Module 6: Agents Affecting the Volume and Ion Content of Body Fluids

Question 1

Isotonic Contraction

Answer 1

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

Question 2

Hypertonic Contraction

Answer 2

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 (0.45% sodium chloride) or fluids that contain no
solutes at all (D5W)
 Initial therapy: Drink water

Question 3

Hypotonic Contraction

Answer 3

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

Question 4

Volume Expansion

Answer 4

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

Question 5

Acid-Base Disturbances

Answer 5

Acid-base balance is maintained by multiple
systems:
 Bicarbonate-carbonic acid buffer system
 Respiratory system
* CO2 (increase lowers pH)
 Kidneys
* HCO3– (increase raises pH)

 Respiratory alkalosis
 Respiratory acidosis
 Metabolic alkalosis
 Metabolic acidosis

Question 6

Respiratory Alkalosis

Answer 6

Causes
 Hyperventilation causes decrease in CO2
 Treatment
 Mild: None needed
 More severe: Treat with sedatives (Diazepam
[Valium])

Question 7

Respiratory Acidosis

Answer 7

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 [pH <6.9]

Question 8

Metabolic Alkalosis

Answer 8

Causes
 Excessive loss of gastric acid
 Administration of alkalinizing salts

Treatment
 Target and treat cause
 Solution of sodium chloride plus potassium chloride

Question 9

Metabolic Acidosis

Answer 9

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

Question 10

Potassium

Answer 10

Most abundant intracellular cation
 Extracellular concentrations are low

Major role in:
 Conducting nerve impulses
 Maintaining the electrical excitability of muscle
 Regulating acid-base balance

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

Question 11

Hypokalemia

Answer 11

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 heart
 Hypokalemia increases risk for hypertension and
stroke

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
* Oral potassium chloride should be taken with meals or a full glass of water
* Dosages for prevention: 16 to 24 mEq/day
* Dosages for deficiency: 40 to 100 mEq/day

IV potassium chloride: Severe or cannot take PO
* Must be diluted and infused slowly
* Potassium must also be infused slowly (generally no faster than 10 mEq/hr in adults)
* Potassium chloride must never be administered by IV push
* Results in cardiac arrest

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

Question 12

Hyperkalemia

Answer 12

Causes
* Severe tissue trauma
* Untreated Addison’s disease
* Acute acidosis (draws potassium out of cells)
* Misuse of potassium-sparing diuretics
* Overdose with IV potassium

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

Treatment
 Withhold foods that contain potassium
 Withhold medicines that promote potassium accumulation:
Potassium-sparing diuretics, potassium supplements
 Counteract potassium-induced cardiotoxicity
 Lower extracellular levels of potassium
* Calcium salt (eg, calcium gluconate)
* Infusion of glucose and insulin
* If acidosis is present: Infusion of sodium bicarbonate
* Oral or rectal administration of sodium polystyrene sulfonate
[Kayexalate, Kionex]
* Peritoneal or extracorporeal dialysis

Question 13

Magnesium

Answer 13

Required for the activity of many enzymes
 Binding of messenger RNA to ribosomes
 Helps regulate neurochemical transmission and
the excitability of muscle

Question 14

Magnesium Imbalances: Hypomagnesemia

Answer 14

Hypomagnesemia
 Causes
* Diarrhea
* Hemodialysis
* Kidney disease
* Prolonged IV feeding
* Chronic alcoholism
* Hypermagnesemia

Prevention and treatment
* Magnesium oxide
* Magnesium sulfate
* IV

Adverse effects
* Neuromuscular blockade
* Suppressed impulse conduction through the atrioventricular (AV) node
* Respiratory paralysis at 12 to 15 mEq/L
* Cardiac arrest when magnesium levels exceed 25 mEq/L

Question 15

Mg Imbalances: Hypermagnesemia

Answer 15

Hypermagnesemia
 Most common in patients with renal insufficiency
 Especially when patient uses magnesium-containing
antacids or cathartics
 Symptoms of mild intoxication: Muscle weakness,
hypotension, sedation, and ECG changes
 Respiratory paralysis: Plasma levels of 12 to 15 mEq/L
 Higher magnesium concentrations: Risk of cardiac arrest
 Muscle weakness and paralysis can be counteracted with IV calcium