PATHOPHYSIOLOGY OF PULMONARY CONTUSION IN DOGS

The authors produced a localized right lower lobe (RLL) contusion in 14 anesthetized ventilated dogs, 7 of which were treated with positive end-expiratory pressure (PEEP group). They measured gas exchange, pulmonary mechanics, and regional function before and 5 hr after the contusion. Arterial P(O2) decreased by 20 Torr and venous admixture doubled in both groups during air breathing. The shunt fraction (Q̇s/Q̇t) was minimally increased, despite a large lobar Q̇s/Q̇t (0.43) in the contussed RLL. These results were explained by reduced ventilation per unit volume [V̇(A)/V] and ventilation-to-perfusion ratios of the contused RLL measured with 133Xe technique. The authors conclude that pulmonary contusion causes a leak of blood and plasma, flooding 25% of the air spaces of the RLL at FRC, reducing the compliance of adjacent air spaces, and resulting in a reduced V̇(A)/V and a large RLL Q̇s/Q̇t These results are consistent with the observed reduction in regional volume and perfusion in the contused RLL, and suggest that Q̇s/Q̇t was not increased because blood flow was markedly reduced to flooded air spaces. PEEP reduced the hypoxemia, but increased the contusion.