Pulmonary dysfunction in sepsis: is pulmonary edema the culprit?

Pulmonary dysfunction is a well-recognized sequela of sepsis, which has been quantitated by calculation of intrapulmonary shunt (Qs/Qt) and, more recently, by measurement of extravascular lung water (EVLW). We sought to demonstrate the relationship between Qs/Qt and EVLW in sepsis. Nine pigs were given live E. coli infusions and five control pigs received only crystalloid. Pulmonary artery pressure (PAP), pulmonary artery wedge pressure (PAWP), arterial blood gases (ABG), and mixed venous blood gas levels were measured serially and Qs/QT calculated. EVLW was measured simultaneously using the thermal-green dye technique. The septic group showed increases from baseline in PAP (2.4 X), EVLW (2x), and Qs/Qt (1.6x). Regression analysis of Qs/Qt or EVLW yielded a correlation coefficient of r = 0.48. We concluded that while sepsis can result in both increased EVLW and Qs/Qt, the correlation is not sufficiently strong to account for the increased Qs/Qt on the basis of elevated EVLW alone. The possible relationships of arterial hypoxemia and pulmonary edema, ventilation-perfusion mismatch, and alterations in the normal hypoxic vasoconstrictive response in sepsis are considered.