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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5854_Библиотеки_им_академика_М_И_Перельмана
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endocrine processes, and balanced output via the kidneys, lungs, skin,
and the gastrointestinal system.
In clinical practice, fluid and electrolyte therapy are undertaken either
to provide maintenance requirements or to replace serious losses or
deficits. Body losses of water and/or electrolytes can result from a
number of causes, including vomiting, diarrhea, profuse sweating, fever,
chronic renal failure, diuretic therapy, surgery, and others. The type of
therapy undertaken (i.e., oral or parenteral) and the content of the fluid
administered depend on a patient’s specific requirements.
For example, a patient taking diuretics may simply require a daily
oral potassium supplement along with adequate intake of water. An
athlete may require rehydration with or without added electrolytes.
Hospitalized patients commonly receive parenteral maintenance therapy
of fluids and electrolytes to support ordinary metabolic function. In
severe cases of deficit, a patient may require the prompt and substantial
intravenous replacement of fluids and electrolytes to restore acute volume
losses resulting from surgery, trauma, burns, or shock.
The composition of body fluids generally is described with regard to
body compartments: intracellular (within cells), intravascular (blood
plasma), or interstitial (between cells in the tissue). Intravascular and
interstitial fluids commonly are grouped together and termed
extracellular fluid. The usual reference ranges of electrolytes in blood
plasma are shown in Table 12.2. Although all electrolytes and
nonelectrolytes in body fluids contribute to osmotic activity, sodium and
chloride exert the principal effect in extracellular fluid, and potassium
and phosphate predominate in intracellular fluid.
Because cell membranes generally are freely permeable to water, the
osmolality of the extracellular fluid (about 290 mOsmol/kg water) is
about equal to that of the intracellular fluid. Therefore, the plasma
osmolality is a convenient and accurate guide to intracellular osmolality
and may be approximated by the formula5:
where sodium (Na) concentration is in mEq/L, and blood urea nitrogen
(BUN) and glucose concentrations are in mg/100 mL (mg/dL).
Example Calculation of Plasma Osmolality
Estimate the plasma osmolality from the following data: sodium, 135
mEq/L; blood urea nitrogen, 14 mg/dL; and glucose, 90 mg/dL.
CALCULATIONS CAPSULE
Milliequivalents, Millimoles, and Milliosmoles
To calculate milliequivalents (mEq), use the following conversion:
where “valence” is the total valence of the cation or anion in the
compound.
To calculate millimoles (mmol), use the following conversion:
To calculate milliosmoles (mOsmol), use the following conversion:
where “number of species produced by dissociation” is one for
substances that do not dissociate, two for substances that dissociate
into two ions, three for substances that dissociate into three ions, and
so on.
Osmolarity (mOsmol/L) is the total number of milliosmoles of
solute(s) per liter of solution.
CASE IN POINT 12.3
A
A hospital pharmacist fills a medication order calling for an
intravenous fluid of dextrose 5% in a 0.9% sodium chloride injection
and 40 mEq of potassium chloride in a total volume of 1000 mL. The
intravenous infusion is administered through an IV set that delivers 15
drops per milliliter. The infusion has been running at a rate of 12 drops
per minute for 15 hours.
During the 15-hour period:
a. How many mEq of KCl have been administered?
b. How many grams of KCl have been administered?
c. How many millimoles of KCl have been administered?
d. What is the total osmolarity of the intravenous fluid?
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Problem courtesy of Flynn Warren, Bishop, GA.
PRACTICE PROBLEMS
Calculations Based on Millimoles, Micromoles, and
Milliequivalents
Convert blood plasma range of 11 to 25 mcmol/L of copper (m.w.
= 63.55) to mcg/mL.
A preparation contains, in each milliliter, 236 mg of dibasic
potassium phosphate (m.w. = 174.18) and 224 mg of monobasic
potassium phosphate (m.w. = 136.09). Calculate the total
concentration of phosphate, in mmol/mL, and potassium, in
mEq/mL, in the preparation.
6
A 10-mL ampul contains 2.98 g of potassium chloride. What is the
concentration of the solution in milliequivalents per milliliter?
A 154-lb patient is to receive 36 mg/kg of ammonium chloride.
How many milliliters of an ammonium chloride (NH4Cl—m.w.
53.5) injection containing 5 mEq/mL should be added to the
patient’s intravenous infusion?
A sterile solution of potassium chloride contains 2 mEq/mL. If a
20-mL vial of the solution is diluted to 1 liter, what is the
percentage strength of the resulting solution?
A certain electrolyte solution contains, as one of the ingredients,
the equivalent of 4.6 mEq of calcium per liter. How many grams of
calcium chloride dihydrate (CaCl2 · 2H2O—m.w. 147) should be
used in preparing 20 liters of the solution?
Ammonium chloride injection contains 267.5 mg of NH4Cl (m.w.
53.5) per milliliter. How many mEq of ammonium chloride are
present in a 20-mL vial?
A solution contains, in each 5 mL, 0.5 g of potassium acetate
(C2H3KO2—m.w. 98), 0.5 g of potassium bicarbonate (KHCO3—
m.w. 100), and 0.5 g of potassium citrate monohydrate (C6H5K3O7
· H2O—m.w. 324). How many milliequivalents of potassium (K+)
are represented in each 5 mL of the solution?
How many grams of sodium chloride should be used in preparing
20 liters of a solution containing 154 mEq/L?
Sterile solutions of potassium chloride containing 5 mEq/mL are
available in 20-mL containers. Calculate the amount, in grams, of
potassium chloride in the container.
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How many milliliters of a solution containing 2 mEq of potassium
chloride per milliliter should be used to obtain 2.98 g of potassium
chloride?
A patient is given 125 mg of phenytoin sodium (C15H11N2NaO2—
m.w. 274) three times a day. How many milliequivalents of sodium
are represented in the daily dose?
If a 40-mL vial of sodium chloride is added to a 1-L container of
water for injection, calculate the concentration of sodium chloride,
in mEq/mL in the original vial, if the resultant dilution is 0.56% in
strength.
How many grams of sodium bicarbonate (NaHCO3—m.w. 84)
should be used in preparing a liter of a solution to contain 44.6
mEq per 50 mL?
A liter of an electrolyte solution contains the following: 131 mEq
Na+, 111 mEq Cl−, 5 mEq K+, 29 mEq C3H5O
3
−
(lactate), and 4
mEq Ca2+. Convert each of these values to mmol/L.
Sterile sodium lactate solution is available commercially as a 1/6-
molar solution of sodium lactate in water for injection. How many
milliequivalents of sodium lactate (C3H5NaO3—m.w. 112) would
be provided by a liter of the solution?
A certain electrolyte solution contains 0.9% of sodium chloride in
10% dextrose solution. Express the concentration of sodium
chloride (NaCl) in terms of milliequivalents per liter.
How many milliequivalents of potassium chloride are represented
in each prescribed dose?
How many milliequivalents of potassium are in 5 million units of
penicillin V potassium (C16H17KN2O6S—m.w. 388)? One
milligram of penicillin V potassium represents 1380 penicillin V
units.
The normal potassium level in the blood plasma is 17 mg/dL.
Express this concentration in terms of milliequivalents per liter.
How many grams of potassium citrate (C6H5K3O7 · H2O—m.w.
324) should be used in preparing 500 mL of a potassium ion elixir
so as to supply 15 mEq of K in each 5-mL dose?
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A potassium supplement tablet contains 2.5 g of potassium
bicarbonate (KHCO3—m.w. 100). How many milliequivalents of
potassium (K+) are supplied by the tablet?
Ringer’s injection contains 0.86% of sodium chloride, 0.03% of
potassium chloride, and 0.033% of calcium chloride dihydrate.
Calculate the sodium, potassium, calcium, and chloride content in
mEq/L.
Calculate the mEq of Na+ in each gram of ampicillin sodium
(C16H18N3NaO4S—m.w. 371).
A 20-mL vial of concentrated ammonium chloride solution
containing 5 mEq/mL is diluted to 1 liter with sterile distilled
water. Calculate (a) the total milliequivalent value of the
ammonium ion in the dilution and (b) the percentage strength of the
dilution.
If a liter of an intravenous fluid contains 5% dextrose and 34 mEq
sodium (as NaCl), calculate the percent strength of sodium chloride
in the solution.
How many milliequivalents of potassium would be supplied daily
by the usual dose (0.3 mL three times a day) of saturated potassium
iodide solution? Saturated potassium iodide solution contains 100 g
of potassium iodide per 100 mL.
An intravenous solution calls for the addition of 25 mEq of sodium
bicarbonate. How many milliliters of 8.4% w/v sodium bicarbonate
injection should be added to the formula?
Calcium gluconate (C12H22CaO14—m.w. 430) injection 10% is
available in a 10-mL vial. How many milliequivalents of Ca2+ does
the vial contain?
A flavored potassium chloride packet contains 1.5 g of potassium
chloride. How many milliequivalents of potassium chloride are
represented in each packet?
How many milliequivalents of Li+ are provided by a daily dose of
four 300-mg tablets of lithium carbonate (LITHOBID) (Li2CO3—
m.w. 74)?
Magnesium chloride is available as magnesium chloride
hexahydrate in an injectable solution that supplies 1.97 mEq of
magnesium per milliliter. What is the percent strength of
magnesium chloride hexahydrate in this solution?
A patient is to receive 10 mEq of potassium gluconate (C6H11KO
7
—m.w. 234) four times a day for 3 days. If the dose is to be one
teaspoonful in a cherry syrup vehicle, (a) how many grams of
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potassium gluconate should be used and (b) what volume, in
milliliters, should be dispensed to provide the prescribed dosage
regimen?
A physician wishes to administer 1,200,000 units of penicillin G
potassium every 4 hours. If 1 unit of penicillin G potassium
(C16H17KN2O4S—m.w. 372) equals 0.6 mcg, how many
milliequivalents of K+ will the patient receive in a 24-hour period?
Five milliliters of lithium citrate syrup contain the equivalent of 8
mEq of Li+. Calculate the equivalent, in milligrams, of lithium
carbonate (Li2CO3—m.w. 74) in each 5-mL dose of the syrup.
How many milligrams of magnesium sulfate (MgSO4—m.w. 120)
should be added to an intravenous solution to provide 5 mEq of
Mg2+ per liter?
K-TAB, a slow-release potassium chloride tablet, contains 750 mg
of potassium chloride in a wax/polymer matrix. How many
milliequivalents of potassium chloride are supplied by a dosage of
one tablet three times a day?
An electrolyte solution contains 222 mg of sodium acetate
(C2H3NaO2—m.w. 82) and 15 mg of magnesium chloride (MgCl
2
—m.w. 95) in each 100 mL. Express these concentrations in
milliequivalents of Na+ and Mg2+ per liter.
An antacid combination liquid contains 520 mg of calcium
carbonate and 400 mg of magnesium carbonate in each teaspoonful
dose. If a patient takes two teaspoonfuls after every meal, how
many milliequivalents of calcium and magnesium is she receiving
per day assuming that she eats three meals per day?
A patient has a sodium deficit of 168 mEq. How many milliliters of
isotonic sodium chloride solution (0.9% w/v) should be
administered to replace the deficit?
A normal 70-kg (154-lb) adult has 80 to 100 g of sodium. It is
primarily distributed in the extracellular fluid. Body retention of 1
g additional of sodium results in excess body water accumulation
of approximately 310 mL. If a person retains 100 mEq of extra
sodium, how many milliliters of additional water could be expected
to be retained?
A patient receives 3 liters of an electrolyte fluid containing 234 mg
of sodium chloride (NaCl—m.w. 58.5), 125 mg of potassium
acetate (C2H3KO2—m.w. 98), and 21 mg of magnesium acetate
(Mg(C2H3O2)2—m.w. 142) per 100 mL. How many
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milliequivalents each of Na+, K+, and Mg2+ does the patient
receive?
Magnesium citrate laxative solution (CITROMA) contains 1.745 g
of magnesium citrate per fluid ounce of solution. Express the
concentration of magnesium in this solution as milliequivalents per
milliliter.
The usual adult dose of calcium for elevating serum calcium is 7 to
14 mEq. How many milliliters of a calcium gluconate injection,
each milliliter of which provides 9.3 mg of elemental calcium,
would provide the recommended dosage range?
The oral pediatric maintenance solution PEDIALYTE liquid has
the following electrolyte content per liter: sodium, 45 mEq;
potassium, 20 mEq; and chloride, 35 mEq. Calculate the equivalent
quantities of each in terms of milligrams.
Calculate the milliequivalents of chloride per liter of the following
parenteral fluid:
The pediatric infusion rate for potassium is 5 mEq/h. If 9 mL of a
39.2% solution of potassium acetate (KC2H3O2) is diluted to 1 L of
infusion solution, calculate the proper infusion rate in mL/h.
GOLYTELY, a colon lavage preparation, contains the following
mixture of dry powder in each bottle to prepare four liters of
solution:
Calculate the milliequivalents each of sodium and chloride present
in the prepared solution.
PHOSPHA 250 NEUTRAL tablets contain 852 mg dibasic sodium
phosphate anhydrous, 155 mg monobasic potassium phosphate, and
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130 mg monobasic sodium phosphate monohydrate in each tablet.
Determine the amount, in milliequivalents, of sodium and
potassium in each tablet and the amount, in millimoles, of
phosphate in each tablet.
TPN ELECTROLYTES solution contains the electrolytes shown
below.
a. How many milliequivalents of sodium are contained in 5 mL of
this solution?
b. Express the concentration of magnesium chloride as mmol/mL.
Calculations Including Milliosmoles
At 3:00 PM, a pharmacist received an order to add 30 mEq/L of
potassium chloride to the already running intravenous fluid for a
patient. After checking the medication order, the pharmacist found
that the patient is receiving a 5% dextrose/0.9% sodium chloride
infusion at a rate of 85 mL/h and that the patient’s liter of fluid was
started at 1:30 PM.
7
a. Assuming that it took 30 minutes to provide the needed potassium
chloride to the floor nurse, how many milliequivalents of
potassium chloride should have been added to the patient’s
running IV fluid to achieve the ordered concentration?
b. How many milliliters of an injection containing 2 mEq of
potassium chloride/mL should have been used to supply the
amount of potassium chloride needed?
c. What was the osmolarity of the infusion with the potassium
chloride added? Assume complete dissociation of the sodium
chloride and potassium chloride.
A solution contains 322 mg of Na+ ions per liter. How many
milliosmoles are represented in the solution?
A solution of sodium chloride contains 77 mEq/L. Calculate its
osmolar strength in terms of milliosmoles per liter. Assume
complete dissociation.
Calculate the osmolarity, in milliosmoles per liter, of a parenteral
solution containing 2 mEq/mL of potassium acetate (KC2H3O2—
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m.w. 98).
Calculate (a) the milliequivalents per milliliter, (b) the total
milliequivalents, and (c) the osmolarity of a 500-mL parenteral
fluid containing 5% w/v of sodium bicarbonate.
What is the osmolarity of an 8.4% w/v solution of sodium
bicarbonate?
A hospital medication order calls for the administration of 100 g of
mannitol to a patient as an osmotic diuretic over a 24-hour period.
Calculate (a) how many milliliters of a 15% w/v mannitol injection
should be administered per hour and (b) how many milliosmoles of
mannitol (m.w. 182) would be represented in the prescribed dosage.
What would be the osmolarity of 500 mL of a solution containing
5% w/v dextrose, 0.3% w/v sodium chloride, and 30 mEq of
potassium acetate?
Magnesium citrate laxative solution (CITROMA) contains 1.745 g
of magnesium citrate per fluid ounce of solution. Calculate the
osmolarity of this solution.
What would be the osmolarity of 1000 mL of a solution containing
10% w/v dextrose, 0.225% w/v sodium chloride, and 15 mEq of
calcium gluconate?
How many (a) millimoles, (b) milliequivalents, and (c)
milliosmoles of calcium gluconate (Ca(C6H11O7)2—m.w. 430) are
represented in 15 mL of a 10% w/v calcium gluconate solution?
The information for a cardioplegic solution states that each 100 mL
of solution contains calcium chloride dihydrate USP 17.6 mg,
magnesium chloride hexahydrate USP 325.3 mg, potassium
chloride USP 119.3 mg, and sodium chloride USP 643 mg, in water
for injection USP. The information also gives electrolyte content
per liter (not including ions for pH adjustment) as sodium (Na+)
110 mEq, magnesium (Mg2+) 32 mEq, potassium (K+) 16 mEq,
calcium (Ca2+) 2.4 mEq, and chloride (Cl−) 160 mEq. Osmolar
concentration 304 mOsmol/liter (calc.).8 Calculate the labeled
concentrations to determine their accuracy.
NAUZENE contains in each tablespoonful dose 4.17 g of fructose
(m.w. = 180), 921 mg of sodium citrate dihydrate, and 4.35 g of
dextrose. (a) What would be the osmolarity of this solution? (b) If a
patient ingests the maximum daily dose of 120 mL of NAUZENE,
how many milliequivalents of sodium would he ingest?
Estimate the plasma osmolality, in milliosmoles per kilogram, from
the following data: sodium, 139 mEq/L; blood urea nitrogen, 26
mg/100 mL; and glucose, 100 mg/dL.
65.
A patient undergoes a CHEM-7 blood test with the following
results:
Estimate the plasma osmolality for this patient.
CALCQUIZ
NOTE: In solving the following problems, refer to Table 12.3 as
needed.
12.A. A veterinarian ordered a liter of Hartmann’s Irrigation (lactated
Ringer’s irrigation) with the following formula:
Calculate the mEq/L of Na+, K+, Ca2+, Cl−, and C3H5O
3
−
.
12.B. Calculate the content of Hartmann’s Irrigation in mOsmol/L.
12.C. A multiple electrolytes injection (PLASMA-LYTE 148)
contains the following electrolytes in each 100 mL:
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