Brain water and electrolyte distribution during the inhalation of halothane

The brain concentration of Na+, K+ and Cl-, water content and total brain osmolality were measured in six normocapnic dogs under pentobarbitone narcosis (30 mg kg-1). These studies were repeated in six additional dogs after exposure for 1 h to the inhalation of halothane 1% (end-tidal); there was an increase (P less than 0.05) in Na+, Cl- and water content but no change in K+ content in the grey matter, but in the white matter only Cl- increased (P less than 0.05). These findings were associated with a decrease in total brain osmolality (P less than 0.05) and a negative brain-cisternal c.s.f. osmotic gradient. The changes in the grey cortical matter were interpreted as a pattern of metabolic brain oedema related to interference with water-ion transport mechanisms across cell membranes. The observed brain-c.s.f. osmolality deficit could be related to a time-lag in the intracellular water-solute adjustment or to a deficit in osmotically active brain amino acids induced by the anaesthetic agent, or both.