Chapter 29: Fluids and Electrolytes

Since water comprises approximately 60 percent of adult body weight, the chapter establishes the distribution of total body water across four compartments: intracellular fluid, extracellular fluid, interstitial fluid, and intravascular fluid. The mechanisms enabling fluid movement between compartments—diffusion, osmosis, filtration, and active transport—are explained as the foundation for understanding how the body maintains homeostasis. Regulatory hormones including antidiuretic hormone, aldosterone, and the thirst mechanism are presented as key physiologic controls that prevent excessive fluid loss or retention. The chapter then addresses common pathologic states such as dehydration, overhydration, and edema formation, with particular attention to the three types of dehydration classified by serum osmolality: isotonic, hypertonic, and hypotonic dehydration. Fluid replacement therapy encompasses three major categories of agents: crystalloid solutions such as sodium chloride and lactated Ringer's solution, which contain water and dissolved electrolytes; colloid solutions including albumin, dextran, and hetastarch, which increase plasma oncotic pressure; and blood products such as packed red blood cells, fresh frozen plasma, and whole blood. Each category is evaluated for mechanisms of action, appropriate clinical indications, dosing protocols, and associated adverse effects. Electrolyte physiology receives extensive coverage, focusing on potassium disturbances including hypokalemia and hyperkalemia, with nursing management of supplementation and exchange resin therapies such as sodium polystyrene sulfonate and patiromer. Sodium imbalances including hyponatremia and hypernatremia are addressed with corresponding pharmacologic treatments such as sodium chloride solutions, hypertonic saline preparations, and vasopressin receptor antagonists. The chapter emphasizes linking clinical symptoms such as weakness, confusion, seizures, cardiac dysrhythmias, and paralysis to their underlying electrolyte pathophysiology to guide appropriate nursing interventions. Nursing responsibilities focus on accurate assessment of fluid intake and output, daily weight monitoring, interpretation of relevant laboratory values, and safe management of venous access devices. Patient education encompasses recognition of hypokalemia and hyperkalemia warning signs, appropriate use of electrolyte supplements, dietary counseling regarding foods containing potassium and sodium, and reporting of adverse effects. The chapter highlights critical safety considerations for high-alert therapies including hypertonic saline infusions and intravenous potassium administration to prevent serious complications such as osmotic demyelination syndrome, phlebitis, and cardiac arrest.