ORIGINAL ARTICLE


https://doi.org/10.5005/jp-journals-10049-2006
Journal of Research and Innovation in Anesthesia
Volume 7 | Issue 1 | Year 2022

Confirmation of Endotracheal Tube Placement in Trachea Ultrasonography vs End-tidal Capnography with Auscultation: An Observational Study


Sanjog Mekewar1, Pritee H Bhirud2, Shrividya Chellam3, Pratibha V Toal4, Prachee Gawade5

1-5Department of Anaesthesia, Bhabha Atomic Research Centre and Hospital, Mumbai, Maharashtra, India

Corresponding Author: Pritee H Bhirud, Department of Anaesthesia, Bhabha Atomic Research Centre and Hospital, Mumbai, Maharashtra, India, Phone: +91 9820669549, e-mail: priteebhirud@gmail.com

ABSTRACT

Background and aim: Early detection of complications after intubation is necessary as outcomes can be fatal. In search of an ideal test, we conducted this study under ideal settings to compare the time required and efficacy of airway ultrasonography (USG) vs Capnography with auscultation to confirm correct placement of endotracheal tube after intubation.

Methodology: In this prospective, randomized, comparative study, we randomly allocated our sample population of 130 posted for general anesthesia in elective cases in operation theater into two groups and then used capnography with auscultation for group A and USG for group B to confirm tube placement in the trachea. We compared the efficacy and time taken by the two methods of confirmation. p value < 0.05 was considered statistically significant.

Results: Tracheal USG confirmation time in group B (2.8 ± 1.9 s) was significantly lower than capnography confirmation time in group A (7.5 ± 2.4 s) (p = 0.03). Time taken to confirm bilaterally equal air entry by auscultation in group A and USG sliding lung sign in group B were comparable. Total time taken for confirmation with USG (16.87 ± 8 s) was faster than auscultation and capnography (24.7 ± 10.6 s) but was not statistically significant (p = 0.43). Both the methods were comparable with respect to efficacy.

Conclusion: We conclude that USG is a faster modality for confirmation of correct placement of endotracheal tube compared to capnography and auscultation. Both methods are compared with respect to efficacy.

How to cite this article: Mekewar S, Bhirud PH, Chellam S, et al. Confirmation of Endotracheal Tube Placement in Trachea Ultrasonography vs End-tidal Capnography with Auscultation: An Observational Study. J Res and Innov Anesth 2022;7(1):5-9.

Source of support: Nil

Conflict of interest: None

Keywords: Airway, Endotracheal tube, Trachea, USG

INTRODUCTION

Endotracheal intubation (ETI) is a rapid, simple, safe, and noninvasive technique that achieves all the goals of airway management, and remains the gold standard.1 However, complications have been described during the process of intubation of which esophageal intubation and Endobronchial intubation are two of the most common mishaps encountered timely confirmation of which is of utmost importance.

Traditionally, confirmation of ETI has been done by direct visualization of endotracheal tube (ETT) during direct laryngoscopy, visualization of bilaterally (B/L) equal chest rise, fogging of the ETT from within, B/L auscultation of the chest, and most importantly by identifying the End tidal carbon dioxide (EtCO2) on capnogram.

However, esophageal intubation can remain undetected despite these methods. End tidal capnography (EtCO2), despite being the gold standard has its own share of limitations like blockage of sampling line, interference in readings due to use of filters, auto zeroing at the time of intubation, and most importantly a lag time or response time for the appearance of the graph which may vary from one multiparameter monitor to the other.2

Search for an ideal test for confirmation of ETT placement in the trachea continues. Ultrasound (US) imaging has recently emerged as a novel, simple, portable, noninvasive tool helpful for airway assessment and management.3 It is generating interest in anesthesiology for airway ultrasonography (USG) after it was found to be effective in confirming ETT placement in the Emergency rooms and Intensive care units (ICU).

Many studies have been conducted in the past comparing the efficacy and timeliness of USG vs the traditional methods (End-tidal capnography with/without auscultation) for confirmation of ETI.4,5,6,7 But most of these studies have been done in an emergency set up in ICU’s which does not provide an ideal setting for adequate assessment of the two methods. Moreover, most of these studies had small sample sizes and none of the studies has calculated the total time taken for confirmation of ETI by USG (i.e., Tracheal time + Lung slide). Thus, the results of these studies cannot be applied to the population of patients posted for general anesthesia in elective cases in operation theatres.

To fulfill these lacunae, we conducted this study in a sample population posted for general anesthesia in elective cases in the operation theatre. We clearly defined the time parameters used in our study to measure the time taken for respective methods of confirmation and calculated the total time taken by USG for confirmation of correct ETT placement. The hypothesis of the study was, USG as a modality is faster and as efficacious as auscultation and capnography for confirmation of ETI.

The primary aim of the study was to compare the time required by USG vs end-tidal capnography with auscultation to confirm correct placement of ETT after intubation. The secondary objective included comparing the efficacy of the two diagnostic modalities.

METHODOLOGY

Institutional Ethics committee approval was taken before starting this prospective, randomized, comparative study. Informed consent was taken from the participants which included all consenting adult patients >18 years of age posted for elective surgery requiring general anesthesia with ETI. Patients not consenting, having distorted neck anatomy, history of neck surgery, or exposure to radiation, and patients with chronic pulmonary diseases with low pulmonary reserve were excluded from the study.

A total of 130 consecutive consenting patients who fulfill the inclusion criteria were randomized based on computer-generated random numbers (www.randomizer.org) into two groups, group A (EtCO2 and auscultation) and group B (Airway USG). Intubations were done by an anesthetist who had the experience of a minimum of 35 successful intubations. Confirmation of ETT placement by auscultation and EtCO2 was done by an anesthetist who had a minimum 1 year of experience in anesthesia. A Dräger Primus anesthesia workstation monitor with a side stream EtCO2 analyzer was used for capnography. USG confirmation was done by an anesthetist who had experience of successfully diagnosing minimum 20 ETI8,9 with the help of USG and had PCPNDT authorization to use USG for diagnostic purposes. A linear USG probe of frequency 6-13 MHz (Sonosite Edge) was used for scanning. Intubation and confirmation of ET placement of tube were done by two different anesthetists. An anesthetist confirming the ET placement of tube by USG was kept blinded to the Capnographic tracing. A third person who was not directly involved in the intubation process was asked to note the time taken for the procedure using a stopwatch.

Time taken for successful confirmation of ETI by traditional methods was taken as from attachment of breathing circuit till confirmation of ET placement of tube by capnography (appearance of first square wave capnogram) and confirmation of B/L equal entry by auscultation. Time taken for successful confirmation of ETI by USG was taken as from placement of the probe in suprasternal notch till confirmation of proper placement of tube by visualizing a single Air-Mucosa (A-M) interface with comet tail artifacts and posterior shadowing in the region of trachea and then looking for sliding lung sign B/L on the chest wall (normally, the pleura moves with respect to the ribs).

Patients were kept nil by mouth for 6 hours for solids and 2 hours for clear liquids before surgery. In the operation theatre, essential anesthesia monitors-electrocardiogram (ECG), noninvasive blood pressure (NIBP), pulse oximeter (SpO2), and EtCO2 were attached and baseline parameters were monitored. A 20 G Intravenous cannula was inserted. Intravenous fluids in the form of crystalloids were started depending on the clinical status of the patient and the surgery for which the patient was posted.

In case of group B patients US machine was kept ready with a selection of adequate depth depending on the Body Mass Index (BMI) of the patient. For tracheal USG depth of 4 cm was kept for patients in both groups. However, for sliding lung sign depth of 4.9 cm was kept for patients with BMI > 25 and of 4 cm for patients with BMI < 25.

Patients were preoxygenated with 100% oxygen for 3 minutes. Injection midazolam 0.03 mg/kg and injection fentanyl 2 mcg/kg were given to sedate the patient. Patients were then given intravenous induction agent - Injection propofol 2 mg/kg or thiopentone 5 mg/kg in titrated doses as appropriate. After the loss of eye lash reflex and confirmation of mask ventilation of the patient, intravenous skeletal muscle relaxant, depolarizing or nondepolarizing agents as appropriate, were given. Patients were mask ventilated for 3 minutes with 100% O2 and Inhalational agents as appropriate to deepen the plain of anesthesia. End tidal capnogram was traced during the mask ventilation.

The first anesthetist did the direct laryngoscopy and intubated the patient with ETT of appropriate size.

In group A, after placement of the tube and attachment of the breathing circuit, the second anesthetist confirmed the endotracheal placement of the tube by interpreting the EtCO2 and then confirmed bilaterally equal air entry by auscultating the chest bilaterally in the second intercostal space in the midclavicular line and then the sixth intercostal space in mid axillary line.

In group B, after the placement of the tube and attachment of the breathing circuit, the second anesthetist confirmed the endotracheal placement of tube by keeping the USG probe on the anterior aspect of neck in the transverse axis just above the suprasternal notch and visualizing single A-M (air mucosal interface) with comet tail artifacts and shadowing. He/she simultaneously ruled out esophageal intubation by looking for two A-M interfaces called “double tract sign.” just lateral to trachea10 (Fig. 1).

Fig. 1: ETT in trachea

After confirmation of the ETI, the linear US probe was placed in the anterior axillary line in the sagittal plane so that the upper part of the probe was over the second intercostal space.11 First, the ribs and then the pleural line was identified. Air entry to the lung field as indicated by lung sliding was sought12 (Fig. 2).

Fig. 2: Sliding lung sign

The presence or absence of these signs bilaterally were noticed and documented. During this course safety of the patient was not compromised and end tidal capnogram was attached and monitored in patients of the USG group too. Second anesthetist confirming the correct placement of tube by USG was blinded to the capnographic tracing on the multipara monitor.

Time required for confirmation of ETI and bilateral equality of lung ventilation in group A and group B was noted in seconds. In both, groups, the correct placement of ETT was confirmed and documented as present or absent. In both the groups, confirmation of bilaterally equal lung ventilation was documented as confirmed, doubtful, or absent.

In both the groups if bilateral equal lung ventilation was not confirmed, check laryngoscopy was done and the length of the tube in the trachea was adjusted under vision till bilateral equal air entry was confirmed by auscultation in group A or by bilaterally equal lung slide sign in group B. Patients requiring check laryngoscopy were noted.

According to a study done by Parab SY et al.,13 the average accuracy rate of clinical methods to confirm the endotracheal placement of tube was 57% and a hypothesized 20% difference in accuracy with USG, the sample size was calculated as follows:

Considering the level of significance 5% and power of the study 80%.

n = [(Zα/2 + Zβ)2 × {2(ó)2}]/ (μ1- μ2)2

n = [(1.96 + 0.84)2 × {2 (0.4)2 }]/ (0.2)2 = 63

n = sample size in each group, total: 126 subjects which was rounded of to 130 patients.

Primary data was collected by observation method which was controlled, structured, and nonparticipant type. After data collection, data entry was done in Microsoft Office Excel 2007. Data analysis was done with the help of SPSS Software version 21. Quantitative data was described using mean ± standard deviation; comparison between the quantitative variables was done by using t -test. Qualitative variables were analyzed using Chi-square test or Fischer’s exact test. p- value < 0.05 was considered as significant.

RESULTS

The demographic details such as age, gender, BMI, and ASA were comparable in both groups (Table 1). Tracheal USG confirmation time in group B (2.8 ± 1.9 sec) was significantly lower than EtCO2 confirmation time in group A (7.5 ± 2.4 sec) (p = 0.03) (Fig. 3 ). There was no significant difference between the time taken to confirm bilaterally equal air entry by auscultation in group A and USG sliding lung sign in group B.

Table 1: Comparison of age, gender, BMI, and ASA of group A and B
Group A Group B
Age (yrs) 46.34 ± 15.7 49.91 ± 9.4
Gender
Male 20 (30.8%) 16 (24.6%)
Female 45 (69.2%) 49 (75.4%)
BMI (Kg/m2) 25.5 ± 6.1 25.6 ± 5.9
ASA status
ASA I 20 (30.76%) 23 (35.38%)
ASA II 45 (69.23%) 42 (64.61%)

Fig. 3: Comparison of time (in seconds) taken for confirmation of correct placement of endotracheal tube between group A (end-tidal capnography) and group B (tracheal ultrasonography)

Total time taken for confirmation with USG (16.87 ± 8 sec) was faster than auscultation and capnography (24.7 ± 10.6 sec) but was not statistically significant (p = 0.43) (Fig. 4).

Fig. 4: Comparison of total time (in seconds) taken to confirm correct placement of endotracheal tube between group A (end-tidal capnography + auscultation) and group B (tracheal USG + USG sliding lung sign)

Both the methods of ETI confirmation, that is, capnography with auscultation and USG identified ETI, endobronchial intubations, and esophageal intubations, in first attempt, and there were no doubtful cases. Thus, both the methods were compared with respect to efficacy.

BMI had a significant association with time, in the auscultation group with a p- value of <0.01 (Fig. 5). However, time required for USG confirmation was comparable across all BMI groups with a p = 0.24.

Fig. 5: Association of BMI (kg/m2) with the time to confirm bilateral equal air entry (in seconds) in group A (auscultation), using ANOVA test

DISCUSSION

In the present study, tracheal USG confirmation time in group B (2.8 ± 1.9 sec) was significantly lower than EtCO2 confirmation time in group A (7.5 ± 2.4 sec) (p = 0.03). Our results were comparable with the study conducted by Karacabey S et al. but their confirmation times were long as the study was done in patients undergoing resuscitation.5 Study conducted by Reddy DA et al. also found USG to be a faster modality than capnography but the comparison of timings with our study is difficult as this study was done in emergency settings in ICU and they did not have clear endpoints for measurements.4 Abhishek C et al. found capnographic confirmation to be faster than USG confirmation which could be due to the fact they scanned both transverse and longitudinal views for confirmation while we scanned only transverse view of trachea.14

Several studies reported that the time required to perform transtracheal USG ranged from 5-45 seconds.4 Many of these studies have been done in an emergency setting in patients requiring emergency intubations or in critically ill patients in intensive care units where conditions may not be ideal adding variability to the results. We conducted our study in an elective setting of the operation theatre with clearer definitions for time measurements. This attributes to the shorter USG timings that we have observed for confirmation of placement of ETT.

In our study we found that time taken to confirm bilateral equal air entry was equivocal by sliding lung sign and auscultation similar to Bache S et al.15 However, the difference in the timings can be attributed to the fact that they calculated time for confirmation from the introduction of the laryngoscope in the mouth while we calculated from attachment of breathing circuit till confirmation of air entry.15

In our study, taking into consideration Tracheal USG with EtCO2 and USG sliding lung with auscultation timings together, confirmation of ETT placement in group B (16.87 ± 8 s) was faster than in group A (24.7 ± 10.6 s) but was not statistically significant (p = 0.43).

In our study both the methods of ETI confirmation, that is, capnography with auscultation and USG identified ETI, endobronchial intubations, and esophageal intubations in the first attempt and there were no doubtful cases. Thus, both the methods were compared with respect to efficacy. Reddy DA et al.demonstrated sensitivity and specificity of USG diagnosis of ETI as 98.63% and 100%, respectively.4 Abhishek C et al. indicated a good agreement between the two methods, that is, EtCO2 and USG, and found the sensitivity of 96.84% and specificity of 100%.14 Another study conducted by Adi et al. showed tracheal USG to have a sensitivity of 98% and specificity of 100%.16 Sim SS et al. in their study found an overall accuracy of USG in confirming ETI to be 88.7%.17 This might be because of their study population which included patients receiving resuscitation and emergency intubations.

In most of the studies done in the past, efficacy has been described in the form of sensitivity, specificity, positive predictive value, and negative predictive values. Here both the methods of confirmation were used in the same patient and doubtful confirmations of one method were confirmed with the other method whereas, in our study, despite having 100% efficacy, the two methods could not be compared as they were used in two different groups of patients.

BMI had a significant association with time, in the auscultation group with a p- value of <0.01. However, time required for USG confirmation was comparable across all BMI groups with a p = 0.24. Our findings were corroborated by Rajan S et al. who studied the rapidity and efficacy of USG sliding lung sign and auscultation in confirming ETI in overweight and obese patients in 20 patients with BMI < 25 (group A) and 20 patients with BMI ≥ 25 (group B). They found out that auscultation was more rapid in group A (9.34 ± 2.43 sec) as compared to group B (14.35 ± 5.53 sec) with a p = 0.001. Whereas there was no significant difference in USG confirmation time in both their groups (8.57 ± 2.05 s vs 8.61 ± 1.66 s).18

Limitations of our study are that we have used only the transverse view of trachea on USG. Use of longitudinal view along with transverse view would have helped in further confirmation of ETI but would have increased the diagnostic time. Further we have used a side stream capnogram, whereas a mainstream capnogram would have given a faster response time.2

Use of real time tracheal USG in the longitudinal view along with transverse view and main stream capnogram are areas that require further investigations.

Future Scope

No previous study has calculated the total time taken for confirmation of ETI in elective settings of operation theatres. More such studies can be done and results compared and this data can be used for meta analysis. In our study we have found better visualization of sliding lung sign at anterior axillary line, especially on left side, against the previous studies which kept the USG probe at mid clavicular line. Studies comparing the two methods of probe placements can be done in the future.

CONCLUSION

We conclude that confirmation of ETT placement in trachea by USG is faster than capnography, whereas time taken to confirm bilaterally equal air entry is equivocal by USG sliding lung sign and auscultation. However, both the methods are comparable with respect to efficacy and can detect endobronchial as well as esophageal intubations with accuracy. In addition, USG is a faster modality for confirming bilaterally equal air entry in patients with higher BMI whereas auscultation takes a longer time.

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