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. METHODS: 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 Tukey?s test. RESULTS: 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). CONCLUSIONS: 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.
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