Abstract
During mechanical ventilation, the resistance of the endotracheal and tracheostomy tube (ETT) highly influences analysis of respiratory system mechanics and imposes additional work of breathing for the spontaneously breathing patient which both can be circumvented by applying the automatic tube compensation (ATC) mode. In the ATC mode, tracheal pressure (ptrach) is continuously calculated on the basis of measured flow and airway pressure using predetermined tube specific coefficients. However, as during long-term ventilation the ETT might become partially obstructed by secretions or tube kinking, the predetermined coefficients are no longer valid rendering calculation of ptrach inaccurate. We propose an easy-to-handle maneuver for the bedside determination of current tube coefficients in the tracheally intubated patient. Based on check-spot measurement of ptrach, current tube coefficients are determined by a least-squares fit procedure valid for the partially obstructed ETT with the indwelling pressure-measuring catheter (PMC). To correct for the removal of the PMC, the relationship between tube coefficients with and those without indwelling PMC has been determined in a laboratory investigation. Accuracy of the procedure was determined during artificial ETT obstruction by comparing calculated with measuredtrach. Correspondence between calculated and measured ptrach has been found excellent. We conclude that by adopting this bedside procedure periodically, accurate calculation of ptrach is guaranteed and the advantages of the ATC mode are ensured even in long-term ventilatory support.