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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5334_Библиотеки_им_академика_М_И_Перельмана
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5. A 4-day-old neonate born at 35 weeks’ gestation and weighing 2210 g is
prescribed gentamicin, 4 mg/kg, in 60 mL/kg of D10W for intravenous
infusion.10 If a pediatric injection contains gentamicin, 10 mg/mL, how
many milliliters each of injection and D10W should be administered?
6. A 2-year-old child weighing 30 lb is hospitalized with severe respiratory
distress. Physicians’ orders include aminophylline 5 mg/kg in 50-mL
D5½NS to infuse over 60 minutes. If aminophylline injection, 25
mg/mL, is available, how many milliliters should be used in the
infusion?
Intravenous Admixtures
The preparation of an intravenous admixture involves the transfer of one or
more additives to a large-volume parenteral fluid. The additive may be
incorporated into the fluid in the pharmacy or at the patient’s bedside by
injecting the additive into a port of the intravenous line or by administering
by piggyback. Additives may include therapy-specific medications,
antibiotics, electrolytes, vitamins, trace minerals, and other agents. Figure
13.4 shows the transfer of an additive to a large-volume fluid prior to
administration.
FIGURE 13.4 A and B.The transfer of an additive to a largevolume parenteral solution.
Examples of calculations involving additives for pediatric patients were
provided earlier in this chapter and further examples are provided as
follows.
Example calculations of additives to intravenous
infusion solutions
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1. A medication order for a patient weighing 154 lb calls for 0.25 mg of
amphotericin B desoxycholate per kilogram of body weight to be added
to 500 mL of 5% dextrose injection. If the amphotericin B
desoxycholate is to be obtained from a constituted injection that
contains 50 mg/10 mL, how many milliliters should be added to the
dextrose injection?
2. An intravenous infusion is to contain 15 mEq of potassium ion and 20
mEq of sodium ion in 500 mL of 5% dextrose injection. Using
potassium chloride injection containing 6 g/30 mL and 0.9% sodium
chloride injection, how many milliliters of each should be used to
supply the required ions?
15 mEq of K+ ion will be supplied by 15 mEq of KCl, and 20 mEq of
Na+ ion will be supplied by 20 mEq of NaCl.
Or, solving by dimensional analysis:
3. A pharmacist working in a hospital pharmacy receives the following
order for an IV admixture:
Meperidine 320 mg in 100 mL NS
How many milliliters of a meperidine 100 mg/mL injection should be
used in preparing this IV admixture?
Rate of Flow of Intravenous Fluids
On medication orders, the physician specifies the rate of flow of intravenous
fluids in milliliters per minute, drops per minute, amount of drug (as
milligrams per hour), or, more frequently, as the approximate duration of
time of administration of the total volume of the infusion. Pharmacists may
be called on to perform or check rate-of-flow calculations as those described
in some previous problem examples as well as those in this section.
Oftentimes, the following equation finds use in rate-of-flow
calculations:
In common usage are macro sets that deliver 10, 15, or 20 drops/milliliter
and microdrip or minidrip sets that deliver 60 drops/milliliter.
Examples of rate-of-flow calculations
1. A medication order calls for 1000 mL of D5W to be administered over
an 8-hour period. Using an IV administration set that delivers 10
drops/mL, how many drops per minute should be delivered to the
patient?
Or, solving by dimensional analysis:
Or, solving by the equation:
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2. Ten (10) milliliters of 10% calcium gluconate injection and 10 mL of
multivitamin infusion are mixed with 500 mL of a 5% dextrose
injection. The infusion is to be administered over 5 hours. If the
dropper in the venoclysis set calibrates 15 drops/mL, at what rate, in
drops per minute, should the flow be adjusted to administer the
infusion over the desired time interval?
Or, solving by dimensional analysis:
Or, solving by the equation:
3. An intravenous infusion contains 10 mL of a 1:5000 w/v solution of
isoproterenol hydrochloride and 500 mL of a 5% dextrose injection. At
what flow rate should the infusion be administered to provide 5 μg of
isoproterenol hydrochloride per minute, and what time interval will be
necessary for the administration of the entire infusion?
10 mL of a 1:5000 solution contains 2 mg.
2 mg or 2000 μg is contained in a volume of 510 mL.
Or, solving by dimensional analysis:
4. If 10 mg of a drug is added to a 500-mL large-volume parenteral fluid:
a. What should be the rate of flow, in milliliters per hour, to deliver 1 mg
of drug per hour?
b. If the infusion set delivers 15 drops/mL, what should be the rate of
flow in drops per minute?
Or, solving by dimensional analysis:
c. How many hours should the total infusion last?
5. A physician’s medication order calls for 800 mg of erythromycin to be
added to 100 mL of D5W for intravenous infusion over 60 minutes. The
source of erythromycin is a 1-g vial requiring dilution to 20 mL with
sterile water for injection before being added to the D5W. Calculate (a)
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the milliliters of the erythromycin dilution that should be added to the
D5W and (b) the rate of flow of the infusion, in milliliters per minute.
a.
b.
6. A physician’s medication order calls for 400 mg of clindamycin to be
added to 600 mL of D5W for intravenous infusion over 90 minutes.
Clindamycin is available as an injection containing 600 mg/4 mL. (a)
How many milliliters of the clindamycin injection should be used, (b)
how many mg/mL of clindamycin will the infusion contain, and (c) how
many milliliters per minute of the infusion should be delivered?
a.
b. Infusion = 600 mL (D5W) + 2.67 mL (clindamycin injection) =
602.67 mL
400 mg clindamycin/602.67 mL infusion = 0.66 mg/mL
clindamycin
c. 602.67 mL/90 min = 6.7 mL/min
7. A patient begins receiving 1000 mL of D5½NS solution at 8:30 AM at a
rate of 90 mL/h. At 3:00 PM an order is received in the hospital
pharmacy that says “Decrease IV fluids to 65 mL/h.” At what time
exactly should the next container of solution be started, assuming that
the rate on the existing container was changed at 3:00 PM?
Time elapsed: 8:30 AM – 3:00 PM = 6.5 hours
Volume remaining = 1000 mL − 585 mL = 415 mL
3 PM + 6 h 23 min = 9:23 PM
IV infusion rate calculations for the critical care
patient
Many patients, including those in critical care, require both a maintenance
fluid, such as D5W, and a therapeutic drug additive, such as an antibiotic
(see Fig. 13.2). However, many critical care patients have fluid restrictions
and must be maintained and treated within a stated maximum volume of
fluid intake per day. Thus, consideration must be given to the rate and
volumes of any infusions administered, including intravenous piggybacked
(IVPB) additives.
1. An order for a patient, with a 3-L daily IV fluid limit, calls for 3 L of
D5W with a 100-mL IVPB antibiotic to be run in alone over a 1-hour
period and administered every 6 hours. The administration set is
calibrated to deliver 10 drops/milliliter. Calculate the following:
a. The flow rate of the IVPB antibiotic
b. The total flow time for the IV antibiotic
c. The total volume for the IV antibiotic
d. The total flow time for the D5W
e. The total volume for the D5W
f. The flow rate for the D5W
Answers:
a.
b. 1 hour × 4 times a day = 4 hours or 240 minutes
c. 100 mL × 4 times a day = 400 mL
d. 24 hours – 4 hours (run time for the antibiotic) = 20 hours or 1200
minutes
e. 3000 mL – 400 mL (the IVPB antibiotic) = 2600 mL
f.
2. A physician’s order calls for the administration of dopamine 800 mg in
500 mL of D5W to be administered at 5 mcg/kg/min using an IV pump.
If the critical care patient weighs 130 lb, calculate the rate of flow of
the infusion in mL/h.
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Or,
3. A pharmacist prepares 250 mL of an infusion to contain 250 mg of
dobutamine for administration to a 190-lb patient. The rate of flow is
determined to be 34 mL/h. Calculate the rate of flow in mcg/kg/min.
Using a nomogram
A nomogram, such as that shown in Figure 13.5, may be used in
determining the rate of flow of a parenteral fluid. Given the volume to be
administered, the infusion time (duration), and the drops per milliliter
delivered by the infusion set, the rate of flow, in drops per minute, may be
determined directly.
FIGURE 13.5 Rate of flow versus quantity of infusion solution
versus time nomogram.
(Reprinted with permission from Diem K, Lentner C, Geigy JR. Scientific Tables. 7th Ed. Basel,
Switzerland: Ciba-Geigy; 1970. Copyright © Novartis AG.)
If 1 L of a parenteral fluid is to be infused over a 12-hour period using an
infusion set that delivers 20 drops/mL, what should be the rate of flow in
drops per minute?
First, locate the intercept of the diagonal line representing an infusion
time of 12 hours with the horizontal line representing 1 L of fluid. Next,
follow the point of the intercept down to the drop counter scale representing
“20 drops/mL” to determine the answer. In the example, the horizontal line
would be crossed between 20 and 30 drops/minute—closer to the 30 or
approximately 28 drops/minute.
As a check to the proper use of the nomogram, the preceding example
may be calculated as follows:
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