The combination of computed tomography measurements and �exible video bronchoscope guidance for accurate placement of the right-sided double-lumen tube: a randomized controlled trial

Background: Accurate placement of the right-sided double-lumen tube (RDLT) is still challenging. This study aims to explore the feasibility and accuracy of a modi�ed intubation strategy by using a combination of computed tomography measurements and �exible video bronchoscope guidance. Methods: 108 adults requiring an RDLT for lung isolation were randomly allocated to 2 groups. Conventional �beroptic bronchoscopy-guided technique was used in the control group. The following speci�cations applied to the modi�cation group. Firstly, the length of the right main bronchus (RMB-L) and the anteroposterior diameter of RMB were measured in preoperative spiral computed tomography to predict the side and size of the tube; Then, a depth marker was made on RUSCH tube according to the difference between the RMB-L and the length of bronchia cuff (12 mm); Under the guidance of �exible video bronchoscope, the depth marker should be paralleled with the tracheal carina, and a characteristic white line on the tube should be paralleled with the secondary carina. Results: Compared with the control group, our modi�ed strategy signi�cantly increased the optimal plus acceptable position rate (76% vs. 98%, respectively; P < 0.039), decreased tube replacement rate (80% vs. 94%; P = 0.042), shortened the intubation time (101.4 ± 7.3 vs. 75.2 ± 8.1 seconds; P = 0.019), and had a lower incidence of transient hypoxemia (25% vs. 6%; P = 0.022), subglottic resistance (20% vs. 6%; P = 0.037), tracheobronchial injury (35% vs. 13; P = 0.037), and postoperative right upper lobe collapse (15% vs. 2%; P = 0.059). Conclusion: These data suggest the superiority of our modi�ed technique compared to the conventional method for RDLT positioning.


Background
At present, a double-lumen tube (DLT) remains the most commonly used device for lung isolation and one-lung ventilation (OLV) especially in our hospital [1,2].The application of the left-sided DLT (LDLT) in preference to the right-sided DLT (RDLT) is recommended for most thoracic surgeries because of its greater safety margin for placement [3].But for some indications, RDLT may be mandatory; and surgeons also tend to require a non-operative sided DLT [4].Many different strategies have been explored to improve RDLT placement, including classical auscultation [5], beroptic bronchoscopy (FOB) guidance technology [6][7][8], FOB evaluation before intubation [9], newly designed RDLT [10][11][12][13], spirometry monitoring [14], contrast-enhanced ultrasound [15], lateral decubitus rotation [16], and so on.However, so far, accurate placement of an RDLT is still a great challenge, as these methods seem to be neither easily mastered nor commercially available.The most clinically utilized method is just a simple FOB guidance technique similar to the LDLT placement.Although it may be acceptable in most situations, the success rate of positioning and the effect of OLV are both signi cantly lower than those of LDLT, especially in patients with chronic respiratory diseases [2,3].
We consider that the key to a successful RDLT intubation is just to determine the depth and angle of the right upper lobe (RUL) ventilatory slot (RUL-VS) of the tube to the RUL bronchus ori ce (RUL-BO) of an individual patient [17].Nowadays, the routine use of preoperative spiral computed tomography (CT) scan and multi-planar reconstruction (MPR) of three-dimensional (3D) tracheobronchial tree could help to predict the size of a DLT and its insertion depth [18][19][20][21].An anatomical feature between RUL-BO and right middle lobe/right lower lobe bronchus carina (RML/RLL carina) has been proposed as a bony marker to guide the angle of insertion [22].A continuous white line marker along RUSCH® tube has been noted as an indicator during FOB examination [7].Besides, exible video bronchoscope (FVB) has facilitated airway observation in endotracheal intubation [23,24].
In this study, we attempt to develop a modi ed strategy for the size selection and precise positioning of RDLT by using a combination of CT measurements and FVB guidance.It is our perspective that this strategy may be more feasible and could provide a more effective one-lung ventilation than the conventional method.

Methods
This study was approved by the Medical Ethics Committee of the First A liated Hospital of Soochow University (approval No. 2019 − 0223) and written informed consent was obtained from all subjects participating in the trial.The trial was registered before patient enrolment at chictr.org.cn(ChiCTR1900021676, Principal investigator: Yongheng Hou, Date of registration: March 5, 2019).This manuscript adheres to the applicable Consolidated Standards of Reporting Trials (CONSORT) guidelines.Before study commencement, randomization was performed by the use of an online random number generator (http://www.randomization.com),with an allocation ratio of 1:1.In the control group, the conventional selection of tube size based on an adult patient's gender and height was used followed by FOB-guided intubation.In the modi cation group, our improved strategy was selected (described below).

Patients and groups
All surgical procedures, anesthesia management, and perioperative care were provided by the same medical team.An independent experienced anesthesiologist assessed RDLT placement and airway change of all patients.

CT measurements
Chest imaging, including spiral CT scans and X-ray, are routinely performed for lung tumor diagnosis and localization in our hospital.Preoperative images of all patients were retrieved and measured directly from the hospital imaging system (NEUSOFT image diagnosis systems, DongSoft Inc., Shenyang, China).Multi-planar reconstruction (MPR) of a three-dimensional (3D) tracheobronchial tree has already been performed in all examinations.Three windows were displayed, the lung window, the mediastinal window, and the coronal MPR window.An independent anesthesiologist, specially trained by a senior radiologist, measured different structural distances within the imaging system.Each distance was measured three times and represented as the mean of three measurements.The measurement criteria are described below.Right main bronchus -length (RMB-L): In the MPR window, draw a line from the proximal edge of RUL-BO and cross vertically to the inner side of RMB, and then measure the distance between the tracheal carina and the intersection (Fig. 1).Right main bronchus -Transverse diameter (RMB-TD): In the MPR window, draw a mid-vertical line based on the above RMB-L to intersect the lateral side of RMB and measures the distance between the two intersections (Fig. 1).Right main bronchus -Anteroposterior diameter (RMB-AD): In the lung window, the anteroposterior diameter of RMB at the RMB-BO plane was measured (Fig. 2).Cricoid cartilage -Transverse diameter (CC-TD) and Anteroposterior diameter (CC-AD): The anterior and posterior diameters of the cricoid cartilage were measured in the lung window (Fig. 2).
The spiral CT examination and 3D reconstruction may not be convenient in some community hospitals.We measured RMB-L on the chest X-ray of the same patient and compared it with CT measurement.Draw a line from the trachea carina and cross vertically to the right side of RMB, and next draw a parallel line from the proximal margin of the right upper lobe ori ce, and then measure the distance between the two lines and record as RMB-Lx (Supplemental digital Fig. 1).

Tube selection
In our study, the right RUSCH bronchopart® double lumen bronchial tube set (RUSCH® 116200, Tele ex medical, Ireland) was initially selected for all patients.According to our improved method, the sizes of RDLT selected were 28F, 35F, 37F, 39F, and 41F for RMB-AD of < 9.0 mm, 11.5 mm, 12.2 mm, 12.9 mm, and > 12.9 mm, respectively (Table 1).We noticed that the distance from the proximal end of the bronchial cuff to the proximal end of RUL-VS was designed to be about 12 mm regardless of different tube sizes.The difference (X) between RMB-L and 12 was calculated if RMB-L > 12 mm.Before intubation, we used a surgical marker pen to draw a black line X mm above the distal end of the bronchial cuff on the external wall of the tube (Fig. 1, 3).We also noticed a full-length white line marker on the tube, which was designed as an X-ray marker for checking position.Its leading-edge is always paralleled with the midline of RUL-VS (Fig. 2, 3).Before use, the endobronchial cuff and endotracheal cuff were prepared with gas leakage measurement, well lubricated with lidocaine cream, and aspirated fully to collapse each balloon [25].Modi ed intubation of RDLT A 3.5-mm diameter electronic portable exible video bronchoscopy (Seesheen SS-2130, Zhuhai, China) was used in the modi cation group (Fig. 3).After general anesthesia induction, the RDLT was inserted into the glottis under a visual laryngoscope (E.an-II L, Tianjin, China) [25,26].Once the endobronchial tip of RDLT was passed through the vocal cords, the stylet would be removed, and the tube was rotated 90°t o the right and slightly advanced until resistance was encountered.The FVB was subsequently passed through the tracheal lumen to ensure that the bronchial portion of DLT was in the right bronchus and then to guide the depth of the tube, noting that the aforementioned black line should be paralleled with the tracheal carina.Then, the FVB was withdrawn and reinserted through the bronchial lumen.An aforementioned white line marker could be seen on the left side of the inner wall through the full length of the tube.Insert FVB downward along the white line marker until the top of the tube, RML/RLL ori ces, and the bronchial carina could be seen.Bronchial carina should be paralleled with the line between the white marker and the X-ray indicator.A rotational motion may be needed to align the two lines on the condition that the cuff is de ated.Next, bend the FVB tip to the right and withdraw slowly to look for the RUL-VS, which was just on the opposite side of the white line marker.Through the RUL-VS slit, we can check the alignment of RUL-VS and RUL-BO.The alignment should be rechecked and repositioned if needed after lateral positioning.A brief description of each option of the strategy is listed in Table 1 for better understanding.

Conventional intubation of RDLT
In the control group, the selection of RDLT size was based on an adult patient's gender and height [5,27].The intubation procedure in the control group was the same as that in the modi cation group before the step of the FOB (Pentax F19BX, Japan) examination.First, FOB was inserted into the trachea lumen.The in ated blue bronchial balloon should be visible beyond the carina on the left side without herniation into the trachea.Then, FOB was withdrawn and reinserted through the bronchial lumen to search for RUL-VS.
When the FOB tip passed through RUL-VS, RUL-BO with three segments should be visible.

Variables and endpoint
The primary endpoint was the number of positioned RDLT, which is de ned as the alignment of the proximal edge of RUL-VS with the proximal edge of RUL-BO (Fig. 1).It is expressed as the visualization score of the RUL-BO: 1, completely visible (the optimal position); 2, partially visible (acceptable position);

Results
A total of 108 patients were assessed for eligibility in our study.After exclusions, 100 patients were enrolled and randomized 1:1 to the modi cation group (n = 50) and the control group (n = 50).Five patients were excluded in further analysis.Among them, two patients in the control group and 1 patient in the modi cation group failed to intubate the RDLTs and changed to LDLTs, and the LDLTs were directly used in another 2 patients in the modi cation group according to the CT measurements (Fig. 4).There were no signi cant differences in demographic data, ASA grade, Mallampati score, Surgical Procedures, and CT measurements between the two groups (Table 2).CT measurements of the two groups were mixed together for further analysis.We found that RMB-L ranged from 7.15 mm to 25.67 mm, with an average of 15.1 ± 3.93 mm.Among them, 6% were > 22 mm, 77% were 12-22 mm, 12% were 9-12 mm and 5% were < 9 mm (too short for an RDLT).No signi cant correlations were found between RMB-L and gender (P = 0.2547) or Height (P = 0.8222), respectively.From the alternative measurement in chest X-ray, the mean (SD) of RMB-Lx was 14.6 (8.78) mm.The inter-observer agreement was substantial with both methods (CT: interclass correlation coe cient [ICC] = 0.84; X-ray: ICC = 0.95).Correlations were strong and signi cant for RMB-L in CT (r = 0.72, P < 0.01) and in X-ray (r = 0.60, P < 0.01).Other measurement results are presented as mean ± SD (max, min) and listed as follows: CC-TD, 16.54 ± 2.865 ( was the smallest (P < 0.0001), suggesting that it could be suitable as a criterion for tube size selection.In general, there was a linear correlation between RMB-AD and height (R 2 = .2727,P < 0.0001): RMB-AD (mm) = 0.133* height (cm) − 9.882.
The intubation data are shown in Table 2.According to the conventional method or our modi ed method, the nal selection of tube size has no statistical signi cance in proportion.RDLTs in 8 patients of the control group needed to be replaced with larger or smaller RDLTs after the rst attempt.For another 2 patients, the LDLTs have to be used because of severe air leakage.FVB/FOB examination showed that the bronchial cuff partially exfoliated outside the carina.However, in the modi cation group, only one case needed to be replaced with a smaller tube.After consulting with the surgeon, the LDLTs were directly selected for 3 patients according to their RMB-L.The time spent on intubation in the modi cation group was statistically shorter than that in the control group (75.2 ± 8.1 vs 101.4 ± 7.3 seconds; P = 0.0186), although it may lack clinical signi cance in the context of surgery.A signi cant difference was found in subglottic resistance between the two groups (P = 0.0293).The accuracy of the bronchial segment size selection was similar between the two groups (P = 0.1220).In the control group, 21 of 48 cases were in the optimal position (43%), 16 (33) in acceptable position, and 9 (19%) in the wrong position.In the modi cation group, 31 of 47 (77%) cases could be were in the optimal position, 10 (21%) were in the acceptable position, and only 1 (2%) was completely invisible to RUL-BO.The difference was statistically signi cant in optimal plus acceptable position between the two groups (62% vs 98%, P = 0.0388).There was no signi cant difference in lung isolation scores between the two groups (P = 0.6018).
Perioperative adverse events data are listed in Table 4.In the control group, the incidence of transient hypoxemia during OLV was 25%, while only 3 cases (8.5%) had hypoxemia in the modi cation group.The incidences of airway hypertension and hypotension during OLV and airway injury were signi cantly lower in the modi cation group than in the control group (P = 0.0104 and P = 0.0357).Right upper lobe collapse was reported postoperatively in 5 patients in the control group and only one patient in the modi cation group by bedside chest X-ray (P = 0.0590).

Discussion
RDLT always had a bad reputation for being di cult to positioning because of its small margin of safety, and so its clinical use was rigorously avoided by many experts in the eld of thoracic anesthesia [3].However, in several certain select cases, the use of an RDLT may be mandatory [7].In our history of clinical practices, there were several accidents that LDLT was sutured to the incision of left sleeve bronchotomy or pneumonectomy, so the bronchial intubation on the non-surgical side is preferred by our thoracic surgeons whenever possible.Many suggestions have been proposed to improve RDLT placement, but are poorly effective.Currently, FOB guidance remains the gold standard for veri cation of the DLT position [28].And FVB, as a portable electronic bronchoscope, is an alternative method for airway observation [23].Its design of a high-de nition screen mounted on the eyepiece could provide a more detailed picture of the bronchial structure, which is very helpful to the anesthesiologists in DLT placement.
As for the selection of ideal DLT size, it is generally accepted that it should be based on the principle of smoothly inserting the largest type of tube into the target bronchus [29,30].Conventionally, the size selection is based on a person's height and gender, which was also adopted in the control group [5].
Although clinically acceptable in most cases, it may be not always appropriate especially for older adults.
According to a recent study, the optimal size of the DLT should be selected based on the combination of the transverse diameter of the cricoid ring and the main bronchus [31,32].In our study, cricoid cartilage was chosen as the measurement plane of tracheal diameter because its diameter is considered the smallest in the whole trachea [33].The RUL-BO plane was chosen to measure RMB diameter because the key to a successful RDLT is just to ensure RUL ventilation.As for the tube, the diameter of the tracheal part other than the bronchial part of RDLT was chosen to match with RMB-AD, because the tracheal part is often inserted too deep into the bronchus during intubation.Benumof et al. [22] have shown that the ideal bronchial diameter of DLT should be 1 to 2 mm smaller than that of the patient's main bronchi.We found that RMB-AD was the smallest in all CT measurements and had a signi cant linear correlation with the height regardless of different genders, suggesting that it could be a suitable criterion for tube size selection [31].The corresponding heights calculated according to the formula were consistent with conventional selection (Table 1) [2].In the modi cation group, almost all selected DLTs were appropriate in the bronchial segment with a lower intubation resistance and could signi cantly reduce the rate.The incidence of tube replacement and the poor airway pressure change during OLV in the modi cation group was signi cantly lower than that in the control group.Besides, our method can effectively prevent tracheal and bronchial injury without sacri cing the effectiveness of lung separation.
Estimating RMB-L is of paramount importance for a successful RDLT.Benumof et al. [34] de ned the margin of safety of Rusch RDLT intubation as the length of the RUL-VS minus RUL diameter.Kim JH et al. [17,35] suggested that LDLT should be considered if the distance between the tracheal carina and the distal edge of the RUL bronchus is less than 23 mm.However, the above studies did not take into account the design and size of different brands of DLTs.Even Rusch DLT's design has changed greatly from 30 years ago [34].We de ne RMB-L as the distance from the tracheal carina to the proximal edge of the RUL-BO because it is the easiest to be distinguished and measured in spiral CT(Fig.1).After a comprehensive analysis of the CT measurements of 100 Chinese patients in the two groups, we found that the RMB-L ranges from 7.15 mm to 25.67 mm with an average of 15.1 ± 3.93.No abnormal tracheal origin of the RUL bronchus was found in all subjects.Because of the inconsistency of the measurement methods, the results were slightly longer than those of Mi et al. [20] (13.6 ± 4.3).The RMB-L showed greater individual variability in Chinese but had a statistically signi cant positive correlation with height regardless of gender.The measurement results from the chest X-ray are also acceptable.There is no signi cant difference between the two methods, except that sometimes the anatomical structure may not develop well.
We noticed that the distance from the proximal end of the bronchial cuff to the proximal end of RUL-VS in a standard Rusch tube is always about 12 ± 0.5 mm.But, the length of RUL-VS of different tubes varied considerably from 8 to 15 mm, suggesting that it is not suitable as an indicator for intubation.If the alignment of the bronchial cuff with tracheal carina is taken as standard, the optimal RMB-L should be about 12 mm.In fact, in the cases of RMB-L 9-12 mm (12%), the bronchial cuff can be partially located in the trachea without leakage, thus increasing the safety range.Therefore, we suggest that Rusch RDLT is inapplicable to the patients with RMB-L less than 9 mm (5%) and the right-sided intubation will inevitably be a failure.When RMB-L is longer than 22 mm (6%) and the bronchial cuff is paralleled with tracheal carina, it could lead to complete blockage.For most patients in the control group (77%) with RMB-L 12-22 mm, effective lung isolation was clinically acceptable without severe hypoxemia as long as RUL-VS is partially paralleled with RUL-BO.Yet we think that we can do even better.We suggest that the optimal depth for an RDLT should be the alignment of the proximal end of RUL-VS with the proximal end of the RUL-BO to ensure the most effective ventilation.Since we have already known RMB-L, we can calculate the difference between RMB-L and 12, and then make a black marker there on the outer wall of the tube before intubation.Under the guidance of FVB, the depth of the right upper lung can be easily and accurately located only by adjusting the relative position of the black marker to the tracheal carina.
The ideal insertion angle should be considered after the optimal depth is determined.Campos JH et al. [13] observed that RDLT must be rotated in some patients to obtain the correct alignment of the endobronchial tube with the RUL-BO.We noticed that the RUL-BO is always directly identical to RML/RLL carina.This structural feature can be seen through CT imaging and 3D reconstruction.We also noticed a full-length white line marker on the inner surface of the whole tube.Campos JH et al. [7] suggested that the side hole is just opposite the white line, which can be used as a sign of intubation.Further observation shows that the front end of the white line marker is precisely paralleled with the middle line of RUL-VS.Therefore, the theoretical optimal insertion angle can be easily achieved by keeping the two lines in parallel (Fig. 2).Our results showed that the number of cases with the best position was signi cantly superior in the modi cation group to that in the control group.Although our method seems a little complex, the intubation time is signi cantly shortened, although it may lack clinical signi cance in the context of surgery (Table 3).In conclusion, our modi ed strategy could easily, safely, and accurately determine RDLT placement by combining CT measurements with FVB guidance, which may be an alternative approach to the conventional method.

Figure 2 CT
Figure 2

Figure 2 CT
Figure 2

Figure 4 Flow
Figure 4

Table 1
Brief description of the modi ed strategy.
Linear regression analysis was used to evaluate how RMB-L in the CT images related to those in the chest X-ray images.The relationship between CT measurements and age were also examined using a linear regression approach.The statistical analysis was done by using GraphPad Prism 7.0 (GraphPad Software Inc.San Diego, CA, USA) and a P-value of < 0.05 was considered statistically signi cant.
3, completely invisible (wrong position).The secondary endpoints included intubation data and perioperative adverse events.Intubation data: tube size; intubation resistance; cuff pressure; intubation time; intubation failure; visual eld score of right bronchial origin under FOB; lung isolation effect.Perioperative adverse events: intraoperative transient hypoxemia (SpO2 < 90%), high airway pressure (> 35 cmH 2 O), air leakage (low airway pressure < 10 cmH 2 O), carina, and bronchial injury.Intubation failure: After 3 attempts, the endobronchial lumen could not be inserted into RMB.Intubation resistance: 1, no resistance; 2, mild resistance; 3, moderate resistance; 4, severe resistance, it cannot pass through the subglottis and must be replaced by the next smaller size.The pressure of the bronchial section: The pressure of the bronchial tube was measured by a hand-held pressure gauge (Rush Endotest 112700).When the required pressure of the bronchial sleeve is 0 cmH 2 O, the bronchial segment is considered too large; when the pressure of the bronchial sleeve is greater than 30 cmH 2 O, the bronchial segment is too small.Lung isolation effect score: 1, excellent (complete collapse); 2, fair (some residual air); and 3, poor (no collapse or residual air interfering with surgical exposure).Trachea and bronchial injury: 1, obvious; 2, a small amount of ecchymosis; 3, combined with ecchymosis, bleeding or ecchymosis; 4, erosion.The collapse of the right upper lobe was examined by bedside chest radiographs at the post-operative stage.Statistical analysisThe sample size was calculated based on previous clinical experience and previous studies.50 patients in each group were required with a test level of 0.05 and an assurance of 80%.Quantitative variables were represented as means (standard deviation) or medians (25th percentile; 75th percentile) and compared using unpaired t-test or paired t-test, with Welch's correction if required.Mann-Whitney ranksum test was used to analyze the non-parametric data and the score-based results.The qualitative variable was represented by a number (proportion) and compared using Fisher exact test or chi-square test, when appropriate.

Table 2
Demographic data and CT measurements data.

Table 4
Perioperative adverse events.