Posttraumatic lung injury after pulmonary contusion and fat embolism: factors determining abnormal gas exchange.

Background: The objective was to investigate changes in pulmonary blood flow after lung contusion and fat embolism.

Methods: Eighteen mongrel dogs were randomly assigned to three groups: fat embolism alone (n = 7); moderate unilateral pulmonary contusion followed by fat embolism (n = 6); and severe unilateral pulmonary contusion followed by fat embolism (n = 5). Fat embolism was produced by intramedullary reaming of left femur and tibia followed by canal pressurization using bone cement. Outcome measures were systemic blood pressure, pulmonary artery pressure, pulmonary artery occluded pressure, cardiac output (CO), and partial pressures of arterial and mixed venous oxygen (Pao2, PvO2). Samples were taken from contused and noncontused contralateral lung to calculate regional pulmonary blood flow.

Results: After the fat embolism, pulmonary artery pressure and pulmonary vascular resistance increased significantly (p < 0.05) in all groups, whereas Pao2 decreased in groups 2 and 3 and at 30 minutes in group 1. CO decreased significantly in group 3. Group 3 also demonstrated a greater initial decrease in Pao2 and PvO2 from baseline and a larger increase in pulmonary vascular resistance. In those animals that underwent contusion, regional pulmonary blood flow was not found to be different between contused and noncontused lung segments. After contusion, flow decreased significantly in contused and noncontused segments in group 3 only.

Conclusions: Gas exchange deteriorates because of decreased CO. For any preexisting intrapulmonary shunt, the decrease of PvO2 will cause worsening of Pao2.