Inhibition of microembolization-induced pulmonary edema by early heparin treatment in dogs

Abstract

We determined the effects in dogs of heparin (500 units/kg) given at either 30 minutes or 60 minutes after pulmonary microembolism (PE) on the microembolization-induced pulmonary edema. The lungs were embolized by injecting non-siliconized glass beads (approx. 100 um in diameter) into the right atrium over 5 minutes so as to produce 2-to 3-fold increases in the mean pulmonary arterial pressure. Extravascular lung water contents were determined in normal control dogs, control dogs embolized for 30 and 120 minutes, and in similarly embolized dogs treated with heparin at either 30 minutes or 60 minutes PE. The pulmonary vascular resistance (PVR) increased 3-to 4-fold and remained elevated at these levels for duration of the study. The increases in PVR in the four groups were not significantly different from each other. Embolization resulted in increases in the extravascular lung water/bloodless dry lung weight ratio (W/D) from control values of 2.88 ± 0.22 to 3.32 ± 0.10 at 30 min PE to 4.17 ± 0.38 at 120 min PE (p<0.05). Heparin treatment at 30 minutes PE prevented the increase in the W/D since the two hour PE W/D value of 2.99 ± 0.19 was not different from the control value; whereas heparin treatment at 60 minutes PE did not affect the degree of pulmonary edema since the two hour PE W/D value of 4.05 ± 0.28 was greater than the control value (p<0.05) but not different from the two hour PE value in untreated dogs. The lack of effect of heparin at 60 PE may be due to vascular injury that cannot be reversed. However, the prevention of the extravascular lung water accumulation after microembolization by treatment with heparin at 30 minutes may be due to inhibition of further intravascular coagulation.