Sodium in Critical Illness: An Overview

Abstract

Water accounts for around 60 % of body weight in humans. Total body water is distributed between the extra- and intra-cellular compartments (Fig. 1). The intracellular space is the largest fluid compartment and contains up to two thirds of the total body water, i. e., around 30–40 % of the body weight. The extracellular compartment comprises one third of the total body water, mainly in the interstitium; only 25 % of the extracellular fluid is present in the intravascular space, i. e., 5 % of body weight. The distribution of electrolytes varies widely between the extra- and intra-cellular compartments.