A Comparison of Proximal and Tracheal Airway Pressures During Pressure Controlled Ventilation

Abstract

BACKGROUND: Airway pressure is usually measured by sensors placed in the ventilator or on the ventilator side of the endotracheal tube (ETT), at the Y-piece. These remote measurements serve as a surrogate for the tracheal or alveolar pressure. Tracheal pressure can only be predicted correctly by using a model that incorporates the pressure at the remote location, the flow through the ETT, and the resistance of the ETT if the latter is a predictable function of Y-piece flow. However, this is not consistently appropriate, and accuracy of prediction is hampered. METHODS: This in vitro study systematically examined the ventilator pressure in dependence of compliance of the respiratory system (C RS ), inspiratory time, and expiratory time during pressure-controlled ventilation by using a small intratracheal pressure sensor and a mechanical lung simulator. Pressures were measured simultaneously at the ventilator outlet, at the Y-piece, and in the trachea during pressure-controlled ventilation with a peak inspiratory pressure of 20 cm H 2 O and a PEEP of 5 cm H 2 O while changing C RS (10,30, 60, 90, and 100 mL/cm H 2 O) and varying inspiratory time and expiratory time. RESULTS: Tracheal pressures were always lower (maximum 8 cm H 2 O during inspiration) or higher (maximum 4 cm H 2 O during expiration) than the pressures measured proximal to the ETT if zero-flow conditions were not achieved at the end of the breathing cycles. CONCLUSIONS: Dependent on C RS and the breathing cycle, tracheal pressures deviated from those measured proximal to the ETT under non-zero-flow conditions. Intratracheal pressure and pressure curve dynamics can differ greatly from the ventilator pressure, depending on the ventilator setting and the C RS . The small pressure sensor may be used as a measurement method of tracheal pressure via integration onto an ETT.