Perfusion distribution and lung thermal volume in canine hydrochloric acid aspiration

We investigated the effects of a brief period of positive end-expiratory pressure (PEEP) ventilation or nitroglycerin (NTG) infusion on the distribution of pulmonary blood flow and extravascular thermal volume (ETV) in anesthetized dogs with unilateral HCl lung injury. ETV was determined by the thermal dye technique by use of a monoexponential extrapolation to exclude recirculating indicator, and regional blood flow was determined by a particle distribution technique (radiolabeled plastic microspheres). The lungs were weighted after the animals were killed, and extravascular lung mass (ELM) was determined with the use of hemoglobin to correct for trapped lung blood. Measurements were obtained before instillation of HCl into the right lung and repeated 3 h later before, during, and after PEEP ventilation or NTG infusion. Fractional perfusion of the severely injured portion of the right lung (Qinj/QT) fell from 44.3 +/- 11.1% at base line to 27.8 +/- 15.4% after the onset of lung injury. PEEP produced an acute reversible increase in ETV (63 +/- 37% over average of pre- and post-PEEP values), and the changes in ETV were closely correlated with changes in Qinj/QT (r = 0.91). NTG infusion produced insignificant increases in ETV (14 +/- 10% over average of pre- and postinfusion values) and Qinj/QT (59 +/- 35%), but the changes in ETV and Qinj/QT were strongly correlated (r = 0.92). The fraction of extravascular lung mass detected by the thermodilution measurement averaged 0.44 (range 0.24-0.77).(ABSTRACT TRUNCATED AT 250 WORDS)