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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.
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.
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.
The subcategories of volume contraction are
- isotonic contraction
- hypertonic contraction
- hypotonic contraction
Volume expansion may be subclassified as
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.
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.
Causes of isotonic contraction include:
vomiting, diarrhea, kidney disease, and misuse of diuretics.
Lost volume should be replaced with fluids that are what in comparison to plasma.
- This can be accomplished by infusing isotonic (0.9%) sodium chloride in sterile water, a solution containing both sodium and chloride.
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.
Causes of hypertonic contraction include:
excessive sweating, osmotic diuresis, and feeding excessively concentrated foods to infants.
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.
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.
The principal cause of hypotonic contraction is:
excessive loss of sodium through the kidneys.
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.
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.
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.
The principal drugs used to correct volume expansion are:
diuretics and the agents used for heart failure.
Potassium is the (most/least) abundant (ICF/ECF) (Anion/Cation)?
most abundant intracellular cation
Potassium plays a major role in:
- conducting nerve impulses and maintaining the electrical excitability of muscle.
- Potassium also helps regulate acid-base balance.
Serum levels of potassium are regulated primarily by what organ?
- the kidneys
- Under steady-state conditions, urinary output of potassium equals intake.
Renal excretion of potassium is increased by:
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.
Potassium depletion can be treated with:
- potassium salts.
- The preferred salt is potassium chloride.
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.
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.
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.
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.
Low levels of magnesium may result from a variety of causes:
including diarrhea, hemodialysis, kidney disease, and prolonged intravenous feeding with magnesium-free solutions.
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.
hypomagnesemia may lead to what condition in what organ?
nephrocalcinosis (formation of minuscule calcium stones within nephrons) in the kidneys
Frank hypomagnesemia is treated with:
parenteral magnesium sulfate
Toxic elevation of magnesium levels is most common in patients with:
renal insufficiency, especially when magnesium-containing antacids or cathartics are used.
Symptoms of mild magnesium intoxication include:
muscle weakness (resulting from inhibition of acetylcholine release), hypotension, sedation, and electrocardiographic changes.
Higher magnesium concentrations pose a risk of: