Chapter 42
Agents Affecting the Volume and
Ion Content of Body Fluids
Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Drugs to Correct Disturbances
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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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Agents Affecting the Volume and Ion
Content of Body Fluids
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Disorders of fluid volume and osmolality
Acid-base disturbances
Potassium imbalances
Magnesium imbalances
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Fluid Volume and Osmolality
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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
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Volume Contraction and
Volume Expansion
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Volume contraction
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Decrease in total body water
Definition, causes, and treatment
• Isotonic, hypertonic, and hypotonic
Volume expansion
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Increase in total body water
Definition, causes, and treatment
• Isotonic, hypertonic, and hypotonic
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Isotonic Contraction
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Definition
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Causes
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Volume contraction in which sodium and water are lost in
isotonic proportions
Decrease in total volume, but no change in osmolality
Vomiting, diarrhea, kidney disease, and misuse of diuretics
Treatment
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Fluids that are isotonic to plasma
0.9% NS
Replenish slowly to prevent pulmonary edema
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Hypertonic Contraction
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Definition
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Causes
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Loss of water exceeds loss of sodium
Reduced extracellular fluid volume and increase in
osmolality
Excessive sweating, osmotic diuresis, concentrated food
given to infants
Secondary to extensive burns or CNS disorders that
interfere with thirst
Treatment
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Hypotonic fluids or fluids that contain no solutes at all (D5W)
Initial therapy: drink water
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Hypotonic Contraction
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Definition
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Causes
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Loss of sodium exceeds loss of water
Both volume and osmolality of extracellular fluid are reduced
Excessive loss of sodium through the kidney (diuretic
therapy, chronic renal insufficiency, lack of aldosterone)
Treatment
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Mild: infusing isotonic sodium chloride solution for injection
Severe: hypertonic solution (3%) NaCl
Watch for signs of fluid overload
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Volume Expansion
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Definition
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Causes
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Increase in the total volume of body fluid
May be isotonic, hypertonic, hypotonic
Overdose with therapeutic fluids
Disease states (congestive heart failure [CHF],
nephrotic syndrome, cirrhosis with ascites)
Treatment
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Diuretics
Agents used for heart failure
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Acid-Base Disturbances
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Acid-base balance is maintained by multiple
systems
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Bicarbonate–carbonic acid buffer system
Respiratory system
• CO2 (increase lowers pH)
Kidneys
• HCO3– (increase raises pH)
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Acid-Base Disturbances
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Respiratory alkalosis
Respiratory acidosis
Metabolic alkalosis
Metabolic acidosis
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Respiratory Alkalosis
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Causes
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Hyperventilation causes decrease in CO2
Treatment
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Mild: none needed
More severe: rebreathe CO2-laden expired breath
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Respiratory Acidosis
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Causes
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Retention of CO2 secondary to hypoventilation
• Depression of the medullary respiratory center
• Pathologic changes in the lungs
Treatment
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Correction of respiratory impairment
Infusion of sodium bicarbonate if severe
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Metabolic Alkalosis
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Causes
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Excessive loss of gastric acid
Administration of alkalinizing salts
Treatment
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Solution of sodium chloride plus potassium
chloride
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Metabolic Acidosis
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Causes
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Chronic renal failure
Loss of bicarbonate during severe diarrhea
Metabolic disorders
Poisoning by methanol and certain medications
Treatment
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Correction of the underlying cause of acidosis
Alkalinizing salt if severe
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Potassium
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Most abundant intracellular cation
Extracellular concentrations are low
Major role in:
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Conducting nerve impulses
Maintaining the electrical excitability of muscle
Regulating acid-base balance
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Regulation of Potassium Levels
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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
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Alkalosis potassium uptake enhanced
Acidosis potassium exits cells
Insulin has a profound effect on potassium
level
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Hypokalemia
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Serum potassium levels less than 3.5 mEq/L
Causes and consequences
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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
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Hypokalemia Treatment
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Potassium salts preferred because chloride
deficiency frequently coexists with
hypokalemia
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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
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Hypokalemia Treatment
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Contraindications to potassium use
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Avoid in patients who are predisposed to
hyperkalemia
• Severe renal impairment, use of potassium-sparing
diuretics, hypoaldosteronism
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Principal complication of hypokalemia is
hyperkalemia
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Assess renal function and changes in ECG
ECG = electrocardiogram.
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Hyperkalemia
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Excessive elevation of serum potassium
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Causes
• Severe tissue trauma
• Untreated Addison’s disease
• Acute acidosis (draws K out of cells)
• Misuse of potassium-sparing diuretics
• Overdose with IV potassium
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Hyperkalemia
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Consequences
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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
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Hyperkalemia
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Treatment
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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
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Magnesium
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Required for the activity of many enzymes
Binding of messenger RNA to ribosomes
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Magnesium Imbalances
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Hypomagnesemia
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Causes
• Diarrhea
• Hemodialysis
• Kidney disease
• Prolonged intravenous feeding
• Chronic alcoholism
• Hypermagnesemia
 Prevention and treatment
• Magnesium gluconate and magnesium hydroxide
• Magnesium sulfate
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Magnesium Imbalances
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Hypermagnesemia
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Most common in patients with renal insufficiency
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