In pediatric anesthesia, the unexpected displacement of the endotracheal tube (ETT) as a result of extension and flexion of the neck can cause serious complications, such as accidental extubation and endobronchial intubation (1). Therefore, the ideal position of the ETT tip would allow some displacement caused by head and neck movements but avoid these complications.
Both chest fluoroscopy and bronchoscopic evaluations can be applied effectively to verify the position and depth of the ETT (2,3). However, fluoroscopy is time-consuming, and the carina cannot always be easily located. In addition, considerable training in fiberoptic bronchoscopy (FOB) is required, and experienced operators are not always available in an operating room when an ETT displacement is suspected. Confirmation using chest radiograph (CXR), FOB, or fluoroscopy during the operation may still be required when there is some question regarding ETT placement or when an accurate ETT depth is essential for a particular surgical procedure (prone position or head and neck surgery).
There are simple methods for positioning the ETT, which consider the patient’s age or ETT size (4). However, these methods are less accurate than CXR or FOB, and there does not appear to be a strong relationship between tracheal length and these previously described methods (4a). Some studies have reported other simple techniques using anatomic references for proper ETT positioning in children. The technique proposed by Bloch et al. (1) is based on auscultation on the bilateral chest during withdrawal of the ETT from a deliberate right endobronchial intubation using the carina as a reference point. Adjusting the ETT length by noting the prescribed mark at the level of the vocal cords has also been suggested as an effective method for ETT positioning (4). Bednarek and Kuhns reported that suprasternal palpation of the ETT tip is a reliable method for positioning the tube in infants (5). Although the purpose of these methods is to place the ETT in the ideal position, it is unclear if these positions are safe from endobronchial intubation or extubation during neck movement.
The aim of this study was to determine if the three clinically prevalent methods for positioning the ETT in children could maintain the proper positioning of the ETT in the trachea during neck movement.
The local IRB of Seoul National University Hospital approved the study protocol, and the parents of all patients provided informed consent. One-hundred-seven children (2–8 yr), scheduled to undergo elective surgery under general anesthesia, were enrolled in this study. Patients with pulmonary diseases, such as bronchial asthma, abnormal breath sounds, and malformations of the trachea or bronchus on CXR, were excluded. Patients with difficulties in neck flexion or extension were also excluded. The patients were randomly allocated to one of three groups according to a computer-generated random number. Induction was performed IV with 5 mg/kg thiopental sodium. Rocuronium (0.6 mg/kg) was injected for neuromuscular blockade. The patients were tracheally intubated with an appropriate size tube that allowed air leakage at a pressure of 20–25 cm H2O. The tube sizes were determined using the formula, Age (yr)/4 + 4. If an audible leak was auscultated at an inflating pressure <15 cm H2O, the tube was replaced with a tube the next size larger. If no leak around the ETT was auscultated at an inflating pressure >30 cm H2O, the tube was replaced with the next smaller size. Tracheal intubation was confirmed by the presence of an end-tidal CO2 and bilateral breath sounds by auscultation. Uncuffed tubes with a bevel facing the left and a right-sided Murphy’s eye (Contour™, Mallinckrodt, Ireland) were used, which enabled the tip of the tube to enter the right main bronchus when being advanced beyond the carina. After positioning the ETT and providing mechanical ventilation, the length of the ETT was measured at the upper incisor teeth and secured to the upper lip.
In Group I, after tracheal intubation, the patient was manually ventilated, and both lung fields were auscultated to confirm that the ETT had been placed correctly in the trachea. With the head held at the midline in the neutral position, the ETT was advanced gently until it entered a mainstem bronchus, usually on the right side. This event was confirmed by a loss of breathing sounds, usually on the left side. The ETT was then slowly withdrawn until equal breath sounds on both sides had returned. Before being secured at the upper lip with adhesive silk tape, the ETT was then withdrawn a further 2 cm in the children aged between 2.0 and 5.0 yr or 3 cm in those aged between 5.1 and 8.0 yr (1).
In Group II, the standard intubation position was used. The ETT was set at the level of the vocal cords, such that an ETT with an internal diameter 4.0 and 4.5 mm was placed with the 4 cm mark from tip at the vocal cords, and an ETT with an internal diameter larger than or equal to 5.0 mm was set at 5 cm from the tip at the cords (4).
In Group III, intubation was performed using the modified Bednarek’s method (5). During intubation, the head was placed in the standard position. The index finger of the palpator was placed perpendicular to the neck at the suprasternal notch. The trachea was compressed gently as the ETT passed the vocal cords. The ETT tip was identified as it passed the palpating fingertip. The person palpating the trachea instructed the intubator to stop when the ETT tip had just passed his fingertip. After removing the laryngoscope, the ETT position was rechecked by withdrawing the ETT in the neutral position, so that the tip could be palpated again. The tube was secured with tape when the last palpation had been achieved during a slow re-advance of the ETT not more than 0.5 cm.
The patients were kept in an anatomically neutral position during the bronchoscopic evaluation. The heart rate, respiration, arterial blood pressure, pulse oximetry, and end-tidal CO2 were monitored. A FOB (Olympus LF-P, outer diameter 2.8 mm, Olympus Optical CO, Japan) was inserted through an ETT/ ventilator adapter (Opti-Port™, Mallinckrodt, Ireland), which allowed the procedure during mechanical ventilation. A single anesthesiologist, who was blinded to the method of intubation, performed all the bronchoscopic evaluations. The first mark was made on the FOB corresponding to the proximal end of the ETT when the tip of the FOB touched the carina. The FOB was then withdrawn until the ETT tip was visualized, and a second mark was made on the FOB. The distance between these two marks on the FOB corresponded to the distance from the tip to the carina (T-C) (2,6). After measuring the T-C in the neutral position, the changes in this distance were measured after full flexion and full extension of the neck. The angle of neck flexion and extension, which is the angle formed by the operation table and a line drawn from the spinous process of C7 to the posterior part of occiput, was measured using a goniometer. When endobronchial intubation was suspected with a bronchoscopic examination, the ETT distance in the main bronchus was measured by withdrawing both the ETT and bronchoscopy to the carina. The relative ETT tip depth along the trachea (= distance from the carina to the ETT tip/tracheal length, carina; 0%, vocal cords; 100%) was assessed in each position during neck movement. The tracheal length was measured in the neutral position using Hartrey and Kestin’s method (6,7). This procedure involved withdrawing the bronchoscope and ETT from the trachea as a single unit, beginning with the bronchoscope at the carina, and stopping when the vocal cords were just visible through the bronchoscope. At this point, a mark was made on the ETT at its point of exit from the upper lip, and the tracheal length was indicated by the amount of tube removed. Each procedure lasted for no more than 30 s.
The number of patients required to demonstrate a difference in the T-C was calculated with the assumption that a 30% change in the distance between the ETT tip and the carina would be clinically relevant. Power analysis suggested that a minimum of 29 patients would be needed for β = 0.1 and α = 0.05. Thirty-five to 36 patients were examined in each group to allow for any methodological difficulties that could lead to exclusion from the study. Statistical analysis was performed using SPSS 11.0 for Windows (SPSS, Chicago, USA). The frequency of endobronchial intubation was compared using a Pearson’s χ2 test. The Cochran-Mantel-Haenszel statistic was calculated to evaluate age as a possible confounding variable. The difference between the T-C and the intended distance from the carina was analyzed using one sample Student’s t-test. The differences among the groups were analyzed using ANOVA, which was followed by a Student–Newman–Keuls correction if necessary. Statistical significance was established at P < 0.05. The data are represented as the mean ± sd.
Table 1 shows the demographic data of the patients. The tracheal length and displacement of the ETT tip after neck flexion or extension was similar in the three groups (Table 2). The ETT migrated upward to the vocal cords during neck extension and downward to the carina during neck flexion. There were significant differences in the T-C in the neutral position (1.7 ± 0.5 cm in Group I, 3.6 ± 1.0 cm in Group II, and 3.4 ± 0.9 cm in Group III, P < 0.05, Table 2). In addition, Group I showed a significantly deeper ETT position in the neutral position (1.7 ± 0.5 cm) than the intended depth, which was 2 cm above the carina (P < 0.05).
In Group I, the relative position of the ETT tip along the trachea in the neutral position was 21.4% ± 6.7%, which is closer to the carina than to the vocal cord (Table 3). The relative position of the ETT tip in Groups II and III was 46.5% ± 13.0% and 43.4% ± 11.1%, respectively, which corresponded to the midtrachea.
After full neck flexion, the relative position of the ETT tip in Group I was 9.5% ± 10.3%, which is closer to the carina than that observed in the other groups (P < 0.05, Table 3). Five cases of endobronchial intubation were observed after full flexion of the neck in Group I, particularly in children aged between 2 and 5 yr (Fig. 1). In the other groups, neither endobronchial intubation nor extubation from the trachea was observed after neck flexion or extension (Figs. 2 and 3). Age was not found to be a confounding variable in the three groups. All patients were followed-up for any airway complications at the postanesthesia care unit and ward (particularly in Group III). There were no postextubation airway complications encountered.
The ETT can be displaced as a result of the neck movement causing accidental endobronchial intubation or extubation from the trachea (1,4). Therefore, it is extremely important to accurately place the ETT to a predetermined depth to ensure safety during neck movement. Several techniques for positioning the ETT correctly have been described. According to previous studies, the ETT can be positioned 2.06 (1) or 1.93 cm (8) above the carina by deliberately intubating the patient’s right main bronchus and then withdrawing the ETT 2 cm into the trachea. However, these results showed that the ETT tips were placed only 1.7 cm above the carina in Group I, even though they had been placed using the same method. In addition, the results were significantly different from the intended ETT position, i.e., 2 cm above the carina. The reason why these results were different from previous studies is unclear. However, Sugiyama et al. (9) reported that bilateral breath sounds are equally audible when the ETT tip is advanced 2 cm beyond the carina in adults, suggesting gas flow to the contralateral lung through the Murphy eye. Therefore, it is possible that the Murphy eye can maintain the appropriate gas flow to the left lung and allow equal breath sounds on both sides when the ETT tip is placed below the carina in the right main bronchus. This might contribute to the deeper than intended depth of the ETT, which would have increased the risk of endobronchial intubation in Group I.
Mariano et al. (3), in a fluoroscopic study, reported that deliberate mainstem intubation combined with auscultation resulted in an appropriate ETT placement (73%) more often than when using the marker (53%) and formula methods (42%). The results that favor deliberate mainstem intubation may be derived from the criterion of “appropriate ETT depth,” which is the location of the ETT tip between the sternoclavicular junction and 0.5 cm above the carina. In this study, 34 of 35 patients in Group I met the criterion in the neutral position in the bronchoscopic study. According to the criterion, deliberate mainstem intubation reliably results in an appropriate ETT depth. However, there were five cases of endobronchial intubation after neck flexion.
Bloch et al. (1) suggested, through auscultation of the bilateral lung sound, that the proper position of the ETT was 2 cm (in children under 5 yr) or 3 cm (in children over 5 yr) above the carina. Neck flexion causes the ETT tip to move towards the carina, thereby shortening the distance between the tip and the carina. In children aged between 16 and 19 mo, the ETT tip moved a mean distance of 0.9 cm with a maximum movement of 1.2 cm (10). Therefore, an ETT positioned 2 cm above the carina can be considered to be safe from endobronchial intubation during neck flexion in children under 2 yr. However, the position of the ETT in children over 2 yr needs to be modified. In this study, the relative position of the ETT tip in Group I was 20.9% ± 6.7%, which was placed closer to the carina than to the vocal cord, and may have increased the risk of endobronchial intubation during neck flexion. Indeed, the relative position of tip from the carina in Group I decreased to 11.0% ± 10.3% after full neck flexion, resulting in endobronchial intubation in 14.3% of children. Moreover, endobronchial intubation occurred only in those children aged between 2 and 5 yr, in whom the aim was to place the ETT tip 2 cm above the carina. Consistent with these results, Verghese et al. (11) reported that a low tracheal position and right mainstem intubation occur more often in children younger than 10 yr, and particularly in younger children with a lower body weight.
On the other hand, the relative positions of the ETT tip in the neutral position in Groups II and III were 46.7% ± 13.3% and 43.8% ± 10.9%, respectively. The positions of the ETT tip were in accord with the midtrachea, which is consistent with the results reported by Freeman et al. and Bednarek and Kuhns (4,5). The midtrachea is considered to be the ideal depth for an ETT (12,13). The tracheal length in children 2–8 yr has been reported to be 6.4–8.2 cm (14) and 7.9 cm (6). In this study, the tracheal length of this age group was 7.8 ± 0.9 cm, whereas the displacement of the ETT was 0.8 ± 0.6 cm (max: 2.6 cm) to the carina after neck flexion, and 1.9 ± 0.7 cm (max: 3.6 cm) to the vocal cords after neck extension. These results show that, despite full flexion or full extension of the neck, there was no endobronchial intubation or extubation in the patients in whom the ETT was positioned using these two methods. Therefore, the midtrachea can be considered safe from neck movement in children aged between 2 and 8 yr. Palpation of the ETT tip on the suprasternal notch has been suggested as a method that allows the midtracheal positioning of the ETT in newborns and infants (5). These results show that this method can be used safely and effectively in children aged between 2 and 8 yr. In addition, this method has been suggested to be useful in emergency situations, or on initial intubations, to avoid improper positioning of the ETT tip (5). However, this method may damage the tracheal mucosa or stimulate a hypersensitive reaction. Therefore, gentle and sensitive handling may be needed.
Freeman et al. (4) reported that the midtracheal positioning of the ETT could be achieved in 79% of patients aged 0–14 yr by setting the tube length at the level of the vocal cord, such that an ETT with an internal diameter of 3.0 and 3.5 could be set 3 cm from the tip at the cords, 4.0 and 4.5 tubes at 4 cm, and 5.0 and 5.5 tubes at 5 cm. The advantage of this technique is that it is easily remembered and setting the tube length at the level of the vocal cord reduces the variability due to the length of the upper airway. In addition, this black safety line on the ETT positioned at the level of the vocal cords has been used as a guide in neonates (15). The results in this study showed this method to be effective for avoiding endobronchial intubation or extubation in older children without creating any difficulties in visualizing the vocal cords. However, the depth markers are not found in the same location in different brands of ETT (13,16). Therefore, the distances of the depth marker from the ETT tip should be identified before tracheal intubation.
None of the methods examined is expected to result in the appropriate placement of the ETT in all cases. In addition, variability in the tracheal length among patients makes it impossible to predict with certainty that a technique based on a formula or markers on the ETT will work in all patients. FOB or CXR can be used to confirm the correct placement of the ETT. FOB has been used to confirm the correct placement of the ETT, but this technique is not widely available. CXR remains the “gold standard” for confirming appropriate tube placement (17).
In conclusion, positioning the depth marker at the vocal cord level and palpation of the ETT tip on the suprasternal notch in children aged between 2 and 8 yr prevented endobronchial intubation and accidental extubation caused by neck flexion but positioning the ETT 2 cm above the carina by auscultation did not.
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© 2007 International Anesthesia Research Society
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