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- Ann Card Anaesth
- v.26(2); Apr-Jun 2023
- PMC10284481
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Ann Card Anaesth. 2023 Apr-Jun; 26(2): 124–132.
Published online 2023 Apr 3. doi:10.4103/aca.aca_140_22
PMCID: PMC10284481
PMID: 37706375
Shagun Bhatia Shah, Uma Hariharan,1 and Rajiv Chawla
Author information Article notes Copyright and License information PMC Disclaimer
ABSTRACT
Appropriate size selection of double-lumen tubes (DLTs) for one-lung ventilation (OLV) in adults is still a humongous task. Several important factors are to be considered like patient height, gender, tracheal diameter, left main bronchial diameter, and cricoid cartilage transverse diameter. In addition to radiological assessment of the airway diameters, the manufacturing details of the particular DLT being used also play a significant role in size selection. Optimal positioning of the appropriately sized DLT is indispensable to avoid complications like airway trauma, cuff rupture, hypoxemia, and tube displacement. It is imperative to know whether the one-size-fits-all dictum holds for DLT size selection as claimed by certain studies. Further randomized studies are required for crystallizing standard protocols ascertaining the correct DLT size. This systematic review article highlights the various parameters employed for DLT size selection and explores the newer DLTs used for adult OLV.
Keywords: Adult height, cricoid diameter, double-lumen tube size, left main bronchial diameter, one-lung ventilation tracheal diameter
INTRODUCTION
Double-lumen tubes (DLTs) are available in a spectrum of sizes because an optimal size is quintessential for optimal positioning (with the goal of avoiding airway trauma; tracheobronchial tree rupture; preventing desaturation/hypoxemia; adequate ventilation)[1,2] In contrast, the dictum of “one-size-fits-all” holds true for most bronchial blockers (BBs) used in most adult patients. This is because DLTs need to conform to the airway anatomy, while BB comes to the rescue in distorted airway anatomy. Demographic parameters (gender, age), clinical parameters (height, weight), and radiological measurement of tracheobronchial tree (tracheal diameter, transverse diameter of the cricoid cartilage) are some surrogates for internal diameter of the mainstem bronchus which should be sufficiently larger than the outer diameter of the selected DLT.[2-5]
Small differences in internal diameter of different DLTs based on the shape of inner tube also affect the gas flows by altering the resistance.
METHODS
Medline (PubMed), Embase (Scopus), Cochrane Central Trials Register (Cochrane library), and CKNI databases were searched using keywords “double-lumen tube size” to locate relevant manuscripts on prediction of DLT size in patients requiring one-lung ventilation (OLV). A total of 58 clinical trials (24 CT.guv + 19 PubMed + 16 Embase + 5 ICTRP with overlapping) and 1 Cochrane review were identified from Cochrane database and 22 clinical trials and randomized controlled trials, 10 reviews and systematic reviews from PubMed database search. Nine additional manuscripts were obtained by reference crawling and citation search on Google Scholar. No standard practice guidelines have been published so far on this topic. After removal of 24 duplicates from 102 manuscripts obtained, 78 records were screened and 53 excluded. None of the Cochrane reviews were relevant. Out of 25 full-text manuscripts assessed for eligibility, two Chinese manuscripts (ChiCTR-INR-17013040 and ChiCTR2100043764) could not be retrieved, and another two were case reports. Twenty-one clinical trials were included in the final analysis (seven clinical trials from Cochrane, five from PubMed, three from Embase, and six from Google Scholar search were found eligible). We fully reviewed the 21 relevant manuscripts.
RESULTS
A total of 21 studies were reviewed wherein different parameters had been used to estimate the size of DLT. This includes demographic parameters (gender, height, weight) and imaging techniques (X-ray, CT scans, USG) to calculate the diameters of various parts of tracheobronchial tree. The details are summarized in Table 1.
Table 1
Analysis of parameters used for calculating DLT size as per current literature
| Study (Year) | Sample size; Design | Result | Conclusion | |
|---|---|---|---|---|
| Height and Gender | Duthie et al. (2012)[6] | n=191 Women < 160 cm-35F Women > 160 cm-37F Men < 170 cm-39F Men > 170 cm 41F | 184 patients could be intubated as per recommended criteria 7/184 patients required smaller tubes;10/184 required a bougie and 1 an exchange catheter 75% DLTs required to be advanced/withdrawn ↓FOB | Height–weight combination formula predicted correct DLT size in 184/191 (96.3%) patients; overestimated size in 3.7% patients |
| Ideris et al. (2017)[7] | n=179 (123M:56F) Women < 160 cm-35F Women > 160 cm-37F Men < 170 cm-39F Men > 170 cm 41F Retrospective Asians | In <160 cm males (9), 22.2% In 160–170 cm males (59), 55.9% In >170 cm males (45), 41.8% In <150 cm females (3), 66.6% In150–160 cm females (33), 54.5% and in >160 cm females 12% received the recommended DLT size | Height–weight combination formula overestimated DLT size in >71% males >170 cm;30.5% males 160–170 cm; and 30% females >160 cm Underestimated in 36.4% females 150–160 cm | |
| Roldi et al.[8] (2019) | n=102 step1 Lt DLT selection based on clinical parameters. USG data collected to determine cut-off points associating height and TD n=50 step2 USG cut-off points used | Step-1: LDLT size was appropriate/undersized/oversized in 40 (39.2%)/23 (22.6%)/39 (38.6%) of patients. Cut-off values derived from USG data would have reduced the use of oversized tubes by 20.6%. Step-2: Selection of adequately sized tubes increased (86.0 vs. 39.2%, P < 0.001) | Combining USG measurement of tracheal diameter and clinical parameters improves the selection of Left DLT size. | |
| Tracheal Diameter | Brodsky et al.[9] (1996) | n=70 (38M:32F) Prospective study Americans TD by CXR | Mean tracheal width was 20.90 mm (range16–35 mm) in men and 16.90 mm (range 13–22 mm) in women Majority of the men used a 41 Fr DLT regardless of their height or weight | All DLTs selected using TD as a guideline were successfully placed; Minor resistance in negotiating glottis in 10 (14.3%) patients and negotiating the bronchus in 19 (27.1%) patients |
| Chow et al.[4] (1998) | n=66 Prospective study Asians TD from CXR- PA for DLT selection | Positive predictive values for the male and female patients were 77.3% and 45.5% | TD not reliable in Asian females since they are smaller and shorter; TD criteria need modification | |
| Hampton et al.[10] (2000) | n=206 (92M:114F) PA chest X-rays review | Males: Mean LMBD=13.0± 2.6, females LMBD=11.8 +/- 1.6. Correlation between LMBD and TD (r=0.74) was not precise enough to be useful as an estimate for clinical use | Only direct measurement of LMBD has sufficient precision to define the appropriate size of Lt DLT | |
| Brodsky et al.[11] (2005) | n=321 Prospective study TD Vs LMBD on chest- Xray | TD and LMBD were directly measured from the chest radiograph. LMBDmm= (0.45)(TDmm(CXR)) + 3.3 mm | When direct measurement of LMBD is not available, LMBD estimated from TD is a better predicter than sex, height, or weight. | |
| Šustić et al.[12] (2008) | n=25+20 Prospective study TD by USG | CT-TD at the coronary plane 0.5 cm above SC joint; USG-TD at transverse section just above SC joint; LMBD 1 cm below carina. Strong correlation between USG-TD and CT-TD (r= 0.882) and CT-LMBD (r= 0.832); Incorrect Lt DLT by USG selected in 25% cases | USG measurement of the outer tracheal width can be a useful method for predicting the LMBD for selecting a Lt DLT | |
| Ideris et al.[7] (2017) | n=179 Retrospective Asians Recommendations TD≥18 mm, 41 Fr DLT TD ≥16 mm, 39 Fr DLT TD ≥15 mm, 37 Fr DLT TD < 5 mm, 35 Fr DLT | 26.8% of males with TD 17.9 ± 2.2 mm used a 41 Fr DLT; Majority used smaller DLTs; Only 41.1% of females with a mean TD of 15.3 ± 2.0 mm used the recommended 37 Fr DLT size. 46.6% with similar TD were intubated with a smaller DLT size 35 Fr. | Recommendations for DLT size based on TD on chest radiograph overestimates DLT size in both males and females | |
| Hannallah et al.[5] (1997) | n=20 Prospective study LMBD by CT scan chest | In 17/20 patients, the DLT size fulfilled both criteria (air leak on bronchial cuff deflation; airtight seal of the left bronchus with a bronchial cuff volume of ≤2 ml); In three women with LMBD≤ 10 mm, the bronchus was sealed without any air in the bronchial cuff of size 35 Fr left DLT | Chest CT scan measurement of left bronchial diameter can successfully guide the choice of left DLT size | |
| Chow et al.[13] (1999) | n=52 (32M:18F) Prospective Asia-born CT-scan chest >12 mm (41Fr); 12 (39 Fr); 11 (37Fr); 10 (35Fr); <10 mm (32Fr) | Mean LMBD=11.6 ± 1.4 mm in males and 9.6 ±1.0 mm in females Tracheas of all patients were successfully intubated with the predicted DLT sizes. Smaller Asian patients <160 cm tall required a DLT size smaller than 35F | LMBD on CT chest maybe considered the gold standard for DLT size selection | |
| Cui et al.[14] (2005) | n=100 Prospective study TD and LMBD measured with 3D image reconstruction using the electronic calipers of the spiral CT scanner | Lt DLT of sizes 41Fr, 39Fr, 37Fr, and 35Fr were predicted according to the inner LMBD; Appropriate size of DLT is correlated with LMBD (r=0.7346). | Clinically, DLT size can be predicted by inner LMBD | |
| Jeon et al.[15] (2005) | n=105 Prospective study | DLT size selection founded only one bronchial diameter differed from the one selected using two perpendicular bronchial diameters in 54.3% of patients (57/105). All patients could be intubated using selected DLT | Measuring two perpendicular bronchial diameters improves preoperative DLT selection | |
| Ideris et al.[7] (2017) | n=179 Retrospective Asians Chest radiography | LMBDmm=6.58 +0.3 (TDmm) for males; mean 11.8±1.8 mm LMBDmm=3.13 + 0.49 (TDmm) for females; mean 10.6 ±1.6 mm. | LMBD can be measured by chest radiograph using digital filmless technique LMBD cannot predict DLT size in Asians. | |
| Seo et al.[16] (2018) | n = CT imaging with bronchial Vs. mediastinal window to guide DLT sizes | On 130 CT images, the bronchial diameter (9.9 mm v 10.5 mm v 11.7 mm) and the selected DLT size were different in the lung, bronchial, and mediastinal windows; oversized tubes were chosen less frequently in the bronchial window vs mediastinal window (6/110 v 23/111; risk ratio 0.38; =0.003). no tubes were undersized in the 2 windows | LMBD measurement in the bronchial window guided more appropriately sized DLTs compared with the lung or mediastinal windows. | |
| Kar et al.[17] (2019) | n=41 Prospective study Indian patients | Males: Weak correlation between DLT size and height (R2= 0.069), TD (R2=0.34), LMBD (R2= 0.238) Females: Better correlation between DLT size and height (R2= 0.266), TD (R2= 0.53), LMBD (R2= 0.50) Males:75% intubated with 37 Fr, 21.4% by 35 Fr, 3.6% by 32 Fr DLT females: 69.2% by 32Fr DLT, 23.1% by 35 Fr and 7.7% by 28 Fr | Despite downsizing the DLT, there was no hypoxemia in any patient. | |
| Suvvari et al.[18] (2019) | n=55 Prospective study Indian patients Rt and Lt DLT Bronchial diameter on chest CT used for DLT size selection | Adequate isolation of lung in 92.7% of patients, out of which 54.9% required different sized DLT (33.33% required larger; 21.56% required smaller) than that predicted by conventional method | Best parameter is LMBD; on multivariate regression analysis, DLT size had positive correlation with height (P=0.026), TD (P=0.029) on chest X-ray, and age (P=0.05) | |
| One size fits all | Amar et al.[19] (2008) | n=300 Prospective study 35Fr DLT used in all patients irrespective of gender/height/ TD/LMBD | The combined incidence of intraoperative transient hypoxemia, inadequate lung isolation, or need for DLT repositioning during surgery did not differ among patients receiving 35, 37, or 39 FR DLT, regardless of gender or height. | Use of smaller than conventionally sized DLT is not associated with any differences in clinical intraoperative outcomes. |
| nguyen et al.[20] (2021) | n=50 Prospective study 35 F DLT for all patients vs using patient height regardless of gender | no statistically significant difference in no. of intubation attempts, Cormack–Lehane grade, no. of times DLT was repositioned, oxygen saturation at 5 min and 10 min after starting OLV, and incidence of sore throat. | Majority of patients receive unnecessarily large DLTs, which makes intubation inherently more difficult and increases risk of post-operative sore throat | |
| Cricoid cartilage diameter | Seymour et al.[21] (2003) | n=108 (59M:49F) Prospective study Human white cadavers | In both sexes, the LMBD-to-cricoid ratio exceeded 83% Coef of correlation (r) Cricoid and LMBD=0.6. Trachea and LMBD=0.5 in male cadavers and 0.45 in female cadavers | Dimensions of the cricoid ring best define those of the main bronchi. |
| Shiqing et al.[22] (2020) | n=80 (All female) Prospective study Asian Measurements taken on CT scan chest | Combined group (TD-Cricoid ring + ED-LMB) versus LMB alone Overall accuracy :87.5% vs 60.0%; selection of tracheal segment 92.5% vs 67.5%; P=.010 Selection of bronchial segment 95.0% vs 86.1%; P=.246 Severity of post-op sore throat was higher in the LMB group at 24 hours (P=.001). | The correct size of DLT for Asian women should be selected based on the combination of transverse diameter of cricoid ring and the ED-LMB measured on CT scan | |
| Shiqing et al.[23] (2020) | n=100 (All female) 50=Lt DLT 50=Rt DLT USG transverse diameter cricoid >14 mm=37 Fr 13.1-14 mm=35Fr 11.8-13 mm=32Fr | CT scan vs USG for TD-Cricoid measurement showed good agreement (r = .946, p < 0.001); Overall accuracy of the DLTs was similar between the Rt and Lt-DLT (86.0% v 92.0%, p = 0.318) | DLT size for Asian women can be predicted by ultrasonography measurement of the cricoid diameter. | |
| Zhang et al.[24] (2021) | n=120 (part-1) Obtaining transverse diameter cricoid range by USG and CT corresponding to different DLT-sizes n=102 (part-2) Prospective study USG Vs CT for transverse diameter cricoid | Accuracy of selecting LDLT by height and gender was 58.3%. USG transverse diameter cricoid range: 32 Fr <15.88, 35 Fr: 15.88-16.80, 37 Fr: 16.75-17.81, and 39 Fr > 17.80. CT- transverse diameter cricoid range: 32 Fr <15.74, 35 Fr: 15.74-16.65, 37 Fr: 16.56-17.68, and 39 Fr > 17.65. Accuracy of intubation in USG Vs CT groups was 90.2% and 94.1% | Accuracy of selecting Lt DLT based on transverse diameter cricoid is significantly higher than gender and height-based selection. USG and CT scan are both equally accurate measures of cricoid diameter |
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DISCUSSION
Medical literature is replete with techniques to determine the correct DLT size. But there is no consensus on the most practical, accurate, and useful method of predicting size and depth of DLT insertion. Since it is not feasible for DLTs to be tailor-made for each patient, the DLT sizes are available as 32F, 35F, 37F, 39F, 41F for adult patients, the best fit allowing the bronchial lumen of DLT to glide into the corresponding mainstem bronchus without resistance producing a tight seal when the bronchial cuff is inflated to a volume that produces intracuff pressure <20 mmHg.[4]
At the time of inception of DLTs, the height and sex of the patient guided the choice of DLT size.[3,6] Outer diameter of the main body of DLT should be smaller than inner diameter of the tracheal lumen, whereas the greatest outer diameter of the bronchial lumen of DLT must be less than the inner diameter of the corresponding bronchial lumen for an adequate fit. Hence, tracheal diameter and left bronchial diameter on chest radiograph or CT imaging were the more accurate improvements down the timeline.[4,5] Sonography is a point-of-care modality of measuring tracheal diameter which correlates well with the DLT size as reported by further studies.[12] Since the clinical practice patterns of the DLT still do not match recommendations from existing literature, the quest for newer determinants of optimal DLT size is still on. The latest correlation is the sonographic cricoid cartilage diameter.[24]
Each of the available parameters for DLT size prediction is reviewed below [Table 1].
Height and gender of the patient
Recommendations are given in standard textbooks which state that for women shorter and taller than 160 cm, 35Fr and 37Fr DLTs, respectively, suffice. Similarly for men shorter than 170 cm, a 39 Fr DLT and for men taller than 170 cm a 41Fr DLT is recommended.[23] Slinger, in addition, advocated 32Fr DLTs for women <150 cm and 37Fr DLTs for men <160 cm.[25]
Duthie et al.[6] reported that in 96.3% of their patients, the correct DLT size could be predicted using the above recommendation. On the contrary, Ideris et al.[7] reported that the DLT size was overestimated in more than half of their male patients using these recommendations. This discrepancy could be due to a racial difference in the two patient populations studied. The Asian population requires modified recommendations. Slingers recommendation of using 32Fr DLT for women <150 cm tall is clinically relevant. In the authors’ own experience in the Indian scenario, we seldom require a size >35Fr for women patients. For patients shorter than 140 cm, bronchial blocker is used electively.
No study has been conducted on transgenders due to paucity of sample size or ethical concerns.
Tracheal diameter (TD)
There exists a linear relationship between tracheal diameter (TD) and DLT size. For TD ≥18 mm, ≥16 mm, ≥15 mm, and <15 mm, recommended DLT sizes are 41 Fr, 39Fr, 37Fr, and 35 Fr, respectively [Table 2].
Table 2
Selection of double-lumen tube (DLT) size based on height, gender, tracheal, bronchial, and cricoid widths of the patient
| DLT Size (Fr. G) | DLT ED (mm) 2πr (Actual) | DLT ID (trachea;mm) | Height (cm) and Gender | Tracheal Width (mm;Brodsky) | Bronchial Width (mm) | Cricoid Width (mm) |
|---|---|---|---|---|---|---|
| 41 | 13.06 (13.7) | 5.4 | >170 cm; M | ≥18 | >12 | NA |
| 39 | 12.42 (13) | 4.9 | <170 cm; M | ≥16 | 12 | NA |
| 37 | 11.78 (12.3) | 4.5 | >160 cm; F | ≥15 | 11 | >14 |
| 35 | 11.14 (11.7) | 4.3 | <160 cm; F | ≥14 | 10 | 13.1-14 |
| 32 | 10.19 (10.7) | 3.4 | <150 cm; F | <14 | <10 | 11.8-13 |
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(2πr=circumference of DLT where r=radius; DLT=double-lumen tube; ED=external diameter; Fr. G=French gauge; ID=internal diameter)
Brodsky et al.[9] measured tracheal width at the interclavicular plane on a posterio-anterior view chest radiograph and reported that the tracheal width was a better predictor for the selection of an appropriate-sized DLT than the parameters of age, height, or weight used alone or in combination. They intubated 36/38 of their male patients with a 41Fr DLT and even used a 41Fr DLT in 10/32 women patients based on measured TD. All the remaining patients were intubated using a 39Fr DLT. The reference TD brackets used by them did not yield encouraging results in a much larger study on Asian patients by Ideris et al.[7] Racial differences could account for this discrepancy. Brodsky et al.[9] did report minor resistance in advancement of the DLT through the trachea and the bronchus in 14.3% and 27.1% patients, respectively, which indicates that the DLT size might have been overestimated in these patients, and a single-size smaller DLT might have worked equally well. They have not reported the incidence of post-operative sore throat in their patients. They also vouch for larger DLTs because in their opinion, DLT malpositioning is more frequent with smaller DLTs since smaller DLTs can easily migrate too deep into the bronchus and obstruct the upper lobe orifice. Brodsky et al.[9] never used fiber-optic bronchoscopic confirmation of DLT placement. In our clinical practice, we have observed that use of smaller DLTs is more prudent since it avoids potential airway trauma (hoarseness, post-operative sore throat, vocal cord palsy, granulomas, arytenoid dislocation, hematomas, ruptured airway) caused by forcing larger DLTs into the tracheobronchial tree. Moreover, the deflated tracheal cuff adds about 0.5 mm to the external diameter of the DLT. DLT malpositioning is amenable to easy rectification by skilled use of a fiber-optic bronchoscope (as per institutional protocols). Additionally, a pressure gauge is used to maintain a cuff pressure <20 mm Hg to avoid any potential ischemic pressure necrosis of the bronchial wall in contact with the cuffs, which allays the second concern raised by Brodsky et al.[9] regarding smaller DLTs. Although the lumen of a smaller DLT offers more airflow resistance during OLV, this aspect usually does not assume clinical significance in mechanical ventilation with pressure control mode, and newer modes are available in high-end anesthesia workstations. Finally, the bronchial diameter variations in currently manufactured DLTs may give up to 0.5 mm smaller bronchial diameter in 41Fr DLT as compared to 39Fr DLT from the same manufacturer, and airway resistance of 41Fr DLT in such cases would be greater than that of the 39Fr DLT as per a prospective study by Russel et al.[26] Another concern about greater difficulty in advancing a fiber-optic bronchoscope through smaller DLTs has been rested by availability of pediatric FOBs which can easily negotiate all DLTs sized 35Fr and above. 32Fr DLTs are manufactured only by Bronchocath, while 28Fr DLTs by both Bronchocath and Sheridan Co. The fact that PortexTM and RuschTM do not manufacture DLTs smaller than 35Fr indicates that these sizes are seldom required and a bronchial blocker can easily be placed in such infrequent cases. In view of the above, a 33Fr or a 34Fr DLT (amenable to FOB bronchoscopy unlike a 32Fr DLT) should also be manufactured. Standardization of bronchial diameters for corresponding tracheal diameters and a mention of tracheal and bronchial diameters on the package insert of DLTs should be included by the manufacturers.
Amar et al. conducted a prospective study on 300 patients, where one investigating team used a 35Fr DLT in all patients irrespective of gender, height, weight, age, tracheal diameter, and left main bronchial diameter (LMBD), while the second investigating team used 35Fr, 37Fr, and 39Fr DLT based on gender and height criteria.[19] Four males and 62 females <165 cm, 30 males and 27 females between 165–177 cm tall, and 17 male and 3 female patients >177 cm tall received 35Fr DLTs. They reported that the combined incidence of intraoperative transient hypoxemia, inadequate lung isolation, or need for DLT repositioning during surgery did not differ among patients receiving 35, 37, or 39 Fr DLT, regardless of gender or height. Their results corroborate with our practice of using smaller DLTs.
Left main bronchial diameter (LMBD)
Chest computerized tomography (CT) is the imaging modality of choice for measuring LMBD. As per Seo et al.,[16] fidelity of bronchial window (width 1,000 Hounsfield unit [HU] and level –450 HU) for LMBD measurement is higher as compared to lung (width 1,500 HU and level –700 HU) and mediastinal (400 HU and 25 HU) windows making it a superior guide to DLT selection. LMBD is measured at the plane one slice (7–10 mm) below the slice that shows the carina and where the left main bronchus can be visualized as a singular structure. The internal diameter of the LMB is measured perpendicular to the portion of the bronchus that is most parallel. Most investigators have reported inability to measure LMBD in chest radiographs in approximately 50-60% of the patients.[5,10] This limitation can be overcome by a picture archiving and communication system (PACS) which provides digital images of enhanced quality superior to conventional radiological films. Ideris et al[7] could accurately measure the LMBD in 98% of their patients by improved air bronchogram visibility achieved by altering contrast settings. We should keep in mind that the actual bronchial width is approximately 90% of the measured size because of radiological magnification in PA chest radiographs.[27] As per a postmortem study conducted by Jesseph et al.,[30] bronchial diameter exhibits a strong correlation with the tracheal diameter, ratio of LMBD-to-tracheal diameter being 0.68. Hence, the tracheal width can be used as a surrogate for bronchial width after multiplying TD with 0.68.[27] Russel et al. measured lengths and diameters of the deflated bronchial cuff segment of 171 left-sided DLTs from four manufacturers (Sheridan, Mallinckrodt, Portex, and Rüsch). For DLTs of the same size from the same manufacturer, the diameter of the segment with the deflated bronchial cuff varied by more than 1 mm in some instances. The diameter of the bronchial cuff segment did not consistently decrease as the nominal size decreased even for the same manufacturer. There was major overlap in diameters of the bronchial segments between Fr 41, Fr 39, and Fr 37 tubes from most manufacturers, so that some of the Fr 39 tubes had a bronchial cuff segment diameter as much as 0.5 mm larger than the Fr 41 tube. They reported that Portex DLTs had the smallest bronchial diameter when bronchial diameters from DLTs of same size from different manufacturers were compared. They concluded that French gauge markings on left tracheobronchial tubes are of very limited value in determining the appropriate size to be selected for a patient.
Until such time, the dimensions of manufactured DLTs become more consistent, DLT selection should involve two steps. The preliminary step should be broad selection based on height-gender combination criteria for that particular race followed by fine-tuning the selection by measuring the outer diameter of the bronchial lumen of the selected DLT and comparing it with the left bronchial diameter of the patient measured on chest CT.
Subtracting the diameter of right upper lobe bronchus (CT chest) from the diameter of right upper lobe ventilation slot of the right DLT gives the safety margin for right DLT. Since the diameter of this slot increases with increasing right DLT size, larger right DLTs are preferred.[18]
Two perpendicularly measured bronchial diameters
The cross-sectional area of the mainstem bronchi is oval. Hence, for preoperative DLT size selection, measurement of both the mediolateral bronchial diameter on chest radiograph and the antero-posterior bronchial diameters on computed tomogram seems prudent. Jeon et al.[15] reported that the arithmetic mean of the above two bronchial diameters should be 0–2.0 mm greater than the upper limit of 95% confidence interval of the averaged outer diameter of the bronchial lumen of the selected DLT. They also found that DLT size selection based on only one bronchial diameter differed from the one selected based on two perpendicularly measured bronchial diameters in 54.3% of patients (57/105).
Cricoid cartilage diameter
Seymour et al.[21] found a better correlation between cricoid diameter and LMBD versus tracheal diameter and LMBD. The correct size of DLT for Asian women should be selected based on the combination of transverse diameter of cricoid ring measured by CT scan or ultrasound and the LMBD measured on CT scan [Table 2].[22,24]
The chief reason behind unsuccessful DLT insertion was reported as difficult passage through the cricoid cartilage in a study including 155 Japanese women. In 7/12 patients with unsuccessful DLT placement (three: 32-Fr and four: 35-Fr), the transverse diameters of cricoid cartilage were smaller than the DLT’s tracheal diameter, and in one patient with 32Fr DLT, cricoid diameter was smaller than DLT’s left bronchial diameter.[29]
Side of main bronchus being intubated
For any given patient, the ideal DLT size would also depend on whether the right or left main bronchus is being intubated. Although sounding paradoxical, both smaller left DLTs and larger right DLTs would be ideal in the same patient. This discrepancy in DLT size between right and left bronchial intubation is because of an enhanced safety margin offered by larger right DLTs owing to their larger right upper lobe ventilation slots,[18] e.g., in a 170-cm-tall male patient, with same right and left bronchial diameters (12 mm) on CT chest, a 39Fr left DLT and a 41 Fr right DLT would be optimal.
Manufacturing details of DLT
DLT size selection carries unwarranted uncertainty because clinically relevant parameters are unidentified and vary considerably between different manufacturers,[30,31] e.g., the outer diameter of the tracheal portion of 35Fr left DLT varies with its make (Vivasight) 13.2 > (Sheridan) 13 > (Well lead) 12.9 > (Mallinckrodt) 12.7 > (Rusch) 12.5 > (Portex) 12.4). The AP diameter of a 35Fr DLT is more than the transverse diameter at distal bronchial cuff in all makes, the AP diameter for VivaSight DLT (9.4 mm) is the largest while that of the Portex DLT (8.4 mm) is smallest. VivaSight, in addition, has the largest cross-sectional area (80.7 mm2) measured at a point just distal to Bronchial cuff and Portex DLT the smallest (64.3 mm2).[31]
The most striking variation concerned the measured angle between the DLT shaft and the bronchial portion, with the largest angle (Sheridan; 39 mm) being more than three times that of the smallest (12 mm) for a given DLT size (35 Fr).
The internal diameters, internal cross-sectional areas of tracheal and bronchial lumens, and cuff inflation tubules of DLTs of the same French gauge from different manufacturers (and different lots from same manufacturer) vary in shape and size translating into differences in resistance to airflow, e.g., for a 35F DLT cross-sectional areas in mm2 for bronchial lumen are Bronchopart/Rüsch (22.69) < Blueline/Portex (25.72) < Coopdech/Daiken Medical (25.57) < Bronchocath/Mallinckrodt (26.86) < Sher-I-Bronch/Sheridan (32.79).[32,33]
As per a prospective study by Olivier et al.[34] on 206 patients, the left main bronchus is usually elliptical (transverse LMBD being greater than antero-posterior LMBD in either sex), and the smallest LBD (transverse LMBD in 25.2%) cannot be accurately evaluated using patient height, gender, or a ratio from TD since the difference between mean estimated LBD and the smallest LBD is 1.6 ± 1.3 mm.
Scans of DLTs superimposed on three-dimensional image reconstruction of tracheobronchial anatomy from routine preoperative spiral CT scans of individual patients had poor correlation with patient height (r < 0.50) but gave clinically appropriate results (fiber-optic bronchoscopically confirmed fit, optimal bronchial cuff volumes, adequate lung isolation oxygenation and ventilation) in all 48 patients where DLT was placed.[35]
Recent advances include automatic measurement of TD and LMBD using dedicated software like Thoracic Volume Computer-Assisted Reading software (GE Healthcare, Chicago, IL, USA).[36]
Newer DLTs
Ambu VivaSight DLT
An integrated camera placed at the distal end of tracheal lumen of Ambu VivaSight DLT allows visualization of each step of DLT placement on the designated monitor screen.[37] These DLTs constitute an upgradation over the traditional blind insertion techniques. As per a recent study comparing VivaSight and conventional DLTs, VivaSight reduces the need for fiber-optic bronchoscopy. Additionally, the size of the DLT was smaller in the VivaSight group.[38]
ANKOR three-cuffed DLT
A third carinal cuff is provided in addition to the routine tracheal and bronchial cuffs. Once the deflated blue bronchial cuff disappears through the vocal cords, the left DLT is rotated 90 degrees anticlockwise, followed by carinal cuff inflation via the carinal pilot balloon. This third cuff blocks the right bronchial opening, so that the bronchial DLT lumen is preferentially directed to the left main bronchus. After DLT positioning is confirmed, the tracheal and bronchial cuffs are inflated and the carinal cuff is deflated.[6] Kim et al.[39] reported a significantly reduced difference between the initial depth of DLT placement and the target depth confirmed by FOB in the ANKOR DLT versus the conventional DLT (1.8 vs. 12.9 mm; p < 0.001)
There exist no randomized controlled trials regarding optimal DLT size utilizing the newer DLTs.
CONCLUSION
To date, there is no consensus on the optimal parameter for DLT size selection. Although main bronchial diameter on chest CT is the most accurate method, it is cumbersome and subject to availability of a high-quality computed tomographic image. Surrogates of LMBD like height, gender, and tracheal diameter on chest radiograph score high on ease of use but are inadequate, although transverse cricoid diameter seems promising. Smaller sizes of left DLTs corresponding to the “sex and height” criteria do not create major problems for patients, and conventional teaching of largest possible DLT that fits right main bronchus for right DLTs is currently the most pragmatic approach, especially in resource-limited settings.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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