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Drugs used to correct disturbances in the volume and ionic composition of body fluids can be divided into three groups:
- (1) drugs used to correct disorders of fluid volume and osmolality,
- (2) drugs used to correct disturbances of hydrogen ion concentration (acid-base status), and
- (3) drugs used to correct electrolyte imbalances.
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Maintenance of fluid volume and osmolality is primarily the job of what organ?
- the kidneys
- even under adverse conditions, renal mechanisms usually succeed in keeping the volume and composition of body fluids within acceptable limits.
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Abnormal states of hydration can be divided into two major categories:
- volume contraction and volume expansion.
- Volume contraction is defined as a decrease in total body water; conversely, volume expansion is defined as an increase in total body water.
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The subcategories of volume contraction are
- isotonic contraction
- hypertonic contraction
- hypotonic contraction
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Volume expansion may be subclassified as
- isotonic
- hypertonic
- hypotonic
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In the clinical setting, changes in osmolality are described in terms of:
- the sodium content of plasma.
- Sodium is used as the reference for classification because this ion is the principal extracellular solute.
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Isotonic contraction is defined as
- volume contraction in which sodium and water are lost in isotonic proportions.
- Therefore, although the total volume of extracellular fluid decreases, the osmolality does not change.
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Causes of isotonic contraction include:
vomiting, diarrhea, kidney disease, and misuse of diuretics.
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Lost volume should be replaced with fluids that are what in comparison to plasma.
- isotonic
- This can be accomplished by infusing isotonic (0.9%) sodium chloride in sterile water, a solution containing both sodium and chloride.
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Hypertonic contraction is defined as:
- volume contraction in which loss of water exceeds loss of sodium.
- Therefore, the extracellular fluid volume decreases and the osmolality increases.
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Causes of hypertonic contraction include:
excessive sweating, osmotic diuresis, and feeding excessively concentrated foods to infants.
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Volume replacement with hypertonic contraction should be accomplished with what type of fluid?
- hypotonic fluids (e.g., 0.11% sodium chloride) or with fluids that contain no solutes at all.
- Initial therapy may consist simply of drinking water.
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Hypotonic contraction is defined as volume contraction in which loss of sodium exceeds loss of water. In this case, both the volume and osmolality of extracellular fluid decrease.
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The principal cause of hypotonic contraction is:
excessive loss of sodium through the kidneys.
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If hyponatremia is mild and if renal function is adequate, hypotonic contraction can be corrected by:
- infusing isotonic sodium chloride solution.
- When this is done, plasma tonicity is adjusted by the kidneys.
- However, if the sodium loss is severe, a hypertonic (e.g., 3%) solution of sodium chloride should be infused.
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Volume expansion is defined as:
- an increase in the total volume of body fluid.
- As with volume contraction, volume expansion may be isotonic, hypertonic, or hypotonic.
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Volume expansion may result from:
- an overdose with therapeutic fluids (e.g., sodium chloride infusion), or
- it may be associated with disease states, such as heart failure, nephrotic syndrome, or cirrhosis of the liver with ascites.
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The principal drugs used to correct volume expansion are:
diuretics and the agents used for heart failure.
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Potassium is the (most/least) abundant (ICF/ECF) (Anion/Cation)?
most abundant intracellular cation
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Potassium plays a major role in:
- conducting nerve impulses and maintaining the electrical excitability of muscle.
- Potassium also helps regulate acid-base balance.
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Serum levels of potassium are regulated primarily by what organ?
- the kidneys
- Under steady-state conditions, urinary output of potassium equals intake.
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Renal excretion of potassium is increased by:
aldosterone.
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Hypokalemia is defined as a:
- deficiency of potassium in the blood.
- By definition, hypokalemia exists when the serum potassium level falls below 3.5 mEq/L.
- The most common cause is treatment with a thiazide or loop diuretic.
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Potassium depletion can be treated with:
- potassium salts.
- The preferred salt is potassium chloride.
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Potassium must be infused:
- slowly (generally no faster than 10 mEq/hr in adults).
- Potassium chloride must never be administered by IV push.
- Potassium chloride is one of the agents used in lethal injections, as this results in cardiac arrest.
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Hyperkalemia can result from a number of causes:
These include severe tissue trauma, untreated Addison’s disease, acute acidosis (which draws potassium out of cells), misuse of potassium-sparing diuretics, and overdose with IV potassium.
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The most serious consequence of hyperkalemia is:
- disruption of the electrical activity of the heart.
- Noncardiac effects include confusion, anxiety, dyspnea, weakness or heaviness of the legs, and numbness or tingling of the hands, feet, and lips.
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The treatment of hyperkalemia begins with:
- withdrawal of potassium-containing foods and drugs that promote potassium accumulation (e.g., potassium supplements, potassium-sparing diuretics).
- Subsequent measures include:
- (1) infusing a calcium salt to offset the cardiac effects of potassium
- (2) infusing glucose and insulin to promote potassium uptake by cells
- (3) infusing sodium bicarbonate if acidosis is present.
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Low levels of magnesium may result from a variety of causes:
including diarrhea, hemodialysis, kidney disease, and prolonged intravenous feeding with magnesium-free solutions.
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Prominent symptoms of hypomagnesemia involve:
- cardiac and skeletal muscle
- In the presence of low levels of magnesium, release of acetylcholine at the neuromuscular junction is enhanced.
- This can increase muscle excitability to the point of tetany.
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hypomagnesemia may lead to what condition in what organ?
nephrocalcinosis (formation of minuscule calcium stones within nephrons) in the kidneys
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Frank hypomagnesemia is treated with:
parenteral magnesium sulfate
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Toxic elevation of magnesium levels is most common in patients with:
renal insufficiency, especially when magnesium-containing antacids or cathartics are used.
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Symptoms of mild magnesium intoxication include:
muscle weakness (resulting from inhibition of acetylcholine release), hypotension, sedation, and electrocardiographic changes.
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Higher magnesium concentrations pose a risk of:
cardiac arrest
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