Rohrer's constant, k2, as a factor for determining endotracheal tube obstruction

The purpose of the study was to apply a method by which to measure Rohrer's constant, k2, in order to estimate endotracheal tube (ETT) resistance (RETT). The resistance drop across the ETT is expressed by the equation RETT = k1 + k2V', as Rohrer described, where k1 is the constant of laminar flow (V') and k2 is the constant of turbulent flow. In our past study we graphed RETT over inspiratory V' for ETTs with inner diameters of 6.5 to 9.0 mm [1]. This graph provided us with k1 and k2 constant values, for each ETT size.