Perfusion distribution and lung thermal volume in canine hydrochloric acid aspiration

Abstract

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)

Positive End Expiratory Pressure Reduces Bronchial Blood Flow after Aspiration Injury

“…Although similar reductions have been reported to occur after a lobar injury using different meth ods o f flow measurements and different experimental preparations [5][6][7][8], our study shows how rapidly this reduction in pulmonary blood flow occurs.…”

“…It is possible that some o f the inflammatory and repair processes are carried out by the bronchial circula tion following injury, since the pulmonary blood How to the injured regions is markedly decreased [5][6][7][8],…”

“…However, one o f the disadvantages o f P EEP is that it may reduce cardiac out put and may actually redistribute pulmonary flow to the injured lung regions [7,8], Since, in normal animals, increasing lung volume and transpulmonary pressure with P E E P decreases the bronchial blood flow [9][10][11][12][13], it is possible that P EEP will also decrease the bronchial flow in A R D S , a reduction that may not be desirable. A previous study o f a smoke inhalation injury showed that 24 h after injury, P E E P decreased total bronchial blood flow [14].…”

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.…”

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

“…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).…”