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Chapter 42

Chapter 42. Agents Affecting the Volume and Ion Content of Body Fluids. Drugs to Correct Disturbances. Drugs used to correct disorders of fluid volume and osmolality Drugs used to correct disturbances of hydrogen ion concentration Drugs used to correct electrolyte imbalances.

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Chapter 42

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  1. Chapter 42 Agents Affecting the Volume and Ion Content of Body Fluids

  2. Drugs to Correct Disturbances • Drugs used to correct disorders of fluid volume and osmolality • Drugs used to correct disturbances of hydrogen ion concentration • Drugs used to correct electrolyte imbalances

  3. Agents Affecting the Volume and Ion Content of Body Fluids • Disorders of fluid volume and osmolality • Acid-base disturbances • Potassium imbalances • Magnesium imbalances

  4. Fluid Volume and Osmolality • Good health requires that both the volume and the osmolality of extracellular and intracellular fluids remain within a normal range • Maintenance of both is primarily the job of the kidneys • Volume contraction and volume expansion

  5. Volume Contraction and Volume Expansion • Volume contraction • Decrease in total body water • Definition, causes, and treatment • Isotonic, hypertonic, and hypotonic • Volume expansion • Increase in total body water • Definition, causes, and treatment • Isotonic, hypertonic, and hypotonic

  6. Isotonic Contraction • Definition • Volume contraction in which sodium and water are lost in isotonic proportions • Decrease in total volume, but no change in osmolality • Causes • Vomiting, diarrhea, kidney disease, and misuse of diuretics • Treatment • Fluids that are isotonic to plasma • 0.9% NS • Replenish slowly to prevent pulmonary edema

  7. Hypertonic Contraction • Definition • Loss of water exceeds loss of sodium • Reduced extracellular fluid volume and increase in osmolality • Causes • Excessive sweating, osmotic diuresis, concentrated food given to infants • Secondary to extensive burns or CNS disorders that interfere with thirst • Treatment • Hypotonic fluids or fluids that contain no solutes at all (D5W) • Initial therapy: drink water

  8. Hypotonic Contraction • Definition • Loss of sodium exceeds loss of water • Both volume and osmolality of extracellular fluid are reduced • Causes • Excessive loss of sodium through the kidney (diuretic therapy, chronic renal insufficiency, lack of aldosterone) • Treatment • Mild: infusing isotonic sodium chloride solution for injection • Severe: hypertonic solution (3%) NaCl • Watch for signs of fluid overload

  9. Volume Expansion • Definition • Increase in the total volume of body fluid • May be isotonic, hypertonic, hypotonic • Causes • Overdose with therapeutic fluids • Disease states (congestive heart failure [CHF], nephrotic syndrome, cirrhosis with ascites) • Treatment • Diuretics • Agents used for heart failure

  10. Acid-Base Disturbances • Acid-base balance is maintained by multiple systems • Bicarbonate–carbonic acid buffer system • Respiratory system • CO2 (increase lowers pH) • Kidneys • HCO3– (increase raises pH)

  11. Acid-Base Disturbances • Respiratory alkalosis • Respiratory acidosis • Metabolic alkalosis • Metabolic acidosis

  12. Respiratory Alkalosis • Causes • Hyperventilation causes decrease in CO2 • Treatment • Mild: none needed • More severe: rebreathe CO2-laden expired breath

  13. Respiratory Acidosis • Causes • Retention of CO2 secondary to hypoventilation • Depression of the medullary respiratory center • Pathologic changes in the lungs • Treatment • Correction of respiratory impairment • Infusion of sodium bicarbonate if severe

  14. Metabolic Alkalosis • Causes • Excessive loss of gastric acid • Administration of alkalinizing salts • Treatment • Solution of sodium chloride plus potassium chloride

  15. Metabolic Acidosis • Causes • Chronic renal failure • Loss of bicarbonate during severe diarrhea • Metabolic disorders • Poisoning by methanol and certain medications • Treatment • Correction of the underlying cause of acidosis • Alkalinizing salt if severe

  16. Potassium • Most abundant intracellular cation • Extracellular concentrations are low • Major role in: • Conducting nerve impulses • Maintaining the electrical excitability of muscle • Regulating acid-base balance

  17. Regulation of Potassium Levels • Primarily by the kidneys • Renal excretion increased by aldosterone • Excretion also increased by most diuretics • Potassium-sparing diuretics are the exception • Influenced by extracellular pH • Alkalosis potassium uptake enhanced • Acidosis potassium exits cells • Insulin has a profound effect on potassium level

  18. Hypokalemia • Serum potassium levels less than 3.5 mEq/L • Causes and consequences • Most common cause is treatment with a thiazide or loop diuretic • Less common: excessive insulin, alkalosis • Adverse effects on skeletal muscle, smooth muscle, blood pressure, and the heart • Hypokalemia increases the risk for hypertension and stroke

  19. Hypokalemia Treatment • Potassium salts preferred because chloride deficiency frequently coexists with hypokalemia • Oral potassium chloride: mild • Sustained-release version has fewer GI effects • Abdominal discomfort, nausea and vomiting, diarrhea • IV potassium chloride: severe or cannot take PO • Must be diluted and infused slowly

  20. Hypokalemia Treatment • Contraindications to potassium use • Avoid in patients who are predisposed to hyperkalemia • Severe renal impairment, use of potassium-sparing diuretics, hypoaldosteronism • Principal complication of hypokalemia is hyperkalemia • Assess renal function and changes in ECG ECG = electrocardiogram.

  21. Hyperkalemia • Excessive elevation of serum potassium • Causes • Severe tissue trauma • Untreated Addison’s disease • Acute acidosis (draws K out of cells) • Misuse of potassium-sparing diuretics • Overdose with IV potassium

  22. Hyperkalemia • Consequences • Disruption of the electrical activity of the heart • Earliest sign patient is in danger • Mild elevation (5–7): T wave heightens; PR prolonged • Severe elevation (8–9): cardiac arrest can occur • Noncardiac signs • Confusion, anxiety, dyspnea, weakness or heaviness of legs, numbness/tingling of hands/feet/lips

  23. Hyperkalemia • Treatment • Withhold foods that contain potassium • Withhold medicines that promote potassium accumulation • Counteract potassium-induced cardiotoxicity • Lower extracellular levels of potassium • Calcium gluconate • Infusion of glucose and insulin • If acidotic: infusion of sodium bicarbonate

  24. Magnesium • Required for the activity of many enzymes • Binding of messenger RNA to ribosomes

  25. Magnesium Imbalances • Hypomagnesemia • Causes • Diarrhea • Hemodialysis • Kidney disease • Prolonged intravenous feeding • Chronic alcoholism • Hypermagnesemia • Prevention and treatment • Magnesium gluconate and magnesium hydroxide • Magnesium sulfate

  26. Magnesium Imbalances • Hypermagnesemia • Most common in patients with renal insufficiency

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