[Airflow resistance of double-lumen tracheal tubes.]

BACKGROUNG AND OBJECTIVES: Double lumen tubes may determine different flow resistances. This disparity may result in non-homogeneous ventilation. This study aimed at comparing the resistive pressure of 37 FR double lumen tubes to distinct flows as compared to conventional adult tracheal tubes.

Tracheal tubes with internal diameters of 7; 7.5; 8 and 8.5 millimeters (mm) and 37 FR double lumen tubes were tested. Flows were generated and maintained by a conventional anesthesia ventilator. Resistive pressure generated in the tubes was measured by a variable inlet pneumotachograph and converted to a digital system. Resistances were obtained by dividing measured pressures by flows. Data were submitted to analysis of variance (ANOVA) and Tukeys test.

Five independent measurements were obtained. All tubes were opened to the environment. Resistances are shown in cmH2O.L-1.s-1. Resistance is linearly increased with increased flow. The 37 FR tube had a resistive pattern similar to the 7.5 mm tracheal tube. The occlusion of any double lumen branch significantly increases flow resistance. Flows set at 0.1 L.s-1 to 0.2 L.s-1 resulted in similar resistive pressures for all tubes, except for the 7 mm or the occluded 37 FR tube (p < 0.001).

Resistive patterns of 37 FR and 7,5 mm tubes were very similar. Any double lumen branch occlusion significantly increases resistance, however in a similar way for both branches for flows below 0.5 L.s-1. These results suggest the use of low inspiratory flow to minimize ventilatory system resistive pressure when any branch of a double-lumen tube is occluded.