Pressure dependency of respiratory resistance in patients with acute lung injury and acute respiratory distress syndrome
KeywordsLung Injury Respiratory Distress Syndrome Acute Lung Injury Distress Syndrome Acute Respiratory Distress Syndrome
The analysis of the nonlinearity of respiratory compliance to guide ventilator settings in ALI and ARDS is well established. The pressure dependency (or volume dependency respectively) of respiratory resistance of these patients is mostly ignored. This study was performed to investigate the pressure dependency of resistance in ALI and ARDS over a wide range of pressures.
Twenty-one patients with ALI or ARDS were analyzed. Ventilation was interrupted by a respiratory manoeuvre: the volume was increased from ZEEP in steps of 100 ml with constant inspiratory flow until the plateau pressure reached 45 cmH2O. Each step was followed by a hold of 3 seconds. Inspiratory resistance during each step was determined by a least-squares fitting procedure.
Inspiratory resistance in ALI and ARDS is not constant. Especially at higher pressures, individual resistance may change unpredictably. The assumption of a constant resistance should therefore be avoided.