Endotracheal intubation confirmation- a review
Dror Lederman, PhD, EMT-P
Department of Radiology, University of Pittsburgh
3362 Fifth Avenue, Pittsburgh, PA, 15217, USA
Tel. 412-641-2581, Fax 412-641-2582
Abstract
In this paper, the problem of endotracheal intubation confirmation is addressed. A review of recent
studies which addressed this life-threatening problem is given. The results are analyzed and discussed.
Commonly used techniques and some state-of-the-art technologies for correct tube position
confirmation are presented, and their advantages and disadvantages are discussed.
Keywords- Airway management, Endotracheal intubation confirmation, esophageal intubation
detection.
1 Introduction
During general anaesthesia, anaesthetic gasses are introduced through the lungs. This
state of deliberate pharmacological unconsciousness might also cause airway
obstruction. In addition, various types of surgeries and lung diseases mandate stopping
spontaneous respiration of a patient and ventilating him artificially. The common
denominator of all of the above instances is the widespread necessity to protect the
patient’s airways by creating a safe artificial corridor for the air to enter the lungs
without obstruction. This task is accomplished by introducing a plastic ventilating
tube (endotracheal tube - ETT) into the trachea by a medical procedure called
“intubation”. The correct position of the endotracheal tube is between 2cm and 5cm
above the bifurcation of the trachea, named “carina”. Unfortunately, the anatomy of
the patient does not always allow easy insertion of the ETT. Failing to insert the ETT
may result in a failure to ventilate the patient, hypoxia and many other complications
such as Pneumonitis [1].
Incorrect positioning of the tube might cause severse complications. Unintentional
esophageal intubation can produce catastrophic results as the patient might be
deprived of oxygen. Late detection of esophageal intubation has been shown to be
correlative with a high mortality rate [2, 3].
Over-insertion might position the tube past the carina. It might therefore be placed
in one of the main bronchuses, usually the right one, such that only one lung is
ventilated. This condition is called endobronchial intubation or one-lung intubation
(OLI). Some patients might suffer oxygen deficiency while ventilated in only one
lung. Prolonged one lung ventilation might also cause other serious pulmonary
complications such as pneumonia, collapse of the contralateral lung and hyperinflation
of the intubation lung. This might cause hypoxia and pneumothorax, respectively, and
has been associated with a significatant increase in morbidity [4, 5]. In addition, tube
dislodgment might occur from many reasons, for example, due to neck flextion during
general anesthesia [6, 7]. Misplacement of the tube during or prior to securing it, or
1
during changes in the patient’s position may result in esophageal intubation
subsequent to correct initial placement [8, 9]. This phenomenan is prominent
especially in infants and neonates [10].
This papers reviews recent studies which investigated the extent and prevalence of
endotracheal tube misplacement both in the hospital and in out-of-hospital setting. The
paper proceeds as follows. Section 2 reviews representative studies which investigated
the rates of tube misplacement both in the hospital and in the out-of-hospital settings.
Section 3 presents the techniques and devices commonly used to confirm tube
position. Some state-of-the art devices are presented as well and a discussion of the
advantages and disadvantages of each one of the techniques and devices are given. A
discussion and summary are given in Section 4.
2 Endotracheal intubation confirmation- a summary of recent
studies
Unrecognized OLI and esophageal intubation are the most serious complications of
attemped tracheal intubation [11]. According to a closed malpractice claims analysis
of the American society of anesthesiologists (ASA), 4.5% of the claims are attributed
to esophageal intubations [12]. A higher proportion of patients are those who
underwent nonoperating-room anesthesia claims than those who underwent operating
room anesthesia. Furthermore, unrecognized esophageal intubation was identified as
an important cause of cardiac arrest attributed solely to anesthesia at one institution
[13].
2.1 In-hopsital intubations
Though the effectiveness and benefits of out-of-hospital intubations have been
depated (see for example [14]), it is still considered the definitive airway securing and
ventilation method. Intubations performed in the hospital, particularly in the intensive
care unit and operating room (OR) are performed under almost ideal conditions- in a
quiet environment, with a number of health providers usually available, equipment,
space, and the availability to muscle-relaxant drugs. Nevertheless, misplacement and
mislodgement of the ETT occur. In [15], 297 trachea intubation performed in the ICU
were re-assessed. Out of 25 intubations, 8% of the intubations were esophageal
intubation. Some of the out of which 32 were detected by clinical criteria, and 3 were
not detected until there was a decrease in the oxyhemoglobin saturation as measured
by pulse oximetry.
In the OR, unrecognized esophageal intubation accounts for 15% of all
catastrophic injuries to patients including brain damage and death, making it the
single-most critical anesthetic incident associated with injuries of this type [16, 17].
2.2 Out-of-hopsital intubations
In most of EMS services around the world, paramedics are the major health providers
rather than physicians. Paramedics gain a relatively short training, while most of their
intubation training is performed on manikins. Additionally, as opposed to the OR
setting, paramedics perform the intubation in adverse scenarios, including noisy,
under total darkness or intense daylight, poor patient positioning, cervical spine
immobilization, lack of neuromuscular blocking agents, combative patients, blood and
2
vomitus in the airway, on the beach or in a crashed car. Out-of-hospital patients are
critically ill and often severly injured, and most would be considered “difficult” or
high-risk intubations by in-hospital anesthesia standards [18]. Hence, intubation
becomes even more challenging and complex when performed in the uncontrolled
out-of-hospital setting than in the hospital. Naturally, the rate of complications in the
prehospital setting will be much higher than in the OR.
Numerous studies have investigated the endtroacheal misplacement rate in the prehospital setting. Several studies reported a misplacement rate between 0% and 7.8%
[2, 19-21]. These studies were based on self-reports by the health providers and are
thus subject to reporting bias [18, 22]. As such, the methodologies used in these
studies, do not allow reliable estimation of tube misplacement error rates.
Misplacement rate varies from 50% for providers who do not frequently perform
tracheal intubation [20], but high misplacement rates were reported even when
experienced anesthesiologists performed the intubation [3, 6, 23, 24] and even in the
hospital [7]. In [25], 136 critically ill patients undergoing endotracheal intubation by
experienced physicians at the intensive care unit were re-assessed. In 39% of all
intubations which were examined, complications occured. Severe complications
occurred in 24% of all intubations, out of which an esophageal intubation rate of 7.4%
was reported. The results coincide with other studies [15, 26-28].
Other studies, based re-assessment by independent observers, consistently report
higher misplacement rates between 6% and 25% [1-3, 29-31]. Timmermann et al. [3]
reported an OLI incidents rate of 10.7% (16 out of 149 cases), and an esophageal
intubation rate of 6.7% (10 cases). The authors reported that the actual error rates
might be higher since some esophageal intubation might not have been detected as
some of the patients died in the scene and were therefore not re-assessed by an
independent observer.
In [31], 108 paramedic endotracheal intubation performed in patients arriving at a
regional trauma center in Florida were evaluated. It was found that more than 25% of
the endotracheal tubes were misplaced. Two thirds of these intubations were
esophageal. A later study by Silvestri et al. [2] reported a decrease in the unrecognized
esophageal intubations by paramedics from 25% to 9% with the implementation of a
new airway management protocol that required continuous end-tidal CO2 monitoring
of all intubated patients. They observed no esopgeal intubations when there was 100%
compliance with the protocol.
A similar study was performed by Jemmett et al. [29]. In this study, 109 paramedic
endotracheal intubations were re-assessed upon arrival at the emergency department in
Maine. A similar tube misplacement rate of 12% was reported.
In a larger multi-center study [1, 32], out of 1953 evaluated endotracheal
intubations, tube misplacement, including esophageal intubation, delayed recognition,
unrecognized, and dislodgment were reported in 3.1% of the intubations. More than
22% of patients experienced 1 or more complications, including multiple intubation
attempts and failure to perform intubation.
A lower rate of 5.8% was reported by Jones et al. [30], which evaluated 208
intubations in Indianapolis. In this study, which included data from one geographical
area, most of the evaluated intubations were performed by one EMS system while the
paramedics were aware of the study, thus allowing the so called Haythorne effect [33].
3
The differences between the reported misplaced rate may be due to the provider’s
experience, the quality assurance protocols used in the participating EMS system, the
prevalence use of secondary confirmation devices and the number of confirmation
devices used. Clearly, many errors are identified only through invasive tests or
autospy [34, 35]. Moreover, many people undergoing resucitation outside the hospital
are pronounced dead at the scene, without being re-assessed by independent
observers. In such cases, tube misplacement errors might not be detected. Table
.‫ שגיאה! מקור ההפניה לא נמצא‬summarizes the results of representative studies.
However, there is no question that even with the use of secondary confirmation
devices, misplaced intubation do occur, where the exact rate heavily depend on the
above-mentioned factors.
The studies presented above confirm the fact that unrecognized misplaced
intubation represents a significant life-threatening problem. Accordingly, systemic
efforts to better equip health providers with continuous tube position monitoring and
screening devices are indicated.
3 Common methods and devices for endotracheal intubation
confirmation
Due to the catastrophical risks associated with misplaced endotraheal intubation, the
problem has attracted increasing attention over the last years. Various techniques and
devices have been proposed for confirmation of correct tube positioning. In this
section, a summmary of the most commonly used techniques for ETT confirmation
will be presented.
3.1 Visualization techniques
Direct visualization is usually used before all other methods. For decades, it has been
considered as “gold standard” for confirming endotracheal intubation. By visualizing
the tube as it is passed through the cords, the operator can reasonably assume that the
tube has been placed in the trachea. Obviously, this method can not be used when the
cords are not visible, due to large tongue, prominent teeth, a short neck, blood and
secretions. In addition, tube dislodgement might occur either before or after it has
been secured. Inadvertent esophageal intubation has been reported in cases where the
operator visualized tube passage through the cords and was certain of endotracheal
placement [36]. Moreover, the method may be used only under optimal clinical
circumstances when the practitioner can easily view the glottis with standard
laryngoscopy [37]. Consequently, this method is unreliable as the sole method for tube
position verification [36]. Obviously, the method does not allow continuous
monitoring.
Fiberoptic bronchoscopy is an excellent method to confirm ETT placement.
Performing bronchoscopy through the ETT and visualizing the carina may reliably
confirm proper placement. However, massive secretions, blood, or gastric contents
may block a bronchoscope view. It is labor intensive, required appropriate training
and not cost-effective to perform in all cases (e.g. [38, 39]).
Recently developed visualization tools include video laryngoscopy and videointuboscopic devices [40, 41]. These tools may aid in visualizing the glottis in many
difficult conditions. As fiberoptic bronchoscopy, these tools require appropriate
4
training, continuous monitoring and they might be obscured due to blood and
secretions. Their use in out-of-hospital setting, such as intensive daylight, is
problematic. In addition, these tools are not cost-effective. Anyway, whether
visualization is performed directly or using visualization devices, without re-checking
by an additional observer, this viewing is not foolproof [42].
3.2 Chest radiography
Chest radiography is commonly performed in patients who underwent tracheal
intubation outside the OR. Chest radiography is not useful for detecting esophageal
intubation as the esophagus lies posterior to the tracha. Furthermore, it requires
appropriate equipment, adequate training, it is expensive per use, and time-consuming.
Obviously, it’s use is limited to in-hospital settings. Moreover, it is not fullproof. For
instance, in [43] an ETT misplacement rate of 14% with the use of chest radiography
was reported.
3.3 Analysis of breath sounds
The stethoscope is probably the most primitive and widely used technique.
Auscultation of the lung sounds using the stethoscope requires high attention, and its
reliability has been shown to be low [9, 43-50]. Auscultation of breath sounds in both
axillae may result in misdiagnosis due to the sounds produced by the air passing
through the esophagus. Auscultation of epigastic sounds may improve accuracy.
However, gastric distention might result also from previous bag-valve-mask
ventilation, regardless of tube placement [45, 46], hence leading to misdiagnosis.
Massive unilateral aspiration can lead to diminished lung sounds, which may be
misinterpreted as bronchial intubation. In addition, in thin patients, tracheal breath
sounds may be transmitted to the epigastic area simulating gastric insufflation [47].
On the other hand, in esophageal intubations, abdominal distention does not always
occur, therefore, leaving the esophageal intubation undetected. In [47, 48], for
example, 90% of esophgeal intubations were incorrectly judged to be tracheal
intubations using auscultation using the stethoscope. In [44], 48% of the esophageal
intubations were not detected though the documented use of auscultation. In [43], 60%
of the reported OLI occurred despite the presence of equal breath sounds on
examination. Similar results were reported in other studies (e.g. [48, 51]).
Detecting incorrect tube positioning based on auscultation may be very difficult in
infants and small children. In fact, according to [7, 32], auscultation of bilateral breath
sounds does not rule out endobronchial intubation in children.
Computerized analysis of breath sounds has been proposed in several papers [5256]. Using two or more microphones located at the back or chest of the patient, the
acoustical breath signals are recorded and analyzed using smart signal processing
algorithms. Basically, these methods mimic ausculation of lung sounds by the health
care providers. Therefore, while they allow continuous automatic monitoring of the
tube position, they heavily depend on background noise and require several
microphones to be attached to the patient’s chest or back, thus making the technique
impractical for both in-hospital and out-of-hospital use. These methods potentially
suffer from the similar disadvantages as auscultation of lung sounds by the health care
providers, and as such their reliability is questionable and in any case yet to be
evaluated.
5
3.4 Gas exchange-based techniques
Pulse oximeter devices, which measure the oxygen saturation, are also in common
clinical use. These devices suffer from a significant and critical latency time of 25min, which makes them irrelevant for detection of tube positioning. In cases of
adequate preoxygenation, oxygen desaturation may take several minutes to occur in
patients with misplaced ETT [47, 57]. At the time of desaturation, the deleterious
consequences of hypoxia to the brain and heart may already be prominent. Moreover,
oxygen saturation is dependent on adequate perfusion and blood pressure, and
therefore pulse oximetry can not be used in many medical conditions such as cardiopulmonary resucitation and hypovalemic shock.
Another disadvantage of pulse oximetry is that it is unreliable for OLI incidents
detection since in such cases oxygen saturation may be high for quite a long time. In
[58], the use of oxygen saturation has been shown to be unreliable for endotracheal
tube verification. Additionally, intense daylight, fluorescent, incandescent, xenon, and
infrared light sources have been reported to cause spurious pulse oximetry readings
[59]. Various other interferences might caused by Hemoglobin variants, hypothermia,
hypotention, anemia, and nail polish [59, 60].
Another well known technique is the esophageal detector device (EDD). The EDD
consists of either a self-in-flating bulb or a 60-mL syringe, has become a widely used
method of verification [61]. This technique relies on the fact that the trachea is rigid
and permits free aspiration of air from the pulmonary dead space, while aspiration
from the esophagus causes collapse of the esophagreal wall and delayed or absent
reinflation. However, in cases in which the patients are ventilated prior to aspiration,
rapid reinflation might occur regardless of tube location [61, 62]. Moreover, incorrect
determination of the tube position might occur in patients with morbid obesity, late
pregnancy or severe asthma or when there are significant tracheal secretions. In such
cases, the trachea may collapse when aspiration is attempted [11, 63]. As pulse
oximetry, neither this technique can be used to detect OLI incidents.
In [64], as low as 50% accuracy in detecting esophgeal intubation in out-of-hispital
scenarios were reported, not including 11 cases in which the paramedic was unable to
interpret the result. Tanigawa et al. [65] investigated 48 intubations in which an EDD
was used to confirm correct intubation. Sensitivity rates of 72.9% and 70.8% were
found for the syringe EDD and bulb test, respectively.
Other similar tools are esophageal intubation detector (EID) and tracheal detectingbolb (TDB). As EDD, significant error rates were reported using these methods.
Inaccurate results have been reported in patients with morbid obesity, pulmonary
edema, bronchospastic disease or ETT obstruction as in the case of an airway
contaminated with blood or vomitus [66, 67]. Specifically in obese patients with a
body mass index (BMI) greater than 35, the device has a false negative rate of 11-30%
[66].
Furthermore, these tools cannot provide continuous breath-to-breath monitoring of
ETT position. Additionally, their use is contraindicated in pregnant patients ahd
children under 5 years old [67]. Poor performances were documents by the use of
paramedics [64].
In recent years, carbon dioxide detection (CO2) has became the gold standard-defacto for confirming the tube position. Measurement of end-tidal CO2 (ETCO2) using
6
either quantitive (capnometer) or qualitive (capnography) devices. Both devices have
been studied in many occations (e.g. [15, 17, 68-70]). Given the efficacy of
capnography, the American Society of Anesthesiology has included ETCO2 detection
in their standards [71]. This action, combined with the availability of inexpensive
devices, has established ETCO2 detection as the standard of care for endotracheal
intubation in the hospital [72].
The use of colorimetric devices in patients in cardiac arrest has some limitations. In
cardiac arrest, low ETCO2 may represent esophgeal intubation, or tracheal intubation
with markedly dimished pulmonary blood flow despite endotracheal placement of the
tube [9]. In this case, it is the low cardiac output that results in very low delivery of
CO2 to the lungs for excretion that causes a low ETCO2. For patients in cardiac
arrest, Ornato [68] and Macleod [17] studies showed sensitivities and specificities of
69-72% and 100%, respectively.
Capnography has some advantage in such cases over quantitive devices- the
threshold for detection of exhaled CO2 is significantly lower in capnography
comparing to colorimetric capnometry [73]. Additionaly, crucial discriminative
information may be obtained from the CO2 waveform. In [74, 75], it has been shown
that capnography is superior to semiquantitative colorimetric devices in a prehospital
setting in both arrest and non-arrest patients.
However, it is well known that measurement of the exhaled CO2 can not be
performed or is unreliable in many emergencies. For instance, during cardiopulmonary resucitation, low CO2 levels may indicate either an esophageal intubation
or tracheal intubation because of profoundly dimished or absent cardiac output,
pulmonary blood blow, and alveolar CO2 concentration [9, 11, 62, 69].
Severe airway obstruction may prevent sufficient CO2 exhalation to be detected by
ETCO2-based devices [76]. If the tube is positioned neigher in the trachea nor in the
esophagus, an open glottis may allow detection of CO2. Li [77] reported that small
concentrations of CO2 may be detected even in esophageal intubation, especially if
bag-and-mask ventilation has insufflated previously exhaled air into the stomach [77].
Likewise, patients who have recently ingested carbonated beverages may have CO2
detected in the stomach [77]. False negative capnograhpy readings might result in
cases of obstructed tube, due to plugging the tip of the tube with mucus or blood, or
when the tube abuts the tracheal wall and thus impedes or prevents exhalation. Apnea
and severe bronchospasm lead to dramatically reduced exhalation and thus to false
negative results [9]. Furthermore, ETCO2-based devices are unreliable for detection
of OLI incidents because the capnograpm is generally typical in shape and shows
normal end-tidal values [9, 78].
A method based on a technology similar to sonar signal processing has been
suggested [79, 80]. The SCOTI device analyses the reflections obtained when sound
waves are emitted from a small sound generator at the tip of the tube. A similar idea,
in which the acoustic reflections are used to generate an image of the airways has been
proposed by Raphael et al. [81, 82]. Both techniques have been tested only on smallsize population, in quiet environment. Their performance in noisy environment, and/or
in the presence of vomitus and secretions, is still to be evaluated.
Table .‫ שגיאה! מקור ההפניה לא נמצא‬present the features calculated:
Recently, methods based on impedance analysis were suggested [83-85] were
suggested. The technique is based on the assumption that a ventilated lung will have
7
increased impedance. Therefore, by measuring the impedance over the chest cavity, a
discrimination between esophageal (constant impedance) and tracheal intubation
(changing impedance) is performed. Preliminary studies showed promising results.
However, it is not clear whether the method may be used to detect OLI incidents.
Furthermore, the method might fail to detect esophageal intubation in spontaneouslybreathing patients.
Ultrasound-based methods have been proposed by several research groups [86-90].
In one type of devices, ultrasound-based imaging are used to visualize the
diaphragmatic and pleural motion. In this way, lung expansion can be measured as an
indication of the tube position in non-breathing patients. Another type of devices is
based on direct ultrasound visualization of the ETT. Small-sized population studies
showed promising results. As in the case of the previous devices, it is not clear
whether this device can be used for OLI detection.
8
Intubation Errors
Authors
Schwartz
et al. [15]
Jacobs et
al. [19]
Steward
et al. [20]
Pointer et
al. [21]
Silvestri
et al. [2]
Timmerm
ann et al.
[3]
Katz et
al. [31]
Wang et
al. [1, 32]
Jemmett
et al. [29]
Jones et
al. [30]
Timmerm
ann et al.
[24]
No
of Patients OLI
Intubatio / study
ns
type
297
ICU
4%1
Esoph.
Intub.
Total
misplaced
11.8%
Comment
s
and
weakness
es
complic Others
ations
15%
3
2
Unexperi
enced
Providers
153
149
108
1953
50%
Prospec
tive
Prospec
tive
Retrosp
ective
Retrosp
ective
109
208
Prospec
tive
--
8.5%
9%
10.7
%
6.7%
17.4%
16%
4
25%
22%
1.8%
11.9%
NR
NR
1
5.8%
NR
were not detected by clinical examination and ofund only in the chest radiograph
obtained immediately after intubation.
2
three esophageal intubations were not recognized until there was a decrease in the
oxyhemoglobin saturation as measured by pulse oximetry. One more patient, not
included in the study, suffered from esophageal intubation which was not detection
before death.
3
8% difficult intubation; 4% post-intubation aspiration; 3% died within 30 min;
requiring more than two attempts at laryngoscopy by a physician skilled in airway
management; 4.4% required four or more attempts, 0.6% required ten or more
attempts.
4
Based on self reports.
5
Up to 40% in selected EMS; based on self-reports
9
5
Griesdale
et al. [25]
136
critically
ill
patients
ICU,
Prospec
tive
7.4%
24%
*13.2%
require
d >= 3
attempt
s; 6.6%
difficult
intubati
ons
253
ICU,
Prospec
tive
5%
28%
Verghese
et al. [7]
Sakles et
al. [26]
Jaber et
al. [27]
Benedett
o et al.
[28]
Katz and
Falk
McGillic
uddy
108
157
ICU,
retrospe
ctive
NR
16.7%
25%
6.5%
0.6%
19%
NR = not rated
4 Summary
In summary, none of the techniques used for confirmation of the ET position, have
been proven to be 100% reliable and none of them are reliable for detection of OLI
incidents [11]. Indeed, according to the guidelines of the American Heart Association
[91] confirmation of correct tube positioning should be performed using several
secondary confirmation devices, and re-confirmation should be performed any time
the patient is moved or neck flexion or extension performed, or any other case in
which tube dislodgement is suspected.
6
Video-laryngoscope or fiber-optic bronchoscope was usually used in multiple
attempts
10
6
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11
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