Monitoring lung mechanics and airway pressures during differential lung ventilation (DLV) with emphasis on weaning from DLV

Abstract

Fifteen polytrauma patients with asymmetric pulmonary contusion were treated with differential lung ventilation (DLV) for a mean of 106 hours (range 24-298, median 83). The differential time constant (Tc), compliance (Ct), inspiratory and expiratory airway resistance (Rawinsp, Rawexp) and peak-airway pressure (Pawpeak) were monitored to evaluate the function of each lung. Values measured after starting DLV were compared to those obtained prior to stopping DLV in order to analyse whether these parameters had returned to symmetrical values when recommencement of conventional mechanical ventilation was considered on clinical parameters and also whether these could be useful criteria for weaning from DLV. The significant difference in Tc of the contused lung compared to the contralateral lung after starting DLV is mainly determined by altered Ct resulting from contusion. During DLV improvement of Ct resulted in identical Tc of both lungs prior to stopping DLV. Changes in the Rawinsp contributed little to changes in Tc. Identical Tc prior to stopping DLV coincided with identical Pawpeak on symmetrical ventilator settings. These data suggest that when less advanced monitoring equipment is available, the differential Pawpeak might be used as a measure of differential lung mechanics in asymmetrical pulmonary contusion.