Background
Airway skills are crucial for emergency physicians. In emergency settings, verification of endotracheal tube (ETT) location is important for critically ill patients. Ignorance of oesophageal intubation can be disastrous [
1]. This usually happens during intubation in emergency conditions. The incidence of oesophageal intubation was reported at 6% to 16% in emergency conditions [
2,
3]. Thus, emergency airway efforts in the emergency department (ED) must concentrate on early detection of unintentional oesophageal intubation.
Over the decades, many methods had been used to verify endotracheal intubation. For example, Vaghadia et al. concluded that end tidal carbon dioxide (ETCO2) is most appropriate for identifying oesophageal intubation [
4]. Capnography had also been found to be the best method for rapid assessment of tube position [
5]. Subsequently, there are reports that the oesophageal detector device has greater accuracy in emergency settings [
6]. Although many techniques have been recommended to verify the ETT location, there is no single verification method that is ideal in every situation [
7,
8]. Nevertheless, there are two studies that are nearest to the ideal. They are two studies of waveform capnography to confirm ETT position in victims of cardiovascular arrest post-intubation which showed 100% sensitivity and 100% specificity in verifying the correct tracheal tube location [
9,
10]. Therefore waveform capnography is considered the standard of care for the primary verification of endotracheal tube location.
Unfortunately, capnography is not always or freely available, especially in small centres. This is in contrast to ultrasound which is relatively more freely available even in small centres as it is an indispensable tool for managing obstetrics and gynaecology cases and also trauma cases.
Ultrasonography (US) is a widely accessible tool in ED. It is easy to carry, has wide availability, does not cause pain, is relatively cheaper, is easily reproducible and has good safety records [
11]. Several studies of ultrasonography confirmation of ETT position provided promising results in a cadaver model [
7] or patient in a controlled operating room setting [
12,
13].
Literature review
There is a prospective study conducted in Taiwan with the objective of determining the accuracy in diagnosis and timeliness of a novel approach, named tracheal rapid ultrasound exam (TRUE), (which uses convex transducer as opposed to linear transducer, as used in our study) to verify endotracheal tube location during intubation in emergency settings. Quantitative waveform capnography was used as the gold standard for verification of tube placement. A good agreement and concordance between the two aforementioned methods were the outcome. Therefore, it is concluded that the use of TRUE to determine endotracheal tube location during intubation is possible and can be performed quickly [
14].
There is a prospective clinical trial in Pusan National University Hospital, South Korea where combined ultrasonography methods using trans-cricothyroid membrane ultrasonography and ultrasonography lung-sliding assessment were found to have 100% sensitivity and specificity in verification of tube placement in emergency settings [
15].
A prospective study to compare diaphragmatic ultrasound and chest radiography to verify endotracheal tube location in paediatric emergency settings is done in Cincinnati, USA where they found no equivalence in diaphragmatic ultrasound compared to CXR for tube location in the airway. Nevertheless, ultrasound results were faster, identified more wrong placements and were repeatable among sonographers. Ultrasound results are 8 min faster to obtain than chest X-ray results [
16].
In another ultrasound method to verify endotracheal tube placement, a study is done in California, USA. The objective is to calculate specificity and sensitivity of trans-cricothyroid sonography to verify endotracheal intubation. It is a prospective, randomised double-blind trial done in a human cadaver. It was found that dynamic assessment had higher sensitivity and specificity than static assessment. Nevertheless, more tests in living beings are needed to validate these data [
7].
In Cleveland, USA, a prospective, randomised, controlled study is done to calculate the accuracy of ultrasonography for identifying the endotracheal tube location in real time. Endotracheal tubes were deliberately placed (with direct laryngoscopy) at random in the trachea and oesophagus. Location of the endotracheal tube was then recorded independently by two blinded physicians. They achieved 100% sensitivity and specificity. Thus, it is concluded that the location of endotracheal tubes during the process of intubation can be accurately identified with ultrasonography in selected patients in controlled settings of the operating room [
17].
Galicinao and colleagues had done a study to assess the use of ultrasound in verifying ETT location among paediatric patients. It showed that linear transducer provides better images but is limited by its size compared to curvilinear ones and has better timeliness of ultrasound as compared to chest radiograph; sniffing is the best position for high-quality images. They also showed that ultrasound can be used accurately when ETCO2 detector shows wrong or ambiguous results [
18].
There is a recent prospective pilot study of newborns admitted to the San Diego Medical Centre that found a good correlation between ultrasound and radiograph in determining the anatomical position of ETT in preterm and term infants [
19]. In Augusta, USA, ultrasound capture of the lung-sliding sign in a cadaver had been found to be accurate in detecting ETT placement in the trachea, oesophagus and right main stem bronchus.
In a paediatric intensive care unit, Hsieh et al. used the motion of the diaphragm to determine the position of ETT placement. It is thus recommended for the secondary confirmation of the ETT position [
20].
In pre-hospital or disaster settings, Chun et al. used handheld ultrasound to confirm ETT placement in extreme conditions where auscultation and capnography may not be appropriate. Their report suggests that thoracic ultrasonography could be used to verify proper ETT placement [
21].
The research question
Is bedside upper airway ultrasonography in good agreement with capnography in verifying endotracheal tube placement after intubation?
Objectives
The following are the objectives of the study:
(a)
To assess the feasibility of bedside upper airway ultrasonography verification of endotracheal intubation as compared to waveform capnography, which is the standard of care in primary/immediate verification process
(a)
To verify ETT location in patients in the ED with bedside upper airway ultrasonography and to compare it with waveform capnography (gold standard)
(a)
To estimate verification time by ultrasound
(a)
Bedside ultrasonography is in good agreement with the ‘gold standard’ test, waveform capnography.
(b)
The mean verification time is about the same as other tracheal ultrasound techniques by other investigators, which is less than 30 s.
Ethical consideration
There is a theoretical possibility of the mentioned investigations causing delay in sending patient to the ward. However, firstly, we would like to clarify that US confirmation of endotracheal intubation takes only a mean time of 14 s, and the maximum time between capnography and US is 60 s [
14]. Thus, it seems that the little delay looks negligible. Secondly, all clinical decisions are dependent on capnography results, and ultrasonography will not be involved in clinical decision-making. All patients will receive routine treatment, and ultrasound would be the only additional investigation added and will not interfere in patient care. Thirdly, previous researches on ultrasound confirmation had a waiver of consent due to the nature of working environment in the emergency department.
Physicians have used ultrasound for many decades. Until now, researchers have not found any side effects clearly caused by ultrasound. Each year, millions of babies born had undergone ultrasound scanning
in utero. This is an enviable safety record. Hence, ultrasonography is not harmful to the patients. It is generally viewed as a safe imaging modality [
22]. The World Health Organization technical report series (1998) states that ultrasound is generally harmless [
23]. A meta-analysis of several published studies (year 2000) reported that ultrasonography had no statistically significant side effects [
24].
Ultrasound is an indispensable tool for emergency physicians to quickly diagnose salvageable conditions in critically ill patients. This is because the usual methods to diagnose will be cumbersome, risky and not timely enough for unstable patients where time is an important factor in determining survivability of the patients. This application is called point-of-care ultrasound [
25]. This research falls into this category. Since US confirmation of endotracheal intubation takes only a mean time of 14 s [
14], any hypothetical risks to the patients seem negligible. There are no known harmful patient outcomes with the use of sonography in the ED in a study done in the UK [
26]. Furthermore, legal actions have been taken against physicians for not performing point-of-care ultrasound [
27].
Fourthly, obtaining informed consent from the patients is impossible because all intubated patients are unconscious, ill and often unstable. Furthermore, their relatives are often not around. Even if they are around, consent will cause significant delay to the care of the patient. This will defeat the whole purpose of emergency ultrasound, which is meant to be kept simple and as fast as possible [
28]. The ultrasound in this research takes only a mean time of 14 s [
14]. To take consent will take minutes to hours which will cause unacceptable delays in patient care. There are no other ways to obtain the information of this research without the patient being unconscious (this research is about intubated patients in the emergency department, and all intubated patients here are unconscious). We think that the potential benefit to the population as a whole outweighs the individual right of the study patients to absolute identification. The reason for this research is important; it is to show that ultrasound is in good agreement to waveform capnography which is the gold standard in the immediate confirmation of endotracheal intubation. Not all hospitals have the facilities of ETCO2, but all district hospitals at least have US at their disposal. If this is successful, we could train all district MOs to use US to confirm ETT placement and thus reduce incidences of unrecognised oesophageal intubation which are sometimes difficult to detect clinically but may cause substantial morbidity and mortality. Medical Research Ethics Committee of Malaysia had given a waiver of consent. This study is registered with the National Medical Research Register and approved by the Clinical Research Centre and National Institute of Health of Malaysia.
Rationale of study
The reason for this research is important; it is to show that bedside upper airway ultrasound is in good agreement to waveform capnography which is the gold standard in the primary/immediate verification of endotracheal intubation. Primary/immediate verification means that verification done before endotracheal tube is secured. Not all hospitals have the facilities for capnography, but they at least have US at their disposal. If this is successful, ultrasound can be used in centres without capnography to reduce incidences of unrecognised oesophageal intubation which are sometimes difficult to detect clinically but may cause substantial morbidity and mortality.
Acknowledgements
This research was made possible through a research grant from WinFocus Malaysia Group. The authors thanked University Malaya and Clinical Research Centre, Hospital Raja Permaisuri Bainun, Ipoh, Perak, Malaysia.
Competing interests
The authors declare that they have no competing interests.
Authors’ contribution
ABO was involved in study conception, study design, discussion, methodology, completed data acquisition, collection and results interpretation, statistical calculation and analysis, result interpretation, and discussion. TWC completed write-up of the manuscript and was involved in study conception, study design, discussion, methodology, data collection, statistical calculation and analysis, result interpretation, and discussion. RM contributed to the initial conception, study design as well as intellectual contents of the study. All authors read and approved the final manuscript.