Tiêu đề 15. FLUIDS AND ELECTROLYTES BALANCE.pdf ✅

PHARMD GURU Page 1 A. SODIUM (NA): 1) Sodium is the major cation of the extracellular fluid. Sodium, along with chloride (Cl), potassium (K), and water, is important in the regulation of osmotic pressure and water balance between Intracellular and extracellular fluids. Normal values: 135 to 147 mEq/L or mmol/L. 2) The sodium concentration is defined as the ratio of sodium to water, not the absolute amounts of either. Laboratory tests for sodium are used mainly to detect disturbances in water balance and body osmolality. The kidneys are the major organs of sodium and water balance. 3) An increase in sodium concentration (hypernatremia) may indicate impaired sodium excretion or dehydration. A decrease in sodium concentration (hyponatremia) may reflect over hydration, abnormal sodium loss, or decreased sodium intake. 4) Patients with kidney, heart, or pulmonary disease may have difficulty with sodium and water balance. In adults, changes in sodium concentrations most oft en reflect changes in water balance, not salt imbalances. Therefore, sodium concentration is oft en used as an indicator of fluid status, rather than salt imbalance. 5) Control of sodium by the body is accomplished mainly through the hormones aldosterone and antidiuretic hormone (ADH). a) ADH is released from the pituitary gland in response to signals from the hypothalamus. ADH’s presence in the distal tubules and collecting ducts FLUIDS AND ELECTROLYTES BALANCE
PHARMD GURU Page 2 of the kidney causes them to become more permeable to the reabsorption of water; therefore, concentrating urine. b) Aldosterone affects the distal tubular reabsorption of sodium as opposed to water. Aldosterone is released from the adrenal cortex in response to low sodium, high potassium, low blood volume, and angiotensin II. Aldosterone causes the spilling of potassium from the distal tubules into the urine in exchange for sodium reabsorption. 6) Hyponatremia is usually related to total body depletion of sodium—as in mineralocorticoid deficiencies, sodium-wasting renal disease, replacement of fluid loss with non-saline solutions, gastrointestinal (GI) losses, renal losses, or loss of sodium through the skin—or to dilution of serum sodium—as in cirrhosis, CHF, nephrosis, renal failure, excess water intake, or syndrome of inappropriate antidiuretic hormone (SIADH) secretion. 7) Hypernatremia usually results from a loss of free water or hypotonic fluid or through excessive sodium intake. Free water loss is most oft en associated with diabetes insipidus, but fluid loss can be via the GI tract, renal, skin, or respiratory systems. Excess sodium intake can occur through the administration of hypertonic intravenous (IV) solutions, mineralocorticoid excess, excessive sodium ingestion, or after administration of drugs high in sodium content (e.g., ticarcillin, sodium bicarbonate [HCO-3]). B. POTASSIUM (K): 1) Potassium is the most abundant intracellular cation (intracellular fluid potassium averages 141mEq/L). Approximately 3500 mEq of potassium is
PHARMD GURU Page 3 contained in the body of a 70-kg adult. Only 10% of the body’s potassium is extracellular. Normal values are 3.5 to 5.0 mEq/L or mmol/L. 2) The serum potassium concentration is not an adequate measure of the total body potassium because most of the body’s potassium is intracellular. Fortunately, the clinical signs and symptoms of potassium deficiency—malaise, confusion, dizziness, electrocardiogram (ECG) changes, muscle weakness, and pain— correlate well with serum concentrations. The serum potassium concentration is buffered by the body and may be ―normal‖ despite total body potassium loss. Potassium depletion causes a shift of intracellular potassium to the extracellular fluid to maintain potassium concentrations. There is approximately a 100 mEq total body potassium deficit when the serum potassium concentration decreases by 0.3 mEq/L. This may result in misinterpretation of serum potassium concentrations as they relate to total body potassium. 3) The role or function of potassium is in the maintenance of proper electrical conduction in cardiac and skeletal muscles (muscle and nerve excitability); it exerts an influence on the body’s water balance (intracellular volume) and plays a role in acid–base equilibrium. 4) Potassium is regulated by  Kidneys (renal function)  Aldosterone  Arterial P H  Insulin  Potassium intake  Sodium delivery to distal tubules. 5) Hypokalaemia can occur. The kidneys are responsible for approximately 90% of the daily potassium loss. Other losses occur mainly through the GI system. Even in states of no potassium intake, the kidneys still excrete up to 20 mEq of potassium daily. Therefore, prolonged periods of potassium deprivation can result in hypokalaemia. Hypokalaemia can also result from potassium loss
PHARMD GURU Page 4 through vomiting or diarrhoea, nasogastric suction, laxative abuse, and by diuretic use (mannitol, thiazides, or loop diuretics). Excessive mineralocorticoid activity and glucosuria can also result in hypokalemia. Potassium can be shifted into cells with alkalemia and after administration of glucose and insulin. 6) Hyperkalaemia most commonly results from decreased renal elimination, excessive intake, or from cellular breakdown (tissue damage, hemolysis, burns and infections). Metabolic acidosis may also result in a shift of potassium extracellularly as hydrogen ions move into cells and are exchanged for potassium and sodium ions. As a general guideline, for every 0.1 unit, pH change from 7.4, the potassium concentration will change by about 0.6mEq/L. If a patient has a pH of 7.1 and measured potassium of 4.5mEq/L, the actual potassium concentration would be: 0.3 (units < 7.4) x 0.6 = 1.8 Potassium concentration = 4.5 - 1.8 = 2.7 mEq/L. Correction of the acidosis in this situation will result in a dramatic decrease in potassium unless supplementation is instituted. C. CHLORIDE (CL): 1) Chloride is the major anion of the extracellular fluid and is important in the maintenance of acid–base balance. Alterations in the serum chloride concentration are rarely a primary indicator of major medical problems. Chloride itself is not of primary diagnostic significance. It is usually measured to confirm the serum sodium concentration. The relationship among sodium, chloride, and HCO-3 is described by the following: Cl- + HCO-3 + R = Na+ Where, R is the anion gap. The normal value for Cl is 95 to 105 mEq/L or mmol/L. 2) Hypochloremia is a decreased chloride concentration, and it is oft en accompanied by metabolic alkalosis or acidosis caused by organic or other acids. Other causes include chronic renal failure, adrenal insufficiency, fasting, prolonged diarrhoea, severe