Correlation between changes in thyromental distance and distance of migration of oral Ring-Adair-Elwyn tubes during neck extension with a shoulder positioner in patients undergoing neck procedures

Abstract

Objectives

To measure the migration of oral Ring-Adair-Elwyn (RAE) preformed tracheal tubes during neck extension compared with the neutral neck position, and to assess the correlation between changes in the thyromental distance (TMD) during changes in neck position and tracheal tube migration.

Methods

This prospective observational study enrolled adult patients undergoing elective neck or thyroid procedures below the mandible. Using fibreoptic bronchoscopy, distances from the RAE tube adapter to the carina and to the tube tip were measured in the neutral position and after neck extension with a 10 cm D-shaped gel shoulder positioner. The change in distance of the RAE tube tip migration was compared with the change in TMD in each patient.

Results

This study enrolled 106 patients. During neck extension with a 10-cm shoulder positioner, RAE tubes cranially migrated 2.7 cm from the neutral position, but RAE tube migration was not correlated with the change in external TMD.

Conclusion

Oral RAE tube migration was not significantly correlated with the change in external TMD. Due to their large variability, changes in TMD were not useful predictors of RAE tube migration.

Introduction

Head and neck surgery, especially thyroid surgery, requires vigilant airway monitoring after changes in neck position. Reinforced anode tracheal tubes are usually used to prevent bending or kinking of the tracheal tubes during head and neck surgery. ¹ Despite several advantages, reinforced anode tracheal tubes can have serious problems because compression of the reinforcing wire coil by biting can give rise to irreversible narrowing or occlusion of the tube, and the elastic recoil force may increase the tendency of the tube to dislodge from the secured position.^2–4 Oral Ring-Adair-Elwyn (RAE) tracheal tubes benefit from a rectangular mark at the preformed curve that aids initial positioning. ⁵ Therefore, oral RAE tubes may be considered as an effective alternative to secure the airway in patients undergoing head and neck surgery, because they avoid irreversible occlusion by biting and they have a reduced likelihood of kinking.^5,6

Migration of the tracheal tube tip after flexion or extension of the neck may cause serious airway problems, such as endobronchial intubation and tracheal extubation.^7,8 In addition, head and neck surgery requires various degrees of neck extension, which may alter the depth of the tube tip.^7,9,10 Outward displacement of the tracheal tube tip after neck extension has been described.^9,11–13 Cranial movement of the tracheal tube can cause vocal cord injury or extubation after neck extension. To our knowledge, tracheal tube migration after neck extension using a 10-cm shoulder positioner has not previously been assessed. In addition, the previously reported findings were not determined in adult patients undergoing neck or thyroid surgery using oral RAE preformed tracheal tubes.^7–13 Therefore, it would be useful to determine the external factors that predict the distance of RAE tube migration after neck extension with a 10-cm shoulder positioner. The aim of this study was to assess whether the change in the thyromental distance (TMD) resulting from a neck position change (i.e. from a neutral neck position to neck extension with a 10-cm shoulder positioner) could predict the distance of RAE tube migration.

Patients and methods

Patients

This prospective observational study enrolled consecutive adult patients (age range, 20–70 years), American Society of Anesthesiologists (ASA) physical status I or II, undergoing elective neck or thyroid procedures below the mandible in the Department of Anaesthesiology and Pain Medicine, University of Ulsan College of Medicine, Asan Medical Centre, Seoul, Republic of Korea, between March 2014 and May 2014. ¹⁴ Patients with previous neck surgery or cervical spine disease were excluded from this study.

The study protocol was approved by the institutional review board of Asan Medical Centre (no. 2014-0184) and written informed consent was obtained from each patient. This study was registered with the Clinical Research Information Service (no. KCT0001272).

Anaesthesia and intubation

After applying a routine haemodynamic monitoring system (incorporating electrocardiogram, noninvasive blood pressure, and pulse oximetry measurement) and train-of-four monitoring, each patient was preoxygenated with 80% oxygen using a facemask.^15–17 Anaesthesia was induced using 2 mg/kg propofol bolus intravenous (i.v.) injection, followed by 0.6 mg/kg rocuronium i.v. Mask ventilation was performed with 2–4 vol% desflurane for 5–7 min before intubation. Tracheal intubation was performed with an oral RAE tube (Mallinckrodt™ oral RAE endotracheal tube with a TaperGuard™ Cuff; Covidien, Dublin, Ireland), and the rectangular mark of the preformed curve of the RAE tube was initially fixed at the right oral commissure in all patients. Subsequently, patients were mechanically ventilated with a tidal volume of 8 ml/kg at a respiratory rate of 10–16 breaths/min to maintain an end-tidal CO₂ partial pressure between 30 and 35 mmHg, and an inspiratory-to-expiratory time ratio of 1 : 2. Anaesthesia was maintained with 6–8 vol% desflurane plus the continuous infusion of 2–5 ng/ml effect-site concentration of remifentanil target controlled infusion with 50% oxygen using medical air.

TMD and RAE tube migration

When haemodynamically stable conditions were reached, measurements were taken in the neutral neck position without head rotation. The external TMD was measured using a calliper, and the distances from the RAE tube adapter to the carina and to the tube tip were measured using a fibreoptic bronchoscope (model XBF-3B40Y1; outer diameter: 3.5 mm; Olympus Optical, Tokyo, Japan). These two measurements were used to determine the distance from the carina to the RAE tube tip in each patient. The same parameters were measured after each patient was moved to the neck extension position using a shoulder positioner (Adult Gel Chest Roll; height: 10 cm; Universal Medical, Norwood, MA, USA). The shoulder positioner used in this study was a D-shaped gel positioned, which provided the benefit of height consistency without compression by body weight. The shoulder positioner was placed beneath the line of both acromions. All measurements of the distances were performed by a single investigator (Y-M.L.).

The distance that the RAE tube migrated when the head was moved from the neutral neck position to the neck extension position using a 10 cm shoulder positioner was measured and compared with the change in TMD in the same patient.

Statistical analyses

All statistical analyses were performed using R version 2.10.1 (R Foundation for Statistical Computing, Vienna, Austria) and SigmaStat version 3.5 for Windows® (Systat® Software, Chicago, IL, USA). Data were presented as n patients, mean ± SD, or mean (min, max) as appropriate. Parametric continuous variables were analysed using Student’s t-test. Regression analyses were used to evaluate the impact of external TMD and demographic data on tracheal tube migration. The correlation coefficient between the change in the distance of the RAE tube migration and the change in TMD was calculated using Pearson’s correlation. A P-value <0.05 was considered statistically significant.

Results

This study enrolled 106 adult patients, age range 24–68 years, undergoing elective neck or thyroid procedures below the mandible. Their clinical and demographic characteristics are presented in Table 1. The mean (min, max) distance from the RAE tube tip to the carina was 3.2 cm (−1.3, 7.8 cm) in the neutral neck position and 5.9 cm (2.4, 9.2 cm) in the neck extension position with a 10 cm shoulder positioner, with a mean (min, max) migration distance of 2.7 cm (0.8, 5.8 cm) (Table 2; Figure 1). The mean (min, max) TMD was 5.1 cm (3.4, 7.0 cm) in the neutral neck position and 6.9 cm (5.0, 9.0 cm) in the neck extension position with the 10 cm shoulder positioner (Table 2). Each of the observed values presented in Figure 1 shows cranial migration of the tip of the RAE tubes after neck extension with a 10-cm shoulder positioner. A negative value (−1.3 cm) for the distance from the carina to the tube tip, where the RAE tube tip was located in the bronchus, was observed in one patient in the neutral neck position (Table 2), which was indicative of endobronchial intubation (Figure 1).

Figure 1.

Distance from the carina to the oral Ring-Adair-Elwyn (RAE) tracheal tube tip in (A) the neutral neck position and (B) in the neck extension position with a 10-cm shoulder positioner. The negative value in A indicates that the oral RAE tube tip was distal to the carina (endobronchial intubation) in one patient. The solid line shows the mean of each observation, while the dashed line indicates that the tube tip was in contact with the carina.

Table 1.

Demographic characteristics of adult patients (n = 106) undergoing elective neck or thyroid procedures below the mandible, enrolled in a study to investigate whether the change in thyromental distance resulting from a neck position change could predict the distance of oral Ring-Adair-Elwyn tracheal tube migration.

Characteristic	n
Sex, male/female	50/56
Age, years	54.9 ± 12.8
Weight, kg	63.8 ± 10.1
Height, cm	162.5 ± 8.6
Body mass index, kg/m2	24.1 ± 3.2

Data presented as n patients or mean ± SD.

Table 2.

Thyromental distance (TMD) and migration of the oral Ring-Adair-Elwyn (RAE) tracheal tube tip in the neutral neck position and in the neck extension position with a 10 cm shoulder positioner.

Parameter	Neutral neck position	Neck extension with a 10-cm shoulder positioner	Statistical significancea
Distance from carina to RAE tube tip, cm	3.2 (−1.3,b 7.8)	5.9 (2.4, 9.2)	P < 0.001
TMD, cm	5.1 (3.4, 7.0)	6.9 (5.0, 9.0)	P < 0.001
Tube migration, cm		2.7 (0.8, 5.8)

Data are presented as mean (min, max).

a

Student’s t-test.

b

Endobronchial intubation noted in the neutral neck position in one patient.

Figure 2 shows the results of linear regression analysis of the change in TMD and the cranial migration of the RAE tube tip after neck extension with a 10-cm shoulder positioner, but these parameters were not significantly correlated (R²= 0.119). In addition, cranial migration of the RAE tube tip did not correlate significantly with patient height (R²= 0.103) (Figure 3). In two patients, the upper cuff margin of the RAE tube nearly reached the vocal cords after neck extension with a 10-cm shoulder positioner (Figure 2), but there were no postoperative complications related to the vocal cords and airways in these two patients.

Figure 2.

Relationship between cranial migration of the oral Ring-Adair-Elwyn (RAE) tracheal tube tip and changes in the thyromental distance (TMD) after neck extension with a 10-cm shoulder positioner. The empty circles indicate observed values, and the solid line indicates the results of linear regression analysis (R²= 0.119). A and B indicates two patients in whom the upper cuff margin of the RAE tube nearly reached the vocal cords after neck extension with a 10-cm shoulder positioner.

Figure 3.

Relationship between cranial migration of the oral Ring-Adair-Elwyn tracheal tube tip and patient height after neck extension with a 10-cm shoulder positioner. The empty circles indicate observed values, and the solid line indicates the results of linear regression analysis (R²= 0.103).

Discussion

Oral RAE tubes are frequently used to secure the airways of patients undergoing head and neck surgery.^5,6 The design of these tubes assures airway patency while reducing the risk of kinking. Moreover, the rectangular mark at the preformed curve aids initial positioning. The preformed curve can also be temporarily straightened to allow easy passage of suction catheters or a fibreoptic bronchoscope.

Tracheal tube tip migration after flexion or extension of the neck may cause serious airway problems.^7,8 Weiss et al. ⁹ demonstrated that head–neck extension moved the tracheal tube tip away from the carina. Tracheal tube tip migration after head and neck movements was reported to be due not only to the increased distance between the carina and the vocal cords, but also to changes in the distance from the lower incisor teeth to the vocal cords with extension of the neck. ¹⁰ The increased distance between the lower incisors and the vocal cord is important for tube tip displacement after neck extension in adults. ¹⁸ Since it is difficult to measure these internal distances in clinical practice, regression analysis was performed to determine whether any external parameter could affect tube migration. Changes in external TMD showed a positive correlation with RAE tube tip migration in a previous study, suggesting that the change in TMD after neck extension may affect the distance from the upper incisors to the sternal notch. ¹⁸ In contrast, this present study found that the linear regression coefficient between these two parameters was not statistically significant, indicating that external measurements do not predict internal changes.

One female patient (height: 148.1 cm; weight: 49.2 kg; RAE tube internal diameter: 7 mm) in the present study showed endobronchial intubation in the neutral neck position, with the tube tip located 1.3 cm below the carina. Usually, the rectangular mark on the preformed curve of the RAE tube is initially fixed to the right oral commissure. This case also occurred when the RAE tube was initially fixed at the rectangular mark. Therefore, auscultation of the bilateral lung sounds should be checked on endobronchial intubation in any position, and fixation of the RAE tube should be readjusted by auscultation.

Cuff displacement toward the vocal cords after neck extension may increase the risk of vocal cord injury or inadvertent extubation.^19,20 Intubation trauma can cause both temporary and permanent vocal fold paralysis. ²⁰ However, although the upper margins of the cuffs migrated close to the vocal cords in two patients after neck extension in the present study, neither experienced vocal cord complications. Intralaryngeal cuff position can result in laryngeal damage, if not recognized. ²¹ However, low rates of clinical morbidity are expected with RAE tubes as these are usually inserted only for short procedures and their polyurethane cuffs with high-volume and low-pressure prevent over-distension of the trachea.

In this present study, cranial migration of the RAE tube tip after neck extension with a 10-cm shoulder positioner demonstrated a large variation up to 5.8 cm, and readjustment of the fixation of the RAE tube was necessary. Although the preformed curve of the RAE tube provides the benefit of assuring airway patency without dislodging due to elastic recoil, the ability to adjust the intubation depth of the preformed oral RAE tubes is limited due to the preformed U-shape curve, and the insertion length is fixed according to the internal diameter of each tube. Intubation depth should not be adjusted, because placing the preformed curve inside or outside of the mouth increases the risk of compression or kinking, as well as essentially eliminating the benefits of preformed tubes. This could result in variable tube positions, which may be exacerbated during head and neck movement. ²² Therefore, inadvertent tube malpositioning could occur more often with preformed RAE tubes than with straight tubes. The present study has only assessed RAE tube migration during neck extension with a 10-cm shoulder positioner, which is a limitation of this study. To overcome this limitation, further research needs to be undertaken using various heights of shoulder positioner for neck extension.

In conclusion, oral RAE tube tip migration after neck extension with a 10-cm shoulder positioner did not significantly correlate with the change in external TMD. Due to its large variability, the change in TMD was not a useful predictor of RAE tube tip migration. Therefore, although oral RAE tubes are commonly used to secure patient airways during head and neck surgery, these tubes should be used cautiously in patients requiring neck extension with a 10-cm shoulder positioner because the preformed curves of the oral RAE tubes can restrict the adjustment of their intubation depth.