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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5576_Библиотеки_им_академика_М_И_Перельмана
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FIGURE 13.1 A depiction of an intravenous fluid with an
administration set.
FIGURE 13.2 A typical intravenous infusion setup with a
piggybacked antibiotic. (Reprinted with permission from Lacher
BE. Pharmaceutical Calculations for the Pharmacy Technician.
Philadelphia, PA: Lippincott Williams & Wilkins; 2008.)
Intravenous infusions may be continuous or intermittent. In continuous
infusions, large volumes of fluid (i.e., 250 to 1000 mL), with or without
added drug, are run into a vein uninterrupted, whereas intermittent
infusions are administered during scheduled periods.2 The rapid infusion of
a medication into a vein is termed IV push and is usually conducted in 1 to
5 minutes depending upon the medication.
Critical care
By definition, critical care (or intensive care) is the specialized care of
patients whose conditions are life-threatening and who require
comprehensive care and constant monitoring. In the hospital, such care is
provided in an intensive care unit (ICU), a critical care unit (CCU), or an
intensive treatment (or therapy) unit (ITU). These units, staffed by
specially trained critical care physicians and nurses, utilize equipment and
medications expressly intended to treat critically ill pediatric and adult
patients. Clinical pharmacy services in the critical care setting have
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expanded dramatically over the years to provide pharmacokinetic services
and patient monitoring for drug efficacy and adverse drug reactions.3 Lists
of drugs used in providing critical care may be found in the references
cited.4,
5
Common Intravenous Infusion Solutions
Aqueous solutions of dextrose, sodium chloride, and lactated Ringer’s
injection are the most commonly used intravenous fluids. Table 13.1
describes the content of these solutions, which may be administered as such
or with additional drug or nutritional components.
Example calculations of basic intravenous
infusions
1. How many grams each of dextrose and sodium chloride are used to
prepare a 250-mL bag of D5½NS for intravenous infusion?
2. Calculate the milliequivalents of sodium and millimoles of dextrose in
the above solution.
3. A pharmacist prepared a liter of a 15% dextrose solution in sterile water
for injection using a dextrose injection, 700 mg/mL. How many
milliliters of the injection were required?
Example calculations of infusion administration
sets
1. Calculate the total drops in the delivery of 250 mL of an infusion when
using the following administration sets: (a) 15 drops/mL, (b) 20
drops/mL, and (c) 60 mcgtts/mL.
15 drops/mL × 250 mL = 3750 drops
20 drops/mL × 250 mL = 5000 drops
60 microdrops/mL × 250 mL = 15,000 microdrops
2. For each of the above, calculate the number of drops delivered each
minute if the infusion is to last 2 hours.
a. 15 drops/mL × 2.08 mL (per minute) = 31.2 or 31 drops/minute
b. 20 drops/mL × 2.08 mL = 41.6 or 42 drops/minute
c. 60 microdrops/mL × 2.08 mL = 124.8 or 125 microdrops/minute
Alternatively, the answers may be derived by dividing the total drops
delivered by each administration set by the delivery time of 120
minutes:
a. 3750 drops/120 minute = 31.25 or 31 drops/minute
b. 5000 drops/120 minute = 41.67 or 42 drops/minute
c. 15,000 microdrops/120 minute = 125 microdrops/minute
3. A rural patient is being transported by ambulance to a hospital 3 hours
away. During transport, the patient is to be infused with 750 mL of
normal saline injection. What would be the flow rate in mL/h, mL/min,
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and drops/min if an infusion set with a drop factor of 15 drops/mL is
used?
4. Compare (a) the number of drops and (b) the length of time, in minutes,
required to deliver 50-mL of intravenous solutions when using a
microdrip set, at 60 drops/mL, and a standard administration set, at 15
drops/mL, if in each case one drop is to be administered per second.
Microdrip set:
a. 60 drops/mL × 50 mL = 3000 drops
b. 3000 drops ÷ 60 drops/minute = 50 minutes
Standard set:
a. 15 drops/mL × 50 mL = 750 drops
b. 750 drops ÷ 60 drops/minute = 12.5 minutes
Or, by dimensional analysis:
Intravenous Push (IVP) Drug Administration
The rapid injection of intravenous medications, as in emergency or critical
care situations, is termed IV push, IVP, or sometimes a bolus dose. For the
most part, drugs administered by IV push are intended to quickly control
heart rate, blood pressure, cardiac output, respiration, or other life-
threatening conditions. Intravenous push medications frequently are
administered in a short time frame (from <1 to 5 minutes), but slowly
enough so as to not cause a too-rapid effect or damage to the veins. The safe
administration of a drug by IV push depends on precise calculations of dose
and rate of administration. When feasible, a diluted injection rather than a
highly concentrated one (e.g., 1 mg/mL vs. 5 mg/mL) may be administered
as an added safety precaution.
6
The IV push may be injected directly into a vein or into a portal of an
intravenous set. If the medication is administered via an administration set,
a second injection of saline may be used to “flush” or help to push the
medication into the bloodstream. A flush also may be used to clean an
infusion line before and/or after use. An example of an intravenous flush
syringe is shown in Figure 13.3.
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FIGURE 13.3 An intravenous flush syringe. (Courtesy and ©
Becton, Dickinson and Company.)
Example calculations of IV push drug
administration
1. A physician orders enalaprilat 2 mg IVP for a hypertensive patient. A
pharmacist delivers several 1-mL injections, each containing 1.25 mg
of enalaprilat. How many milliliters of the injection should be
administered?
Or, by dimensional analysis:
2. A physician orders midazolam hydrochloride 2 mg IV Stat. A pharmacist
delivers a vial containing midazolam hydrochloride 5 mg/mL. How
many milliliters should be administered?
Or, by dimensional analysis:
3. General guidelines in the treatment of severe diabetic ketoacidosis
include an initial bolus dose of 0.1 unit of insulin/kg IVP, followed by
an insulin drip. Calculate the bolus dose for a 200-lb patient.
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Special Considerations in Pediatric IV Infusion
Delivery
b
b
Although all calculations pertaining to drug dosage and administration must be performed with
100% accuracy, it must be emphasized that pediatric patients are most vulnerable to medication
errors, with often dire consequences. The report cited here underscores this point: Levine SR,
Cohen MR, Blanchard NR, et al. Guidelines for preventing medication errors in pediatrics.
Journal of Pediatric Pharmacology and Therapeutics 2001;6:427–443.
Medication error in pediatric patients is a special concern in institutional
practice.7 There is the ever-present need for weight-based dosing and highly
individualized dose calculations that must be diligently performed. A
reduction in errors has been achieved by the use of web-based calculators to
perform infusion calculations, use of a limited number of standardized drug
concentrations to prepare infusions (as noted later in this section), and the
utilization of smart-pump technology that reduces the number of human
calculations required in dose and rate-of-flow determinations.
Depending on the institutional protocol, a medication order for an
intravenous infusion for a 10-kg child may be stated as, for example,
“dopamine 60 mg/100 mL, IV to run at 5 mL/h to give 5 mcg/kg/min.” At
some institutions in which standardized drug products and established
protocols have been developed, the same medication order may be written
simply as “dopamine 5 mcg/kg/min IV” to provide equivalently accurate
drug dosing of the patient.8 This is because the standard solution of
dopamine used in the institution, containing 60 mg of dopamine in each 100
mL and run at 5 mL/h, would deliver the same dose of 5 mcg/kg/min to the
10-kg patient. Calculate it:
Because the 50 mcg/min are administered to a 10-kg child, the dose, per kg
per minute, is:
Or, by dimensional analysis:
All medication doses for pediatric patients, including those administered
intravenously, must be carefully determined from available literature and
reference sources.
In addition to medications administered by intravenous infusion to
pediatric patients, fluid and electrolyte therapy is especially important in the
clinical management of preterm and term neonates, particularly those with
extremely low birth weights who tend to have greater loss of water through
the skin, especially when they are maintained in a warm incubator.
9
Example calculations of pediatric infusions
1. Calculate the daily infusion volume of D10W to be administered to a
neonate weighing 3 lb. 8 oz. on the basis of 60 mL/kg/day.
2. Calculate the flow rate, in microliters per minute, for the above infusion.
3. Gentamicin sulfate, 2.5 mg/kg, is prescribed for a 1.5-kg neonate.
Calculate (a) the dose of the drug and, (b) when the drug is placed in a
50-mL IV bag, the flow rate, in mL/min, if the infusion is to run for 30
minutes.
a. 2.5 mg/kg × 1.5 kg = 3.75 mg gentamicin sulfate
b. 50 mL ÷ 30 minutes = 1.67 mL/minute
4. A neonate born at 32 weeks’ gestation weighs 2005 g and is transferred
to the hospital’s neonate intensive care unit with a diagnosis of sepsis.
Among the physician’s orders are aminophylline 5 mg/kg IV q6h,
cefotaxime 50 mg/kg q12h, and vancomycin 10 mg/kg q12h.
10
a. Calculate the initial dose of each drug, in milligrams.
b. If aminophylline injection, 25 mg/mL, is available, how many
milliliters of injection should be added to a 100-mL container of
D10W for IV infusion?
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