The role of the canine spleen in cardiovascular homeostasis during halothane anesthesia.

Barbiturate anesthesia is known to increase canine splenic sequestration of red blood cells. In our laboratory, high halothane concentrations have produced a decreased arterial hematocrit in the dog. In order to assess the role of the spleen in this phenomenon, central hematocrit, plasma volume, and ventricular hemodynamics were studied at low and high halothane concentrations before and after splenectomy in the same group of dogs. Although the hematocrit difference was less after splenectomy, it was not abolished. In addition, there was more cardiovascular depression by equivalent or lower halothane doses after splenectomy. It appears that the dog has other areas of red cell sequestration than the spleen accounting for the persistently lower hematocrit with high halothane concentrations after splenectomy. The modifying effect of the canine spleen on the circulatory depression produced by halothane should be taken into account when the drug is used in the dog.