Type of lung injury influences the thermal-dye estimation of extravascular lung water

Abstract

To determine the effect of the type of lung injury on the thermodilution estimation of extravascular lung water, we produced pulmonary edema in 25 anesthetized dogs by injection of alloxan or alpha-naphthylthiourea (ANTU) into the pulmonary circulation or by instillation of hydrochloric acid (HCI) into the airway. HCl injury was bilateral, unilateral with tidal volume equal in each lung, or unilateral with equal airway pressure. Extravascular thermal volume (ETV) was measured at base line and 4 h after lung injury, and the final measurement was compared with the postmortem determination of extravascular lung mass (ELM). In 11 of 15 animals with HCl injury final ETV was less than the base-line measurement. The ratio of final ETV to ELM for all HCl animal (group I) averaged 0.31 +/- 0.14, which was different from the value for animals with alloxan or ANTU injury (group II), 1.04 +/- 0.14 (P less than 0.01). Extravascular lung water per gram of blood-free dry tissue was not different for the two groups (8.1 +/- 1.2 and 8.7 +/- 2.6 for I and II, respectively), indicating equally severe lung injury; however, shunt fraction was less in group I (P less than 0.01). ETV/ELM correlated with the shunt fraction for group I (r = 0.70) but not for group II (r = 0.32). These findings indicate that ETV underestimates lung water after HCl injury due to the redistribution of pulmonary blood flow away from edematous areas.