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Chapter 25 Fluid, Electrolyte, and Acid–Base Balance
Learning Objectives Theory • List the various functions water performs in the body • List the major electrolytes and the function of each • Describe three ways in which body fluids are continually being distributed among the fluid compartments • Identify the signs and symptoms of the common fluid and electrolyte imbalances
Learning Objectives Clinical Practice • Assess an assigned patient for signs of fluid and electrolyte imbalance • From patient laboratory results, identify electrolyte values that are abnormal • Implement teaching for the patient with hypokalemia • Develop a plan of care for a patient who has a fluid and electrolyte imbalance
Composition of Body Fluids Water • The two largest constituents of the body are water and electrolytes • Water serves four functions: 1. Is a vehicle for transporting substances to and from cells 2. Aids in heat regulation 3. Assists in hydrogen(H+) balance in the body 4. Is a medium for enzymatic action of digestion
Water • More than half of the body’s weight is water • Amount varies with age, sex, and health status • Males: approximately 60% • Females: approximately 50% • Infants and the elderly more easily affected by changes in fluid balance
Water • Infants and the elderly become dehydrated more rapidly • Infants because of the large body surface area compared to body weight-looses more through the skin than the adult • Infants’ kidneys reabsorb less fluid • Elderly have less antidiuretic hormone, decrease in urine concentrating ability of the kidney, and diminished thirst sensation • Water is critical to maintaining homeostasis
Water is critical to maintaining a state of homeostasis because water is the medium in which most metabolic and chemical reactions in the body take place. Without sufficient water, cells cannot function and death results
Sources of Water and Avenues of Loss • Intake • Oral 1500 mL • Food 800 mL • Metabolism 200 mL • Total 2500 mL • Output • Urine 1500 mL • Perspiration 400 mL • Feces 200 mL • Expired air 400 mL • Total 2500 mL
Composition of Body Fluids Electrolytes • Minerals or salts dissolved in body fluids • In solution, they break up into ions • Ions have electrical charges • Cations have positive charges • Anions have negative charges • Each cation must be balanced by an anion • The major source of electrolytes is diet
Electrolytes • Sodium: water regulation and balance • Potassium: nerve impulse transmission, muscle contraction, plasma, acid–base balance • Calcium: muscle activity, blood coagulation • Magnesium: nerve impulse transmission, muscle contraction • Phosphate: ATP production • Chloride: hydrochloric acid production, acid–base balance • Bicarbonate: acid–base balance
Major Electrolytes: Normal Range Table 25-2 ElectrolyteNormal Range • Sodium 135-145 mEq/L • Potassium 3.5-5 mEq/L • Calcium 8.4-10.6 mg/dL • Magnesium 1.3-2.5 mg/dL • Phosphate 2.5-4.5 mg/dL • Chloride 96-106 mEq/L • Bicarbonate 22-26 mEq/L
Non-Electrolytes • Amino acids (proteins), glucose, and fatty acids • Remain bound together when dissolved in body fluid • In the healthy individual who is eating normally, the nonelectrolytes circulating in the body fluid remain stable
Non-Electrolytes: Blood • Normal circulating blood volume is 4 to 6 L • Composed of: • Erythrocytes (red cells) • Leukocytes (white cells) • Platelets (thrombocytes) • Carried in plasma
Non-Electrolytes: Blood • Plasma proteins and colloids contribute to plasma osmotic pressure, which keeps fluid in the vascular compartment • Anything that alters body fluid volume also alters plasma volume • Plasma volume can affect blood pressure • Plasma volume can affect circulation
Distribution of Body FluidsTable 25-3 page 437 • Body fluids are: 1. Intracellular (within the cell) 2. Extracellular (outside the cell) • Intravascular • Interstitial • Transcellular
Extracellular Fluid • Makes up approximately 1/3 of the total body water • Transports nutrients, oxygen, and waste products to and from cells • Is regulated by renal, metabolic, and neurologic factors • Is high in sodium content
Intravascular Fluid • The fluid within the blood vessels • Consists of plasma and fluid within the blood cells • Contains large amounts of protein and electrolytes, which help maintain intravascular volume
Transcellular Fluids • Aqueous humor (in the eyes) • Saliva • Cerebrospinal fluid • Pleural, peritoneal, synovial, and pericardial fluids • Gastrointestinal secretions • Fluid in the urinary tract • Lymphatic system fluids
When fluid shifts form the plasma in the vascular space out to the interstitial space, blood volume drops and dehydration and hypovolemia may occur. • Dehydration – removal of water from a tissue • Hypovolemia – decreased volume of plasma
Movement of Fluids and Electrolytes • Water taken in by ingesting fluids and food and through metabolism • Thirst mechanism in the hypothalamus regulates thirst based on concentration of electrolytes and solutes in circulation • Kidney’s are the main organ of water secretion, with some loss in feces, perspiration, and breathing. • Water retention is based on aldosterone levels, antidiuretic hormone (ADH) levels, and atrialnatriuretic peptide levels.
Fluid, Electrolyte, and Nutrient Transport Mechanisms • Diffusion—passive transport • Process by which substances move back and forth across the membrane until evenly distributed throughout the available space • Substances move from high to low concentration until concentration on both sides of the membrane is equal • Glucose, oxygen, carbon dioxide, water, and other small ions and molecules move by diffusion
Fluid, Electrolyte, and Nutrient Transport Mechanisms • Osmosis—passive transport • Movement of pure solvent (liquid) across a membrane • Water moves from area of less solute concentration to area of greater concentration until the solutions in the compartments are of equal concentration • Takes place via a semipermeable membrane • A membrane that allows some substances to pass through but prevents the passage of other substances.
Osmosis • Fluid moves between the interstitial and intracellular and the interstitial and intravascular compartments by osmosis. • Cell wall membranes are semipermeable, as are the walls of the blood vessels.
When living cells are surrounded by a solutions that has the same concentration of particles, the water concentration of the intracellular and extracellular fluids will be equal. - ISOTONIC (equal concentration) • If cells are surrounded by a solution that has a greater concentration of solute than the cell, the water in the cell will move to the more concentrated solutions and the cell will dehydrate and shrink. –HYPERTONIC (of greater concentration) • If the cells are surrounded by a solution that has less solute than the cells – HYPOTONIC – (of lesser concentration)
OSMOSIS • The process of osmosis is essential to the life of the cells and to the balance of water and electrolytes in the body. • Osmotic pressure within vessels helps to keep fluid from leaking out into the interstitial spaces
Fluid, Electrolyte, and Nutrient Transport Mechanisms • Filtration—passive transport • Movement of water and suspended substances outward through a semipermeable membrane • Hydrostatic pressure • Causes fluid to press outward on the vessel • The force promotes filtration, forcing movement of water and electrolytes through the capillary wall to the interstitial fluid
Fluid, Electrolyte, and Nutrient Transport Mechanisms Active transport • Requires cellular energy • Can move molecules into cells regardless of their electrical charge or the concentrations already in the cell • The energy source for the process is adenosine triphosphate (ATP) • ATP is produced during the complex metabolic processes in the body's cells. • Can move amino acids, glucose, iron, hydrogen, sodium, potassium, and calcium through the cell membrane
Fluid Volume Deficit • At risk: • Patients unable to take in enough fluid • Impaired swallowing, extreme weakness, disorientation or coma, or unavailability of water • Patients who lose excessive amounts of fluid • Prolonged vomiting, diarrhea, hemorrhage, diaphoresis (sweating), or excessive wound drainage • Result is dehydration
Dehydration • Dehydration • When too little water in the plasma, water drawn out of the cells by osmosis to equalize concentration, and the cells shrivel • Treated by fluid administration, either orally or intravenously
Signs and Symptoms of Dehydration • Thirst • Weakness • Dizziness • Postural hypotension • Decreased urine production • Concentrated urine • Dry, cracked lips • Dry mucous membranes • Thick saliva • Dry, scaly skin • Poor tissue turgor • Flat neck veins • Increased pulse rate • Weak, thready pulse • Elevated temperature
Fluid Volume Excess • Healthy people do not ordinarily drink too much water • When people become ill they may take in more water than they excrete • Receive intravenous fluid too quickly • Given tap water enemas • Drink more fluids than they can eliminate
Fluid Volume Excess • Signs of overhydration • Weight gain • Crackles in the lungs (wet lungs) • Slow bounding pulse • Elevated blood pressure • Possibly edema
Edema • Excessive accumulation of interstitial fluid. may be a sign of fluid overloads • In ambulatory patients its usually in lower extremities • In bedridden patients its usually in sacral area • Generalized edema occurs when excess interstitial fluid is spread thought the body ( hands face) • Kidney failure • Heart failure • Liver failure • Hormonal disorders
Electrolyte Imbalance: Sodium Hyponatremia ( less than 135 mEq/L) • Sodium deficit; can be from decreased sodium or increased water intake and retention • May be caused by excessive vomiting or diarrhea • Decrease secretion of aldosterone • CHF, liver disease, chronic renal failure • Most common electrolyte imbalance • Average sodium intake 6-12 g/day
Hypernatremia • Sodium levels above 145 mEq/L • Sodium excess; most commonly from water loss from fever or respiratory infection • Hypernatremia causes an osmotic shift of fluid from the cells to the interstitial spaces, causing a cellular dehydration and interruption of normal cell processes • Sodium must be restricted from patients with hypernatremia
Electrolyte Imbalance: Potassium Hypokalemia ( below 3.5 mEq/L) • Occurs with excess potassium or loss of body water; may be from poor diet, vomiting, diarrhea, excessive sweating, or diuretic therapy • Severe hypokalemia less than 2.5 may cause cardiac arrest Hyperkalemia( above 5.0 mEq/L) • Occurs with burns, crush injuries, uncontrolled diabetes mellitus • Renal failure, overuse of potassium sparing diuretics digitalis toxicity ,and overuse of potassium containing salt substitutes • Can cause life threatening cardiac arrhythmia!
Electrolyte Imbalance: Calcium Hypocalcemia( below 8.4 mg/dL) • Occurs with nutritional deficiency of calcium or vitamin D or in bone disorders such as metastatic cancer of the bone • Removal or injury of he parathyroid, excessive infusion of bicarbonate solution, blood transfusions, hypoparathyroidism. Hypercalcemia( above 10.6 mg/dL) • Most cases related to hyperparathyroidism or malignancy such as multiple myeloma • Lengthy immobilization when calcium is mobilized from the bone or when exces of calcium or vitamin D is taken into the body. • Hyparathroidism, lung or renal cancer.
Electrolyte Imbalance: Calcium • Calcium imbalances • Hypocalcemia • Calcium level drops below 8.4 mg/dL • Can occur from nutritional deficiency of calcium or vitamin D • Occurs in disorders in which there is a shift of calcium into the bone • Hypercalcemia • Calcium level above 10.6 mg/dL • Most cases are related to hyperparathyroidism or malignancy in which there is metastasis with bone resorption
Electrolyte Imbalance: Magnesium Hypomagnesemia( below 1.3mEq/L) • Results from malabsorption, malnutrition, renal tubular dysfunction, thiazide diuretic use, extensive gastric suction, or diarrhea • Usually is present when hypokalemia and hypocalcemia occur Hypermagnesemia (above 2.1 mEq) • Occurs only in presence of renal failure • Magnesium containing laxatives or antacids or severe dehydration may be the cause
Electrolyte Imbalances Anion imbalances • Hypochloremia • Chloride level below 96 mEq/L is associated with hyponatremia • Severe vomiting and as compensatory decrease in acid base disorders • Hyperchloremia • Chloride level above 106 mEq/L • Occurs along with hypernatremia and a form of metabolic acidosis
Electrolyte Imbalances Anion imbalances • Hypophosphatemia • Occurs when the level of phosphate falls below 3.0 mg/dL • May result from use of aluminum-containing antacids, from vitamin D deficiency, or from hyperparathyroidism • Hyperphosphatemia • A phosphate level above 4.5 mg/dL • Commonly occurs in renal failure
Table 25-4 Electrolyte Imbalances Patient Teaching 25-1 Foods High in Sodium Patient Teaching 25-2 Foods High in Potassium
Acid–Base Balance • Important in maintaining homeostasis • pH: measure of the degree of acidity or alkalinity • Normal serum pH is 7.35 to 7.45 • Death may occur if pH is less than 6.8 or greater than 7.8 • Balance between bicarbonate and carbonic acid • Carbonic acid retained or removed by respiratory system • Bicarbonate retained or removed by kidneys
Acid–Base Balance • Bicarbonate (HCO3) • Normal range is 22 to 26 mEq/L • Acts as buffer to neutralize excess acids in the body and maintain bicarbonate-to–carbonic acid ratio at 20:1 • Kidneys selectively reabsorb or excrete bicarbonate to regulate serum levels and help maintain acid–base balance