Physiological Salt Solutions for Brain Surgery

Abstract

Chambers for observation and irrigation were screwed into trephine holes in cats lightly anesthetized with nembutal or dial-urethane. Two types of sterile irrigation solutions were used: an unbuffered (without carbonate or bicarbonate) similar to Locke''s and Tyrode''s solns.; and one to which Na2CO3 had been added. If unbuffered soln. flowed slowly across the brain surface, pH at the pial face fell from about 6 to 5.5; if the soln. was static, the pH rose to 6.3-6.8. The pH of the Na2CO3-containing soln., originally more than 8, or bicarbonate-buffered soln. or spinal tap fluid exposed to air (pH 8.0 to 8.8), exhibited similar falling of pH in contact with pia, to about 7.4. Pial bloodvessels dilated, sometimes with petechiae, when pH at the surface was less than 7, but blanched when buffered soln. was used for irrigation. After long exposure, vessel responsiveness was lost, usually in irreversible dilatation. Since unbuffered soln. contained as much CO2 as buffered fluid, the dilatation seemed to be a pH and not a CO2-concn. effect. When no obvious change in the animal was taking place, brain surface pH varied (7.07 to 7.34) from point to point, tending to be lower than pH of blood supply to the same area. Surface pH was higher near larger vessels. Pia-arachnoid surface pH was not affected by marked drop in irrigating-fluid pH (e.g., 7.7 to 5.3).