Double-lumen endobronchial tubes (DLT) are used to isolate and/or to collapse lungs selectively during thoracic surgical procedures. A left double-lumen tube (LDLT) can be used successfully in most patients for right-sided and left-sided procedures.1,2 LDLT size should be chosen carefully: if oversized, it may cause bronchial or tracheal trauma; if undersized, the bronchial section can migrate too far into the left lower bronchus and may offer more resistance to gas flow or the tracheal part may not reach the carina, resulting in failure in lung isolation or separation. Thus the choice of an appropriately sized LDLT is crucial and is normally based on the sex and height of the patient.
Ultrasound imaging can provide rapid assessment of airway anatomy in the operating theatre,3 ICU, emergency department and even in hostile environments.4 Ultrasound is a reliable tool for the assessment of the subglottic airway, having been validated by MRI and computed tomography (CT).5 Moreover, ultrasound needs minimal training and does not require complete immobility or sedation.4 A correlation between outer tracheal diameter measured by ultrasound just above the sternoclavicular junction and left bronchial diameter measured by CT scan has been described.5–7 However, left bronchial diameter cannot be predicted accurately by ultrasound alone.
The aim of the current study was to test the hypothesis that matching ultrasound findings to standard clinical parameters would help in optimising selection of LDLT size.
In a first step, we prospectively studied the relationship between sex, height, tracheal diameter and adequacy of LDLT. Data on ultrasound tracheal diameter were collected to determine combined cut-off points (associating height and tracheal diameter); these cut-off points were then applied retrospectively to test their capability to reduce the frequency of insertion of an inappropriate size of tube, mainly aiming to reduce the use of an oversized and potentially traumatic tube. In a second step, we prospectively tested a new approach for the choice of LDLT based on sex, height and tracheal diameter measured with ultrasound; we aimed to increase the frequency of insertion of appropriately sized LDLT, especially by reducing the number of oversized LDLTs.
Ethical approval for this prospective observational cohort study was obtained by our Ethical Committee Est I. Written consent was obtained by participants or surrogates.
From January 2016 to February 2017, we enrolled all consecutive patients requiring a LDLT for thoracic surgery. All patients were scheduled for wedge or lobectomy surgery using minimally invasive video-assisted thoracic surgery or by thoracotomy. Exclusion criteria were age less than 18 years, refusal to participate, previous otolaryngeal or cervical surgery, previous cervical radiotherapy or disease that narrowed the trachea or main left bronchus (to exclude patients with predicted difficulty in positioning of the DLT). Clinical data (height, sex, weight) and medical history were obtained from the medical record.
Tracheal ultrasound was performed just before induction of anaesthesia using a ultrasound machine (SonoSite NanoMaxx; Ultrasound System, Bothell, USA) with a linear 5 to 10 MHz probe. With the patient lying supine, the probe was placed just above the sternoclavicular junction perpendicular to the neck in transverse section and the tracheal diameter was measured (Fig. 1).
Anaesthesia was administered using a standardised protocol. Intubation was performed using a Bronchopart Robertshaw left bronchus DLT (Rüsch, Athlone, Ireland). The lungs were ventilated using a tidal volume of 8 ml kg−1 of ideal body weight with regular ventilation using a Zeus anaesthetic machine (Drager, Lübeck, Germany). Proper placement was confirmed by fibre-optic bronchoscopy; the bronchial cuff was visualised lying completely within the left bronchus with its proximal end just beyond the carina. Lung collapse was judged as satisfactory or not by standard clinical parameters.
The bronchial cuff was inflated by increments of 0.5 ml until sealed, as assessed by absence of difference between inspiratory and expiratory volumes when the single left lung was ventilated. The LDLT size was deemed appropriate if the air volume required for isolation was between 0.5 and 2.5 ml, as previously shown.8 LDLTs showing no air leakage with a deflated bronchial cuff or those requiring a bronchial cuff volume greater than 2.5 ml were considered oversized or undersized, respectively.7
In the first step, from January 2016 to June 2016, LDLT size was selected according to formulae using the height and sex of the patient.9,10 A smaller tube was chosen if any undue resistance was met. The aim of this first step was to assess the frequency of inadequate LDLTs using usual clinical parameters, and to determine a combined cut-off point (associating height and tracheal diameter) which could be useful to reduce the number of oversized LDLTs.
In the second step from, November 2016 to February 2017, LDLT size was chosen according to combined cut-off points determined in the previous step (see below).
Data are shown as mean (SD) or median [IQR] for quantitative data, and number and percentage for categorical data. Normality was assessed by the Shapiro–Wilk test. Normal variables were compared using the unpaired t test. Percentages were compared by Pearson χ2 or Fisher exact test. The power analysis for Step 2 was performed on the basis of Step 1 results, to reduce the use of oversized tubes (from 0.38 to <0.18, power 0.9, alpha 0.05, number required 47 rounded to 50).
The overall characteristics of patients in Steps 1 and 2 are summarised in Table 1. No patients were excluded. No significant differences were found between the two populations.
Of 102 LDLTs, 40 (39.2%) were considered as adequate, 39 (38.2%) oversized and 23 (22.6%) undersized. Oversizing was more frequent in women (P < 0.05). Neither height nor tracheal diameter alone avoided the use of oversized LDLTs in women (Fig. 2a) or men (Fig. 2b).
Matching tracheal diameter and patient height, we identified cut-off points for selection of appropriately sized LDLTs (Fig. 3). On the basis of the scatter plots in Fig. 3a and b, we determined visually the cut-off points for tracheal diameter and patient's height associated with an appropriately sized LDLT. We used these results to design a new approach for the selection of LDLTs (Fig. 4).
Retrospective application of cut-off points indicated that a different selection of LDLT size would have been made in 51 cases (50%), with a significant reduction of oversized LDLTs (20.6 vs. 38.2%, P < 0.001); the percentage of patients in whom the same size of LDLT would have been selected was unchanged (43.1 vs. 39.2%; P = 0.261) and the percentage in whom an undersized LDLT would have been chosen was increased (36.3 vs. 22.6%; P < 0.001).
When chosen on the basis of combined clinical and ultrasound parameters (as shown in Fig. 4), the LDLT size was appropriate in a higher percentage of patients than in Step 1 (43 of 50 patients, 86.0 vs. 39.2%; P < 0.001, Table 2), while it was considered oversized in only three patients (6.0 vs. 38.2%; P < 0.001) and undersized in four (8.0 vs. 22.6%, P < 0.001, Table 2). Of the undersized LDLTs, only one required a change to a larger tube. In all patients, the collapse of the excluded lung was considered complete.
Ultrasound measurement of tracheal diameter just before induction of anaesthesia when combined with usual criteria (height and sex) increased the number of appropriately sized LDLTs by reducing the number of both oversized and undersized LDLTs.
There is no universal consensus on the best method of selecting the size of a DLT. Usually, the choice of LDLT is based on the height and sex of the patient.11 This approach based on anthropometric characteristics is limited because anatomical variations are important within both sex and height.7,12 The left main bronchus is elliptical and individual variations in diameter are significant. Anthropometric characteristics do not allow reliable prediction of the diameter of the left main bronchus. A poor but significant correlation is found only in men.7 Measuring tracheal diameter on the chest radiograph has also been proposed13 because tracheal diameter is correlated to the size of the left main bronchus.7 Tracheal diameter measured by ultrasound correlates well with tracheal diameter measured by CT and has been suggested to predict LDLT size.5 However, tracheal diameter measured by ultrasound alone is also inaccurate for predicting LDLT size.5
Ideally, precise knowledge of the airway anatomy of the patient, with particular attention to the size and length of the main bronchus to be selectively intubated, may help in choosing the correct DLT.14,15 CT scan is the gold standard to obtain a simultaneous study of the morphology and patency of the left main bronchus; however, CT scan studies are not routinely used in pre-operative evaluation of the airways by anaesthesiologists.14–17
In most cases, LDLT size choice is based on the anaesthesiologist's clinical experience.18–20 Our investigation showed that when the choice of LDLT size is based on clinical experience and anthropometric parameters, an oversized LDLT is frequently selected (Fig. 2). Some authors recommend the use of a small DLT because undersizing can usually be corrected easily by overinflation of the cuff; in contrast, oversizing may result in tracheal trauma.21
For this reason, we tried to combine the classical anthropometric parameters with ultrasound-measured tracheal diameter to optimise LDLT choice for an individual patient with the principal aim of reducing the use of oversized LDLTs while accepting a potential increase in insertion of undersized tubes. This combined clinical and ultrasound approach increased significantly the number of correct tubes by reducing both oversized and undersized LDLTs.
The current study has some limitations. First, the investigation was conducted on a relatively small number of patients. Second, the measurement of tracheal diameter requires skill to be performed, thus involving a training period. The operators were experts in ultrasound and required only a short training on tracheal examination. Third, we did not compare our method with the gold standard (CT measurement of the left main bronchus), but only with current practice.
In conclusion, ultrasound measurement of tracheal diameter, when combined with the individual patient's characteristics, can accurately guide the choice of LDLT. Further studies are needed to test the success rate of this approach compared with others based on CT measurement of left bronchial diameter, the operator's experience and conventional criteria.
Acknowledgements relating to this article
Assistance with the study: none.
Financial support and sponsorship: this study was supported by the Department of Anaesthesiology and Critical Care. C.H.U. Dijon, France and the Department of Anesthesia and Intensive Care, Istituto di Ricovero e Cura a Carattere Scientifico, Policlinico San Matteo Foundation, Pavia, Italy.
Conflicts of interests: none.
Presentation: preliminary data from this study were presented as a poster at the Simposio Mostra in Anestesia Rianimazione e Terapia Intensiva (SMART), Congress, Milan from 10 to 12 May 2017 and at the European Society of Intensive Care Medicine (ESICM) Lives, Vienna from 23 to 27 September 2017.
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