1 Department of Anaesthesiology and 2 Department of Thoracic Surgery, Nara Medical University, 840 Shijo-cho, Kashihara, Nara 634-8522, Japan
*Corresponding author. E-mail: seninoue@nmu-gw.naramed-u.ac.jp
Accepted for publication: August 24, 2003
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Abstract |
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Methods. We recruited 152 ASA physical status III patients about to have elective thoracic surgery. The trachea was intubated with a left-sided DLT. Tube position was assessed by fibre-optic scope and correction was made after patient positioning and during OLV. If PaO2 was less than 10.7 kPa, the DLT position was checked and then PEEP, continuous positive airway pressure (CPAP), oxygen insufflation, or two lung ventilation (TLV) were tried.
Results. The DLT was found to be misplaced in 49 patients (32%) after patient positioning, and in 38 patients (25%) during OLV. PEEP to the dependent lung, CPAP or apneic oxygen insufflation to the non-dependent lung, or brief periods of TLV, were applied in 46 patients (30%). Patients who had DLT malposition after placing the patient in the lateral position had a greater incidence of DLT malposition during OLV (59 vs 9%) and also required each intervention more frequently (57 vs 10%). Patients with DLT malposition during OLV also required interventions more often (84 vs 12%).
Conclusions. Patients who have DLT malposition after placing the patient in the lateral position had more DLT malposition during OLV and hypoxaemia during OLV.
Br J Anaesth 2004; 92: 195201
Keywords: complications, hypoxaemia; complications, tube, malposition; equipment, double lumen tube; surgery, thoracic; ventilation, one lung
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Introduction |
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Most DLTs are specifically designed to fit the anatomy of the trachea, bronchial carina, and main bronchus according to Robertshaws suggestion.10 Guidelines are available to choose a properly sized DLT.11 12 Nevertheless, significant malposition of a DLT can occur after a patient is moved, and some degree of DLT movement is unavoidable.6 7 DLT displacement may indicate poor matching with the anatomy of the patients airway. In such patients who develop significant malposition of the DLT after patient movement, there may also be more problems with DLT use and more hypoxaemia during OLV compared with other patients, even if the DLT position is corrected by fibre-optic bronchoscopy after the patient has been moved into the lateral position. We studied whether DLT malposition after placing the patient in the lateral position is related to hypoxaemia and frequent DLT malposition during OLV.
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Methods |
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All patients were pre-medicated with roxatidine (H2 blocker) 75 mg orally 2 h preoperatively. Before induction of anaesthesia, an epidural catheter was inserted at the 67th, 78th, or 89th thoracic interspace. General anaesthesia was induced with propofol 1.52.5 mg kg1, fentanyl 12 µg kg1, and vecuronium 0.15 mg kg1. Anaesthesia was maintained with oxygen 100%, propofol 35 mg kg1 h1, and an epidural bolus injection of 610 ml of lidocaine 1% followed by a continuous infusion of 48 ml h1. Routine monitoring included an ECG, a non-invasive arterial pressure cuff, pulse oximetry, and capnogram. Blood gas samples were analysed with a commercial blood gas analyzer (Bayer 860, Bayer Diagnostic Manufacturing Ltd, Bury St Edmunds, UK). To obtain continuous arterial blood gas values, pressure measurements, and intermittent blood samples, we used a continuous arterial blood gas monitoring system (Paratrend 7TN, Diametrics Medical Limited, High Wycombe, UK). A 20-gauge intravascular catheter was inserted into the radial artery. The intravascular sensor, calibrated with gases in a tonometer, was advanced through the arterial catheter into the radial artery to a length of 15 cm. Systolic arterial pressure was maintained within 20% of the preoperative value by controlling doses of anaesthetics, and giving ephedrine or nicardipine as necessary to treat changes in arterial pressure.
We managed DLTs in the way described by Klein.6 The trachea and bronchus were intubated with a left-sided DLT (Bronchocath; Mallinckrodt, Argyle, NY, USA). The size of DLT was chosen according to Brodsky,11 but could be changed to meet the following criteria: a small air leak detectable with the endobronchial cuff deflated and no leaks when inflated with a maximum of 3 ml air. Immediately after blind insertion, the correct position was confirmed by ausculation and fibre-optic bronchoscopy. The position was checked and corrected by fibre-optic bronchoscopy once again after positioning the patient for thoracotomy (lateral position). The criteria for correct DLT position were defined as follows: an unobstructed view into the left upper and lower lobe bronchus through the endobronchial lumen with the bronchial cuff immediately below the carina and just visible in the main left bronchus through the tracheal lumen.15 We defined malposition if the tube had to be moved (in or out) by more than 1.0 cm to correct its position. The DLT was taped securely in place after each fibre-optic bronchoscopic confirmation.
A Siemens servo 900 C ventilator (Siemens Life Support Systems, Solna, Sweden) was used for controlled ventilation of the lungs. A pressure-controlled mode was used. The inspiration/expiration ratio was set 1:1.9 (25% inspiration and 10% pause). For two lung ventilation (TLV), the inspiratory pressure was set at 14 cm H2O and the ventilatory frequency was adjusted to maintain PaCO2 at around 5.3 kPa (40 mm Hg). Inspiratory and expiratory tidal volumes (ITV and ETV) were monitored. OLV was started just before the pleura was opened. After the endobronchial cuff was inflated, the corresponding part of the DLT was opened to the atmosphere and suctioned through a fibre-optic scope to facilitate lung collapse. The inspiratory pressure was then adjusted to 20 cm H2O. During OLV, lung isolation was assessed by surgeons using the following grade: 1=excellent, 2=acceptable, 3=difficult to perform surgery. The first assessment was done after the pleura was opened and the lung could be seen. OLV was stopped just after the pleura was closed. The lung on the side of the surgery was suctioned and inflated sufficiently and then the endobronchial cuff was deflated. TLV was re-started with the same initial ventilation settings.
A PaO2 value less than 10.7 kPa (80 mm Hg) was defined as hypoxaemia.4 Hypoxaemia during OLV was treated by the following strategies. First, 5 cm H2O of PEEP was applied to the dependent lung. Secondly, 5 cm H2O of continuous positive airway pressure (CPAP) (for thoracotomy) or 5 litre min1 of apnoeic oxygen insufflation (for video-assisted thoracoscopic procedures) was applied to the non-dependent lung. Thirdly, brief periods of TLV were used. Each time these interventions were performed, bronchoscopy was done to allow correction of the tube position, the tube was sucked out, and arterial blood gases (ABGs), ITV and ETV were measured. Then, lung isolation was reassessed by the surgeons. The following measurements were collected at initial DLT placement under TLV (supine position), just before the end of OLV (lateral position), and after surgery under TLV (supine position): ABGs, ITV, ETV, and bronchoscopic assessment for DLT position. However, more frequent measurements were made in patients who required interventions for hypoxaemia during OLV, with sets of data measured just before the application of each intervention.
Statistical analysis
The study population size was determined as follows. Assuming DLT malposition after patient positioning would occur in 30% of patients and severe hypoxaemia would occur in 10% of patients during OLV, we assumed that those who had malposition after patient positioning would be twice as likely to show to hypoxaemia during OLV. Using the formula for normal theory and assuming a type I error protection of 0.05 and a power of 0.90, 152 patients were required for this study.
Analysis was done using descriptive statistics. Data for continuous variables are expressed as mean (SD) with range (minimum maximum values). Hypothesis testing was done using the 2 test or Fishers exact test accompanied with the relative risk (RR) and its 95% confidence interval (CI). To assess lung isolation, the MannWhitney test or Wilcoxon signed-ranks test was used. In regard to changes of PaO2, ITV, and ETV among the subgroups, to facilitate statistical analysis, the several values recorded for each patient during OLV were averaged to yield a single number. They were compared using analysis of variance (ANOVA) for repeated measures followed by Scheffes test. To compare other values among the subgroups, ANOVA was used. Results were considered significant at P<0.05.
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Results |
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Discussion |
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Hypoxaemia is a major concern during OLV. This problem appears to consist of two main parts. One is based on changes in lung function during OLV. The other is based on the smaller margin of safety of positioning for DLTs. Several researchers have tried to discover good predictors for arterial oxygenation during OLV, mainly studying pulmonary pathophysiology.1 35 However, despite their efforts we have no good predictors. Others have studied DLT placement intensively;2 4 6 79 but the small margin of safety in the DLT placement has not been related to arterial oxygenation during OLV. We suggest that this small safety margin has more effect on hypoxaemia during OLV than pulmonary pathophysiology because DLT malposition accounts for poor ventilation and hypoxaemia during OLV.
Some factors may predispose to DLT malposition and hypoxaemia during OLV. Factors such as the surgical procedures, movement of the mediastium by gravity, and compression by abdominal contents might change the relationship between the DLT and the patients tracheo-bronchial anatomy. Those who did not show DLT malposition during OLV were probably tolerant to these intra operative factors, and those who develop DLT malposition after patient positioning are more susceptible to such intraoperative factors.
Oxygenation during OLV is affected by several factors.16 17 DLT malposition will have an important influence on hypoxaemia if it happens. The position of the DLT is usually checked first when hypoxaemia is detected during OLV. We found that DLT malposition can happen repeatedly. Patients with hypoxaemia (928% of all patients) may involve patients with persistent DLT malposition. Hurford and colleagues2 reported 730% of patients required DLT position readjustment during OLV. Klein and colleagues6 also reported that 13 and 13.5% of patients required position readjustment or suctioning blood or secretions with the aid of a fibre-optic scope. Campos and co-workers detected DLT malposition, despite initial adjustment using fibre-optic bronchoscopy, in 12.525% of patients during OLV although it did not happen repeatedly.8 9 Taking these results with ours, DLT position is probably one of the main factors for hypoxaemia during OLV.
There are two ways to treat hypoxaemia during OLV. One is to apply CPAP or oxygen insufflation to the non-dependent lung.1820 The other is to apply PEEP to the dependent lung to reduce atelectasis.4 21 In this study, we applied PEEP first according to Lewis.4 If PaO2 decreased further, we applied brief TLV.4 20 We found that patients whose oxygenation improved had a better lung isolation score than those patients in whom oxygenation did not improve although each intervention per se made conditions of the operative field progressively worse. These interventions, which exert an effect by airway pressure or flow, may support the airway and reduce the misfit between the DLT and the airway. On the other hand, this anatomical misfit may persist in the unsuccessful interventions, which then worsened the operative conditions. Support for this comes from ITVs and ETVs during OLV. The patients who required more interventions and correction of DLT placement had smaller ITVs and ETVs. This could mean that these patients developed ventilation failure during OLV, caused by persistent DLT malposition, at least partially because of the misfit between the DLT and the patients lungs. Patients with a previous thoracotomy were at risk. They had almost normal preoperative chest X-ray films, but probably had intrathoracic adhesions. This could distort lung structure and enhance the misfit between the DLT and the lung.
We defined DLT malposition in this study as a 1.0 cm deviation from optimal position. We set this value to provide a simple quantitative measure. The average margin of safety in positioning is 19 mm for a left-sided Mallinckrodt tube.13 However, some consider only 0.5 cm of deviation from an optimal placement could be dangerous.6 The Japanese patients we studied are smaller compared with patients in other studies (Table 1), and 1.0 cm deviation could be critical for them, so we decided to use 1.0 cm as a cut-off value. In fact, all patients with DLT malposition in this study met the bronchoscopic criteria for DLT malposition of Campos and colleagues.9 How can we stop DLTs becoming misplaced? We have no solution so far, but we could try an alternative method for OLV. UniventR tubes, which are single-lumen tubes with enclosed bronchial blockers, can be easier to insert and have less risks than DLTs.2225 However, the frequency of malposition for the UniventR can be greater than for the DLT.8 Therefore, frequent fibre-optic assessment of tube position seems necessary although further studies are needed.
In this study we used pressure-controlled ventilation, which is not standard practice.26 With volume-controlled ventilation, we could have had different results. With pressure-controlled ventilation, tidal volume decreases during OLV, as it did in this study (Fig. 1). Any airway narrowing from DLT malposition will increase resistance and reduce tidal volume further. The reduced tidal volume could allow atelectasis in the dependent lung and lead to hypoxia during OLV. Consequently, DLT malposition could be a more frequent cause of hypoxia during OLV if pressure-controlled ventilation were used. Our conclusions may be only applicable for pressure-controlled ventilation. Studies with volume-controlled ventilation might be needed to address this concern.
In conclusion, we showed that patients with DLT malposition after being placed in the lateral position were more likely to have misplacement of the DLT during OLV and develop hypoxaemia, even if the DLT position had been corrected with fibre-optic bronchoscopy. In addition, patients who have had a previous thoracotomy are at increased-risk of developing hypoxaemia during OLV because of DLT malposition.
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Acknowledgement |
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References |
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