“An esophageal intubation is no sin, but there is great sin in not recognizing such a placement.” — Special Operations Combat Medical Skills Sustainment Course (U.S. Special Operations Command)

How hard is it take to properly intubate the trachea? Actually, it’s far more difficult than most people think. Recent anesthesia research shows that at least 75 live adult intubations are needed to achieve a 90% initial competency.1 Yes, 75! Not the very limited live number that are experienced in many paramedic schools, and certainly not only practicing with manikins.

And how hard is it to intubate the esophagus? Unfortunately, way too easy.

So, when faced with the need to secure an airway in emergency situations, how likely is it that the tube will end in the proper place?

If you’re a pessimist at heart (or possibly a realist), the odds seem pretty good for a misplaced tube. That’s not a good thing. After all, having a patent airway is critical to breathing—and life in general.

How do we increase the odds in our favor? Well, certainly practice, practice, practice would be a key. The other thing we need to do is use the tools at our disposal to verify proper tube placement, and we must trust the findings that those tools provide.

And this applies not occasionally, not most of the time, but rather, we need to use the tools and trust the results with every tube, every time, and with every major move.

How do we verify tube placements? What evidence are we looking for, and what tools do we have on hand that will provide that evidence and confirm that the tube is actually in the right place?

Let’s begin with one basic concept: Carbon dioxide (CO2) should be present in exhaled air, and only there. So, if we have a method or a tool that enables us to detect CO2 and attach it to an artificial airway device, the presence or absence of CO2 in the exhaled breath, referred to as end-tidal carbon dioxide (EtCO2), would provide a very high level of confidence that the airway was properly placed (i.e., presence of CO2) or improperly placed (i.e., absence of CO2).

Well, we have tools for verification of endotracheal tube placement with EtCO2 and they come in three categories:

  1. Colorimetric devices rely on materials which change colors in the presence (or absence) of CO2. These devices provide an indication of CO2 within a range of values, but don’t give specific numbers.
  2. Capnometric devices measure and display a numerical value for the concentration of CO2 at end of the exhalation phase of respiration.
  3. Capnography devices display a waveform in addition to the numerical values found with capnometry. The real-time waveform provides us with a picture of both respiratory rate and depth as well as ventilatory effectiveness.

Colorimetric Considerations           

Whether one remembers that “gold is good” or “yellow is mellow” (indicating that the endotracheal tube is in the right spot), or that “blue is bad” or “purple paper means purple patient” (indicating that the endotracheal tube is in the wrong place, or something worse), colorimetric devices can be useful in evaluating placement.

The colorimetric CO2 detector has a plastic housing which contains a pH-sensitive chemical indicator that undergoes color changes with each inspiration and exhalation, thus reflecting the change in CO2 concentration.

These devices aren’t reliant on any power source and easily fit in a pocket or small jump bag. In the absence of other CO2 detecting technology, depending on the manufacturer, colorimetric devices can be reliable for from to 2–24 hours of continuous use.

Colorimetric devices should turn yellow when an endotracheal tube or another alternative airway is properly inserted into a patient with intact circulation. These devices start at baseline color when minimal CO2 is present and undergo gradual color change with increasing CO2 concentration.

These devices provide semi-quantitative, on-going EtCO2 monitoring by detecting breath to breath color changes through the metacresol purple on filter paper which acts as a pH indicator and changes from purple to yellow in the presence of CO2.

Figure 1: Colorimetric EtCO2 Device
Image courtesy Mercury Medical

Colorimetric devices have several drawbacks when compared to other forms of EtCO2 monitoring. They provide no numeric or waveform data, no numbers to validate findings, and no alarms for clinicians. In addition, they’re easily contaminated and can be difficult to read in the dark or by color-blind providers.

Colorimetric devices can also give false readings. False positive readings (suggesting a correct placement when the tube is in the esophagus) can occur when the device is contaminated with acidic substances such as gastric acid.

The most common example of this would be vomitus in the airway (natural or otherwise). Contamination can also occur in the rare causes of endotracheal administration of lidocaine or epinephrine.

Furthermore, these devices may not provide an accurate reading if the detector is expired, clogged with secretions, or if the package has been open to air for more than a few minutes prior to use.

Another drawback to the use of colorimetric devices is the potential for a false-positive reading when intubation is performed shortly after the patient has consumed a quantity of any carbonated beverage (which contains CO2).

When providing ventilations to confirm initial tube placement, CO2 present within the stomach can be expelled from the relaxation of the esophageal sphincter yielding the false-positive reading on the device.

Additionally, the recent ingestion of calcium carbonate products (e.g., Tums, Rolaids, etc.) can result in the same false-positive readings. This occurs when these over-the-counter medications are digested and the breakdown of the calcium carbonate forms calcium oxide and carbon dioxide.

To provide greater reassurance of the accuracy of the color change, it is recommended that at least 6 breaths be given via the endotracheal tube to “wash out” any CO2, which may have entered the airway from the belly before confirming the placement of the tube through breath-to-breath color changes on the colorimetric device.

False-negative results (suggesting improper placement when the airway device is actually correctly located) can occur in the event of cardiac arrest, situations involving low pulmonary blood flow due to pulmonary emboli, or in cases of a large alveolar dead space condition.

These erroneous findings can be due to the lack of enough CO2 in the lungs for detection by the colorimetric device and would result in the clinician not seeing a colorimetric change despite positive clinical assessment findings (e.g., symmetrical chest rise and fall, bilateral breath sounds, good compliance with your bag-valve devices, and changes in skin parameters). It’s always important to correlate your clinical assessment findings with the device findings and be aware of their limitations.

One final consideration with the use of any colorimetric devices is the use of one when faced with a pediatric airway emergency. Any patient under the weight of 15 kg (or other specific manufacturer recommendation) requires the use of an infant or pediatric colorimetric device. For any patient over 15 kg, the adult colorimetric device may be used. Failure to utilize the correct size device has the potential to result in false results and tragic consequences.

Capnometry and Capnography

Capnometry, like capnography, is the continuous analysis and recording of the CO2 concentration in exhaled respiratory gas. (The name comes from the Greek word Kapnós, which translates in English to “smoke.”)  The technology behind capnometry and capnography provides a breath-to-breath clinical picture of your patient’s condition.

Most capnometers are small, battery-powered devices that can easily fit in the palm of your hand. They provide digital read outs of EtCO2 and often display the respiratory rate as well.

Figure 2: Capnometer
Image courtesy Masimo

Although capnometry provides only numerical output, capnography provides both numerical and waveform displays, providing additional information about the patient’s condition.

In addition to initial/ongoing verification of correct airway placement, waveform capnography is also commonly used in the assessment of pulmonary circulation, respiratory status and in the optimization of mechanical ventilation.

Figure 3: Normal capnography waveform

Figure 4: Capnography waveform indicating proper tube placement
Image courtesy Bob Page

Figure 5: Capnography flat line indicating improper tube placement
Image courtesy Bob Page

Capnography is used for respiratory monitoring in the same way that ECGs are used for cardiac monitoring. It is the 12-lead of the lungs. Waveforms are good … flat lines are bad!

Much as with colorimetric devices, false-positive results can occur after the recent consumption of carbonated beverages (including beer) or common over-the-counter antacids. However, if the tube is correctly placed in the trachea, after just a few breaths, the waveform should continue indicating true positive results versus the waveform flattening if the tube is misplaced. False-negative results can occur in cardiac arrest states, low pulmonary blood flow states due to pulmonary emboli, or in the case of a large alveolar dead space condition.

To avoid this type of error, in cases where low perfusion is suspected or known, you may need to adjust your machine’s EtCO2 scaling down to 0–20 mmHg from the common default setting of 0–50 mmHg. Reducing the scale’s range will increase the visibility of changes in the readings, allowing low perfusion (< 10 mmHg) conditions to show a big enough waveform to be easily recognizable.

It’s important to note that during cardiac arrest resuscitation efforts, hands-only CPR won’t move enough air in and out of the body to facilitate a full gas exchange, where CO2 is emptied from alveoli and purged from the airways. Therefore, compressions and ventilations are required for endotracheal tube placement verification.

The technology that measures EtCO2 needs to have a minimum sample size to assure an accurate reading and produce a waveform necessary for tube confirmation. So, with a cardiac arrest patient, you must ventilate a normal tidal volume through the tube to assure the volume necessary to read the EtCO2.

Without sufficient quantities of CO2 available during exhalation, the clinician may not see a waveform despite clinical assessment findings (e.g., symmetrical chest rise and fall, bilateral breath sounds, good compliance with your bag-valve devices, and changes in skin parameters).

Always correlate your clinical assessment findings to the device findings and be aware of their limitations.

One final consideration is that the CO2 detection device must match the size of the endotracheal tube or alternate airway used. Pediatric patients with endotracheal tube sizes or alternate airway devices of 4.5 mm or smaller require the use of a special neonatal-infant capnometry or capnography adaptor (or per specific manufacturer recommendations). For patients with endotracheal tubes 5.0 mm or larger, the pediatric-adult capnography device should be used.

Failure to utilize the correct size device has the potential to result in false results and tragic consequences. If you have a teeny tiny patient with a teeny tiny tube, use a teeny tiny adaptor.

Figure 6: Capnographic EtCO2 adapters with backup/alternate airways
Photo courtesy Pedi-Ed-Trics


Ongoing confirmation of proper placement of an airway device is critical. Whether by a colorimetric device, capnometry, or, ideally, capnography, the tools should always be available and always be used. Note that there’s no mention of when this confirmation should take place. That’s because it’s essential to ensure that the tube is in the right spot and stays in the right spot. Each time, every time, all the time!

As a healthcare provider, it’s essential to know your equipment, its uses and its limitations. You’re responsible for understanding not only how and why these tools work, but also how and why they might not work. You’ll use that knowledge to guide your actions when unexpected results or situations occur. In other words, you must use your tools and trust the technology!

In part 2 of this article, we explore some real-life situations which demonstrate the medical-legal consequences when airway confirmation tools were either not used, or the technology wasn’t trusted.


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