Left-sided DLTs of the sizes 35Fr, 37Fr, 39Fr, and 41Fr from six different manufacturers were included in this in-vitro study (Table 1).
One brand new DLT of each type and size was measured twice by two investigators (NH, SS), i.e. four measurements of each dimensional parameter were taken. Dimensions of the tube (diameter and length), cuff (diameter and length), and the angle of the endobronchial tube portion were determined (Figure 1). All measurements were performed with the intubation stylet removed from the DLT. For all measurements, a commercially available ruler (measurement accuracy 1 mm), a sliding caliper (measurement accuracy of 0.1 mm), an orthopedic protractor, 10-ml syringes (B. Braun, Melsungen, Germany) for inflating the cuffs, and a manual cuff pressure manometer (Rüsch Endotest®; Teleflex, Athlone, Ireland) to adjust cuff pressure were used.
The following dimensional parameters of the DLT were measured or calculated (Figure 1):
Outer tube diameter (OD, always both: lateral and anterior-posterior)
ODMIDDLE = diameter in the center (B) between the beginning of the shaft of the tube (A) and the proximal edge of the tracheal cuff (C)
ODPTC = diameter directly at the proximal edge of the tracheal cuff (C)
ODDTC = diameter directly at the distal edge of the tracheal cuff (D)
ODPBC = diameter directly at the proximal edge of the bronchial cuff (E)
ODDBC = diameter directly at the distal edge of the bronchial cuff (F)
Internal tube diameter (ID)
The tracheal and endobronchial lumen of all investigated DLTs were assessed for passability of a fiber-optic bronchoscope (Karl Storz, Germany) with diameter 5.5 mm and 4.0 mm, respectively.
Lengths
Length A-C = distance from beginning of DLT shaft (A) to the proximal edge of the tracheal cuff (C)
Length C-D = length of the tracheal cuff
Length D-E = distance from the distal edge of the tracheal cuff (D) to the proximal edge of the bronchial cuffs (E)
Length E-F = length of the bronchial cuff
Length F-G = distance from the distal edge of the bronchial cuffs (F) to the tip of the tube (G)
Length A-G = tube length from bifurcation (A) to the tip of the tube (G)
Outer cuff diameters
Outer cuff diameters were assessed with the cuffs not being in contact with a model of tracheal/bronchial lining. For the measurement of the tracheal and bronchial cuff diameters, the respective cuff inflation line was connected via a three-way stopcock to the manual cuff pressure gauge and inflated with air to the target pressure of 20 H2O using a 10 ml syringe. Upon reaching the target pressure, the three-way stopcock was closed so that no air could escape. The volume of air necessary to generate the target pressure of 20 H2O was noted.
Angle
Angle H-I = mediastinal angle between a virtual longitudinal line through the middle of the tube shaft and the bronchial tube section
Since DLTs rarely present with a truly round cross-sectional area but are rather elliptically shaped, the cross-sectional area (CSA) was calculated at the points indicated below, utilizing the measured width and height of the tube according to the formula CSA = π * width/2 (= lateral) * height/2 (= anterior-posterior).
CSAMIDDLE = cross-sectional area of the endobronchial tube in the middle (B) between the beginning of the tube shaft (A) and the proximal edge of the tracheal cuff (C)
CSAPTC = cross-sectional area of the endobronchial tube directly at the proximal edge of the tracheal cuff (C)
CSADTC = cross-sectional area of the endobronchial tube directly at the distal edge of the tracheal cuff (D)
CSAPBC = cross-sectional area of the endobronchial tube directly at the proximal edge of the bronchial cuff (E)
CSADBC = cross-sectional area of the endobronchial tube directly at the distal edge of the bronchial cuff (F)
For all DLTs investigated, it was noted whether the package insert provides information on the above-mentioned parameters besides the nominal tube size given in French (1/3 mm).
Calculations and statistics
Descriptive statistics were used to compare measured data. All data are presented as median (minimum - maximum). The analysis was performed using Microsoft Excel 2010 (Microsoft, Redmond, USA).