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Correspondence |
Seoul National University Hospital, Seoul, Korea, E-mail: bahkjh{at}snu.ac.kr
To the Editor:
Adequacy of a double-lumen tube (DLT) size has been determined depending on whether the bronchial cuff volume required for isolation is > zero but 
the resting volume.1,2 Recently, direct measurement of the left mainstem bronchial diameter on plain chest radiographs or computed tomographic scans has been performed with the goal of establishing an objective criterion for DLT size.3,4 The purpose of this study was to determine the maximum allowable mainstem bronchial diameter for left-sided Broncho-Cath® DLTs.
Left-sided DLTs (Broncho-Cath®; Mallinckrodt Medical Ltd., Athlone, Ireland) with sizes of 32, 35, 37, 39 and 41 Fr (n = 5 for each size) were tested as previously described.2 The pressure-volume curve for each bronchial cuff was drawn by incrementally injecting 0.5 mL of air (0.25 mL for 32 Fr). Exponential curve fitting analysis was performed on the values of each pressure-volume curve using Matlab software (Mathworks Inc., Natick, MA, USA). The resting volume, where the slope of the tangential line is 10 mmHg/0.5 mL (Dcuff pressure/Dcuff volume), was calculated by differentiation on the fitted curve. The resting cuff volumes (mean ± SD) for 32–41 Fr DLTs were 0.6 ± 0.1, 2.5 ± 0.1, 2.2 ± 0.1, 2.0 ± 0.1 and 2.3 ± 0.1 mL, similar to those previously described.2 To prevent ischemic bronchial injury, the intracuff pressure should be < 44 cm H2O, at which pressure mucosal capillary perfusion reported to decrease.5 The calculated cuff volumes (mean ± SD) at a cuff pressure of 44 cm H2O on the fitted curve for each DLT size were 1.0 ± 0.2, 3.3 ± 0.1, 3.0 ± 0.1, 2.8 ± 0.1 and 3.0 ± 0.1 mL, respectively.
After inflating the bronchial cuff with the calculated volume at a pressure of 44 cm H2O, we measured the outer diameter of the bronchial tube with a precision caliper (0.1-mm intervals) at the mid-cuff level. This largest allowable cuff diameter was regarded as the theoretical maximum bronchial diameter because the resultant intracuff pressure could be less than the critical pressure on the assumption that the bronchial cuff is in contact with the bronchus. Outer diameter of the bronchial tube with the cuff completely collapsed4 was regarded as the theoretical minimum bronchial diameter (Figure
).
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35 Fr seem to be the same regardless of DLT size (Figure
). In spite of the fact that only two sizes of DLT (32 Fr and another larger one of any size) seem to suffice in all adult patients, what is the best DLT size for each patient remains to be determined.
References
1 Campos JH. Lung separation techniques. In: Kaplan JA, Slinger PD (Eds). Thoracic Anesthesia, 3rd ed. Philadelphia: Churchill Livingstone Inc; 2003: 159–73.
2 Hannallah MS, Benumof JL, Bachenheimer LC, Mundt DJ. The resting volume and compliance characteristics of the bronchial cuff of left polyvinyl chloride double-lumen endobronchial tubes. Anesth Analg 1993; 77: 1222–6.
3 Hannallah M, Benumof JL, Silverman PM, Kelly LC, Lea D. Evaluation of an approach to choosing a left double-lumen tube size based on chest computed tomographic scan measurement of left mainstem bronchial diameter. J Cardiothorac Vasc Anesth 1997; 11: 168–71.[Medline]
4 Jeon YS, Ryu HG, Bahk JH, Jung CW, Goo JM. A new technique to determine the size of double-lumen endobronchial tubes by the two perpendicularly measured bronchial diameters. Anaesth Intensive Care 2005 (in press).
5 Knowlson GT, Bassett HF. The pressures exerted on the trachea by endotracheal inflatable cuffs. Br J Anaesth 1970; 42: 834–47.
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