Chapter 12. Confirmation of Endotracheal Intubation

This chapter will review the various methods utilized to confirm appropriate endotracheal (ET) intubation. Direct visualization of the ET tube passing through the vocal cords is the preferred method for the initial assessment of a properly placed airway. Unfortunately, this is not always feasible. Rates for incorrect ET tube placement have been noted to be up to 25%.1,2 The verification of correct ET tube placement is as or more important than the intubation procedure. Lack of proper confirmation of ET tube placement has the potential for serious patient harm and catastrophic outcomes if unrecognized and uncorrected.

For approximately 20 years, there has been ongoing research and development to improve upon the basic techniques of physical examination confirmation of ET intubation. Physical examination with auscultation has been found to be inadequately sensitive (94%) and specific (83%) as an independent method for confirmation of correct ET tube placement.3 This chapter discusses the use of physical exam findings, esophageal detection devices (syringe and bulb), carbon dioxide (CO2) detection devices (a qualitative detector and a continuous quantitative monitor), and imaging techniques (radiography and ultrasound). Each method is described for a patient with normal anatomy and the absence of any pathology (e.g., neck or chest trauma). While all these methods can be used in all patients, certain patient conditions or pathology may affect the accuracy of some methods. No single method is universally or completely reliable, obviating the need for a multiple method approach. This multiple method approach to confirmation of ET intubation is now the accepted practice according to The American College of Emergency Physicians (ACEP) Board of Directors policy statement as of April 2009.4

Since the advent of ET intubation, the use of physical examination methods has been the mainstay for the initial evaluation of proper ET tube placement. Direct visualization of the insertion of the ET tube through the vocal cords and into the trachea is the first method to confirm proper ET tube placement. Postintubation direct visualization of the ET tube using laryngoscopy or bronchoscopy, noting tracheal rings past the end of the ET tube, is the next best method of assessing correct ET tube placement.

Secondary methods for confirmation of ET intubation are an absolute requirement. Auscultate the chest and abdomen to assess for delivery of air to the lungs via either a bag-valve device or a mechanical ventilator (Figure 12-1). First, auscultate over the epigastrium to assess for the absence of sounds in the stomach. The presence of an enlarging abdomen or audible air inflation into the stomach with each positive-pressure ventilation may be the initial sign of an ET tube in the esophagus or an esophageal intubation. The next auscultation points are located at the chest wall lateral to the nipples. Auscultate bilaterally from top to bottom for the presence and equality of breath sounds. Avoid auscultating over the central portion of the chest. This may lead to the misinterpretation of the transmission of esophageal or gastric inflation.5 These sounds may mimic airway breath sounds and lead to failure in detecting an esophageal intubation.

The final note pertaining to auscultation involves equality of breath sounds. The anatomy of the left and right mainstem bronchi allow for a preferential right mainstem bronchial intubation when the ET tube is placed too deep. As a general rule, insertion in centimeters to a depth three times the diameter size of the ET tube (e.g., 21 cm for a 7.0 mm size ET tube) at the level of the incisor teeth is preferred. This will generally place the ET tube approximately 3 to 4 cm above the carina in an adult.6 If breath sounds are stronger over the right lung fields, deflate the ET tube cuff and gradually withdraw the ET tube in 1 cm increments until the bilateral breath sounds are equal. This will prevent complications from inadequate ventilation and oxygenation as well as resultant pulmonary edema in the nonventilated lung.7 Please refer to Chapter 11 for a more complete discussion of ET tube size, insertion depth, and placement for adults and children.

The next assessment involves taking a step back and visualizing the chest wall and ET tube characteristics with each breath. Unequal or a lack of chest rise and fall with each instilled breath may indicate a misplaced ET tube either in a mainstem bronchus or in the esophagus, respectively. Condensation and/or fogging in the ET tube with each breath has been used frequently in the past to confirm proper ET tube placement. This has been proven to be an unreliable source of confirmation.8 It should only be used in conjunction with auscultation and visualization of bilateral chest wall movement. The presence of vomit in the ET tube, in the absence of an aspiration event, may be a sign of an esophageal intubation.

The final postintubation physical assessment is an evaluation of oxygenation via skin signs and, more reliably, pulse oximetry. Cyanosis and a downtrending oxygen saturation seen on a pulse oximeter are delayed findings. The patient may experience significant hypoxemia before cyanosis appears or before there is a significant drop in the pulse oximetry. Do not rely upon cyanosis and pulse oximetry as a first-line assessment to confirm proper ET tube placement.

Esophageal manometer devices utilize the structural differences between the trachea and esophagus in determining correct ET tube placement. The semicircular tracheal cartilaginous rings provide a constant open passage for the flow of air. The tubular esophagus with its lack of a luminal support structure collapses and prevents movement of air when suction is applied.9 The two types of ET tube confirmation devices that rely on this anatomical variance are the syringe and the manometer or bulb methods (Figures 12-2 & 12-3).

The syringe method relies on a gradual and constant retraction of the plunger, while its tip is attached to the proximal end of the ET tube utilizing a manufactured connector (Figure 12-3).10 The plunger will draw back easily and without resistance if the ET tube is correctly placed in the trachea (Figure 12-3A). The volume of aspirated air should be greater than 30 mL over a period less than 4 seconds.11 Resistance when drawing back the plunger is seen when the distal end of the ET tube is incorrectly placed in the esophagus (Figure 12-3B). An airtight seal must be created between the syringe and the ET tube to prevent any air leak that would lead to a false-positive test and result in the assumption that the ET tube is in the trachea.

Similarly, the manometer or bulb method relies on the collapse of the esophageal wall. Compress the bulb to remove any air contained within. Firmly and securely apply the bulb to the proximal end of the ET tube while still compressing the bulb. Release compression on the bulb. If the bulb inflates fully and easily, the ET tube is presumably in the trachea. If the bulb does not inflate fully and easily, the ET tube is presumably in the esophagus.

There are numerous circumstances with which an esophageal detector device has repeatedly failed to identify an improperly placed ET tube.9–14 Most notably is after bag-valve-mask ventilations in the absence of cricoid pressure. The stomach and esophagus can inflate with air and allow for easy flow of air into the device simulating airflow from the airway. The device may fail to detect a misplaced ET tube when the distal end of the ET tube is just above the vocal cords. In this instance, there is no resistance to airflow and the bulb or syringe device easily fills with air.

This method has been shown to falsely identify an esophageal intubation when the ET tube is placed into a mainstem bronchus or the tip of the ET tube is pressed against the tracheal wall. The subsequent resistance to back flow of air into the syringe or bulb mimics that of the collapsed wall of the esophagus. If this should occur, withdraw the ET tube 1 cm and attempt using the esophageal detector device again. Repositioning should continue to result in resistance to aspiration or bulb inflation if the ET tube is in the esophagus. The presence of heavy or thick pulmonary secretions or fluid in the lungs can plug the airways and reduce the flow of air to prevent air aspiration by the syringe or bulb inflation.12 Care must be taken so as not to rapidly aspirate and potentially draw the tracheal mucosa into and obstructing the ET tube yielding a false-negative result.11 In the obese patient, the posterior noncartilaginous segment of the tracheal has been shown to collapse into the trachea and prevent the flow of air.13–16

When taking into account the limitations of esophageal detection devices and their use as an adjunct to other methods, they can provide a rapid and inexpensive method for confirming ET tube placement.17–19 This is especially evident in the patient with circulatory collapse, hypotension, cardiac arrest, or a pulmonary embolism where other devices are limited.18

Since 1985, the utility of end-tidal CO2 detection as a means for confirming proper ET intubation has been studied and recently confirmed to be the “most accurate” modality according to ACEP.20 The premise of end-tidal CO2 detection devices requires the presence of exhaled CO2 passing through and exiting the ET tube. Adequate circulation is required for CO2 to be produced and transported from the lung parenchyma. The accuracy of this modality relies on its use in the noncirculatory collapsed/cardiac arrest patient. The April 2009 ACEP Board of Directors statement goes further to state that end-tidal CO2 detection, using either qualitative or quantitative methods, approaches 100% sensitivity and specificity in the patient with an inflated cuffed ET tube and spontaneous circulation. Nearly every case of a false-negative detection of a correct ET tube placement (i.e., correct ET tube placement in the absence of end-tidal CO2 detection) has been discovered in the cardiac arrest patient.15,16,21–25

End-tidal CO2 detection devices can be utilized either qualitatively as a one-time spot check using a colorimetric detector or can be monitored continuously via capnography. Both are utilized in a similar fashion. They are in-line devices that have two connectors, one of which attaches to the proximal end of the ET tube and the other attaches to the oxygen delivery device (bag-valve device or mechanical ventilator tubing).

The colorimetric end-tidal CO2 detector utilizes a piece of pH-sensitive material that lies beneath a clear plastic window. The presence of CO2 flowing through the device, typically using six manual breaths as the maximum number needed and the minimum amount to clear any gastric CO2, causes a color change from purple to yellow that then changes back to purple in the absence of CO2 (Figure 12-4). The minimum concentration of end-tidal CO2 required for a color change is 0.5%. This is one reason that the recent literature has focused on whether newborns and children produce sufficient quantities of end-tidal CO2 for accurate detection.

Capnography, or continuous quantitative graphical demonstration of end-tidal CO2 detection, involves placement of an infrared detector in-line between the end of the ET tube and the oxygen delivery device (bag-valve device or ventilator tubing). The infrared detector is then connected with a cable to the electronic monitor that interprets the reading and generates a waveform representation of the end-tidal CO2 levels. One of the advantages of this method over the qualitative approach is the ongoing monitoring of CO2 production. This allows a continuous assessment of the airway as well as the overall quality of resuscitative efforts with some determination of outcome.3

The main disadvantage CO2 detectors for confirmation of ET intubation are false-negative results in poor perfusion states, cardiopulmonary arrests, and the presence of secretions on the device. In the noncardiac arrest patient with adequate cardiac output and pulmonary flow, sensitivities approach 100% (76% in cardiac arrest) for ruling out esophageal intubation have been found in patients of all ages.26–28

If the distal end of the ET tube is located just above the vocal cords in the hypopharynx, a false-positive result may lead the physician to believe the airway is secure. The device may detect adequate levels of CO2 without a properly secured and definitive airway in the trachea. False-positive results from an improperly placed ET tube erroneously believed to be in the trachea may occur when the device is used a short time after the patient has consumed a carbonated beverage. The device cannot recognize that the CO2 is actually coming from the stomach.

The universal presence of capnography is not yet a reality. Its utility in most circumstances with few exceptions is undeniable. The colorimetric end-tidal CO2 detector is equally reliable to capnography. It is a disposable, rapid, less expensive, and more widely available means to assess proper ET tube placement in the noncardiac arrest patient.20

Although there may be a lack of availability of capnography in most Emergency Departments, this is far less an issue with either radiography or ultrasonography.29 These methods, unlike those mentioned previously, are unique in that they rely on anatomic relationships for confirmation of ET tube placement. Radiography and ultrasonography may be particularly useful in the cardiac arrest patient.

The main utility for radiography in the confirmation of ET intubation lies in its ability to detect whether the ET tube is placed too deeply into the trachea. Locating the end of the ET tube approximately 3 to 4 cm above the carina may prevent some of the complications associated with a right mainstem intubation. The postintubation chest radiograph can assist in identifying any complications that may have resulted during the intubation. This includes aspiration, tracheal injury, a pneumomediastinum, or a pneumothorax. The postintubation chest radiograph does little to distinguish between esophageal versus tracheal intubation. The delay in obtaining a radiograph to confirm ET tube placement puts the patient at significant risk.

The use of ultrasound (US) in the Emergency Department has gained significant popularity in the diagnosis of various diseases and pathology. There are multiple methods for utilizing US guidance to assess for proper ET tube placement. Two common methods of confirming proper ET tube placement are described below. The benefits of these two methods are that ventilation is not required for ET tube placement confirmation and, in the case of an accidental esophageal intubation, there is no risk of inflating the stomach, or its resultant emesis and aspiration of gastric contents.

The first method uses a high frequency linear US transducer. Place the US probe horizontally at the level of the suprasternal notch. A properly placed ET tube in the trachea will show the shadowing of the ET tube posteriorly without direct visualization of the esophagus (Figure 12-5A). In the event of an esophageal intubation, the trachea appears similarly to the previously described image but the esophagus will be visualized just to the left of the trachea with posterior shadowing due to the presence of the ET tube (Figure 12-5B). A small, prospective, randomized, controlled study found 100% sensitivity and 100% specificity in the accuracy of US as a modality to confirm ET tube placement.30

The second technique uses similar methodology over the cricothyroid membrane. Place the US transducer longitudinally over the cricothyroid membrane to identify and the hyperechoic anterior and posterior laryngeal walls are identified. The appearance of a “snowstorm” pattern between the two lines indicates correct ET tube placement.31

Foreign bodies are often hyperechoic and appear bright white on US. One study looked at using US to confirm ET tube placement both with and without a stylet within the ET tube.34 The basic idea being the addition of the stylet would increase the sensitivity and specificity of identifying correct ET tube placement. It would add additional hyperechoic shadows to those of the ET tube. The use of a stylet did not improve the US localization of the ET tube within the trachea.

Ultrasonography of the chest wall has been studied as a method of confirming ET tube placement.32 This method does require ventilation of the patient in that it utilizes the visceral–parietal pleural interface of the lungs to confirm inflation of the lung. Apply the US probe to the anterior-superior chest wall. Orient the US probe vertically over the second and third ribs in the midclavicular line. The visceral and parietal pleural interface can be seen and appreciated as the so-called “sliding lung sign” (Figure 12-6). The hyperechoic interface will be seen moving back and forth with each respiration.32

The tracheal tube introducer (TTI) or gum elastic bougie has long been used by Anesthesiologists to intubate in difficult conditions. The TTI is a flexible rod-like device whose distal end is slightly angled. It is inserted through the patient's vocal cords with the angled tip facing anteriorly during direct laryngoscopy. It is then advanced into the trachea. Advancement of the TTI causes the tip to slide along the anterior tracheal cartilage rings. A “click” is palpable as the tip crosses each tracheal ring. Eventually, the TTI will stop or “hang-up” as it passes into smaller bronchi. The ET tube is then advanced over the TTI and into the lung.

Intubate the patient using direct laryngoscopy. To verify proper positioning of the ET tube, insert the lubricated TTI into the ET tube with the angled tip facing anteriorly. Advance the TTI through the ET tube. The tip should catch on each tracheal ring and “click” to verify proper ET tube position. The lack of any “clicks” or “hang-up” suggests an esophageal intubation. Like all other methods of confirming ET intubation, this method is not 100% perfect.33

Insertion of an ET tube always requires verification that it is properly placed. No one tool or technique is sufficient for any or all situations or circumstances. The best method to confirm proper ET tube placement involves utilizing multiple methods, keeping limitations in mind, and ongoing repeat assessments. Any change in a patient's clinical condition requires reverification that the ET tube is still properly positioned. The ongoing research and development of improved methods obviates the critical importance of rapid and accurate confirmation of ET intubation.