Predicted vs. Actual Endotracheal Tube Size in Pediatric Cardiac Surgery for Children with Down Syndrome

ABSTRACT

Background:

Children with Down syndrome have a higher risk of upper airway obstruction and smaller tracheal lumens due to conditions like subglottic stenosis and laryngomalacia. While the Cole formula is widely used to predict endotracheal tube (ETT) size in non-syndromic children, this formula may be inappropriate for children with Down syndrome undergoing cardiac surgery.

Objectives:

The primary objective was to determine whether the actual endotracheal tube size used in children with Down syndrome undergoing cardiac surgery matches the size predicted by the Cole formula. The secondary objectives included age-stratified comparisons (<1 year vs. ≥1 year) of predicted versus actual endotracheal tube size used, along with the impact of airway characteristics, drug usage, and postoperative outcomes on the actual endotracheal tube used.

Settings and Design:

A retrospective cohort study at a single tertiary pediatric cardiac center.

Measurements and Main Results:

A total of 182 pediatric patients with Down syndrome who had cardiac surgery were enrolled. Data were collected from patients with Down syndrome who had cardiac surgery with tracheal intubation using uncuffed ETTs. Patients were divided into two groups: those under one year of age and those one year or older.

Results:

The actual ETT size used was statistically different from the size predicted by the Cole formula across all patients (P < 0.001). The difference between the actual and predicted ETT sizes remained significant in both age groups and did not decrease with age [both groups: P <0.001]. For the entire cohort, the actual ETT size was smaller than predicted by the standard Cole formula, with a correlation coefficient of 0.797. Infants with Down syndrome under one year of age were more likely to be on anti-failure medications (64.2% vs. 43.9%, P = 0.011) and have more complex cardiac anomalies (RACHS-1 score) compared to older children. These conditions had not impact on the endotracheal tube size used. The incidence of reintubation was 11.9% in the younger group and 7.0% in the older group, with respiratory causes being the most common reason.

Conclusions:

The Cole formula consistently overestimated the required ETT size for children with Down syndrome undergoing cardiac surgery. While Cole’s formula can serve as a general guide, in children with Down syndrome, individual anatomical variations necessitate clinical judgment and adjustments. This highlights the need for improved methods to predict ETT size in this population.

INTRODUCTION

Children with Down syndrome are at an increased risk of upper airway obstruction due to various anatomical differences, including tracheal and subglottic stenosis, laryngomalacia, and tracheomalacia.[1,2] These children have smaller tracheal lumen diameters compared to their non-syndromic peers. Therefore, it has been widely suggested that an endotracheal tube [ETT] two sizes smaller than the standard for their age group should be used during intubation.[3]

The use of an appropriately sized ETT is critical during cardiac surgery to ensure an adequate airway seal, airway recruitment, and effective postoperative ventilatory maneuvers. The age-based Cole formula [ID (mm) = (age/4) +4.0] has long been used to select the appropriate ETT size in non-syndromic children.[4] We aimed to determine if the ETT size calculated based on age is appropriate for children with Down syndrome undergoing cardiac surgery and whether the endotracheal tube size used in these children matches the predicted age-appropriate size as they grow. This study was designed to address this research gap. We hypothesized that the actual ETT size used during pediatric cardiac surgery in children with Down syndrome would correspond with the age-predicted size derived from the Cole formula. Furthermore, we anticipated that concordance between predicted and actual ETT size would improve with increasing age, reflecting progressive airway growth and anatomical maturation.

The primary objective was to determine if the actual ETT size used for children with Down syndrome who had cardiac surgery differs from the size predicted by the established Cole formula. The secondary objectives included age-stratified comparisons (<1 year vs. ≥1 year) of predicted versus actual endotracheal tube size used, Cormack–Lehane grade at the time of tracheal intubation. The impact of anti-failure drug administration, pulmonary hypertension incidence, respiratory complications, and Risk Adjustment for Congenital Heart Surgery [RACHS-1] scores was assessed on the selection of the ETT used during surgery. The reintubation rates, stridor incidence, use of non-invasive ventilation, and in-hospital mortality were also analyzed.

MATERIALS AND METHODS

This retrospective cohort study was conducted at a single tertiary pediatric cardiac center that serves as a national referral center for congenital heart disease. The institution performs approximately 400 pediatric cardiac surgeries each year, including a significant number of syndromic and high-complexity cases. The study period spanned ten years, from January 1, 2010, to December 31, 2019. The study was approved by the institutional Scientific Research Committee [MoH/CSR/24/26170], and parental consent was waived due to its retrospective design.

The study included pediatric patients with Down syndrome, diagnosed by clinical features or karyotyping, who had cardiac surgery with tracheal intubation using uncuffed ETTs. Children on preoperative mechanical ventilation or those intubated with a cuffed ETT were excluded. Children who met the inclusion criteria but had missing documentation of key variables, including ETT type and size used, and Cormac–Lehane Grade evaluation, were excluded.

Eligible participants were divided into two groups: Group 1 (<1 year of age) and Group 2 (≥1 year of age) at the time of surgery. Data collected included demographic and clinical information, such as Cormack–Lehane Grade, actual ETT size used, anti-heart failure medication, incidence of pulmonary hypertension, postoperative tracheal extubation time, reintubation rates, and in-hospital mortality. The actual ETT size that was used was recorded from electronic intraoperative anesthesia records. Data were collected by independent investigators using a structured data-collection form. To reduce bias, the investigators were blinded to the study hypotheses during data extraction.

The actual ETT size referred to the internal diameter (ID in mm) of the final tube successfully placed and used for ventilation. The final ETT size used was determined by the clinician’s judgment based on resistance during tube passage, adequacy of air leak at peak inspiratory pressures, and confirmation of proper placement via auscultation and capnography.

The predicted ETT size for each patient was calculated using the Cole formula: ID (mm) = (Age in years/4) +4.0, rounded down to the nearest 0.5 mm to match available tube sizes. The Cole’s formula served as a theoretical guide, while the actual size was determined through individualized clinical assessment. All intubations were performed by pediatric cardiac anesthesiologists with at least five years of subspecialty experience.

Throughout the 10-year study period, uncuffed Portex^® endotracheal tubes (Smiths Medical, UK) were used. This minimized variability in outer diameter across different brands of endotracheal tubes. Consistency in the manufacturer prevented inter-brand differences in outer diameter that could otherwise confound comparisons between predicted and actual tube sizes. All intubations in our cohort were performed via the orotracheal route. Nasotracheal intubation was not routinely performed at our institution for pediatric cardiac surgical patients due to concerns about potential nasopharyngeal trauma.

Sample size

A minimum of 56 patients per group was required, for a total of 112 patients, as determined by G*Power 3.1 software with an expected correlation value of 0.80, an alpha error of 5%, and a power of 80%. Data were analyzed using IBM SPSS Statistics 29.0.

Statistical analysis

Data were analyzed using IBM SPSS Statistics 29.0 (IBM Corp. Released 2023. IBM SPSS Statistics for Windows, Version 29.0 Armonk, NY: IBM Corp). Categorical variables are reported as frequency and percentage. Associations between age groups and categorical clinical variables were evaluated using the Chi-square test, with Fisher’s exact or likelihood ratio applied as appropriate. Spearman’s rank correlation was used to assess the relationship between predicted and actual endotracheal tube size used in children. A two-tailed P value < 0.05 was considered statistically significant. A Bland–Altman analysis was performed to assess agreement between predicted and actual tube sizes, quantifying the mean bias and the limits of agreement.

RESULTS

A total of 807 pediatric anesthesia records for children with Down syndrome were initially screened during the 10-year study period. Of these, 272 procedures involved general anesthesia with tracheal intubation. We then identified 216 cases specifically involving cardiac surgery. From this group, 34 patients were excluded based on predefined criteria: 22 had been intubated preoperatively, and 12 had incomplete documentation of key variables, including ETT type and size used and Cormac-Lehane Grade. No imputation was performed. The excluded records did not demonstrate clustering by age, RACHS-1 score, or perioperative outcome, suggesting that missingness was random and unlikely to bias the final sample. The final study cohort that completed the study consisted of 182 children with Down syndrome who underwent cardiac surgery with tracheal intubation using uncuffed ETTs [Figure 1]. There were statistically significant differences between the actual and predicted ETT sizes in the entire cohort as well as in both < and ≥ age 1 year groups (P < 0.001). The actual ETT size used was smaller than the size predicted by Cole›s formula. The tube size predicted by Cole’s formula showed only a moderate correlation with the actual tube size chosen by clinicians (r = 0.553 for <1 year, r = 0.589 for ≥1 year; overall r = 0.797; P < 0.001 for all). Across both age groups, the formula consistently predicted larger ETT sizes than were actually used in practice [Table 1]. The Spearman’s rank correlation was chosen after evaluating data distribution, as skewness, kurtosis, and mean–SD plots showed that the actual ETT size and the difference between predicted and actual sizes were non-normal. Therefore, Spearman’s rank correlation was used as a suitable non-parametric alternative to Pearson’s correlation. No adjustments were made for multiple testing because the analyses were exploratory and aimed to identify patterns rather than to make inferential comparisons across many independent hypotheses. The Bland–Altman plots for the entire cohort and the <1 year and ≥1 year groups showed a median bias of 0.0 mm, with 95% confidence intervals ranging from −1.0 mm to +0.5 mm, −0.7 mm to +0.5 mm, and −1.0 mm to +1.05 mm, respectively. This indicated an overestimation by the Cole formula, with greater variability in the differences. The Bland–Altman analysis clearly demonstrated the direction of the differences, supporting the conclusion that the Cole formula tends to overestimate ETT size in this cohort, especially in those younger than 1 year [Figures 2–4].

Figure 1.

Patient flow chart

Table 1.

Comparison of predicted and actual endotracheal tube [ETT] sizes in children with Down syndrome undergoing cardiac surgery

Age group	Variable	n	Correlation coefficient	P
<1 year	Predicted ETT	126	0.553**	<0.001
	Actual ETT
≥1 year	Predicted ETT	56	0.589**	<0.001
	Actual ETT
Overall	Predicted ETT	182	0.797**	<0.001
	Actual ETT

Correlation coefficients reflect the relationship between predicted and actual ETT sizes. **Indicates statistically significant deviation from predicted values

Figure 2.

Bland–Altman plot comparing predicted and actual ETT sizes, showing mean bias and 95% limits of agreement for the overall cohort

Figure 4.

Bland–Altman plot for children ≥1 year of age

Figure 3.

Bland–Altman plot for children <1 year of age

Among the 182 children with Down syndrome, when perioperative characteristics were compared between those aged <1 year and ≥1 year, the route of anesthesia induction (inhalational vs. intravenous) did not differ significantly between groups (P = 0.477), nor did the distribution of Cormack–Lehane grades (P = 0.222), with Grade I views predominating in both cohorts. On-table extubation was significantly more frequent in older children (40.0% vs. 10.9%, P < 0.001), reflecting greater physiological stability. Reintubation rates were lower in the ≥1 year group (7.1% vs. 12.2%), though not statistically significant (P = 0.435), and respiratory causes remained the predominant reason for reintubation in both age groups (P = 1.000). Post-extubation stridor occurred more often in older children (5.4% vs. 1.6%), but without statistical significance (P = 0.175). Use of non-invasive ventilation post-extubation was significantly higher in infants <1 year (11.3% vs. 1.8%, P = 0.040), suggesting increased vulnerability to respiratory compromise. In-hospital mortality was higher in the younger cohort (12.1% vs. 7.1%), though this difference did not reach statistical significance (P = 0.435) [Table 2].

Table 2.

Comparison of perioperative variables between age groups (<1 year vs. ≥1 year)

Variable	<1 year (n=118)	≥1 year (n=56)	P
Induction of Anesthesia
Inhalational	37 (31.4%)	14 (25.0%)
Intravenous	81 (68.6%)	42 (75.0%)	0.477
Cormack–Lehane Grade
Grade 1	59 (52.7%)	36 (65.5%)
Grade 2	52 (46.4%)	18 (32.7%)
Grade 3	1 (0.9%)	1 (1.8%)	0.222
Tracheal Extubation Timing
On-table	13 (10.9%)	22 (40.0%)
Postoperative	106 (89.1%)	33 (60.0%)	<0.001
Reintubation
Yes	15 (12.2%)	4 (7.1%)
No	109 (87.8%)	52 (92.9%)	0.435
Cause of Reintubation
Respiratory	12 (80.0%)	3 (75.0%)
Non-respiratory	3 (20.0%)	1 (25.0%)	1.000
Post-Extubation Stridor
Yes	2 (1.6%)	3 (5.4%)
No	122 (98.4%)	53 (94.6%)	0.175
Non-Invasive Ventilation (BiPAP)
Required	14 (11.3%)	1 (1.8%)
Not Required	110 (88.7%)	55 (98.2%)	0.040
In-Hospital Mortality
Yes	15 (12.1%)	4 (7.1%)
No	109 (87.9%)	52 (92.9%)	0.435

Clinical characteristics and comorbidities were compared between children aged <1 year and those ≥1 year. Anti-failure medications were administered significantly more often in the younger cohort (63.7% vs. 42.4%, P = 0.010), consistent with increased myocardial vulnerability in infancy. Pulmonary hypertension was more prevalent in children <1 year (14.5% vs. 7.1%), though this difference was not statistically significant (P = 0.220). Respiratory and airway-related findings, including recurrent infections and laryngomalacia, were common across both groups, with no significant age-based differences (P = 0.094). Central nervous system anomalies, predominantly mental retardation, were uniformly present in the younger group and nearly universal in older children (P = 0.307). RACHS-1 scores differed significantly between groups (P = 0.031), with younger children more frequently assigned higher surgical complexity scores. Cardiac comorbidities also varied by age: complete atrioventricular septal defect was more common in the <1 year group (56.5% vs. 32.1%), whereas older children had a broader distribution of associated lesions including atrial septal defect, patent ductus arteriosus, and ventricular septal defect (P < 0.001) [Table 3]. There was no association between patient characteristics such as airway comorbidities (including recurrent infections, laryngomalacia, or suspected subglottic stenosis), pulmonary hypertension, and surgical complexity (RACHS-1) and variability in predicted versus actual endotracheal tube size [Table 4]. Spearman’s rho for weight was –0.178 [P = 0.018], indicating a weak but statistically significant negative correlation between weight and the difference between predicted and actual ETT size. Increasing weight was associated with a small, statistically significant tendency for the Cole formula to overestimate the required ETT size [Table 4].

Table 3.

Clinical and comorbidity profile by age group (<1 year vs. ≥1 year)

Variable	<1 year (n=124)	≥1 year (n=56)	P
Anti-Failure Medications
Yes	79 (63.7%)	24 (42.4%)	0.010
No	45 (36.3%)	32 (57.6%)
Pulmonary Hypertension
Yes	18 (14.5%)	4 (7.1%)	0.220
No	106 (85.5%)	52 (92.9%)
Respiratory and Airway Issues
Recurrent Infection	122 (98.4%)	53 (94.6%)	0.094
Obstructive Sleep Apnea (OSA)	–	2 (3.6%)
Laryngomalacia	2 (1.6%)	1 (1.8%)
Central Nervous System Findings
Mental Retardation	124 (100.0%)	54 (98.2%)	0.307
Microcephaly	–	1 (1.8%)
RACHS-1 Score
Score 1	47 (38.5%)	33 (62.3%)	0.031
Score 2	16 (13.1%)	5 (9.4%)
Score 3	54 (44.3%)	13 (24.5%)
Score 4	5 (3.8%)	2 (3.8%)
Associated Cardiac Comorbidities
AVSD	70 (56.5%)	17 (32.1%)	<0.001
VSD	31 (25.0%)	10 (18.9%)
PDA	16 (12.9%)	9 (17.0%)
ASD	–	12 (20.8%)
TOF	5 (4.0%)	4 (7.3%)
PVD	2 (1.6%)	2 (3.8%)

Table 4.

Association between patient characteristics and variability in predicted versus actual endotracheal tube size

Variables	Age-appropriate ETT size Median (IQR)	Actual ETT size Median (IQR)	Difference Median (IQR)	P
Age (spearman’s rho)			−0.119	0.112
<1 year	4.0 (4.0–4.0)	4.0 (4.0–4.0)	0 (−0.5–0)	0.296
>1 year	4.5 (4.5–5.0)	5.0 (4.5–5.0)	0 (−0.5–0)
Weight (Spearman’s rho)			−0.178	0.018
Respiratory and Airway Issues
Recurrent Infection	4.0 (4.0–4.5)	4.0 (4.0–4.5)	0 (−0.5–0)	0.867
Obstructive Sleep Apnea (OSA)	5.0 (4.5–5.0)	5.0 (5.0–5.0)	0 (−0.5–0)
Laryngomalacia	4.0 (4.0–4.0)	4.5 (3.5–4.5)	0 (−0.5–0)
RACHS-1 Score
Score 1	4.0 (4.0–4.5)	4.5 (4.0–5.0)	0 (−0.5–0)	0.582
Score 2	4.0 (4.0–4.5)	4.0 (4.0–4.5)	0 (−0.5–0)
Score 3	4.0 (4.0–4.0)	4.0 (4.0–4.5)	0 (−0.5–0)
Score 4	4.0 (3.5–4.0)	4.0 (3.0–4.5)	0 (−0.5–0)
Anti-Failure Medications
Yes	4.0 (4.0–4.5)	4.0 (4.0–4.5)	0 (−0.5–0)	0.489
No	4.0 (4.0–4.5)	4.5 (4.0–5.0)	0 (−0.5–0)
Pulmonary Hypertension
Yes	4.0 (4.0–4.5)	4.0 (4.0–4.5)	0 (−0.1–0)	0.677
No	4.0 (4.0–4.5)	4.0 (4.0–4.5)	0 (−0.5–0)

DISCUSSION

The study found that the actual ETT size used was statistically different from the predicted size (P < 0.001), which rejected the hypothesis that the two would be similar. The differences in predicted versus actual ETT sizes were quantified as follows: 55 children (30.2%) needed a tube 0.5 mm smaller, 104 children (57.1%) needed no change, and 21 children (11.5%) needed a tube more than 0.5 mm smaller. The difference between the predicted and actual ETT sizes remained consistent as the children grew, rejecting the second hypothesis that the difference would narrow with age. This finding supports the idea that every child with Down syndrome has a degree of subglottic stenosis as a fundamental feature of the syndrome.[1]

Airway management remains a cornerstone of safe anesthetic practice, particularly in pediatric populations and those with Down syndrome, where anatomical variations may pose unique challenges. Our findings are consistent with existing literature suggesting that tracheal intubation is generally straightforward in children, with difficult laryngoscopy being rare. Borland et al.[5] reported an incidence of difficult intubation of only 0.5% in pediatric patients with Down syndrome undergoing noncardiac procedures. In our cohort, the incidence of difficult laryngoscopy, as reflected by Cormack–Lehane Grade 3 views, was similarly low and was observed in only one patient in each age group.

Our data shows that infants with Down syndrome are more vulnerable to early cardiac decompensation, as evidenced by the significantly higher use of anti-failure medications in children <1 year of age compared to those ≥1 year (63.7% vs. 42.9%, P = 0.010). This likely reflects the hemodynamic burden of complex congenital heart defects, particularly complete atrioventricular septal defects, which are prevalent in this population and often manifest with congestive heart failure in early infancy. Furthermore, surgical complexity appeared to differ by age, with older children more frequently assigned a RACHS-1 score of 1 (62.3% vs. 38.5%, P = 0.031), suggesting either stabilization of cardiac anatomy over time or selection for less complex procedures in later childhood. Pulmonary hypertension remained a clinically significant concern in children with Down syndrome, particularly in the context of congenital heart disease. Prior studies have reported PH incidence rates as high as 28% in this population, with congenital heart disease-associated pulmonary arterial hypertension accounting for 44.8% and primary pulmonary hypertension for 35.3%.[6,7] In our cohort, the overall incidence of PH was lower, observed in 14.9% of children below 1 year, and in those ≥1 year, it was 8.8%.

It is essential to recognize the possible impact of potential confounders that may influence both ETT selection and perioperative outcomes in children with Down syndrome. Factors such as airway comorbidities (including recurrent infections, laryngomalacia, or suspected subglottic stenosis), pulmonary hypertension, and surgical complexity [RACHS-1] could theoretically alter the relationship between predicted and actual ETT size. In this retrospective dataset, we performed stratified analyses based on these clinical characteristics, and the discrepancy between Cole-predicted and actual ETT size remained consistent across all potential confounders. As for the weight of the cohorts, the effect size was small; nonetheless, a relationship that was not clinically significant existed, indicating that increasing weight was associated with a small but statistically significant tendency for the Cole formula to overestimate the ETT size [Table 4]. This supports the stability of the observations. However, because certain airway-specific variables like definitive subglottic stenosis grading or previous airway interventions were not consistently documented, the feasibility of a strong multivariable model was limited. As a result, some residual confounding might still exist.

Children with Down syndrome are known to have a high burden of respiratory comorbidities, including obstructive sleep apnea, recurrent pneumonia, chronic aspiration, and intermittent or sustained hypoxia. McDowell and Craven reported that these complications are common during childhood and contribute significantly to perioperative risk.[8] In our cohort, recurrent respiratory tract infections were nearly universal, affecting 98.5% of children <1 year and 94.7% of those ≥1 year, underscoring the pervasive nature of airway vulnerability in this population. Laryngomalacia was observed in both age groups, and one infant was diagnosed with obstructive sleep apnea. Although the incidence of obstructive sleep apnea was low in our study, this may reflect underdiagnosis or limited preoperative screening rather than actual absence. Post-extubation stridor is a recognized airway complication in pediatric patients with Down syndrome, particularly those undergoing cardiac surgery. To mitigate this risk, pediatric anesthetists often opt for smaller endotracheal tubes, balancing airway protection with the potential for subglottic injury. The incidence of post-extubation stridor in our study was higher in children ≥1 year of age (5.3%) compared to those <1 year (1.5%), although this difference did not reach statistical significance (P = 0.175). The slightly higher rate in older children may reflect cumulative airway trauma or anatomical rigidity. These rates are comparable to Borland et al.’s[5] reported 1.83% incidence of postintubation croup in children with Down syndrome undergoing noncardiac procedures.

In our cohort, the reintubation rate was 11.9% in children <1 year and 7.0% in those ≥1 year. Respiratory causes predominated in both age groups, accounting for 81.3% of reintubations in infants and 75% in older children, while non-respiratory etiologies were less frequent (18.8% and 25%, respectively). These rates are consistent with general pediatric cardiac surgery literature, which reports extubation failure rates ranging from 3 to 10%, with a higher incidence in neonates and complex congenital heart disease cases.[9] In children with Down syndrome specifically, Salgado et al.[10] reported extubation failure rates of 9.3%, with younger age and hypotonia contributing to increased risk. Our findings align with these data, reinforcing the vulnerability of infants with Down syndrome to perioperative respiratory complications due to factors such as smaller airway diameter, immature respiratory control, and a higher incidence of pulmonary hypertension or residual cardiac lesions. The relatively lower rate of reintubation in children over one year, along with a greater proportion of non-respiratory causes (25% vs. 20%), may reflect improved respiratory reserve and a more stable perioperative course in older patients. In the current study, the relationship between overprediction of ETT size and the incidence of reintubation or stridor was not statistically significant (P = 0.435).

In-hospital mortality in the current study was 6.0% in infants under 1 year and 1.8% in children 1 year or older, consistent with population-based studies of Evans et al.,[11] who showed that children with Down syndrome undergoing congenital heart surgery had lower odds of in-hospital death (OR = 0.60; 95% CI: 0.47–0.76; P < 0.05) compared to non-syndromic peers. This protective effect may be attributed to standardized perioperative protocols, early surgical intervention, and multidisciplinary care.

Congenital heart disease remains one of the most prevalent and clinically significant comorbidities in children with Down syndrome, with reported incidence ranging from 38% to 60% across populations.[12] Atrioventricular septal defect is consistently identified as the most common lesion, accounting for approximately 27% of cases in population-based studies.[13] Our findings reflect a markedly higher prevalence of atrioventricular septal defect, particularly in infants [P < 0.001], compared to 31.5% in children ≥ 1 year. This age-stratified distribution suggests that infants with Down syndrome not only present earlier with congenital heart disease but also tend to harbor more complex lesions requiring timely surgical intervention. Ventricular septal defect was the second most common lesion in the younger group (23.3%), while atrial septal defect predominated among older children (22.2%). These findings align with prior reports from consanguineous populations and underscore the importance of early echocardiographic screening and multidisciplinary planning.[13]

Accurate ETT sizing is critical in pediatric cardiac anesthesia, particularly in children with Down syndrome, where airway anatomy may deviate from age-based norms. Our findings revealed a statistically significant discrepancy between the predicted ETT size (based on Cole’s formula) and the actual size used intraoperatively (P < 0.001). This supports the growing consensus that conventional formulae may overestimate ETT size in syndromic children, increasing the risk of airway trauma or post-extubation complications. Shibasaki et al.[14] demonstrated that ultrasonographic measurement of the subglottic airway diameter significantly improves ETT size prediction in pediatric patients. Their findings underscore the potential utility of ultrasound-guided airway assessment in children with atypical anatomy, such as those with Down syndrome. Incorporating such techniques into preoperative planning may enhance safety and reduce complications, such as post-extubation stridor, which occurred more frequently in older children (5.3%) than in infants (1.5%). However, this difference was not statistically significant.

This study emphasizes the limitations of age-based formulas in predicting ETT size in pediatric patients with Down syndrome. Our findings are consistent with earlier reports, showing that the Cole formula consistently overestimates ETT size across all age groups in pediatric patients with Down syndrome.[3] Instead of proposing new formulas, we validate the anatomical differences within a cardiac surgical cohort. By correlating discrepancies between predicted and actual ETT sizes with clinical outcomes such as reintubation, stridor, and non-invasive ventilation, this current study emphasizes the importance of tailored airway management strategies. The consistency of these findings across a decade of practice, under standardized institutional protocols and with experienced pediatric cardiac anesthesiologists, underscores the need for refined airway assessment strategies.

The actionable recommendations for ETT sizing in children with Down syndrome, based on the study findings, suggest that a more structured approach to selecting ETTs can benefit pediatric patients undergoing cardiac surgery. When possible, preoperative ultrasound measurement of the subglottic diameter should be included in airway assessments, as ultrasonography is more accurate than age-based formulas in predicting the correct ETT size.[14] If ultrasonography is unavailable, a practical interim approach is to try an ETT one size smaller than the size predicted by the Cole formula, considering the tendency to overestimate in this group. Additionally, recording the brand and outer diameter of the tube is recommended, as manufacturer differences can affect tube selection and hinder comparison across clinical settings. Incorporating these guidelines into preoperative discussions, especially for infants and children with high RACHS-1 scores or known airway anomalies, may improve airway safety and promote consistent ETT sizing practices in this vulnerable group.

Limitations

The current study has a few limitations, primarily due to its retrospective design. First, selection bias may be present, as the survey relied on existing medical records that may not accurately reflect the entire data. Second, intraoperative tracheal tube changes were not consistently documented due to the retrospective study design and limitations in electronic records, and were therefore not included in our analysis. Third, height measurements were unavailable in this retrospective cohort; hence, a height-based alternative predictor could not replace age in the analysis. Additionally, due to inconsistent recording of prior airway surgery data and the small number of children with extreme RACHS-1 scores, the usefulness and interpretive value of subgroup-restricted sensitivity analyses were limited. As a result, formal sensitivity analyses were not performed. These limitations should be considered when interpreting the study results.

In conclusion, our study demonstrates that the ETT size predicted by Cole’s formula consistently overestimates the actual size required in pediatric cardiac surgical patients with Down syndrome. This discrepancy was statistically significant across age groups and highlights the limitations of age-based formulas in syndromic populations with atypical airway anatomy. Given the importance of precise ETT sizing in minimizing airway trauma, post-extubation stridor, and reintubation risk, these findings underscore the need for refined prediction strategies. Incorporating adjunctive techniques, such as ultrasonographic airway assessment, may enhance accuracy and improve perioperative safety. Future prospective studies are warranted to validate and expand on the results of the current study. They should focus on developing Down syndrome-specific ETT sizing algorithms that incorporate anatomical variability and surgical context.

Ethical approval and consent to participate

Study approved by the Institutional Scientific Research Committee [MoH/CSR/24/26170].

Author’s individual contribution

Madan Mohan Maddali: This author contributed toward the conception the work; acquisition of data: interpretation of data; drafting of the manuscript; intellectual content; final agreement of manuscript; and agreement to be accountable for all aspects of the manuscript

Haitham Khalaf Al-Abri: This author contributed toward the acquisition of data: interpretation of data, final agreement of manuscript, and agreement to be accountable for all aspects of the manuscript

Is’haq Al Aamri: This author contributed toward the conception the work, final agreement of manuscript, and agreement to be accountable for all aspects of the manuscript

Panchatcharam Murthi Sathiya: This author contributed toward statistical input and data analysis, the final agreement of the manuscript, and the agreement to be accountable for all aspects of the manuscript.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.