Electrolytes

Cell function and thus life depend on the preservation of several electrochemical gradients. Evolutionary pressures have developed several regulatory mechanisms, the penultimate goal of which is to maintain total body and distribution of each electrolyte within the intracellular and extracellular compartments at concentrations compatible with life. Ultimately, patient survival depends on this balance despite the continual changes imposed by both internal physiologic processes and external stressors. During periods of critical illness, however, these mechanisms can be overwhelmed, necessitating additional support. Indeed, disorders of electrolyte homeostasis are highly prevalent among intensive care unit patients, and severe disturbances are associated with elevated mortality. As has been previously learned, merely normalizing laboratory abnormalities without addressing the underlying pathophysiology does little to improve outcome. Thus, for those providing this care, an in-depth understanding of the biochemistry and physiology of electrolyte disorders and a systematic approach to diagnosis and therapy are complementary components essential for patient survival. This chapter discusses the major electrolytes—sodium, potassium, calcium and phosphate, and magnesium—and covers the hyper- and hypodeficiencies and disturbances for each electrolyte. This review contains 7 Figures, 6 Tables, 5 Etiologic Algorithms, and 106 References.