Abstract
Background
Swift and accurate airway management is crucial in the emergency department. Failure to secure the airway in hypoxic individuals can lead to severe outcomes, including brain damage or death. When a difficult airway is anticipated or intubation fails, alternatives such as cricothyroidotomy or tracheostomy must be considered, taking into account patient characteristics.
Aim
Analysis of the relationship between patient’s characteristics and the depth of the cricothyroid membrane (CTM) and tracheostomy sites (TSs).
Methods
We conducted a retrospective cross-sectional study of patients who underwent neck CT scans in the emergency department and 475 patients were included. The shortest distance from the skin to the innermost surface of the CTM (CTM depth) was measured in the sagittal view of the CT. For tracheostomy, depths were measured from the skin at the cricoid cartilage (1–2 cm below) to the membranes between the second and third tracheal rings (TS1) and between the third and fourth rings (TS2). Patient characteristics, including age, sex, height, and weight, were recorded to assess correlations with depth through multiple linear regression analysis.
Results
The average CTM depth was 10.87 ± 3.93 mm, while the depths at TS1 and TS2 were 12.38 ± 4.72 mm and 14.75 ± 6.30 mm, respectively. Significant correlations were found between patient age, body mass index, sex, and the depths of the CTM and TSs 1 and 2. Older age and increased obesity were associated with greater depths, particularly at TS2. Notably, females exhibited greater depths at CTM and TS1 than males, with no significant differences at TS2.
Conclusions
These findings offer valuable insights for anticipating incision depth during urgent surgical airway procedures, potentially minimizing complications and improving treatment outcomes.
1
Introduction
In the emergency department, timely and precise airway management and oxygen delivery for critically ill patients are of paramount importance [ ]. In cases of hypoxia, failure to maintain adequate ventilation with a bag-mask or to promptly secure the airway can lead to hypoxic brain injury and death [ , ]. Approximately 0.28 % of emergency department cases require rescue surgical airway management due to failed intubation [ ]. When a difficult airway is anticipated and intubation fails, the attending physician must promptly consider surgical options. The surgical procedures commonly performed in the emergency department include cricothyroidotomy and tracheostomy [ ].
Cricothyroidotomy is typically preferred in cases where airway management is impossible due to an obstruction at or above the level of the vocal cords, as it can be performed rapidly in the emergency setting. However, any delay in the procedure may result in hypoxemia [ , ]. Thus, it is crucial for physicians to have a comprehensive understanding of the relevant anatomy to swiftly and accurately carry out cricothyroidotomy in emergency situations. The cricothyroid membrane (CTM) is bordered superiorly by the thyroid cartilage, inferiorly by the cricoid cartilage, and laterally by the bilateral cricothyroid muscles [ ]. However, the depth from the skin to the CTM varies among individuals, increasing the risk of inadvertently puncturing posterior structures during the procedure, which can lead to complications such as recurrent laryngeal nerve injury and esophageal perforation. Additionally, increased tissue depth could make it more challenging to recognize and stay within the midline of the incision site. This may increase the risk of damaging crucial structures like vessels and nerves [ ]. To minimize this risk, bedside ultrasound can be employed, although it is not always feasible in emergency situations [ ].
While cricothyroidotomy is recommended according to Advanced Trauma Life Support guidelines, some institutions prefer tracheostomy for certain trauma cases, particularly in patients with multiple facial fractures, airway obstruction, or gunshot wounds to the head or neck [ ]. In such situations, the tracheostomy incision is typically made 1–2 cm below the cricoid cartilage along the anterior midline of the neck [ ]. The procedure generally involves inserting a tube between the second and fourth tracheal rings [ ]. Complications associated with tracheostomy include arterial injury, esophageal perforation, and tracheal laceration. Damage to the posterior tracheal wall is a serious complication that can result in a tracheoesophageal fistula, thus requiring careful attention during the procedure [ , ].
To reduce the incidence of complications during surgical airway procedures, several studies have investigated the relationship between patient characteristics, such as body mass index (BMI) and age, and anatomical landmarks using partial ultrasonography or computed tomography (CT) scans [ , , ]. However, no studies have simultaneously analyzed the anatomy of both the CTM, where cricothyroidotomy is performed, and the tracheostomy site (TS).
In this study, we measured the skin-to-CTM depth and tracheostomy site depths and analyzed their correlation with patients’ general characteristics (e.g., age, weight, and BMI) in those who underwent neck CT scans in the emergency department. By evaluating these factors, we aim to enhance clinical decision-making in challenging airway management situations. Additionally, the findings may provide a more comprehensive anatomical understanding.
2
Materials and methods
We conducted a retrospective cross-sectional study of patients who underwent CT scans of the neck in the emergency department of a tertiary hospital, which averaged 63,105 visits per year, from January 1, 2016, to December 31, 2020. Patients under the age of 18 years were excluded, as well as those for whom accurate measurements were not possible due to motion artifacts or severe anatomical deformities resulting from conditions such as significant trauma, cervical surgery, or malignancy. Trauma patients without neck deformities and those capable of undergoing neck positioning for imaging were included in the study. Nexus criteria were applied to exclude patients who could not have their neck collars removed, and only those with neck collars removed were included. All examinations were performed with the patients in a supine and anatomical neutral position. Images were acquired using a SOMATOM Scope CT scanner (Siemens Healthineers, Germany). The CT scans were enhanced with the contrast agent Iohexol. The entire dataset was sliced at 2 mm intervals with a thickness of 2 mm, and depth measurements were performed using the sagittal view images.
2.1
Study variables and definitions
Two blinded emergency physicians reviewed the medical records of patients who presented to the emergency department to confirm variables, such as sex, height, weight, BMI, medical history (e.g., hypertension, diabetes, and asthma), and chief complaints at the time of admission. Then these variables were analyzed for their correlations. BMI was calculated according to the World Health Organization (WHO) criteria, as weight divided by the square of height. Obesity was classified into three categories according to WHO criteria for Asian population: underweight (BMI <18.5 kg/m 2 ), normal weight (BMI 18.5–25 kg/m 2 ), and obese (BMI ≥25 kg/m 2 ) [ ].
In the sagittal view of the CT scans, the shortest distance from the skin to the innermost surface of the CTM (CTM depth) was measured. For tracheostomy measurements, depths were taken from the skin at the cricoid cartilage (1–2 cm below) to the membranes between the second and third tracheal rings (TS1) and between the third and fourth rings (TS2) ( Fig. 1 ). To minimize measurement bias, these assessments were conducted independently by two blinded radiologists.
2.2
Statistical analysis
Continuous variables were analyzed using Student’s t-test, while categorical variables were assessed using the chi-square test. Participant variables are expressed as means ± standard deviations (SDs) or as a number (proportions). The associations between participants’ characteristics and the depths of the CTM, TS1, and TS2 were analyzed using a univariate linear regression model, with the results reported as intercepts, coefficients, and 95 % confidence intervals (CIs). Based on these findings, a multivariate linear regression model was developed to create a predictive equation for estimating depths according to BMI. Scatter plots were also generated to visualize the relationship between BMI and the depths of surgical airway sites. All statistical analyses were performed using R software version 4.2.2 (The R Foundation for Statistical Computing, Vienna, Austria) and IBM SPSS Statistics software (version 26.0; IBM Corp., Armonk, NY, USA). A p -value <0.05 was considered statistically significant.
Ethics approval
This study was approved by our Institutional Review Board (IRB No. 2024–07–008) and was conducted in accordance with the Declaration of Helsinki. The purpose of the study was explained to all participants, and informed consent was obtained from each participant.
3
Results
We analyzed a total of 717 patients who presented to the emergency department and underwent CT scans of the neck from 2016 to 2020. Patients under the age of 18 years (n = 106), for whom accurate measurements were difficult due to motion artifacts (n = 56), with severe deformities resulting from trauma (n = 43), with a history of cervical surgery (n = 24), and/or diagnosed with malignancy (n = 15) were excluded. This left a total of 475 patients eligible for the study ( Fig. 2 ).
3.1
Baseline clinical characteristics
The patient cohort had a mean age of 41.83 ± 16.13 years, an average height of 167.26 ± 9.58 cm, and an average weight of 67.38 ± 14.45 kg. Among the participants, 283 were male (59.58 %) and 192 were female (40.42 %). Based on BMI classifications, 25 patients were underweight (5.89 %), 289 had normal weight (60.84 %), and 158 were classified as obese (33.26 %). The average CTM depth was 10.87 ± 3.93 mm, while the depths at TS1 and TS2 were 12.38 ± 4.72 mm and 14.75 ± 6.30 mm, respectively ( Table 1 ). Stratifying by BMI, the CTM depths were 7.65 ± 1.77 mm for the underweight group, 9.47 ± 2.62 mm for the normal weight group, and 13.99 ± 4.25 mm for obese patients. The TS1 depths were 8.47 ± 1.76 mm, 10.77 ± 3.20 mm, and 16.04 ± 5.18 mm, and the TS2 depths were 9.74 ± 2.41 mm, 12.66 ± 4.27 mm, and 19.46 ± 7.11 mm, respectively (all p < 0.05) ( Table 2 ).
| N = 475 | |
|---|---|
| Age, y | 41.83 ± 16.13 |
| Sex, n (%) | |
| Male | 283 (59.58) |
| Female | 192 (40.42) |
| Height (cm) | 167.26 ± 9.58 |
| Weight (kg) | 67.38 ± 14.45 |
| BMI | 23.88 ± 3.68 |
| Obesity (BMI, kg/m 2 ), n (%) | |
| Underweight (<18.5) | 28 (5.89) |
| Normal (18.5–24.9) | 289 (60.84) |
| Obese (≥25) | 158 (33.26) |
| CTM depth (mm) | 10.87 ± 3.93 |
| TS 1 depth (mm) | 12.38 ± 4.72 |
| TS 2 depth (mm) | 14.75 ± 6.30 |
| Comorbidities, n (%) | |
| Hypertension | 71 (14.95) |
| Diabetes mellitus | 34 (7.16) |
| Asthma | 8 (1.68) |
| Chief complaints, n (%) | |
| Sore throat | 194 (40.84) |
| Fever | 144 (30.32) |
| Swelling | 44 (9.26) |
| Trauma | 28 (5.89) |
| Foreign body | 19 (4) |
| Etc. | 46 (9.68) |
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