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.

Accuracy of the double indicator method for measurement of extravascular lung water depends on the type of acute lung injury*

“…The DI method was shown to be sensitive to alterations in the distribution of pulmonary blood flow, as in air or glass bead embolization models (9 -11) or after occlusion of a pulmonary artery (20). Moreover, this method was shown to variably underestimate EVLW evaluated by gravimetry in case of direct HCl injury (12,13).…”

“…Several issues suggest that further validation of the DI method may be needed. Indeed, in the 1980s, the DI method used by different devices was shown to variably underestimate lung water in pulmonary vascular embolization models (9 -11) and in a canine model of hydrochloric acid-induced focal lung injury (12,13).…”

Extravascular lung water measurements and hemodynamic monitoring in the critically ill: bedside alternatives to the pulmonary artery catheter

“…The thermal indicator, being blood borne, gains access to the extravascular compartment of ITTV via the diffusion of heat. The exact distance over which such diffusion can take place during a typical measurement period is not clear [the diffusion coefficient of heat in water is estimated at 1.5 ϫ 10 Ϫ3 cm 2 /s (55)], but factors such as vascular obstruction caused by embolism (2,6) or by physiological hypoperfusion [from positive end-expiratory pressure (PEEP) (1,17), hypovolemia, or hypoxic vasoconstriction (16,44)] result in an underestimation of EVLW as measured by gold standard gravimetric methods. The underestimates due to PEEP are less likely to occur if pulmonary artery pressures are significantly higher than PEEP levels (11), which clinically is almost always the case.…”

Transpulmonary dilution-derived extravascular lung water as a measure of lung edema

“…As alluded to above, some types of pulmonary edema, in animal studies [18,[39][40][41], are less well reflected by EVLW measurements than others, partly associated with redistribution of intrapulmonary blood flow. Cardiac output may also be too high for thermal equilibration with the extravascular distribution volume, and positive end-expiratory pressure ( …”