Effects of isovolumic hemodilution on massive pulmonary emboli.

Massive pulmonary emboli obstruct the pulmonary outflow tract and release vasoactive amines that further increase vascular resistance in the pulmonary vascular bed. Lowering blood viscosity by isovolumic hemodilution has been suggested as a possible therapeutic modality to increase pulmonary blood flow. This study was performed to determine if hemodilution could affect the aberrancies caused by massive emboli. Ten pairs of mongrel dogs were instrumented and injected with autologous clot until pulmonary artery (PA) pressure rose to 40 mm Hg. One doe was then isovolumically hemodiluted to a hematocrit of two thirds of control with Ringer's lactate. Hemodynamic data, including PA, and arterial and pulmonary capillary wedge pressure (PCW), were obtained immediately following injection of the clot and one hour later. Following this, the dog was sacrificed and all clot was removed and weighed. Three dogs in the control group arrested and could not be resuscitated, while two dogs in the hemodiluted group survived arrest. The hemodynamic data was identical in the two groups. Clots in the control group weighed 9.6 +/- 7 grams while retrieved clot in the hemodiluted dogs was 3.6 +/- 2. Although the hemodynamic data was similar for both groups, the survival rate and decrease in the size of the clot was significantly favorable in the hemodiluted dogs to encourage further study on this technique.