Confirmation of correct endotracheal tube placement in adults

INTRODUCTION — 

Confirmation of endotracheal tube (ETT) placement in the trachea is required immediately after intubation. An unrecognized incorrectly placed ETT can result in hypoxemia, and ultimately hypoxic encephalopathy or death. Placement of ETTs into incorrect anatomic positions can occur in all practice settings including the emergency department, intensive care unit, and operating room [1]. Objective means of placement confirmation (eg, waveform capnography, flexible intubating scope) have supplanted historically used approaches (eg, misting in the tube, chest auscultation, chest rise), which have proven to be unreliable, both individually and collectively.

This topic will discuss best practices for confirming correct ETT placement within the trachea in adults. Confirmation of ETT placement in children and neonates is discussed separately. (See "Technique of emergency endotracheal intubation in children", section on 'Confirming tube position' and "Neonatal resuscitation in the delivery room", section on 'Endotracheal intubation'.)

Techniques for tracheal intubation are discussed separately.

●(See "Direct laryngoscopy and endotracheal intubation in adults".)

●(See "Videolaryngoscopes and optical stylets for airway management for anesthesia in adults".)

●(See "Flexible scope intubation for anesthesia".)

●(See "Awake tracheal intubation".)

LOCATIONS OF ENDOTRACHEAL TUBE PLACEMENT — 

The correct location for an ETT for adult patients is within the trachea, with the tip 3 to 5 cm above the carina when the neck is in the neutral position (image 1). The rationale for this depth is to avoid migration of the ETT proximally to above the vocal cords or distally into a mainstem bronchus with neck motion. Neck flexion moves the tip of the ETT closer to the carina and neck extension moves the tip closer to the vocal cords (figure 1) [2].

Incorrect ETT placement can occur as follows (figure 2):

●Esophagus – The most dangerous incorrect location since no ventilation or oxygenation occurs.

●Supraglottic space, above the laryngeal opening – Although some ventilation and oxygenation may occur if the tip of the ETT is above the laryngeal opening, the tube is not located securely within the trachea and can migrate into the esophagus. There is no protection from aspiration of oral or gastric contents into the trachea and lungs.

●Mainstem bronchus – Only one lung will receive ventilation. This can result in hypoxemia and barotrauma.

INCIDENCE OF UNRECOGNIZED ESOPHAGEAL INTUBATION — 

Despite technologic advances in detecting ETT location, unrecognized esophageal intubation continues to occur in all practice settings, is usually judged to be avoidable, and can result in poor patient outcomes including death and hypoxic encephalopathy [1,3-6]. Since most estimates are based on very few events, the true incidence of unrecognized esophageal intubation is unknown.

Unrecognized esophageal intubation is likely rare during anesthesia for surgery or other procedures and more common in other settings. In reports to the 4th National Audit Project (NAP4) of the Royal College of Anaesthetists and Difficult Airway Society in the United Kingdom, unrecognized esophageal intubation resulting in severe harm (brain damage or death) was estimated to have occurred in 1 in one million tracheal intubations in the operating room, 1 in 15,000 in the intensive care unit, and 1 in 10,000 in the emergency department [5,6]. Of the nine reported instances, seven resulted in brain damage or death.

Unrecognized esophageal intubation may be more common during prehospital emergency intubation. Rates reported in observational studies vary widely, from 0.3 to as high as 17 percent [7-15].

CONFIRMING TRACHEAL INTUBATION — 

Following tracheal intubation, prompt confirmation of endotracheal tube placement is required. We recommend using detection of exhaled carbon dioxide (CO₂) to confirm tracheal placement of the ETT, rather than relying on chest auscultation and/or visualization of the ETT passing through the vocal cords. If flexible bronchoscopy is immediately available, using it for confirmation is a reasonable alternative for clinicians experienced in its use.

For confirmation of tracheal placement of the ETT, we suggest using waveform capnography when available rather than other forms of exhaled CO₂ detection. If waveform capnography is unavailable, digital capnometry is a reasonable alternative. Colorimetric CO₂ detection should be used if waveform capnography and digital capnometry are not available (algorithm 1).

During tracheal intubation, the ETT is ideally visualized passing between the vocal cords into the laryngeal opening. This provides confidence that the tube is correctly placed in the trachea, but tube misplacement can occur even when the operator believes they saw the tube pass between the vocal cords [1]. (See 'Pitfalls of laryngoscopy confirmation' below.)

Preferred: Waveform capnography — We suggest using detection of exhaled CO₂ with waveform capnography (when available) in patients with or without cardiac arrest rather than other methods to confirm tracheal placement of the ETT. Studies have consistently found the sensitivity and specificity of waveform capnography for tracheal placement to be approaching 100 percent [16-21].

Waveform capnography devices measure the partial pressure of CO₂ in exhaled gas and display the result as a waveform of CO₂ concentration over time on a monitor (picture 1). A normal CO₂ waveform consists of four phases and is shown in the figure (figure 3). End-tidal CO₂ (EtCO₂), the highest quantitative CO₂ value during exhalation, is typically displayed on the monitor next to the waveform. Operation of capnography monitors and the phases of CO₂ waveforms are discussed in detail separately. (See "Carbon dioxide monitoring (capnography)", section on 'Principles of operation'.)

Following intubation, the sustained presence of a CO₂ waveform with all four phases confirms that the ETT is in the trachea. We agree with consensus guidelines that the criteria for sustained presence of exhaled CO₂ requires all of the following [1] (algorithm 1):

●The wave rises during exhalation and falls during inspiration

●The amplitude is consistent or increasing over seven breaths

●The peak amplitude is >7.5 mmHg (1 kPa) over baseline

●The reading is clinically appropriate

Rise and fall of expired CO2 — An ETT placed in the trachea will produce a capnography trace that rises during exhalation and falls during inspiration and continues to rise and fall during ongoing ventilation. An ETT placed in the esophagus can also produce a CO₂ tracing for one to five breaths by detecting gastric CO₂, but the amplitude would not be consistent or increasing (figure 4) [22,23]. In several studies, the presence of a valid CO₂ waveform on the seventh breath had 100 percent sensitivity and specificity for tracheal placement [18,21]. The CO₂ readings for the first few delivered breaths should not be relied upon for ETT confirmation.

Peak amplitude — A peak amplitude threshold of 7.5 mmHg (1 kPa) over baseline is sensitive to differentiate tracheal versus esophageal intubation in patients with normal physiology as well as critically ill patients in a low flow, pre-cardiac arrest, or even cardiac arrest state; a reading <7.5 mmHg should be presumed to indicate esophageal intubation under any physiology. The peak EtCO₂ following intubation is usually >30 mmHg [18,24]. EtCO₂ typically remains above 7.5 mmHg even in low-flow shock states caused by medical issues or trauma or in severe bronchospasm, with mean EtCO₂ values most often exceeding 15 to 20 mmHg [25-29]. Thus, an EtCO₂ between 7.5 and 15 mmHg that cannot be explained by the patient's physiology should be attributed to esophageal placement. EtCO₂ values in cardiac arrest are discussed below. (See 'Cardiac arrest' below.)

The peak amplitude should be compared to baseline since the CO₂ value may not return to zero if the patient is rebreathing CO₂, which is uncommon but can occur from mechanical complications of the ventilator or anesthesia circuit [30,31].

Clinically appropriate reading — The reading and waveform should be clinically appropriate. A waveform with abnormal morphology (eg, attenuated), however, can still satisfy criteria for sustained presence of exhaled CO₂ if the morphology is appropriate for the clinical context. As examples, an attenuated tracing can occur with use of an uncuffed ETT in a small child or from mechanical or technical issues with ventilation or the CO₂ monitoring setup (figure 4) [32]. Attenuated tracings can also occur from low pulmonary blood flow and cardiac output but would still be expected to rise and fall indefinitely with an amplitude >7.5 mmHg. Most patients have a normal morphology or morphology that can be explained by their cardiopulmonary pathology, such as obstructive lung disease (figure 5) or a low-flow state (N in (figure 4)). An attenuated or irregular tracing in the setting of normal physiology suggests esophageal intubation or a tube positioned above the vocal cords in the oro- or hypopharynx.

Waveform capnography unavailable — If a waveform capnography monitor is not available, we recommend use of an alternative device for detection of exhaled CO₂ (ie, digital capnometry or colorimetric CO₂ detection). Colorimetric detection is less accurate, particularly in patients in cardiac arrest. If flexible bronchoscopy is immediately available, it is a reasonable alternative to exhaled CO₂ detection for clinicians experienced in its use. (See 'Flexible bronchoscopy' below.)

Digital capnometry — Digital capnometers measure EtCO₂ and provide a digital readout but do not provide a waveform. These devices are often small and thus, portable. They are available as mainstream (placed directly between the ETT and the resuscitator bag or ventilator circuit) and sidestream (exhaled gas is diverted through tubing to a sensor, similar to conventional waveform capnography) devices. Given the useful information that can be obtained from waveform capnography, capnometers should only be used if waveform capnography is not available. Use of a capnometer to confirm tracheal intubation is similar to use of waveform capnography (algorithm 1).

Data reporting sensitivity and specificity are limited, but available data show that capnometers are slightly less sensitive than waveform capnography and have similar specificity of 100 percent [18,21,33]. In several studies of tracheal intubation in emergency situations in patients who were not in cardiac arrest, the sensitivity of digital capnometry was 97 to 100 percent [18,21,33]. Sensitivity is lower in patients in cardiac arrest as discussed below. (See 'Cardiac arrest' below.)

Criteria that confirm tracheal placement of the ETT with digital capnometry are similar to the criteria for peak expired CO₂ when using capnography: EtCO₂ >7.5 mmHg, and EtCO₂ consistent or increasing over seven breaths. (See 'Peak amplitude' above.)

Colorimetric CO2 detectors — Colorimetric CO₂ detectors use specially treated litmus paper that changes color when exposed to exhaled CO₂ (eg, purple for EtCO₂ <3 mmHg; tan for 3 to 15 mmHg; and yellow for >15 mmHg). When the patient is not exhaling, the color returns to purple, and these color changes occur with each breath. To ensure an accurate reading, the color must be visualized changing to yellow and back to purple over at least seven breaths. Most colorimetric devices, once opened, are valid for approximately two hours.

We use colorimetric CO₂ detectors only if waveform capnography and digital capnometry are not available. Colorimetric CO₂ detection is slightly less accurate than waveform capnography for confirming tracheal placement of an ETT, with estimates of sensitivity ranging from 97 to 100 percent [34-37]. In addition, waveform capnography provides additional information from the tracing. However, most studies have found colorimetric devices have 100 percent specificity (ie, esophageal ETT placement does not result in sustained color changes) [34-37]. Colorimetric devices are single-use and inexpensive, so may be appropriate for resource-limited settings, including the out-of-hospital environment.

There are circumstances in which a color change can occur with esophageal ETT placement and thus, falsely suggests a tracheal location.

●The esophagus or stomach may yield small but detectable amounts of CO₂ during the first few positive-pressure ventilations and turn the colorimetric device yellow. Thus, the clinician should ensure that the device color continues to change to yellow after seven breaths [38].

●The paper inside the colorimetric device can also be permanently converted to the color that indicates expired CO₂ if there is contamination with gastric secretions [39,40]. Thus, the clinician should ensure that the color of the device turns back when the patient is not exhaling. If there is doubt, the device should be discarded and replaced with a new device.

No CO2 detector available — Infrequently, CO₂ monitoring will be unavailable. Visualizing the ETT pass between the vocal cords during the intubation attempt should be considered only provisional evidence of correct placement. (See 'Pitfalls of laryngoscopy confirmation' below.)

Even more infrequently, the larynx cannot be visualized with a laryngoscope and there is no CO₂ detector available. For example, this might occur in a patient with upper airway distortion or copious oral body fluids for whom the CO₂ tubing has been fouled or the monitoring equipment is malfunctioning. In both situations supportive techniques should immediately be used to ascertain the ETT location. (See 'Supportive techniques to confirm tracheal placement' below.)

If both CO₂ monitoring and supportive techniques are not available, the patient should be carefully monitored. If the oxygen saturation drops, the tube should be removed and ventilation by facemask or supraglottic airway (SGA) performed.

Pitfalls of laryngoscopy confirmation — Laryngoscopy alone (either during intubation attempt or repeat visualization) should not be used to confirm correct ETT placement. Visualizing the ETT between the vocal cords and anterior to the arytenoid cartilages (also known as the posterior laryngeal cartilages) suggests correct placement in the trachea. However, evidence is limited regarding the accuracy of visualization to exclude esophageal intubation. There are reported fatalities in cases of esophageal intubation in which the tube position was rechecked using repeat laryngoscopy and felt to be in the trachea [1].

In addition, the anatomy can be easily misinterpreted, particularly when there is not full glottic visualization or the operator is inexperienced, hurried, or stressed. With a forceful anterior lift of a laryngoscope blade, the walls of the hypopharynx (ie, entrance to the esophagus) can become elongated and whitened, thus mimicking the glottis, particularly if the blade's tip is placed beneath and distal to the larynx (picture 2).

During the initial intubation attempt, a deliberate brief pause after passing the ETT and before removing the laryngoscope can help to visually confirm correct placement. However, it is sometimes not possible to visualize the larynx during or after attempted intubation, although this may be less likely with the use of video laryngoscopy.

Absent or equivocal exhaled CO2 (cannot confirm tracheal placement) — A patient with absent or equivocal exhaled CO₂ following attempted tracheal intubation should be presumed to have incorrect ETT placement until proven otherwise. This finding should not be attributed to an underlying medical condition (eg, bronchospasm or hypotension). We start with a very brief check for an obvious and quickly remediable equipment issue. Examples include an uninflated ETT cuff or a CO₂ detector that is not turned on or appropriately connected.

Subsequent management when CO₂ detection is absent or equivocal is discussed further here and summarized in the algorithm (algorithm 1).

●If at any time oxygen saturation falls without a clear alternative clinical explanation, remove the ETT and ventilate by face mask or SGA.

●When exhaled CO₂ is absent or equivocal, the default action should be to remove the ETT and ventilate by face mask or SGA with waveform capnography monitoring. In addition to reoxygenating and preoxygenating for another tracheal intubation attempt, this will help confirm that the waveform capnography equipment is functioning properly.

•If an adequate tracing is not visualized during presumptively effective ventilation by mask or SGA, troubleshoot the CO₂ monitoring equipment.

•Once a CO₂ tracing can be visualized, proceed with tracheal intubation. This allows confidence that a CO₂ waveform should be seen after tracheal intubation with proper ETT location.

•If a CO₂ tracing is never visualized during what appears to be effective ventilation, even after troubleshooting, this likely indicates an equipment malfunction, but can rarely occur from complete airway obstruction (eg, upper airway edema, foreign body aspiration, mucous plug), which is usually clinically obvious and will cause significantly increased resistance to ventilation.

•If there is no alternate capnography or capnometry equipment available, proceed with a repeat intubation attempt and use a supportive technique to confirm tube location. (See 'Supportive techniques to confirm tracheal placement' below.)

●For patients in whom there is strong expectation that the ETT is correctly placed (usually because the ETT was visualized passing through the vocal cords), and for whom removing the ETT is judged to be potentially hazardous, keep the tube in place and immediately use supportive techniques to confirm the location of the tube. (See 'Supportive techniques to confirm tracheal placement' below.)

It is potentially hazardous to remove an ETT if face mask or SGA ventilation has been or is predicted to be difficult or airway patency is deteriorating (eg, due to angioedema), or if the patient is at high risk of gastric regurgitation and aspiration.

In this setting, difficult intubation by itself should not be the basis for considering ETT removal hazardous. However, it is crucial to acknowledge that esophageal intubation is more likely during difficult intubation. It may be more hazardous to the patient to continue to attempt ventilation through an improperly placed ETT than to make another attempt at intubation.

●If esophageal intubation cannot be excluded with supportive techniques described below or sustained exhaled CO₂ has not been restored, remove the ETT and ventilate by mask or SGA with capnography monitoring.

●Complete absence of exhaled CO₂ (flatline waveform on capnography) can rarely occur if the patient has had prolonged cardiac arrest with diffuse cellular death (in which no CO₂ is produced because of an absence of cellular respiration and severely compromised alveolar CO₂ exchange). This is discussed below. (See 'Cardiac arrest' below.)

The exceedingly rare false negative capnography result can lead to unnecessarily repeat laryngoscopy and/or repeat removal and replacement of the ETT unless the clinician maintains a broad focus on the overall patient instead of narrowly focusing on the tracheal intubation procedure and its confirmation [1,41,42]. Focusing solely on absent or equivocal exhaled CO₂ may distract from identifying other pathology such as tension pneumothorax, airway obstruction, or equipment malfunction [41]. In some situations, it may make sense to delay reintubation and ventilate by facemask or SGA or to use supportive techniques while reassessing the overall clinical picture. Repeatedly performing tracheal intubation, checking for confirmation and finding none, then extubating, and so on, should be avoided.

Supportive techniques to confirm tracheal placement — These techniques by themselves (except for flexible bronchoscopy) may not reliably confirm correct ETT placement but can provide supportive evidence that the ETT is correctly placed in the trachea. These techniques are inferior to EtCO₂ detection by any method because they are either less sensitive or specific, or require special equipment and expertise. Thus, they should not be used as a substitute for CO₂ detection unless the latter is not available. If tracheal placement cannot be confirmed with exhaled CO₂, we suggest repeat visualization with a laryngoscope and using at least one other supportive technique described here (ie, flexible bronchoscopy, ultrasound, or an esophageal detector device).

In a patient with absent or equivocal exhaled CO₂, repeat laryngoscopy alone should not be used to confirm correct ETT placement. (See 'Pitfalls of laryngoscopy confirmation' above.)

Flexible bronchoscopy — Flexible bronchoscopy can be performed rapidly and is the only one of the supportive techniques described here that alone can confirm tracheal tube location. The equipment must be readily available and the clinician must have prior experience with use of the device. We still prefer to have additional confirmation with capnography or visualization of the ETT between the vocal cords with laryngoscopy.

For ETT confirmation, a flexible intubating scope or bronchoscope is passed through the ETT and beyond the tip of the tube. Visualization of the tracheal rings, the trachealis smooth muscle posteriorly, and the carina confirms tracheal tube placement (movie 1).

The sensitivity and specificity of flexible bronchoscopy for confirming tracheal intubation may be >95 percent [43-45], though there are limited available data. This method will be more difficult if the airway contains a significant amount of secretions or fluid, which can obscure the camera view.

Ultrasound — Point-of-care sonography can assist in determining the location of the ETT. During or immediately after the intubation attempt, a linear transducer is placed on the anterior neck in a transverse orientation. The trachea appears as a hypoechoic round structure [46]. The anterior aspect of the ETT appears as a hyperechoic line and may be easier to visualize if the ETT is rotated on its axis or wiggled back and forth during the scan.

●ETT located in the trachea – There is one hypoechoic round structure visualized and the hyperechoic curved line representing the ETT is inside it. The esophagus will not be visualized (image 2).

●ETT located in the esophagus – There are two hypoechoic round structures visualized and the hyperechoic curved line is inside the hypoechoic round structure lateral to the trachea, sometimes called the "second trachea." This represents the ETT in the esophagus (image 2).

A meta-analysis of 30 studies including 2534 patients who underwent sonographic ETT confirmation found the sensitivity for confirming tracheal ETT placement to be 98 percent (95% CI 97-99 percent) and the specificity to be 96 percent (95% CI 90-98 percent) [47]. Similar to flexible bronchoscopy, this technique requires prior experience to achieve high sensitivity [48].

If the operator does not clearly visualize the ETT passing between the vocal cords during intubation and post-intubation laryngoscopy does not clearly identify the tube positioned between the vocal cords, ultrasound may be used to obtain as much information as possible about the location of the ETT. However, in this setting ultrasound does not provide the same level of accuracy compared with having visualized the tube passing through the cords or with flexible bronchoscopy on its own, so monitoring the patient's clinical course and ventilation characteristics closely is essential.

Esophageal detector device — We suggest using an esophageal detector device only when methods for exhaled CO₂ detection are unavailable or as an adjunctive method when the waveform using capnography is absent or equivocal (algorithm 1). (See 'Absent or equivocal exhaled CO2 (cannot confirm tracheal placement)' above.)

The esophageal detector device uses suction applied with a syringe or a self-inflating suction bulb to distinguish between the trachea (which is rigid and allows a free flow of air into the device) and the esophagus (which is collapsible, permitting little airflow when brisk suction is applied).

A meta-analysis of 25 studies (3024 patients) that evaluated the use of esophageal detector devices found a false positive tracheal ETT placement rate of 5 percent, meaning that 1 in 20 patients with an esophageal intubation would not be correctly identified [49]. These devices may perform less well in adults with severe obesity [50,51], patients with obstructing pathology in the lower airway [52,53], advanced pregnancy [54], and infants of <1 year of age [55].

If the ETT cannot be visualized between the vocal cords and only an esophageal detector device is available, it should still be used to obtain as much information as possible about the location of the ETT. An esophageal detector device may be a helpful adjunct when the patient is in cardiac arrest with suspicion that little or no CO₂ is being exchanged.

No supportive equipment available — In some settings, no supportive confirmatory equipment will be available. When repeat laryngoscopy is undertaken by the initial intubator, confirmation of tube location with a laryngoscopic view alone may not be sufficient because tubes placed in the esophagus can appear to be in the trachea, especially in situations where there is upper airway distortion (eg, upper airway injury or angioedema) or difficult airway anatomy (eg, obesity). (See 'Pitfalls of laryngoscopy confirmation' above.)

Whenever possible, a second experienced clinician should perform repeat laryngoscopy, using a video laryngoscope, if one is available. If the ETT is visualized passing anterior to the arytenoid cartilages and between the vocal cords, this represents only provisional evidence of tracheal intubation. The tube can be left in place while the patient is carefully monitored. If the oxygen saturation drops without a clear alternative clinical explanation, the tube should be removed and ventilation by facemask or SGA performed, as described above.

EXCLUDING BRONCHIAL INTUBATION — 

After the endotracheal tube (ETT) is confirmed in the trachea (as discussed above), the next step is confirming its position within the trachea. An ETT may be malpositioned within the tracheobronchial tree (eg, close to the carina or in a mainstem bronchus) especially in children and in female patients undergoing urgent tracheal intubation [56-59]. Ventilation with an ETT tip in a mainstem bronchus can lead to barotrauma and hypoxemia [60]. Exhaled CO₂ detection cannot distinguish between a correctly placed tube in the mid-trachea from a misplaced tube in a mainstem bronchus. Waveform capnography and end-tidal carbon dioxide (EtCO₂) values are typically normal with ETT placement in a mainstem bronchus.

●We place the tube to a depth of 20 to 21 cm at the teeth for average size women and 22 to 23 cm for average size men to avoid bronchial intubation [60-62]. Shorter or taller than average patients will need different tube depths, which will normally range from 19 to 24 cm at the teeth in adult patients. (See "Direct laryngoscopy and endotracheal intubation in adults", section on 'ETT insertion depth'.)

●In the acute care setting, we use chest radiography to ensure the ETT tip is 3 to 5 cm above the carina (image 1). Radiography is never available in the prehospital setting, is not usually immediately available in the operating room, and is often delayed in other settings.

●In the operating room, ETT depth and auscultation are routinely used to assess for mainstem bronchial intubation. Auscultation, evaluating tube depth, combined with observation of symmetrical chest movement has a sensitivity that approaches 100 percent and a specificity of approximately 95 percent for excluding bronchial intubation [61]. Used alone, auscultation has low sensitivity (approximately 65 percent) while assessing tube depth is slightly better (approximately 88 percent) [61].

●When chest radiography is not routinely available and auscultation or ETT depth are deemed inadequate, other options to exclude mainstem bronchial intubation are ultrasound or flexible endoscopy.

A small, randomized trial found that bedside ultrasound can provide an accurate assessment of ETT depth, and is superior to auscultation (approximately 93 percent sensitive) to rule out endobronchial intubation [63]. In this trial, bedside ultrasonography was used to identify bilateral pleural "lung sliding" (a sign of proper ventilation) and the position of the inflated ETT cuff. Further study is needed to confirm these findings in a broad array of patients.

If available, a flexible endoscope can be passed down an ETT to visually confirm that the ETT tip is appropriately located above the carina.

SPECIAL POPULATIONS

Cardiac arrest — For patients in cardiac arrest, we suggest using waveform capnography when available to confirm correct endotracheal tube (ETT) placement rather than other forms of confirmation. If waveform capnography is not available, digital capnometry is a reasonable alternative. During cardiac arrest, colorimetric carbon dioxide (CO₂) detectors have lower sensitivity (ability to detect that the tube is in the trachea). However, specificity (ability to detect that the tube is placed in the esophagus) is high with all three CO₂ detection techniques.

During cardiac arrest with high quality chest compression, end-tidal CO₂ (EtCO₂) is usually maintained above 15 mmHg [64-68]. Early in cardiac arrest and when the patient is receiving effective chest compressions, complete failure of CO₂ exchange is unlikely. In prolonged cardiac arrest, the EtCO₂ may be near or fall below 7.5 mmHg, but a waveform is almost always visualized [66-68]. Thus, esophageal intubation should be presumed if the CO₂ waveform is absent after intubation.

Prolonged cardiac arrest will infrequently result in complete absence of exhaled CO₂, reflecting lack of CO₂ production and cellular respiration instead of an incorrectly placed ETT. However, a complete lack of exhaled CO₂ should be presumed to represent esophageal intubation; the ETT should be removed and the patient should be ventilated by mask or with a supraglottic airway (SGA). Less preferably, correct ETT placement can be verified as discussed above; an esophageal detector device may be a helpful adjunct in this situation. (See 'Absent or equivocal exhaled CO2 (cannot confirm tracheal placement)' above.)

Interpretation and evidence depending on CO₂ detector used during cardiac arrest are the following:

●Waveform capnography – In patients with low perfusion states and cadavers, studies using waveform capnography to determine tracheal location of the ETT have shown 100 percent sensitivity and specificity [19-21,69]. If a four phase capnogram is present after intubation but suddenly disappears, it is likely the ETT has become dislodged.

●Digital capnometry – Sensitivity of digital capnometry is lower than waveform capnography in patients in cardiac arrest. A study of 246 patients in cardiac arrest who were intubated in the prehospital setting by emergency physicians found that digital capnometry had a sensitivity of 88 percent (95% CI 84-92 percent) and specificity of 100 percent for both CO₂ detection techniques [21]. However, there were only four cases of esophageal intubation, thus limiting conclusions.

●Colorimetric CO₂ detectors – The sensitivity of colorimetric detectors for patients in cardiac arrest ranges from 62 to 70 percent [36,37]. However, if waveform capnography or digital capnometry is unavailable, a colorimetric CO₂ detector can provide useful information because specificity is estimated to be 100 percent, even in the setting of cardiac arrest [34-37]. This means that:

•A color change (eg, to yellow) that continues to occur over at least seven breaths indicates with high confidence that the tube is located within the trachea.

•Interpreting the lack of sustained and robust color change can be difficult, since color change may not occur in approximately 30 percent of tracheal intubations in patients with cardiac arrest.

In general, lack of color change should be presumed to represent esophageal intubation, but subsequent management (eg, tube removal, supportive technique) is a clinical judgment that depends on factors such as the duration of cardiac arrest, quality of cardiopulmonary resuscitation (CPR), whether there is a reasonable expectation that the ETT is correctly located, and rapid availability of supportive techniques.

The use of capnography as an early indicator of return of spontaneous respiration or for prognosis in cardiac arrest is discussed separately. (See "Carbon dioxide monitoring (capnography)", section on 'Return of spontaneous circulation'.)

Bronchospasm — The absence of a CO₂ waveform in patients with bronchospasm should be presumed to represent esophageal intubation. Severe bronchospasm (eg, due to asthma or anaphylaxis) does not abolish exhaled carbon dioxide if any ventilation is occurring. Waveform capnography should still be used in this patient population. Data on EtCO₂ in near-fatal asthma or other causes of severe bronchospasm are lacking. However, in a study of 299 adult patients in the emergency department who presented with asthma, including 32 who were intubated, EtCO₂ was measurable in all patients, with a range of values from 14 to 82 mmHg [29]. We are not aware of any literature reporting a lack of exhaled CO₂ in the setting of ongoing ventilation. It should be noted that in the patient with known or suspected bronchospasm, application of higher than usual inspired airway pressure may be required to effect gas exchange resulting in CO₂ return.

UNRELIABLE METHODS TO EXCLUDE ESOPHAGEAL INTUBATION

Pulse oximetry — Adequate oxygen saturation cannot be used to confirm endotracheal tube (ETT) placement, for the following reasons:

●Preoxygenation prior to intubation can result in a large reservoir of oxygen that prevents oxygen desaturation for some minutes, even with esophageal intubation. In fact, prolonging the safe apnea time is the goal for preoxygenation. (See "Preoxygenation and apneic oxygenation for airway management for anesthesia", section on 'Physiologic basis for preoxygenation and apneic oxygenation'.)

●Peripheral oxygen desaturation may be a late sign of lack of effective ventilation. Once arterial oxygen tension starts to decline rapidly with lack of effective ventilation, there is further delay before this is reflected in peripheral oxygen desaturation, which is referred to as "pulse oximeter lag."

A continuously declining pulse oximetry reading after intubation should be presumed to represent esophageal intubation until this is excluded by deliberate reassessment of tube placement.

Chest radiography — Chest radiography should not be used to exclude esophageal intubation. With a standard anteroposterior portable chest radiograph, the tracheal air column is often directly superimposed over an ETT located in the esophagus, making the distinction between the two locations impossible.

It may be possible to improve detection of esophageal intubation by taking the radiograph in an oblique position [70]. In a study of portable chest radiographs in supine patients with both an ETT and a nasogastric tube in place, discrimination between the trachea and esophagus was best with a right posterior oblique radiograph with the patient's head turned to the right [70]. The esophagus was superimposed on the trachea in only seven percent of patients in this position, compared with 24 percent of straight anterior-posterior (AP) radiographs, and up to 96 percent of other positions.

Nonetheless, the time required to correctly position the patient, take the oblique radiograph, and interpret the results precludes the safe use of chest radiography for confirming tracheal intubation, especially in the patient rendered apneic with neuromuscular blockade. After confirmation of tracheal intubation with capnography, chest radiography may be useful for assessing the depth of the tube within the trachea. (See 'Excluding bronchial intubation' above.)

Other clinical tests — Clinical signs (eg, chest auscultation, misting or condensation in the ETT, chest rise, use of a tracheal tube introducer) lack the sensitivity and specificity to confirm proper ETT location and should not be considered evidence of tracheal placement.

Chest auscultation — Chest auscultation after intubation should not be used to distinguish tracheal from esophageal intubation. Chest auscultation can be performed after correct tracheal intubation has been confirmed with waveform capnography to help assure that breath sounds are equal. Along with the depth of placement of the tube, this can indicate that mainstem bronchus intubation has not occurred.

The presence of breath sounds does not confirm tracheal placement since sounds from positive pressure applied after esophageal intubation can be transmitted and incorrectly interpreted as pulmonary breath sounds. However, the absence of breath sounds should prompt actively excluding esophageal intubation by other means.

Breath sounds can be difficult to hear in noisy environments, in patients with thicker chest walls, or with high airway resistance. Low-quality stethoscopes can compound these limitations.

A systematic review of studies of the diagnostic accuracy of various tests used to confirm tracheal intubation found that the false positive rate (ie, esophageal intubation incorrectly interpreted as tracheal intubation) was 14 percent for chest auscultation alone (three studies) and 18 percent for 5 point auscultation (bilateral anterior chest and axillae plus epigastrium; four studies) [49].

Misting or condensation appearing within an endotracheal tube — We do not evaluate for the presence or absence misting after intubation, as this is not a reliable method for confirming successful intubation. A meta-analysis of three studies of the diagnostic accuracy of misting presence in the ETT found a false positive rate (ie, esophageal intubation incorrectly interpreted as tracheal intubation) of 69 percent [49].

Chest rise with positive pressure ventilation — Chest rise with ventilation suggests correct placement of an ETT in the trachea but should not be used to confirm successful tracheal intubation. The accuracy has not been well studied in humans and the false positive rate is unknown. Gastric insufflation with esophageal intubation could cause lower chest rise, especially in the patient with a very compliant chest wall (eg, a child) [71]. Misleading chest rise could also occur after intubation in a spontaneously breathing patient, despite esophageal intubation.

Tracheal clicks or resistance when passing a bougie — We do not recommend use of this technique to confirm tube position. Insertion of an ETT introducer (bougie) through and beyond the ETT may be a helpful method to confirm tracheal placement when no other means is possible, or to provide supplemental information when carbon dioxide (CO₂) detection and flexible bronchoscopy are not available. However, this technique is not reliable, has unclear risks, and has not been studied in patients. Theoretically, when the bougie is passed through an ETT in the trachea, the clinician may feel clicks as the bougie advances along the tracheal rings and eventually, there will be resistance ("hang up") when the tip passes beyond the carina and reaches the distal airways. By contrast, when passed through an ETT in the esophagus, no clicks would be felt and the bougie would advance deeply without resistance. However, a false positive result could occur with abnormal esophageal anatomy (eg, a diverticulum) and the risk of injury with intentionally inserting a bougie until resistance is encountered is unknown.

There have been no studies of this technique in live patients. In a study using 20 human cadavers, clinicians without prior experience using an ETT introducer were able to determine esophageal placement in 95 percent of cases (95% CI 88-98 percent) and tracheal placement in 93 percent (95% CI 86-97 percent) using tracheal clicks and hang up [72].

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Airway management in adults".)

SUMMARY AND RECOMMENDATIONS

●Location of endotracheal tube placement – The correct location for an endotracheal tube (ETT) for adult patients is within the trachea, with the tip 3 to 5 cm above the carina (figure 2). If unrecognized, an incorrectly placed ETT can result in hypoxemia, and ultimately hypoxic encephalopathy or death. (See 'Locations of endotracheal tube placement' above.)

●Preferred method to confirm tracheal intubation – Following tracheal intubation, prompt confirmation of ETT placement in the trachea is required (algorithm 1). We recommend using detection of exhaled carbon dioxide (CO₂) to confirm tracheal ETT placement, rather than relying solely on any combination of chest auscultation, other clinical signs (ie, chest rise, misting in the ETT), or visualization during laryngoscopy (Grade 1B). If flexible bronchoscopy is immediately available, it is a reasonable alternative for clinicians experienced in its use.

For confirmation of tracheal placement of an ETT we suggest using waveform capnography, if available, rather than other forms of exhaled CO₂ detection (Grade 2C). Waveform capnography has sensitivity and specificity approaching 100 percent for tracheal placement. In addition, the waveform provides clinical information beyond the peak or end-tidal CO₂ (EtCO₂). (See 'Preferred: Waveform capnography' above.)

Following intubation, the sustained presence of a CO₂ waveform with all four phases (figure 3) confirms that the ETT is in the trachea. The criteria for sustained presence of exhaled CO₂ requires all of the following:

•The wave rises during exhalation and falls during inspiration

•The amplitude is consistent or increasing over seven breaths

•The peak amplitude is >7.5 mmHg (1 kPa) over baseline

•The reading is clinically appropriate

●Alternative exhaled CO₂ detectors – If a waveform capnography monitor is not available, digital capnometry is a reasonable alternative. A third option is colorimetric CO₂ detection, although it is less accurate than either waveform capnography or digital capnometry, particularly in patients in cardiac arrest. Either approach is superior to methods of tube confirmation not involving detection of exhaled CO₂. (See 'Waveform capnography unavailable' above.)

•Capnometers – These provide a digital readout of the EtCO₂ without a waveform. The sensitivity and specificity of capnometers is slightly less than waveform capnography. (See 'Digital capnometry' above.)

•Colorimetric CO₂ detectors – These are less accurate compared with waveform capnography and digital capnometry. To ensure an accurate reading, the color must be visualized changing (eg, from purple to yellow) on at least seven breaths and back to the baseline color between breaths. For patients intubated following cardiac arrest, we avoid using a colorimetric CO₂ detector by itself because of low sensitivity for demonstrating color-change after tracheal placement in this setting. (See 'Colorimetric CO2 detectors' above.)

●Absent or equivocal exhaled CO₂ – Absent or equivocal exhaled CO₂ should be presumed to represent incorrect ETT placement until proven otherwise. This finding should not be attributed to an underlying medical condition (eg, cardiac arrest, bronchospasm, or hypotension). Management should be as follows (algorithm 1) (see 'Absent or equivocal exhaled CO2 (cannot confirm tracheal placement)' above):

•Start with a very brief check for an obvious and quickly remediable equipment issue (eg, an uninflated ETT cuff, CO₂ detector that is not turned on or appropriately connected).

•If at any time oxygen saturation falls without a clear alternative clinical explanation, remove the ETT and ventilate by face mask or supraglottic airway (SGA).

•The default action should be to remove the ETT and ventilate by face mask or SGA with use of waveform capnography monitoring. This will oxygenate the patient and confirm that C_O2 detection equipment is functioning.

•Once a CO₂ tracing can be visualized, proceed with reintubation of the trachea. If a CO₂ tracing is not visualized during what the operator is confident to be effective ventilation, this likely indicates an equipment malfunction.

•For patients in whom there is reasonable expectation that the ETT is correctly placed and for whom removing the ETT would be potentially hazardous, keep the tube in place and immediately use supportive techniques to confirm the location of the tube. Perform repeat laryngoscopy and one other method (flexible bronchoscopy, ultrasound, or esophageal detector device). (See 'Supportive techniques to confirm tracheal placement' above.)

It is potentially hazardous to remove an ETT if face mask or SGA ventilation has been or is predicted to be difficult, or if the patient is at high risk of gastric regurgitation and aspiration. Difficult intubation by itself should not be the basis for considering ETT removal hazardous. If the initial intubation was relatively easy with good glottic visualization, repeat intubation can be anticipated to be similarly straightforward in the absence of deteriorating upper airway anatomy (eg, due to angioedema).

•If esophageal intubation cannot be excluded with supportive techniques or sustained exhaled CO₂ has not been restored, remove the ETT and ventilate by mask or SGA with capnography monitoring.

●Patient in cardiac arrest – Specificity (ie, ability to detect esophageal intubation) is high with all forms of exhaled CO₂ detection, but colorimetry, and perhaps to a lesser extent digital capnometry, have decreased sensitivity and may show lack of CO₂ despite appropriate ETT placement.

An absent CO₂ waveform or EtCO₂ <7.5 mmHg should be presumed to represent esophageal intubation even with prolonged cardiac arrest. The ETT should be removed and the patient should be ventilated by mask or with an SGA. (See 'Cardiac arrest' above.)

●Unreliable methods to confirm placement – The following methods should not be used to confirm ETT placement: adequate pulse oximetry, chest radiography, chest auscultation, chest rise, and tracheal clicks or hang up passing a bougie. (See 'Unreliable methods to exclude esophageal intubation' above.)

●Excluding bronchial intubation – During intubation for anesthesia, bronchial intubation is usually excluded by inserting the ETT to the appropriate depth (20 to 21 cm at the teeth for women of average height and 22 to 23 cm for men of average height) and confirming bilateral equal breath sounds with chest auscultation. In other settings, chest radiography is often used. (See 'Excluding bronchial intubation' above.)