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Principles for Nursing Practice. Fluid, Electrolyte, And Acid-Base Balances. Dr. Belal M. Hijji, RN, PhD Febraury 18 & 19, 2012. Learning Outcomes. By the end of this lecture, students will be able to: Describe the distribution, composition, movement, and regulation, of body fluids.
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Principles for Nursing Practice Fluid, Electrolyte, And Acid-Base Balances Dr. Belal M. Hijji, RN, PhD Febraury 18 & 19, 2012
Learning Outcomes By the end of this lecture, students will be able to: • Describe the distribution, composition, movement, and regulation, of body fluids. • Describe the processes involved in the regulation of electrolytes and acid-base balance. • Discuss common disturbances in fluid, electrolyte, and acid-base balances. • Identify types of intravenous solutions and their effect on blood cells.
Distribution, Composition, Movement, And Regulation, of Body Fluids • Distribution: • Intracellular fluid (ICF): Contains dissolved solutes [مواد مذابة] essential to fluid and electrolyte balance and metabolism. It comprises 40% of adult body weight • Extracellular fluid (ECF): Is divided into two smaller compartments: interstitial and intravascular fluids. Interstitial fluid exists between cells and outside the blood vessels; intravascular fluids is blood plasma. • Composition: • Electrolytes: Positively charged (cations) or negatively charged (anions). • Water • Movement: • Diffusion: A solute in a solution moves from an area of higher concentration to an area of lower concentration.
Osmosis: Is the movement of water across a semipermeable membrane from an area of lower concentration to one that has higher concentration. • Osmotic pressure: Draws water from a less concentrated solution to the more concentrated side. Osmolality is the measure of a solution’s ability to create osmotic pressure. • Regulation: Homeostasis is the process by which body fluids are maintained in balance. Body fluids are regulated through: • Fluid intake: The thirst mechanism influences fluid intake. Through its control centre in the hypothalamus, thirst develops when osmolality increases. Eating salty food can increase osmotic pressure of the body fluids and stimulate the thirst mechanism. Increased plasma osmolality can occur in impaired oral fluid intake, hypertonic fluid intake, or when fluids are lost.
Hormonal regulation: Antidiuretic hormone (ADH), stored in the pituitary gland, is released when there is an increase in osmolarity. ADH acts on the kidneys and prevents diuresis. • Fluid output regulation: Fluid output occurs through the: • Kidneys: They receive about 180 L of plasma to filter each day, and produce 1.2 to 1.5 L of urine. • Skin: Fluid loss of 500 to 600 ml daily. • Lungs: They expire about 400 ml of water daily.
Regulation of Electrolytes and Acid-Base Balance • Electrolytes: • Cations: • Sodium Na+: (90% ECF). Regulated by dietary intake and aldosterone secretion. Aldosterone increases the reabsorption of sodium and water, and this increases blood volume and, therefore, elevates blood pressure. • Potassium K+: (2% ECF). Regulated through dietary intake and renal excretion. • Calcium Ca ++: (1% in ECF). Regulated through dietary intake, vitamin D, and parathyroid hormone.
Anions: • Chloride Cl−: Regulated through dietary intake and the kidneys. • Bicarbonate HCO3-: Essential to acid-base balance. It is regulated by the kidneys. • Phosphorus-phosphate (PO4-3): Assists in acid-base regulation, bone and teeth development. Regulated by dietary intake, renal excretion, intestinal absorption, and PTH. • Acid-base: For an optimal functioning of cells, a balance between acids and bases must be maintained. • Arterial pH indirectly measures hydrogen ion (H+) concentration. • The greater the concentration of H+ ions, the more acidic the solution and the lower the pH. • The lower the concentration of H+ ions, the more alkaline the solution and the higher the pH.
pH also reflects the balance between carbon dioxide (CO2) and bicarbonate HCO3-. • Acid-base balance exists when the net rate of acids or bases production is equal to the rate of their excretion.
Disturbances in Electrolyte, Fluid, And Acid-Base Balances • Electrolyte imbalance: • Sodium imbalance: Treatment depends on the cause. • Hyponatremia: May result from kidney disease, psychogenic polydepsia & using diuretics • Hypernatremia: May result from diabetes insipidus, ingestion of large amounts of salts, and increased water loss. • Potassium imbalance: • Hypokalemia: most commonly caused by potassium-wasting diuretics such as thiazide and loop diuretics. If severe, it can affect cardiac function and conduction • Hyperkalemia: Primarily caused by renal failure. It produces marked cardiac conduction abnormalities. • Calcium imbalance: • Hypocalcemia: Caused by Vit. D deficiency, renal failure, pancreatitis, hypoparathyroidism.
Fluid disturbance • Isotonic deficit and excess: These exist when water and electrolytes are either gained or lost in equal proportions. Isotonic fluid volume deficit (FVD) result from diarrhea, vomiting, burns, bleeding, fever, decreased oral intake, and use of diuretics. Isotonic fluid volume excess (FVE) result from renal failure, congestive heart failure (CHF), excessive salt intake, or liver cirrhosis. • Osmolar imbalances: These are losses or excesses of only water so that the concentration of the serum is affected. In hyperosmolar imbalance, dehydration exists due to diabetes insipidus, diabetic ketoacidosis, and interruption of neurologically driven thirst drive. Dehydration results following the osmotic movement of water into urine (Osmotic diuresis). In hypoosmolar imbalance, water excess exists due to excess water intake and syndrome of inappropriate secretion of antidiuretic hormone.
Acid-base imbalance: Arterial blood gas (ABG) analysis best evaluate acid-base balance. Measuring ABG provides insight about the following components: • pH: pH measures H+ ion concentration in body fluids. A slight change can be dangerous. An increase in concentration of H+ makes a solution more acidic; a decrease makes the solution more alkaline. The normal arterial blood pH value is 7.35 to 7.45. • Oxygen saturation: Saturation is the point at which hemoglobin is saturated by oxygen. Range is 95% to 100%. • Serum Bicarbonate: Is the major component of acid-base balance. It is reproduced by the kidneys. Less than 22 mEq/L indicates metabolic acidosis; more than 26 mEq/ L indicates metabolic alkalosis.
Types of acid-base imbalances • Respiratory acidosis: This is a condition in which decreased respiration (hypoventilation) causes increased arterial carbon dioxide and decreased pH. Causes include airway obstruction, pneumonia, and respiratory failure. • Respiratory alkalosis: This is a medical condition in which increased respiration (hyperventilation) elevates the blood pH. The PaCO2 is decreased. Causes include asthma, anxiety, salicylate overdose. • Metabolic acidosis: Results from high acid concentration in the blood, which also causes a loss of sodium bicarbonate. Causes include starvation, diabetes ketoacidosis (DKA), and renal failure. • Metabolic alkalosis: Results from heavy loss of acid from the body or increased levels of bicarbonate. Causes include vomiting and use of drugs (steroids, diuretics).
Effect of Different Solutions on Blood Cells • Isotonic solutions: (Sodium chloride concentration is equal to that of blood, 0.9%). Cells in isotonic solution are normal in size and shape because the same amount of water is entering and leaving them. • Hypotonic solutions: (Sodium chloride concentration is less than that of blood). In these solutions, water moves into the cells, causing them to swell and burst. • Hypertonic solutions: (Sodium chloride concentration is greater than that of blood). Cells in the hypertonic solution are losing water because water moves from a weaker concentration inside the cell to a greater concentration outside the cell membrane.
