Fluid and electrolyte disturbances are extremely common in the
perioperative period. Large amounts of intravenous fluids are frequently
required to correct fluid deficits and compensate for blood loss
during surgery. Anesthesiologists must therefore have a clear understanding
of normal water and electrolyte physiology. Major disturbances in
fluid and electrolyte balance can rapidly alter cardiovascular,
neurological, and neuromuscular functions. This chapter examines
the body’s fluid compartments and common water and electrolyte
derangements, their treatment, and anesthetic implications. Acid–base
disorders and intravenous fluid therapy are discussed in subsequent
The system of international units (SI) has still not gained universal
acceptance in clinical practice, and many older expressions of concentration
remain in common use. Thus, for example, the quantity of a solute
in a solution may be expressed in grams, moles, or equivalents.
To complicate matters further, the concentration of a solution may
be expressed either as quantity of solute per volume of solution
or quantity of solute per weight of solvent.
One mole of a substance represents 6.02 × 1023 molecules.
The weight of this quantity in grams is commonly referred to as
gram-molecular weight. Molarity is the standard SI unit of concentration
that expresses the number of moles of solute per liter of
solution. Molality is an alternative term that expresses moles ...