Electrolyte Disorders

C.M. Elwood MA VetMB CertSAC MSc PhD MRCVS DACVIM DECVIM
Davies Veterinary Specialists

Hypernatraemia

Hypernatraemia occurs when there is an excessive concentration of sodium in the extra-cellular fluid. This can occur as a result of excess sodium input (e.g. salt poisoning or prolonged administration of high sodium fluids) but more commonly occurs in the primary case as a result of loss of free water. The sodium content of plasma has a major effect on osmolality:

Plasma osmolality (and thus sodium concentration) is controlled by osmoreceptors in the hypothalamus; increased osmolality increases thirst and stimulates ADH release, leading to ingestion of free water and retention of free water by the kidneys. Non-osmolar stimuli such as volume affect stretch receptors in the left ventricle and aortic and carotid baroreceptors can also stimulate ADH release, even in the face of reduced osmolality (effective circulating volume depletion).