Gas exchange and regional redistribution of pulmonary blood flow during resuscitation of acute pulmonary bead embolization

Abstract

Acute pulmonary embolism (PE) was induced by injecting polystyrene beads into the right atrium of 18 anaesthetized dogs. The animals were resuscitated for 45 min with either Ringer's Lactate (RL), norepinephrine (NE) or isoproterenol (IP). The multiple inert gas elimination technique (MIGET) was used to estimate the distributions of ventilation (V) and blood flow (Q) to different V/Q regions. Measurements were made prior to embolism, 10 min after PE and during the resuscitative phase. Microspheres with three different radioactive labels were also used to mark blood flow distribution to different lung regions in these three phases. The data show that cardiac output decreases after PE, while perfusion to shunt and low V/Q regions increases. Pulmonary blood flow heterogeneity, estimated from the MIGET data, is also increased after PE. Resuscitation by RL or NE consistently increases cardiac output but IP does so inconsistently and is associated with systemic hypotension. All three methods of resuscitation cause increases in perfusion to the shunt and low V/Q regions but no change in perfusion heterogeneity in the remaining V/Q units. Increases in regional blood flow during resuscitation occur preferentially in the less embolized areas. The concomitant increase in perfusion to shunt and low V/Q units suggests that increased perfusion to these less embolized regions results in further hypoxemia despite improvement in cardiac output.