**1. Introduction**

Electrolytes are elements that naturally occur in the human body and help balance pH, facilitate passage of fluid through osmosis and regulate the function of neuromuscular, endocrine and excretory systems. Disturbances in these electrolytes are common clinical problems encountered in the intensive care unit with serious complications when they are depleted. Recent studies report that electrolyte imbalances are associated with increased morbidity and mortality. Possible mechanisms include damage to the kidney, activation of hormonal systems (such as RAAS) or the myriad of medication given in a critically ill patient. This chapter will focus on various electrolyte abnormalities seen in the critical care setting then touch on important ICU scenarios which could affect electrolytes.
