Extravascular Lung Water Index and Pulmonary Vascular Permeability Index Assessed by the Transpulmonary Thermodilution Method in Patients After Minimally Invasive Cardiac Surgery With Cardiopulmonary Bypass and One Lung Ventilation

Acute respiratory distress syndrome (ARDS) occur with an incidence of 12% after cardiac surgery with the use of cardiopulmonary bypass (CBP). Using one-lung ventilation (OLV) in addition, as it is common practice in minimally invasive cardiac surgery (MICS), one can hypothesize that the risk for ARDS increases.

The objective of this prospective, observational study is to measure extravascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI) as parameters of lung edema through alteration in the pulmonary permeability by comparing three groups of surgery patients: I) patients with CPB, II) patients with OLV and III) patients with both CPB and OLV.

MICS allows coronary artery bypass grafting and cardiac valve surgery through small incisions, does not appear to be inferior to conventional surgery, but likely reduces postoperative pain, accelerates postoperative recovery and improves the cosmetic result. However, based on the available data, respiratory failure after MICS occurs at the same rate as after conventional cardiac surgery. In addition, unilateral re-expansion pulmonary edema, rarely seen after conventional cardiac surgery, has been described after MICS with CPB and OLV.

The pathophysiology of ARDS is characterized by massive inflammation that leads to a diffuse damage of both the alveolar epithelium and pulmonary vascular endothelium. Although the etiology of ARDS is multifactorial, the uniform result is an acute, nonhydrostatic, high-permeability lung injury with interstitial and alveolar protein-rich edema, epithelial damage and rapid onset of pulmonary fibrosis. This leads to the vast reduction of the pulmonary gas exchange and to hypoxemia.

Extravascular lung water (EVLW) comprises all fluids of the extravascular compartment of the lung, ie, intracellular water, lymphatic fluid, surfactant and extravasated plasma. Increased EVLW may be caused by an increased hydrostatic intravascular pressure, as it occurs in cardiogenic pulmonary edema, and/or by an increase of lung endothelial and epithelial permeability, as in ARDS. The EVLWI estimates the EVLW by using the transpulmonary thermodilution technique.The pulmonary vascular permeability index (PVPI) is the ratio between the EVLWI and the pulmonary blood volume, which is also measured by the transpulmonary thermodilution technique. The PVPI is thought to reflect the permeability of the alveolar-capillary barrier.