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We investigated the effect of positive end-expiratory pressure (PEEP) on the extravascular thermal volume of the lung (ETV) determined by the thermal-dye technique in three canine models of pulmonary edema created by injection of alpha-naphthylthiourea (ANTU) or oleic acid (OA) into the pulmonary circulation or intrabronchial instillation of hydrochloric acid (HCl). ETV was determined before, during, and after ventilation with 14 cmH2O PEEP, and final ETV was compared with the extravascular lung mass (ELM) determined postmortem. Final ETV correctly estimated ELM in 12 animals with ANTU injury, ETV/ELM = 1.04 +/- 0.13, but underestimated after HCl injury (n = 5), ETV/ELM = 0.61 +/- 0.23, and OA injury (n = 6), ETV/ELM = 0.73 +/- 0.19. Whereas PEEP had no consistent effect on extravascular thermal volume in ANTU edema, there was a reversible increase in ETV during PEEP in animals with HCl or OA injury and underestimation of ELM. The increase in ETV during PEEP averaged 9.3 +/- 3.8 ml/kg (62 +/- 42%) over the mean of the pre- and post-PEEP values after HCl injury (P less than 0.01) and 6.7 +/- 4.4 ml/kg (47 +/- 35%) after OA injury (P less than 0.02). There was an inverse correlation between the change in ETV during PEEP and the ETV/ELM ratio for animals with HCl and OA injury (r = -0.94). We conclude that PEEP produces a reversible increase in ETV in some models of lung injury by allowing for distribution of thermal indicator through a larger fraction of the lung water and that this response may be useful to detect underestimation when gravimetric measurements are not available.

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The extravascular volume of distribution for heat in the lung has been advocated for the measurement of lung water. The purpose of these experiments was to investigate how extremes of ventilation-perfusion mismatch influence this measurement. Twenty-six dogs were studied with right and left atrium-to-aorta thermal and dye-dilution curves before and 60 min after total right main-stem bronchial obstruction or microembolization of the pulmonary circulation with 0.275-mm glass beads. Whereas atelectasis had no influence on our measurements, embolization with 0.32 g/kg of beads decreased the detected pulmonary blood volume from 10.63 to 8.55 ml/kg and increased the extravascular thermal volume (ETV) from 9.89 to 10.99 ml/kg. Embolization with 0.65 g/kg decreased the detected ETV from 9.29 to 8.38 ml/kg, while the extravascular wet-to-dry weight ratio was increased, and the regression of postmortem extravascular mass on ETV differed from control. We conclude that microembolization but not atelectasis causes errors in the measurement of lung fluid when the thermodye technique is used. The errors are variable and depend on the degree of embolization.