Do the data obtained by the PiCCO system enable one to differentiate between direct ALI/ARDS and indirect ALI/ARDS?

Abstract

It is known that measurement of the intrathoracic blood volume (ITBV) is a more accurate estimate of cardiac preload than pressure measurements using central venous or pulmonary artery occlusion pressures. Extravascular lung water (EVLW) is defined as the value of the intrathoracic thermal volume minus the ITBV. An increase in EVLW is the pathophysiological basis for the development of pulmonary edema (PE). There is evidence to suggest that therapy to reduce EVLW may improve outcome in the critically ill patient. The bedside assessment of EVLW may be very useful in identifying and quantifying PE, and hence in selecting patients who might benefit from a fluid restriction/depletion therapeutic strategy based on EVLW monitoring. The PiCCO (Pulsion, Munich, Germany) provides an estimate of the ITBV, EVLW, and permeability index (PI) via a single transpulmonary thermodilution technique. PE is defined as the abnormal accumulation of fluid in the extravascular space of the lung. ALI/ARDS is characterized by pulmonary edema. PE consists of increased hydrostatic PE (cardiogenic PE) and increased permeability PE (ALI/ARDS). Increased permeability PE (ALI/ARDS) is further classified into direct lung injury type and indirect lung injury type. PI was calculated as the ratio of EVLW to ITBV, which was previously shown to reflect permeability of the alveolar-capillary barrier. The early recognition and differential diagnosis of direct lung injury and indirect lung injury may be challenging.