Bromide and Chloride Distribution Between Serum and Cerebrospinal Fluid

Abstract

The report that bromide, after administration by mouth, exists in a higher concentration in the blood serum than in the cerebrospinal fluid attracted our attention because of the following considerations. If equilibrium exists between serum and cerebrospinal fluid, if bromide ions are freely diffusible, and if the protein ions are the only restraining factor, the application of the Gibbs-Donnan Law would lead to a predicted distribution ratio of (Br)s/(Br)csf = 0.95. The bromide distribution ratios of Malamud, Fuchs and Malamud were approximately 3.0 for normal individuals and did not fall below unity in patients with damaged permeability, as in paresis. Since the colorimetric method employed by these investigators did not permit the determination of actual bromide concentrations, observations have been made using the electrometric titration method previously described as well as the colorimetric gold chloride method. The procedure followed was to administer to the patients 0.01 gm. of sodium bromide per pound of body weight 3 times a day for 5 days. Twenty hours following the last dose of bromide, blood and cerebrospinal fluid were drawn for analysis. This procedure was followed with 5 patients. Two others, O and R, were given larger doses of sodium bromide for a longer period before analyses were made. The results of 3 paretic and 2 non-paretic patients are given in Table I. Concentrations have been expressed in millimols per kilogram of water. In all instances, with both methods, the ratio (Br)s:(Br)csf was greater than unity. This substantiates the theory that bromides are not freely diffusible between serum and cerebrospinal fluid. In all except one instance the bromide ratio determined electrometrically was lower than that obtained colorimetrically.