Fluid and Electrolyte Concepts
Learning Objective: Relate principles of nursing care to disturbances in fluid volume and electrolytes.
Fluid and Electrolyte Balance:
Necessary to maintain homeostasis.
Requires equal balance of intake and output to help maintain proper equilibrium within all body systems.
Regulated by:
Kidneys
Pulmonary system
Hormonal and neural functions.
Foundation for nursing decisions regarding patient care.
Body Fluid Compartments
Total Body Fluid (TBW): Contains fluid in two major compartments.
Intracellular Fluid (ICF): Fluid within body cells.
Makes up approximately 40% of TBW.
Extracellular Fluid (ECF): Fluid outside of cells.
Comprises approximately 20% of TBW, further divided into subcompartments:
Interstitial Compartment: Surrounds tissue cells (15% of TBW).
Intravascular Compartment: Contains plasma and blood vessels (5% of TBW).
Transcellular Compartment: Third space, contains:
Mucus
Gastrointestinal fluid
Cerebrospinal fluid
Pericardial fluid
Synovial fluid
Ocular fluid
Table 12.1: Adult Body Fluid Volume:
ICF: 40%
ECF: 20%
Interstitial: 15%
Intravascular: 5%
Transcellular: Approximately 1–2 L
Total body fluid: 60% of weight; for a 70-kg male = ~60% (40 L).
Fluid Movement: Fluids move freely between compartments to maintain balance and homeostasis.
Electrolytes
Electrolytes: Substances dissociating into ions in solutions, critical for cellular functions.
Cations: Positively charged ions (e.g.,
Potassium (K+)
Sodium (Na+)
Calcium (Ca2+)
Magnesium (Mg2+)
Anions: Negatively charged ions (e.g.,
Chloride (Cl−)
Bicarbonate (HCO3−)
Phosphate (PO4−)
Sulfate (SO4−)
Most prevalent electrolytes in body fluids include sodium, potassium, calcium, magnesium, and chloride.
Table 12.2: Lists major cations and anions.
Potassium (K+), Chloride (Cl−), Sodium (Na+), Bicarbonate (HCO3−), Calcium (Ca2+), Phosphate (PO4−), Magnesium (Mg2+), Sulfate (SO4−).
Electrolyte imbalances can arise from various illnesses and body changes.
Homeostasis
Learning Objective: Describe homeostasis and fluid and electrolyte balance in patient care.
Homeostasis maintains constant internal balance despite external changes.
Key Principles:
Anions and cations must balance in compartments to remain electronegative neutral.
Fluid compartments maintain osmotic equilibrium except for transient changes.
Processes Controlling Fluid Movement:
Osmosis: Movement of water across semipermeable membranes from low to high solute concentration.
Diffusion: Movement from high to low concentration of molecules.
Hydrostatic Pressure: Force exerted within a fluid compartment.
Osmolality: Concentration of solution measured by osmoles.
Normal Serum Osmolality: Ranges from 275 to 295 mOsm/kg.
Osmolarity Classification
Fluid Concentrations based on Osmolality:
Iso-osmolar: Equal solute concentrations and water.
Hypo-osmolar: Fewer solutes than water.
Hyperosmolar: More solutes than water.
Conditions Leading to Hyponatremia (deficiency of sodium, often from excess water) and Hypernatremia (excess sodium or loss of water) must be understood to administer safe fluid therapy.
Fluid Replacement and Care
Understanding Fluid Intake and Loss:
Recommended water intake: 2300 to 2900 mL per day.
Oral intake: 1200-1500 mL; solid foods: 800-1100 mL; oxidative metabolism: ~300 mL.
Daily water loss from:
Kidneys: 1200-1500 mL of urine.
Skin: Insensible (not measurable) and sensible loss (500-600 mL).
GI tract: 200 mL on average.
Minimum adult urinary output: 0.5 to 1 mL/kg/h (35 to 70 mL/h for a 70-kg person).
IV Fluid Use; Considerations:
Purpose of IV therapy (replacement vs. maintenance).
Assessment factors: Patient's weight, caloric needs, body surface area, and disease states.
Types of IV Solutions
Crystalloids:
Solutions with fluids and electrolytes, do not contain proteins.
Used for short-term maintenance and treating dehydration:
Hypotonic: Fluid moves into cells, can cause hemolysis.
Isotonic: Maintains fluid balance, does not affect RBCs' size.
Hypertonic: Pulls fluid from cells, may cause cellular shrinkage.
Colloids: Contain larger molecules that stay in vascular compartment, including:
Albumin.
Dextrans.
Blood Products: PRBCs, plasma, platelets; essential for acute care and management of hemorrhage.
Nursing Interventions for Fluid and Electrolyte Balance
Assessment: Monitor vital signs and assess for dehydration (FVD) or overload (FVE).
Educate: Teaching patients about symptoms of imbalance (thirst for FVD, weight gain for FVE), dietary recommendations, and sodium restrictions.
Monitor Intake and Output: Important for assessing patient's fluid status and to prevent complications related to imbalances.
Documentation: Track lab values reflecting the patient's hydration status (e.g., BUN, creatinine).
Electrolyte Management
Potassium (K+):
Major intracellular cation, vital for muscle and nerve functions.
Normal level: 3.5 to 5.0 mEq/L.
Hypokalemia: Causes include GI losses, medications, and certain diseases.
Hyperkalemia: Increased potassium due to renal failure or excessive intake.
Sodium: Major extracellular cation, normal range 135-145 mEq/L; crucial for fluid balance.
Calcium: Essential for bone health and muscular function; normal range 8.6-10.2 mg/dL.
Hypocalcemia and Hypercalcemia present significant health risks.
Magnesium: Normal serum level is 1.5 to 2.5 mEq/L, affects neuromuscular function, imbalance can lead to cardiac issues.
Phosphate: Major anion in ICF, important for bone health and cellular functions, regulated often alongside calcium. \n\nManagement of Electrolyte Imbalances: Determine and treat the underlying cause, monitor levels, dietary considerations, and proper administration techniques/medications is crucial for nursing care.