Body Fluids and Electrolytes Disorders

Body Fluids and Electrolytes Disorders Part I 09/23/2024 Learning objectives:  Describe the two body water  Describe the clinical compartments. significance of electrolytes.  Evaluate the anion gap.  Describe osmolali...

Body Fluids and Electrolytes Disorders Part I 09/23/2024 Learning objectives:  Describe the two body water  Describe the clinical compartments. significance of electrolytes.  Evaluate the anion gap.  Describe osmolality and its use.  Compare and contrast sodium (Na+) and potassium  Describe mechanisms that (K+) ions in terms of location, produce edema. regulation, functions, and  Compare and contrast effects of high and low exudates and transudates concentrations. and their clinical  Compare and contrast significance. chloride (Cl−) and bicarbonate (HCO3−) ions in terms of location, regulation, functions, and effects of high and low concentrations. Body fluid  Human body is about 60% water of total body weight  Human blood is approximately 83% water  The body’s cells, tissues, and organs have physical barriers to keep water inside  Distribution throughout the body is maintained by:  Electrolyte concentrations  Pressure gradients  The difference in hydrostatic pressure on either side of a membrane.  As the difference in pressures rises, filtration increases from the area of high pressure to the area of low pressure. Body fluid compartments  Approximately 67% of total body water is in the intracellular fluid (ICF) compartment  Approximately 33% of the total body water is in the extracellular fluid (ECF) compartment  The extracellular fluid (ECF) compartment is further subdivided into two compartment separated by a thin layer of cells called the capillary epithelium:  25 % of ECF is in the intravascular compartment (blood vessel and lymph)  75% of ECF is in the extravascular compartment Body fluid compartments  Extravascular compartment is further subdivided into two compartment:  Interstitial fluid (approximately 95%):  Interstitial fluid is the fluid that directly bathes the cells and tissues in the body  Transcellular fluid (approximately 5%):  This fluid is generally separated from the plasma by an additional epithelial layer in addition to the capillary endothelium (e.g., cerebrospinal fluid) Body fluid compartments Interstitial fluid Extravascular transcellular 75% Intracellular fluid fluid Extracellular fluid 67% 33% Plasma Intravascular Lymph 25% Fluid balance  The rate of water lost from the body must equal the rate of water intake to maintain the water balance  Ingest: eating and drinking  Excrete: urine, feces, sweat, and aerosols during respiration  Dehydration: excessive water loss or decreased water intake  Regulation: through the thirst mechanism, electrolyte gradients, antidiuretic hormones, and excretion or reabsorption by the kidneys Electrolytes functions  Electrolytes (“lytes”) are charged atoms or molecules (e.g., ions)  It regulates many functions in the body:  Water distribution  Osmotic pressure  Nerve transmission to muscles (e.g., heart),  Cell permeability (i.e., passage of solvents and solutes into and out of cells)  Oxidation-reduction reactions  Maintenance of blood pH in the narrow range of 7.35 to 7.45 Electrolytes composition  Cations electrolytes (e.g., positively charged ions):  Sodium (Na+)  Potassium (K+)  Anions electrolytes (e.g., negatively charged ions):  Chloride (Cl−)  Bicarbonate (HCO3−) Electrolytes imbalance  Electrolyte imbalances are life-threatening situations  Recovery from a traumatic event or illness depends on the body’s ability to regulate body water and electrolytes.  Causes:  Vomiting, excessive urination, sweating, diarrhea, bleeding, or exudation (i.e., oozing of fluids) from burns or other skin injuries can cause fluid imbalances Electrolytes compartmentalization  Each type of body fluid contains specific amounts of cations and anions, and fluids can be identified by their ion compositions:  plasma and interstitial fluid have high level of:  Sodium  Chloride  Bicarbonate  intracellular fluid has high level of:  Potassium Electrolytes and Osmosis  Osmosis:  The diffusion of solvent molecules from a higher-concentration solution through a semipermeable membrane(cell membrane)to a lower-concentration solution  Osmotic pressure:  The physical force exerted during osmosis where the more solute particle across the cell membrane, the higher the osmotic pressure Electrolytes and Osmosis  Osmotic pressure:  The movement of water between intracellular and extracellular compartments is dependent on osmotic pressure  In the case of dehydration, hypertonic extracellular fluid (too many ions and/or too little fluid) will occur  The body compensates by moving water from the intracellular space to the extracellular  Osmotic pressure is created by the many ions inside and outside of the cell  Because intracellular ions are difficult to measure, it is more practical to measure the ion concentration in serum or plasma instead (most common) Electrolytes and Osmosis  Osmotic pressure:  Measurement can also be obtained from urine, spinal fluid, and sweat  The extracellular electrolytes measured in serum or plasma indicate the functional integrity of the cell membrane, balance, and patient condition Electrolytes and Osmosis  Types of osmosis conditions:  Isotonic solution:  Is any external solution that has the same solute concentration and water concentration compared to body fluids.  Hypotonic solution:  A solution outside of a cell is called hypotonic if it has a lower concentration of solutes relative to the cytosol  Hypertonic solution:  Solute concentration is higher outside than that inside the cell, and the solutes cannot cross the membrane. Electrolytes and Osmosis  Normal electrolytes values: Anion Gap  A test to examine the electrolytes balance to check for acid-base status  Ideally the total positive charges must equal the total negative charges of electrolytes  The anion gap is a mathematical calculation and is used to estimate a patient’s anions and cations measurements  The routinely measured electrolytes include:  Sodium  Potassium  Chloride  Bicarbonate Anion Gap  High level of anion gap:  Elevated anion gaps are often seen in patients with acidosis due to kidney disease, diabetes mellitus (ketoacidosis), or Aspirin and methanol poisoning  Low level of anion gap:  Decreased anion gaps are often an indication of instrument error and must be investigated by the instrument operator to ensure electrolyte measurements are accurate  If low value is true, patient might have hypoalbuminemia due to sever kidney disease, heart disease, or liver disease Anion Gap  Laboratory test:  A commonly used equation for measurement:  anion gap = [Na+ + K+] – [Cl- + Hco3-]  Normal range of anion gap is 4 to 12 mEq/L  Normal range varies between laboratories  Commonly requested for routine bloodwork  Electrolyte panel, basic metabolic panel, comprehensive metabolic panel, and renal function panel Sodium (Na+)  90% of plasma cations  Sodium enters the body in many forms (e.g., Salt)  Absorption of sodium causes a temporary increase in extracellular fluid volume  Amount of sodium in the body remains constant (136-145 meq/L)  Cell uses ATP pump to exchange sodium for potassium  Because sodium concentration outside the cell is 10 times that inside the cell, sodium ions are pumped across the semipermeable cell membrane, and potassium ions are pumped in Sodium (Na+)  Na+ Regulation:  Aldosterone: a hormone that is secreted by the adrenal gland, influences the kidneys to resorb sodium and accelerates the exchange of sodium and potassium ions across the cell membranes  This exchange helps the body retain sodium and excrete potassium  Atrial natriuretic peptide (ANP): a hormone that is secreted by the heart, which causes the excretion of sodium  This will lead to a decrease of blood pressure Sodium (Na+)  Na+ Functions:  Transmitting nerve impulses  Maintaining the osmotic pressure of extracellular fluid and retaining water  Facilitating muscle contractions  Maintaining acid-base balance  Maintaining blood viscosity Sodium (Na+)  Clinical significance of Na+ :  Hyponatremia:  is more common, which means a decreased level of sodium level. Can be caused by:  Low sodium intake, diarrhea, prolonged vomiting, sweating due to fever, or renal disease  Hypernatremia:  is less common, which means an increased level of sodium. Can be caused by:  Severe dehydration, Cushing syndrome (excessive resorption of sodium), inappropriate saline solution therapy, and ingestion of high- sodium foods with little water intake Sodium (Na+)  Lab Procedures: A. Ion-selective electrodes (ISEs)  Sodium electrodes have a glass membrane that allows sodium ions to flow into the tip of the electrode, where they interact with the measuring and reference electrode wires  Direct ISE type are used in undiluted samples and found in point of care instruments and blood gas analyzer  Indirect ISE type are used in diluted samples (plasma and serum) and found in most large analyzers Sodium (Na+)  Lab Procedures: B. Sources of error:  Indirect ISE type uses diluted samples and is prone to high lipid or protein content, which displace fluid that may contain sodium ions result in false decreased value  Electrodes coated with protein and competing ions. Manufacturers require specific cleaning regimens for ISEs to remove the protein coating and enable more accurate readings  Severely hemolyzed samples my result in dilutional effect error C. Specimen type:  Serum, lithium heparinized plasma, whole blood, sweat, urine, feces, and gastrointestinal fluids