioxide Detector?
Procedural sedation and analgesia (PSA), which is sometimes known as “conscious sedation”, involves administering medication to help patients relax (sedation) and block pain (analgesia) during certain procedures. A common practice during this treatment is end-tidal CO2 monitoring, which helps doctors detect if a patient’s breathing slows down or stops (“respiratory depression”) because of the administered medications.
There’s a range of sedation levels – from mild (just enough to relax the patient) to deep (where the patient needs support to breath and might need help maintaining blood pressure). It’s crucial to note that while PSA is designed to help keep a patient’s heart rate and breathing stable, the medications involved can sometimes cause side effects, including lower blood pressure, loss of protective reflexes in the throat (“airway reflexes”) which prevent choking, and slower or harder breathing.
Respiratory depression is one of the main risks when using PSA. To detect hypoventilation (when breathing becomes slower and shallower), continuous CO2 monitoring is often used. Previously, oxygen saturation was used as an indicator to measure a patient’s breathing, but if extra oxygen is being administered during the procedure, it could be a late signal.
Specialty societies, which are expert groups in different fields, have various recommendations about CO2 monitoring. Some argue that there isn’t enough evidence to show that CO2 monitoring makes a significant difference in patient outcomes, whereas others believe CO2 monitoring is essential, especially during moderate and deep sedation. CO2 monitoring adoption might be slow, especially outside of operating rooms, due to reasons like lack of evidence, lack of available equipment, and need for special training.
CO2 detection doubles as an accurate method to confirm the correct placement of an endotracheal tube – a device that helps patients breathe during surgeries or serious illness. An accurate CO2 waveform indicates that the tube is properly placed. If the wrong placement is indicated, it could mean that the tube is not inside the trachea (the part of the windpipe that leads to the lungs) but elsewhere, which could affect breathing.
Continuous CO2 monitoring is also useful for identifying if the endotracheal tube gets displaced during patient movement or if blockages occur due to bending or mucus. This ensures that any sudden loss in the CO2 waveform, which could signal an issue, is detected swiftly.
In emergency situations like cardiac arrests, where the heart suddenly stops beating, immediate CPR (Chest compressions and artificial ventilation) helps generate enough blood circulation to create a CO2 waveform. The presence and strength of the CO2 waveform can indicate the effectiveness of the CPR. If there’s no CO2 detected, then it means CPR is not working properly. This reading helps medical staff know when chest compressions need to be improved or when to switch to another person performing CPR, based on their exhaustion level.
Additionally, an increase in CO2 levels can signify the restart of spontaneous heart activity. Lastly, end-tidal CO2 values can aid doctors in deciding when it might be appropriate to stop resuscitation efforts. This reading can be a crucial point of consideration in emotionally and medically challenging decisions like stopping CPR.