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Table of Contents
Year : 2022  |  Volume : 6  |  Issue : 3  |  Page : 177-181

Accuracy Comparison between Four Methods of Endotracheal Tube Diameter Estimation for Pediatric Patients: An Observational, Cross-sectional Study

Department of Anesthesiology and Intensive Care, Faculty of Medicine, Udayana University, Bali, Indonesia

Date of Submission28-Feb-2022
Date of Decision28-Mar-2022
Date of Acceptance04-Apr-2022
Date of Web Publication10-May-2022

Correspondence Address:
Christopher Ryalino
Department of Anesthesiology and Intensive Care, Faculty of Medicine, Udayana University, Jl. PB Sudiman, Denpasar 80232, Bali
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/bjoa.bjoa_69_22

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Background: Successful intubation with the correct endotracheal tube (ETT) size is more difficult to achieve in pediatric patients. Several estimation methods exist, including ultrasonography and several conventional methods, but it is unclear which would be the most accurate method. Thus, this study aimed to compare the accuracy between several ETT diameter estimation methods. Materials and Methods: This was an observational study with a cross-sectional design. The sample includes pediatric patients (0–6 years) at a tertiary hospital recruited from January 2022 to March 2022. Primary data evaluated included age, gender, height, weight, actual ETT size used in the procedure, and the estimation of ETT size obtained by four different methods: ultrasonography, little finger diameter, little fingernail width, and age-based formula. Primary analysis was linear regression test between estimated diameter and the actual ETT diameter used in the procedure, controlling for potential confounders. The accuracy of each ETT size estimation method was seen from the values of the B and R2 coefficients from the linear regression test results. Results: Ultrasonography was found as the most accurate method, with B and R2 coefficients of 0.963 and 0.991, respectively. Among conventional methods, the diameter of the little finger was the most accurate (B = 0.918, R2 = 0.772). The age-based formula method was found to be the least accurate (B = 0.797, R2 = 0.735). Conclusion: Linear regression tests confirmed that the ultrasonography was the estimation method with the highest accuracy. For healthcare facilities with limited resources, the estimation method with little finger diameter should be considered.

Keywords: Cross-sectional study, intratracheal, intubation, ultrasonography

How to cite this article:
Putra SR, Senapathi TG, Hartawan IG, Ryalino C, Pradhana AP. Accuracy Comparison between Four Methods of Endotracheal Tube Diameter Estimation for Pediatric Patients: An Observational, Cross-sectional Study. Bali J Anaesthesiol 2022;6:177-81

How to cite this URL:
Putra SR, Senapathi TG, Hartawan IG, Ryalino C, Pradhana AP. Accuracy Comparison between Four Methods of Endotracheal Tube Diameter Estimation for Pediatric Patients: An Observational, Cross-sectional Study. Bali J Anaesthesiol [serial online] 2022 [cited 2022 Aug 10];6:177-81. Available from: https://www.bjoaonline.com/text.asp?2022/6/3/177/344955

  Introduction Top

Endotracheal tube (ETT) intubation in pediatric patients has been known to be difficult. It is caused by a variety of reasons, mainly the different anatomy between children’s respiratory tract and an adult. Pediatric respiratory tracts are funnel-shaped with its narrowest point at the cricoid cartilage, higher larynx, and relatively larger tongue.[1] This anatomic difference led to difficulties in intubation, especially in regard to the selection of the appropriate ETT diameter to use for the procedure.

Inappropriate ETT diameter used in intubation may lead to complications, both during the intubation process and after extubation including cases of intubation-related lesions at the larynx.[2] These cases were mostly related to inappropriately large ETT diameter used in pediatric patients.[3],[4] On the opposite end, inappropriately small ETT diameter may lead to leaks, increased airflow resistance, and inadequate ventilation, which may require traumatic reintubation process.[5]

In the face of this condition, there is a real need for a method to accurately estimate ETT diameter for pediatric patients. Currently, there are several methods available. There are conventional methods that approximate ETT diameter with physical examinations such as little finger diameter or width of little fingernail. These structures were used to approximate ETT diameter based on the similarity of its underlying cartilage-based anatomical structure with that of the pediatric trachea.[6] Other methods include age-based formula.[1] Newer technology has also emerged as alternatives, with ultrasonography being the most likely candidate.[7],[8]

Nevertheless, there have been few studies comparing the accuracy of different ETT diameter estimation methods. Most importantly, very few, if any, studies reported the accuracy of these methods in Southeast Asian population. The few studies available mostly reported results from Caucasian, Indian, or East Asian population.[8],[9],[10] As such, we conducted this study to provide evidence-based literature on the comparison of accuracy in ETT diameter estimation between four estimation methods in Southeast Asian population.

  Materials and Methods Top

This study was an observational study with cross-sectional design. Subjects were pediatric patients (aged 0–6 years) undergoing surgical procedure in a tertiary hospital in Bali, Indonesia between February 2022 and March 2022. The study was approved by the institutional ethical committee (registry number 160/UN14.2.2.VII.14/LT/2022 issued on January 24, 2022). We specifically recruited patients using uncuffed ETT during the surgical procedure and excluded patients with physical status classification of ASA IV. Other exclusion criteria were airway difficulties, including congenital disorders of the airway or neck region as well as premature and/or low birth weight neonates; patients with a past history of airway surgical procedure; and allergic reaction to ultrasonography gel.

Data collection procedure was initiated with eligibility screening from medical record data during presurgical examination. At the same time, we collected basic characteristics data, including age, sex, body weight, and body height/length. After the subjects’ parents consented to the study, ETT diameter estimation was conducted using four methods: ultrasonography, little finger diameter, little fingernail width, and age-based formula. During presurgical intubation procedure, we further take note of the actual ETT diameter used.

The ultrasonography estimation was conducted at the cricoid cartilage level using a linear transducer (Mindray Medical International, Ltd., Shenzhen, China). The ultrasonography probe was placed transversally to the body axis at suprasternal notch. The probe was then moved cranially until vocal cord was identified as V-shaped hyperechoic structure. The probe was then slowly moved caudally until cricoid cartilage was identified as hyperechoic curved structure. Airway would be identified as hypoechoic structure, which was estimated to be corresponding to the outer diameter of ETT.

Of the conventional estimation methods, the little finger diameter and little fingernail width were examined at the distal phalanges of the fifth finger of the patient’s right hand using a digital vernier caliper produced by PT. Micha Teknologi Indonesia Bersatu, Tangerang, Indonesia, which was accurate until one one-tenth of a centimeter. Meanwhile, the age-based estimation was conducted using Cole’s formula as described by Pillai et al.[11]

Estimated ETT diameter figures were then tested for its correlation with the actual ETT diameter used in the surgical procedure. Bivariate correlation analysis was conducted to this end. Further, we also conducted linear regression between each estimated ETT diameter and the actual ETT diameter controlling for patient’s age, sex, body weight, and height. Accuracy was determined based on the degree of correlation between estimated ETT diameter and actual ETT diameter, both in bivariate and multivariate tests. All statistical analyses were conducted using IBM SPSS 25.0 (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp.). A P value of <0.05 was considered significant.

  Results Top

Characteristics of subjects can be seen in [Table 1]. The final analysis included 40 subjects, including 26 (65%) males and 14 (35%) females, with a median age of 8 months (interquartile range, IQR: 8–48 months). Body weight and height were distributed normally with a mean of 12.09 ± 4.67 kg and 89.18 ± 20.73 cm, respectively. Meanwhile, an actual ETT diameter used for the subjects showed nonnormal distribution with a median of 6.0 (IQR: 5.5–6.0) mm.
Table 1: Characteristics of subjects

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The estimation of ETT diameter showed considerable variation between the different methods described in this study as shown in [Table 2]. The estimation using ultrasonography found an estimated ETT diameter of 6.1 (IQR: 5.5–6.3) mm. This is considerably higher than the estimation with other methods. Age estimation found wider variation with a median of 5.5 mm and IQR from 5.5 to 7.0 mm. Meanwhile, the estimation by little finger diameter and little fingernail width found similar estimates with a median of 5.6 (5.3–6.0) mm and 5.5 (5.1–5.9) mm, respectively.
Table 2: Estimated ETT diameter based on several estimation methods

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Bivariate correlation analysis showed an estimated ETT diameter figures from different estimation methods to be correlated significantly with an actual ETT diameter (P < 0.001) as seen in [Figure 1]. However, the estimation from ultrasonography was shown to have the most linear correlation with actual ETT diameter with Spearman’s Rho of 0.972. The estimation by little finger diameter and little fingernail width was found to have an equal correlation with an actual ETT diameter, with Spearman’s Rho of 0.867 for both methods. Meanwhile, age-based estimation was found to have the weakest correlation with Spearman’s Rho of 0.842.
Figure 1: Scatter plot showing correlation between actual and estimated ETT diameter using (a) ultrasonography, (b) age-based formula, (c) little finger diameter, and (d) little fingernail width

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Furthermore, a multivariate linear regression also found similar results as shown in [Table 3]. Although all estimate figures were independently associated with an actual ETT diameter after controlling for confounders, the ultrasonography estimate has the most linear association with B and R2 values of 0.963 and 0.991, respectively. Among conventional estimation methods, the little finger diameter has the highest accuracy with B and R2 values of 0.918 and 0.772, respectively.
Table 3: Multivariate linear regression for each estimation method (controlling for sex, age, body weight, and height)

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  Discussions Top

The accuracy of ultrasound in the estimation of ETT size in pediatric patients is in accordance with previous studies. One of the previous studies has found that the estimation of ETT size using ultrasound can predict ETT size used with up to 90% accuracy in pediatric patients.[7],[12] At the same time, there were several studies that did not find a significant difference in the estimated size of the ultrasonographic ETT compared with other methods, as reported in one study in Egypt.[13]

Several alternative methods studied include estimation based on age, diameter of the little finger, and width of the little fingernail. The accuracy of the diameter of the little finger with the actual size of the ETT is still controversial. One study found that this method is not an accurate method for predicting ETT size.[12] However, other studies have reported that the diameter of the little finger is an estimate of the ETT size with precise accuracy, although it is not always the method of highest accuracy.[8],[14]

A literature review on the accuracy of the estimated ETT size with the age-based formula also found contradictory results. One of the findings found that there was no significant difference between the accuracy of the ETT size estimation using the fairly high precision method.[11] However, another study found that the accuracy of estimation based on age is only about 50% of the accuracy of estimation using ultrasound.[12]

The discussion above shows that there is a significant controversy regarding the method with the highest accuracy in estimating ETT diameter in pediatric patients. Our findings add to this plethora of evidence by showing all of these methods found an estimated ETT diameter with statistically significant association with an actual ETT used in procedure. Therefore, the selection of the best estimation method must also consider the advantages and disadvantages of each estimation method.

Consistent results were only found for the estimation by ultrasound method. The ultrasound method has consistently been found to have adequate accuracy, and several studies have found ultrasound to be the method with the highest accuracy for estimating ETT diameter.[12],[15],[16] The previous results are also consistent with those found in this study. Our results shown that not only ultrasonography accurately estimates actual ETT diameter, it was also the most accurate estimation method controlling for confounding effects from patients’ age, sex, weight, and height characteristics.

However, problems related to the use of ultrasound as an operational standard in estimating ETT diameter are constrained by several things, especially related to resources. Ultrasound equipment and expertise in using it are not universally available in all services requiring an ETT, such as intensive therapy or surgery. Hospitals with limited resources often do not have ultrasounds for all the rooms that require them or trained health workers to use them. The shortage of trained health personnel also exacerbates this problem. The accuracy of ETT size estimation using ultrasound is strongly correlated with the skill level of the operator, thus providing an element of subjectivity to this estimation method. These limitations certainly force health services to find alternative methods.

Estimating the ETT diameter using the age-based formula is an alternative that is easy to use, does not require large resources, and has high objectivity because it uses a standard formula. The discussion above has shown that there is controversy regarding the accuracy of estimating ETT diameter with the age-based formula. There are results that show this method has adequate accuracy.[11] On the other hand, there are also results that show this method is not appropriate.[12] In addition to the constraint regarding the lack of consistent evidence supporting the accuracy of this method in estimating ETT diameter, this method also cannot be applied to all age groups. In the age group less than 4 years, this formula refers to a fixed estimate.[11] This causes the accuracy of estimation with this method tends to decrease along with the younger age of the patient.[17]

Another alternative studied in this research is the little finger diameter and little fingernail width method. As described above, several studies have found this method to have adequate accuracy for estimating ETT diameter[8],[15],[17] although there are also studies with the opposite result.[12] The results of this study found that both of these methods have higher accuracy than the age-based formula method, where estimates of the diameter of the little finger or the width of the little finger nail have adequate accuracy at the age of less than 4 years and even less than 1 year.[8] In addition, although the measurement of the diameter of the little finger and the width of the little fingernail still has an element of subjectivity stemming from differences in measurement expertise between clinicians, the resources needed to train clinicians to estimate with this method are lower than the resources required for procurement and training ultrasound operator. Therefore, this estimation method can be used as an option in healthcare facilities with limited resources.

To the best of the authors’ knowledge, this study is one of the first to study the comparative accuracy of several methods of estimating ETT size in pediatric patients. Although there are previous studies conducted in various countries, research with samples from local populations is important given the anthropometric and anatomical differences of different ethnic groups, ethnicities, and races.[18] Therefore, the data from this study can be used as a more accurate reference for clinical practice in the Indonesian population in general and Bali in particular.

This research is not free from weaknesses. Some of the weaknesses of this study are the relatively small sample size of 40 people. Although it has met our calculated minimum sample size, this sample size cannot be generalized too broadly. Further studies are needed with a larger sample size and representing several healthcare facilities from various regions to increase the generalizability of the data of this study.

  Conclusions Top

Our results found that an estimated ETT diameter obtained by all estimation methods described in this study showed statistically significant association with an actual ETT diameter used in the surgical procedure of pediatric patients, which can be interpreted to have adequate accuracy. Further comparison of accuracy, as indicated by B and R2 coefficients, as well as practicability found ultrasonography to be the most accurate estimation method followed by little fingernail diameter method. In healthcare facilities with limited resource setting, little fingernail diameter should be considered as it does not require advanced equipment or personnel training required for ultrasonography.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Gehlaut P, Golhar M, Johar S, Kumar P, Nain R. A comparative evaluation of age based formula and ultrasonography to predict endotracheal tube size in paediatric patients. Indian J Clin Anesth 2020;7:477-82.  Back to cited text no. 1
Lambercy K, Pincet L, Sandu K. Intubation related laryngeal injuries in pediatric population. Front Pediatr 2021;9:594832.  Back to cited text no. 2
Wood JW, Thornton B, Brown CS, McLevy JD, Thompson JW. Traumatic tracheal injury in children: A case series supporting conservative management. Int J Pediatr Otorhinolaryngol 2015;79:716-20.  Back to cited text no. 3
Singh S, Grieve A, Loveland J. Spontaneous tracheal rupture in a 1-year-old child. J Pediatr Surg Case Reports 2015;3:104-6.  Back to cited text no. 4
Shrasti DT. 5th finger nail width as size of endotracheal tube—A case report. IOSR J Dent Med Sci 2013;11:50-2.  Back to cited text no. 5
Kim HY, Cheon JH, Baek SH, Kim KH, Kim TK. Prediction of endotracheal tube size for pediatric patients from the epiphysis diameter of radius. Korean J Anesthesiol 2017;70:52-7.  Back to cited text no. 6
Shibasaki M. Selection of pediatric endotracheal tube size by ultrasonography. Japanese J Anesthesiol 2011;60(Suppl. November):819-24.  Back to cited text no. 7
Singh S, Jindal P, Ramakrishnan P, Raghuvanshi S. Prediction of endotracheal tube size in children by predicting subglottic diameter using ultrasonographic measurement versus traditional formulas. Saudi J Anaesth 2019;13:93-9.  Back to cited text no. 8
Bae JY, Byon HJ, Han SS, Kim HS, Kim JT. Usefulness of ultrasound for selecting a correctly sized uncuffed tracheal tube for paediatric patients. Anaesthesia 2011;66:994-8.  Back to cited text no. 9
Schramm C, Knop J, Jensen K, Plaschke K. Role of ultrasound compared to age-related formulas for uncuffed endotracheal intubation in a pediatric population. Paediatr Anaesth 2012;22:781-6.  Back to cited text no. 10
Pillai R, Kumaran S, Jeyaseelan L, George SP, Sahajanandan R. Usefulness of ultrasound-guided measurement of minimal transverse diameter of subglottic airway in determining the endotracheal tube size in children with congenital heart disease: A prospective observational study. Ann Card Anaesth 2018;21:382-7.  Back to cited text no. 11
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Mahran E, Adlan S. Routine use of ultrasonography in prediction of uncuffed endotracheal tube size in pediatric patients. Ain-Shams J Anesthesiol 2019;11:9.  Back to cited text no. 13
Rajasekhar M, Moningi S, Patnaik S, Rao P. Correlation between ultrasound-guided subglottic diameter and little finger breadth with the outer diameter of the endotracheal tube in paediatric patients—A prospective observational study. Indian J Anaesth 2018;62:978-83.  Back to cited text no. 14
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Man R, Srilata M, Patnaik S, Rao P. Correlation between ultrasound-guided subglottic diameter and little finger breadth with the outer diameter of the endotracheal tube in paediatric patients—A prospective observational study. Indian J Anaesth 2019;49:257-62.  Back to cited text no. 15
Sharma D, Tabatabaii SA, Farahbakhsh N. Role of ultrasound in confirmation of endotracheal tube in neonates: A review. J Matern Fetal Neonatal Med 2019;32:1359-67.  Back to cited text no. 16
Kim EJ, Kim SY, Kim WO, Kim H, Kil HK. Ultrasound measurement of subglottic diameter and an empirical formula for proper endotracheal tube fitting in children. Acta Anaesthesiol Scand 2013;57:1124-30.  Back to cited text no. 17
Yamamoto T, Schindler E. Ideal depth of endotracheal intubation at the vocal cord level in pediatric patients considering racial differences in tracheal length. J Clin Med 2022;11:864.  Back to cited text no. 18


  [Figure 1]

  [Table 1], [Table 2], [Table 3]


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