Estimation of Trachea Size for an Emergency Tracheostomy

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J Acute Care Surg. 2024;14(3):88-93

Publication date (electronic) : 2024 November 21

doi : https://doi.org/10.17479/jacs.2024.14.3.88

Hokyun Noh^a, Sungwoo Jang^b, Younghwan Kim^c, Howon Lee^d, Seok Hwa Youn^c,

^aDepartment of Surgery, National Medical Center, Seoul, Republic of Korea

^bDepartment of Surgery, Soon Chun Hyang University Hospital, Seoul, Republic of Korea

^cDepartment of Surgery, National Trauma Center, National Medical Center, Seoul, Republic of Korea

^dDepartment of Laboratory Medicine, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea

^*Corresponding Author: Seok Hwa Youn, Department of Surgery, National Trauma, Center, National Medical Center, 245 Eulji-ro, Joong-gu, Seoul, Republic of Korea, Email: iguassufalls@nmc.or.kr

Received 2024 August 14; Revised 2024 September 18; Accepted 2024 October 11.

Abstract

Introduction

Tracheostomy is a surgical procedure that creates an opening in the front of the neck for direct access to the trachea. It plays a vital role in the management of patients with respiratory distress due to airway obstruction [1]. It is a common procedure in trauma and critical care medicine, and the tracheostomy tube size is one of the critical factors that significantly impacts patient outcomes [2–4]. An improperly sized tube can cause discomfort, lead to airway trauma, decrease ventilation efficiency, and potentially result in life-threatening airway obstruction in patients with compromised respiratory function [5,6].

When selecting a tracheostomy tube, it is important to consider several factors, including the tracheal inner diameter (ID), patient age, anatomy, cuff type, and tube material [6–9]. Among these considerations, tracheal ID is the most crucial [3,5]. Tracheal size varies among children, adults, and elderly patients, necessitating the use of different tube sizes and designs. The normal range for tracheal IDs in adults is 15–25 mm for males and 10–21 mm for females [10]. Since the range of normal tracheal ID differs by more than 10 mm, it is usually helpful to measure tracheal ID from chest X-ray (CXR) or chest computed tomography (CT) scans. However, these imaging techniques are not always available, especially in emergencies or in settings with limited resources. In emergencies, clinicians usually depended on their experience to estimate the appropriate tube size. However, this approach sometimes leads to complications like tube obstruction, bleeding, aspiration, unintentional tracheal injury, and subsequent infections.

This research aimed to determine whether there were associations between tracheal ID and various body size parameters, including height, actual body weight, and either ideal body weight (IBW) or adjusted body weight (ABW) [11]. By identifying these relationships, we hope to provide healthcare professionals with a more informed basis for selecting tracheostomy tube size when radiological imaging is not an option. The development of a reliable model for tracheostomy tube selection may reduce complications related to ill-fitting tubes and enhancing patient safety during tracheostomy procedures.

Materials and Methods

1. Study population

This retrospective study analyzed the medical records of 643 trauma patients who visited the National Medical Center, Seoul, Republic of Korea, between 2019 and 2022. The study applied exclusion criteria, which involved excluding patients under 18 years of age, cases where intubation or tracheostomy were performed before radiology, and cases with missing radiological test results. In the final analysis, a total of 468 patients were included in the study (Figure 1). The medical records of these patients were examined to collate information on their age, sex, height, and weight at the time of admission. Using this information, the patient’s IBW or ABW was calculated. The formulas for calculating IBW and ABW are as follows:

Figure 1

Flow chart of patient selection.

Equation 1 “IBW  (kg)”=(50 for Male or 45.5 for Female)+2.3×{[Height (cm)÷2.54]-60}

Equation 2 “ABW (kg)”=[IBW (kg)]+{0.4×[Actual body weight (kg)-IBW (kg)]}

If the patient’s actual weight was lower than the IBW, the IBW was used. If the patient’s actual weight was higher than the IBW, indicating the patient was overweight or obese, the ABW was used instead.

The Institutional Review Board of the National Medical Center, Seoul, Republic of Korea approved the study (no.: NMC-2023-08-090). As a retrospective study based on the analysis of medical records this research did not require informed consent.

2. Measuring the ID of the trachea

Tracheal ID was measured using a cross-checking method, in which 3 researchers examined CXR and chest CT images. The inner width of trachea was measured between the upper part of the jugular notch and the midpoint of both sternal ends of the clavicle using both CXR and chest CT scans (Figure 2).

Figure 2

Flow chart of patient selection.

Measuring the ID of the trachea. The inner width of the trachea was measured from the upper part of the jugular notch to the midpoint of the sternal ends of both clavicles, using (A) chest CT scan; and (B) CXR.

CT = computed tomography ; CXR = chest X ray ; ID = inner diameter of the trachea.

Results

The study included a total of 468 patients, 355 (75.9%) of which were male and 113 (24.1%) were female. Mean tracheal IDs in males was significantly larger than in females, confirming the influence of the patients’ sex on trachea size. Mean height, weight, and ABW of the patients were 167.3 ± 9.0 cm, 66.9 ± 14.4 kg, and 65.2 ± 9.9 kg, respectively, and there were significant differences between sexes in all variables. (Table 1). Statistical analysis revealed that tracheal ID was not consistently measured between imaging modalities, with values of 18.7 ± 2.5 mm obtained from CXR and 18.5 ± 2.4 mm from chest CT scans.

Table 1

Baseline Characteristics of Enrolled Patients

When mean tracheal IDs measured by CT and CXR were compared using the Wilcoxon rank sum test, no significant difference was found (p = 0.180). Consequently, univariate analysis was performed on tracheal ID using chest CT, followed by multivariate analysis that included sex, height, and either IBW or ABW. The odds ratio (OR) for height was 7.38 (95% CI, 1.59 – 13.57) and the OR of square weight was −0.80 (95% CI, −1.69 – 0.08). The variables most strongly correlated with tracheal ID were sex and height (Table 2).

Table 2

Univariate and Multivariate Linear Regression Analysis for Tracheal Inner Diameter Measured by Computed Tomography

Using these variables, a regression equation was developed to estimate tracheal ID:

“Expected ID of the trachea (mm)” = [11.0781 + (1.9682 for Male or 1 for Female)] + [7.3767 × height (cm)] − {0.8022 × √ [(IBW (kg) for non-obese or ABW (kg) for obese]}

The derived regression equation was statistically significant, with p-values less than 0.001 for key variables such as sex and height, further supporting the reliability and robustness of the model. To support the regression equation derived for estimating tracheal ID, we analyzed the mean and standard deviation of measured tracheal ID in patients categorized by both height and weight. This analysis demonstrated a clear correlation between these physical parameters and tracheal ID (Table 3).

Table 3

Mean and SD of Tracheal ID in Patients Categorized by Height and Weight

The regression equation derived from this retrospective study was employed to calculate tracheal ID for height and either IBW or ABW. These calculations guided the selection of tracheostomy tubes with ODs ranging from 1/2 to 2/3 of the estimated ID. For instance, a male patient with a height of 170 cm and an actual body weight of 70 kg would yield an estimated tracheal ID of 18.9 mm (Supplementary Table 1). Consequently, a tracheostomy tube with an OD falling between 9.45 mm and 12.47 mm would be chosen. To provide a practical example, Portex^® Blue Line Ultra^® Suctionaid^® tracheostomy tubes were used in this study. With reference to the specifications of the tracheostomy tubes, suitable tube sizes would include 7.0 mm, 7.5 mm, and 8.0 mm (Supplementary Table 2). The regression equation can be applied to select appropriate tube sizes (Table 4). This approach allowed the suitable tube sizes for the products used in our center to be determined.

Table 4

Possible and Recommended Tracheostomy Tube Sizes Determined by the Internal Diameter of the Trachea (mm) Calculated Using the Coefficients Derived from the Regression Equation

Discussion

Analysis of the results in this study revealed that height strongly correlated with tracheal ID, followed by calculated body weight, whether IBW or ABW. Despite the importance of using the correct tube size to perform a tracheostomy, there is currently a lack of comprehensive studies. Our research addresses this gap, providing a practical method for estimating tracheal ID. This could be particularly beneficial in resource-limited settings where access to advanced imaging methods may be restricted.

The selection of the appropriate tracheostomy tube size is a critical decision that requires careful consideration of the patient’s individual anatomy, particularly the size of the trachea [7,10]. One of the key factors in this decision is the OD of the tracheostomy tube, which must precisely fit the patient’s anatomy. In our clinical experience, we have found that Portex^® Blue Line Ultra^® Suctionaid^® tracheostomy tubes, offer a range of sizes that can accommodate a variety of patients. For example, the ID 8 mm, 9 mm, and 10 mm products have ODs of 11.9 mm, 13.3 mm, and 14.0 mm, respectively [12]. The recent guidelines from the Intensive Care Society and Tracheostomy in Critical Care Society suggest that the OD of the tracheostomy tube should not exceed roughly 3/4 of the tracheal ID [13]. However, considering the statistically significant abnormal airway findings reported in both open tracheostomy and percutaneous dilatational tracheostomy procedures, particularly in trauma patients, we advocate for a more conservative approach when determining tracheostomy tube size [5,11,14–17]. Based on these product specifications and our clinical experience, we have concluded that the optimal size for tracheostomy tube OD is 1/2 to 2/3 of the tracheal ID. This range ensures a good fit between the tube and the trachea, minimizing the risk of complications related to improper tube size. Also, this approach is designed to maintain adequate airflow via the tracheostomy tube while also preserving natural tracheal ventilation when the cuff is deflated during the weaning process in the future.

The selection of a tracheostomy tube is a multifactorial decision that considers various patient-specific factors, including age, anatomy, and overall health status. Our method can thus serve as an effective supplementary tool when integrated with the clinician’s experience and judgment.

In the point-of-care testing, ultrasound guidance can be used to measure tracheal ID in real time. It provides quick and accurate measurements, helping to ensure the correct tube size as well as significantly reducing procedure-related complications. Additionally, it is noninvasive, widely available, and radiation-free. However, this technique has not yet been standardized, and its use can be limited by operator dependency, which may introduce variability [16,17]. In contrast, the regression formula developed in this study offers a practical, consistent, and operator-independent method for quickly estimating tracheal ID using readily available patient data such as height, sex, and weight (IBW or ABW). Both methods have unique advantages, and combining them in clinical practice may enhance tracheostomy outcomes. It is important to note that sonography data were not available in this study, limiting direct comparison between the 2 methods. Future research incorporating sonography data would allow for a more comprehensive evaluation of both approaches.

The data on tracheal ID in patients may initially appear to contradict the regression equation (Table 3). However, it supports the model by illustrating the correlation between height and weight. As weight increases, height tends to increase, which aligns with the results of the regression equation. This relationship reinforces the validity of this study’s predictive model for estimating tracheal ID.

While our study provides valuable insights, there are several limitations. The retrospective design and single-center data may limit the generalizability of the findings. Future research should aim to increase the sample size, and use a multicenter approach with prospective study design. Additionally, further investigation into other factors influencing tracheostomy tube selection could provide a more comprehensive understanding of this complex decision-making process.

In conclusion, this study contributes to ongoing effort to improve patient safety and outcomes in tracheostomy procedures. By providing a practical method for estimating tracheal ID, we hope to reduce tracheostomy complication rates and improve patient outcome.

Supplementary Material

Data Availability

All relevant data are included in this manuscript.

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