Clinical meaning
Fluid balance is a fundamental concept in nursing care that reflects the relationship between fluid intake (all sources of fluid entering the body) and fluid output (all sources of fluid leaving the body). The human body is approximately 60% water in adult males and 55% in adult females, distributed between two major compartments: the intracellular fluid (ICF) compartment containing approximately two-thirds of total body water within cells, and the extracellular fluid (ECF) compartment containing the remaining one-third, which is further divided into intravascular fluid (plasma, approximately 3 liters), interstitial fluid (fluid between cells, approximately 11 liters), and transcellular fluid (cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid, approximately 1 liter). The kidneys are the primary regulators of fluid balance, filtering approximately 180 liters of plasma daily through the glomeruli and reabsorbing approximately 99% of this filtrate back into the blood. Normal urine output in adults is 0.5 to 1.0 mL/kg/hour, meaning a 70 kg adult should produce approximately 35 to 70 mL of urine per hour, or roughly 1,500 to 2,000 mL per day. Urine output below 30 mL/hour (oliguria)...