European Journal of Cardiovascular Medicine

Endotracheal intubation is essential for airway maintenance and adequate ventilation to carry out various surgical procedures usually without any complications². Pediatric patients, because of their anatomical differences in airway compared to adults pose many challenges during endotracheal intubation. One such challenge is, in selecting the proper size endotracheal tube (ETT) required for intubation³.

Use of inappropriate size of ETT can cause significant morbidity and mortality. If ETT is too small it may result in inadequate ventilation, unreliable end tidal gas estimation, leakage of anaesthetic gases into the operating room environment, and an increased risk of aspiration. If a large ETT is used it may lead to upper airway complications like ulceration, local ischemia, scar formation, and also increased risk for subsequent subglottic stenosis and post extubation stridor³.

To avoid excessive airway instrumentation, repeated laryngoscopies and minimizing risk of trauma, the preanesthetic assessment of tracheal diameter is important to select appropriate ETT size estimation². Selection of ETT based on children demographic data like age, weight, height, diameter of childs little finger. The success rate of these demographic data in correct prediction of ETT size is variable.

The level of the cricoids cartilage plays an important role for selection of appropriate size ETT being the narrowest diameter of upper airway². Recent studies have documented that the anatomical structures in the supraglottic, glottis and subglottic regions can be determined by ultrasonography.

The ultrasonography is a simple, reliable, safe, and noninvasive pain free modality for evaluation of the upper airway’s narrowest transverse diameter at the subglottic region and may be helpful to estimate the proper size endotracheal tube⁴. Hence, we undertook this study to assess the accuracy of USG guided tracheal diameter measurement in predicting ETT size in pediatric patients and its comparison with that determined by age based formula.

After institutional ethical committee approval and written consent from parents, this prospective observational study was carried out in pediatric patients of either sex, aged between 2 and 6 years posted for elective surgery under general anaesthesia in hospitals attached to Bangalore medical college and research institute, Bangalore. The sample size was 50.

Inclusion criteria:

• Pediatric patients( 2 – 6yrs) of both genders will be included after receiving informed written parental consent
• ASA class 1&2
• Those who undergoing elective surgeries under general anesthesia with orotracheal intubation.

Exclusion criteria

• Patients with anticipated difficult intubation
• Patients with history of facial , cervical, pharyngeal, and epiglottis surgery or trauma.
• Facial dysmorphism, syndromic children, recent history of URTI.
• Patients with anterior neck swelling like thyroid swellings.
• Patients with tracheostomy tube

All patients were subjected to a routine pre anaesthetic check up. During this thorough history, general examination and calculation of ETT size using age related formula was carried out.

Age based formula used was Motoyama

ID in mm = 0.25×( age in years ) + 3.5

On the day of surgery, all children were nil per oral according to ISA guidelines. General anesthesia was induced with a dose of 2mg/kg propofol after appropriate premedication as per institutional protocol . An intubating dose of atracurium 0.5mg/kg was injected to all patients for muscle relaxation. Patient was then mask ventilated with sevoflurane and oxygen for 3mins for optimal muscle relaxation prior to intubation. During mask ventilation subglottic tracheal diameter was measured using an ultrasound.

The subglottic diameter was determined using a high resolution linear small foot print probe ( 7-15 Hz ) of ultrasound machine placed on midline of the anterior neck with the head extended and neck flexed during mask ventilation. The cricoid arch is visualized as a round hypoechoic structure with hyperechoic edges. The transverse air column diameter was measured at the lower edge of the cricoid cartilage which is considered as the subglottic tracheal diameter

Figure 1

The endotracheal tube size estimated by ultrasonography was used for endotracheal intubation. The same brand of uncuffed ETT (portex ) was used for all children. Endotracheal tube size was confirmed by performing leak test. Leak was measured on ventilator ,using closed pediatric circle absorber system. ETT size was considered optimal when the tracheal leak (auscultation over trachea) was detected at an inflation pressure of 10-20cm of H2O. If there was no audible leak when the lungs were inflated to a pressure of 20-30cm H2O, the tube was exchanged with 0.5mm smaller tube. But if a leak occurred at an inflation pressure of less than 10cm H2O the ETT was exchanged with a 0.5mm larger tube. After leak test thorough throat packing done.

In this study analysis, Data was entered in MS Excel and analyzed using SPSS 22 Software. Statistical analysis was done using mean and standard deviation for the agreement for selected ETT selected by means of USG, age based formula. Kappa statistics was performed to see the variability and agreement level between 3 measurement variables.

*p < 0.05 is statistically significant.

*p > 0.05 is statistically insignificant.

Demographic characteristics:

In our study, 46% of patients were female children while remaining 54% of patients were male children belonging to different age groups, ranging from 2 to 6years.

Table 1: Comparison of ETT size (in mm) estimated by Age related formula with ETT size used clinically

The mean difference between ETT estimated by diameter of little finger and actual ETT inserted was -0.135. There was a statistically significant difference(p value < 0.019) between ETT estimated Age related formula and actual ETT inserted.

Table 2: Comparison of ETT size (in mm) estimated by USG with ETT size used clinically.

The mean difference between ETT measured by USG and actual ETT inserted was 0.018. There was statistically significant difference (p value = 0.001which is < 0.05) between ETT measured by USG and actual ETT inserted.

Table 3: Agreement between actual ETT inserted with ETT measured by age-based formula and ultrasonography

Agreement between actual ETT inserted and ETT estimation by age-based formula was weak (52.18) and the kappa value was 0.399, but agreement between actual ETT inserted and ETT estimation by USG was strong (88%) and the kappa value is 0.853. this agreement was statistically significant (p=<0.001).

The selection of the appropriate endotracheal tube size during pediatric anesthesia remains one of the most important and challenging task. The most commonly used method for determination of ETT size is age based formula. The most common among them are modified Cole’s (age in years /4+4 for cuffed ETT ), Motoyoma [0.25×( age in years ) + 3.5], Penlington’s ( age in year /3 +3.5 ), Khine’s ( age in years /4 +3 ) and Broselow tape. We used Motoyoma formula. In our study, age based formula predicted correct ETT size in only 52% of pediatric patients.

Neha Bhardwaj and co workers compared age based formula, diameter of little finger and ultrasonography for estimation of correct ETT size in 50 patients aged between 2 to 6 years. The correct ETT predicted by age based formula was only 56% and by USG was 90% , which strongly correlates with our study.

Schramm and colleagues, reported that USG estimation of ETT was associated with reduced repeated intubation attempts compared to that determined by age based formula in pediatric patients below 5 years of age. The results of our study were comparable to the study conducted by Altun et al., who also found that subglottic diameter measured by USG was a better predictor for estimation of appropriate ETT size. But they used cuffed ETT for their study.

Gupta K et al. in his study found that there was high correlation between clinically used ETT and predetermined ETT by USG than predicted by age based formula. Their study also showed that direct measurement of the subglottic diameter by USG predicted the appropriate ETT size. Our study results were comparable with their findings. However, their study does not clearly indicate whether cuffed or uncuffed ETT was used.

Shibasaki et al., in his study conducted on 192 pediatric patients of aged 1month to 6 years. He found that rate of agreement between the predicted ETT size based on USG and final ETT size selected clinically was 98% for cuffed ETTs and 96% for uncuffed ETTs. Our study results were comparable with their findings. But they used both uncuffed and cuffed ETTs.

Pughal vendan et al. concluded that the subglottic diameter at the cricoid region is a better tool in predicting the appropriate size uncuffed ETT than modified cole’s formula. Similarly , in our study we found that subglottic diameter at the cricoid region is a better tool in predicting the appropriate size uncuffed ETT.

The recent report on feasibility of USG to examine the subglottic diameter showed a strong correlation between USG and MRI.

This study has revealed the potential utility of ultrasound to measure the transverse diameter of the upper airway at the subglottic region for the selection of appropriate sized ETT. It has future scope in small for age, neonates and Prediction of post extubation stridor.

Determination of endotracheal tube size by ultrasound is a good predictor of proper sized endotracheal tube in pediatric age group when compared with age based formula and it reduces the number of reintubation.

Financial support and sponsorship: Nil

Conflicts of interest: There are no conflicts of interest.

Acknowledgements:

First and foremost I thank our institution for providing platform and opportunities for conductind this study and also for providing required equipment. I also thank our HOD and other senior professors for guiding me throughout the study and for constant support from topic selection, methods and methodology, proofreading and interpretatuion of results. I would like to thank statistical team for the analysis of the data. I thank the study subjects and their parents for taking part in the study and also thank our surgical colleagues for their support.

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