Unit IX Calculating Medication Doses PROCEDURE Calculating Doses, 141 Flow Rates, and Administration of Continuous Intravenous Infusions Shelley Burcat and Maribeth Kelly PURPOSE: Calculation of doses and fl ow rates and administration of continuous intravenous (IV) infusions are performed to ensure accurate delivery of medications administered via the IV route. Many of the medications delivered via continuous IV infusion have potent effects and narrow margins of safety; therefore accuracy in calculation and administration of these agents is imperative. PREREQUISITE NURSING • Smart pumps are infusion pumps with comprehensive KNOWLEDGE libraries of medications and dose calculation software that can perform a “test of reasonableness” to check that pro- • Knowledge of aseptic technique is necessary. gramming is within preestablished institutional limits • Nurses must be aware of the indications, actions, side before the infusion can begin, which can reduce medica- effects, dosages, administration/storage, assessment, and tion errors, improve workfl ow, and provide a source of evaluation for medications administered. data for continuous quality improvement. 10 • Many different types of medications are delivered as con- • Use of smart infusion pumps with activated dosage error tinuous IV infusions in acute and critical care settings. reduction software alerts the nurse when safe doses and These medications include, but are not limited to, vasoac- infusion rates have been exceeded. 7 The nurse must use tive, inotropic, antidysrhythmic, sedative, and analgesic the technology consistently to avoid serious medication agents. infusion errors. 6 • Hemodynamic assessment and electrocardiographic • Be aware that double key bounce and double keying errors (ECG) monitoring are frequently necessary to evaluate the may occur when pressing a number key once on an infu- patient ’ s response to medication infusions. The nurse must sion pump, resulting in the unintended consequence of a be familiar with monitoring equipment such as cardiac repeat of that same number. This can result in infusing monitors, arterial catheters, pulmonary artery catheters, medications at a higher rate than expected. 5 and noninvasive blood pressure cuffs. • Three factors are involved in the calculations for continu- • Titration refers to the adjustment of the dose of a medica- ous IV infusions: tion, either increasing or decreasing, to attain the desired ❖ The concentration is the amount of medication diluted patient response. in a given volume of IV solution (e.g., 400 mg dopa- • Alterations or interruptions of the fl ow rate can signifi - mine diluted in 250 mL normal saline [NS] solution, cantly affect the dose of medication being delivered and resulting in a concentration of 1.6 mg/mL, or 2 g lido- adversely affect the patient. For accurate delivery of IV caine diluted in 500 mL 5% dextrose in water [D5 W], medications, volume-controlled infusion devices are yielding a concentration of 4 mg/mL). The concentra- required. tion is also expressed as amount of medication per • “Smart technologies” are electronic devices, such as com- milliliter of fl uid. puters, bedside monitors, and infusion pumps, that perform ❖ The dose of the medication is the amount of medication calculations of doses and fl ow rates after information is to be administered over a certain length of time (e.g., entered and programmed by the user. Although these dopamine 5 mcg/kg/min, lidocaine 2 mg/min, or diltia- devices are not universally available, their use may reduce zem 5 mg/hr). The units of measure for the dose differ medication errors. 4 for various medications. The length of time is 1 minute 1236 141 Calculating Doses, Flow Rates, and Administration of Continuous Intravenous Infusions 1237 or 1 hour. If the medication is weight based, the dose BOX 141-1 Basic Formula * of the medication is per kilogram of patient weight. ❖ The fl ow rate is the rate of delivery of the IV fl uid 1. To determine an unknown fl ow rate: solution expressed as volume of IV fl uid delivered per Dose() mg/hr or mcg/hr = Flow raate() mL/hr unit of time (e.g., 20 mL/hr). The unit of measure of Concentration() mg/mL or mcg/mL the fl ow rate is milliliter per hour. 2. To determine an unknown dose: • All units of measure in the formula must be the same. It Flow rate() mL/hr× Concentration ( mg/mL or mcg/mL ) frequently is necessary to perform some conversions on = Dose( mg/hr or mcg/hr) the concentration before entering it into the formula. The 3. To determine the concentration of drug in 1 mL of fl uid: units of measure of the concentration must be converted Total amount of drug() mg or mcg ()mg or mcg to the same units of measure of the dose (e.g., the concen- = Cooncentration tration of dopamine is measured in milligrams, but the Total volume of fluid() mL ()mL dose of dopamine is measured in micrograms). Example: When fl ow rate is unknown, diltiazem 125 mg/125 mL • The mathematical formula for continuous IV infusions D5 W to be administered at 10 mg/hr. uses three factors ( Box 141-1 ). When two factors are A. Calculate concentration of drug in 1 mL of fl uid: 125 mg 1mg known, the third can be calculated with the basic formula. = Therefore when the concentration of the solution and the 125 mL mL prescribed dose are known, the fl ow rate can be deter- B. Enter known factors into the formula and solve: Flow rate() mL/hr× Concentration ( mg or mcg/mL ) mined. When the concentration of the solution and the fl ow rate are known, the dose can be determined. Varia- = Dose( mg or mcgg/mL) 10 mL/hr tions on the basic formula are used to allow for medica- = 10 mL/hr tions delivered per hour or per minute and for medications 1mg/mL that are weight based ( Boxes 141-2 and 141-3 ). Example: When dose is unknown, diltiazem 125 mg/125 mL D5 W is • Calculations for weight-based medications include the infusing at 15 mL/hr. patient ’ s weight in the formula. The choice of which A. Calculate concentration of drug in 1 mL of fl uid: weight to use can be challenging. Much disagreement and 125 mg 1mg = inconsistency are found in the literature as to which weight 125 mL mL to use, ideal body weight, actual body weight, or dry body B. Enter known factors into the formula and solve: 2,7 weight. Distribution of specifi c medications across fat 15mL/hr×= 1 mg/mL 15 mg/hr and fl uid body compartments varies, thus affecting the therapeutic level. Because most medications are titrated * Because there are units on the top of the equation and units on the bottom of to patient response and a desired clinical endpoint, a con- the equation, to ensure that the fi nal units are correct, the units on the bottom sistent approach is to use the patient ’ s admission weight of the equation must be inverted and multiplied by the units of the top of the for initial dose calculations. The clinical pharmacist then equation. 1800 mcg/hr 9 ×mL should be consulted for obese patients and for medications Example: = = 9 mL/hr that have potentially dangerous toxicities. 200 mcg/mL hr • Central IV access should be used for vasoconstrictive medications and medications that can cause tissue damage when extravasated. 3 Mechanisms and agents that may cause tissue damage include osmotic damage from hyper- EQUIPMENT osmolar solutions, ischemic necrosis caused by vasocon- strictors and certain cation solutions, direct cellular • Prepared IV solution with medication to be administered toxicity caused by antineoplastic agents, direct tissue • IV tubing damage from pH strong acids and bases, and direct • IV infusion device irritation. 9 • Nonsterile gloves • The Joint Commission goal for medication safety includes • Alcohol pads standardization and limiting the number of drug concen- Additional equipment, to have available as needed, includes trations available in organizations. 11 Standardized dosing the following: methods for the same medications reduce IV infusion • Calculator errors. 7 • Medication compatibility table • The Institute of Healthcare Improvement (IHI) recom- mendations for IV medication safety include conducting PATIENT AND FAMILY EDUCATION independent double checks, dose calculation aids on IV solution bag labels, use of IV smart infusion pumps with • Explain the indications and expected response to the phar- safety features, and use of premade dose and fl ow-rate macological therapy. Rationale: Patients and families charts. 1 need explanations of the plan of care and interventions. • A review found there is insuffi cient evidence to suggest • Instruct the patient to report adverse symptoms, as indi- that medication errors are caused by nurses ’ poor calcula- cated. Reportable symptoms include, but are not limited tion skills. More research and direct observational studies to, pain, burning, itching, or swelling at the IV site; diz- are required to examine calculation errors in practice. 8 ziness; shortness of breath; palpitations; and chest pain. 1238 Unit IX Calculating Medication Doses BOX 141-2 Variation for Medication BOX 141-3 Variation for Weight-Based Doses Measured Per Minute Medication Doses Measured (mg/min or mcg/min) * Per Minute (mcg/kg/min)* 1. To determine unknown fl ow rate: 1. To determine unknown fl ow rate: Dose() mg/min or mcg/min× 60 min/hr Dose() mcg/kg/min××60 min/hr Patient weight () kg = Flow rate() mL/hr = Flow rate() mL/hr Concentration( mg/mL or mcg//mL) Concentration (mmcg/mL) 2. To determine unknown dose: 2. To determine unknown dose: Flow rate() mL/hr× Concentration ( mg/mL or mcg/mL ) Flow rate() mL/hr× Concentration ( mcg/mL ) = Dose() mcg/kg/min 60 min/hr 60 min/hr× Patient weigght() kg = Dosse() mg/min or mcg/min Example: When fl ow rate is unknown, dopamine 400 mg/250 mL Example: When fl ow rate is unknown, nitroglycerin 50 mg/250 mL D5 W to infuse at 5 mcg/kg/min.