# IV Administration – Dosage Calculation

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Keith Rischer, RN Talk about chapter 13….alternate way to do problems. Dimensional analysis advantages – conversions can be included in the problem.

Alternate Methods Dosage Calc.
Formula Ratio proportion Dimensional analysis Talk about chapter 13….alternate way to do problems. Remember in 3,2 1 calc, you have options to see problems calculated using all three methods. Formula: D X Q = X H D - dose ordered, H – dose on hand Q – quantity that contains the dose on hand We have used this method successfully to figure out oral med dosages, and we will use it again to figure out IV Push meds. Ratio Proportion: used to convert (like mg to grams) and also to determine oral med dosages. Ratio of dose on hand (on label) = ratio for desired dose (MD order) EX: order- 500 mg amoxicillan 250 mg = 500 mg Available – 250 mg/capsule 1 capsule X cap X cap = 500 mg 250 mg X = 2 cap Formula method: mg X 1 cap = X Dimensional analysis: advantages – conversions can be included in the problem. One stop shopping! Conversions needed are included on right side of equation – you must set up the equation so that all units cancel except for the one you are seeking! SEE notes on examples of dimensional analysis.

IV solutions Administered in plastic bags/bottles
Administered continuously and/or intermittently Components: Water Glucose(dextrose) Saline Electrolytes Salts Intravenous (IV) fluids come in plastic solution bags and glass bottles ranging from 50 mL to 1000 mL or more. Components of IV solutions vary depending on the need replace fluids maintenance of fluids and electrolyte balance admin. Of meds nutritional support – they are administered continuously and/or intermittently Bolus – solution over a short period of time IV push – medication given using a syringe (pain med) Made up of water, glucose (dextrose), saline, electrolytes, and salts. Is specified combinations and concentrations.

IV solutions Labeled Letters – solution components
Numbers – concentration LR – Lactated Ringers NS: Normal Saline 0.9% NaCl D5W – 5% Dextrose in water = 5 g dextrose / 100 ml solution D5 NS with 20 mEq KCL The IV fluid is labeled using special abbreviations and notations. The letters indicate the solution components and the numbers indicate the concentration or solution strength. It is important to understand that when you administer IV fluids, you are not just giving fluid but different solutes or electrolytes such as dextrose. DEXTROSE AND NACL MOST COMMON IV COMPONENTS D5W – 5% dextrose in water = components are 5 g/ 100 ml of water In 1000 ml bag of D5W – how many grams of dextrose will be contained in it? (ans.= 50 grams) = Isotonic solution = 252 mOsmol/L D5LR – 5% dextrose in Lactated Ringers = 5 g dextrose in 100 ml and lactated ringers(contains specific amounts of K, NaCL, Cacl, Lactate. hypertonic solution = 525 mOsmol/L Often you will see electrolytes added in pharmacy like potassium

IV Solution Label Calculate components: D5 0.45% NS in 1000 mL

Tonicity of IV Solutions
Hypotonic Isotonic Hypertonic 0.9 NS D5W LR ½ (0.45%) NS ¼ (0.225%) NS D5 ½ NS D5 NS D5 LR 3% NS CHOICE OF IV SOLUTIONS DRIVEN BY PATIENT NEEDS AND CURRENT LYTES Hypotonic - < 250 mOsmol/L – dilute excess serum electrolytes Lower tonicity ½ NS ¼ NS Isotonic – mOlmol/L – expand volume and maintain tonicity Same tonicity as blood and body serums .9 NS D5W LR Hypertonic > 375 mOlmol/L – to correct electrolyte imbalances, as in loss from excess vomiting and diarrhea Higher tonicity D5 ½ NS D5NS D5LR 3%NS

Calculating Flow Rates IV Pumps
Total mL ordered = mL per hour Total hours ordered Vancomycin 1000 mg (250 mL) IV over 2 hours by infusion pump Vancomycin 750 mg (250 mL) IV over 1.5 hours Order  Give Vancomycin 250 mL over the next two hours by infusion pump Remember this: Infusion pumps only calibrate in mL/hr. There are pumps that infuse using more sophisticated mechanisms such as IV heparin can be infused in units…but for our purposes we will be using pumps which infuse in mL per hour.  Step 1:think Pump is set by the rate of mL per hour So, if 250 mL is to be infused in two hours, how much will be infused in one hour? 125 mL will be infused in one hour You would set the pump at 125 mL per hour Step 2: Use the formula Therefore set the pump at 125 ml/hr Step 2 Use the formula Step 2: Use the formula:

IV Flow Rate in mL per hour: Infusion Rate is less than 1 hour
Total mL ordered X 60 min/hr = mL/hr Total min ordered Order: Ampicillin 500 mg IV in 50 mL NS over 30 minutes Give Amiodarone 150mg in 100 ml of D5W over 10 minutes (rounded to a whole number)

Setting Flow Rates for Manually Regulated IVs
Adjusting the rate by hand Counts drops per minute Use the roller clamp to adjust rate When an electronic infusion device is not used, the nurse must set and adjust the IV rate by hand.  The nurse counts the number of drops per minute in the drip chamber to set the rate of the IV. The roller clamp is the part of the IV tubing that regulates the flow. It is located below the drip chamber farther down on the tubing. To increase the flow rate, the roller clamp is rolled upward or opened.  The roller clamp is rolled downward or closed to decrease the rate.

Calculating flow rates - Manually
Formula method V X C (gtt factor) = R T Volume (mL) X drop factor (gtt per mL)= Rate (gtt/min) Time (min) Physician orders: D5W IV at 125 mL/hr. The IV infusion set is calibrated with a drop factor of 10 gtt/mL. Calculate the IV flow rate Physician orders: 0.9 NS IV at 75 mL/hr. Carry calculations to one decimal Round drops per minute to the nearest whole number Watch Count only whole drops Answer 20.8 gtts=21 gtts/minute Rischer rule-divide by ¼-5 drops every 15 seconds…1 gtt every 3 seconds

Calculating gtts per/minute
Once gtts/minute determined... Divide this total by a factor of 4 20 gtts/minute… 5 gtts every 15 seconds 12 gtts/minute… 3 gtts every 15 seconds How many gtts every 15 seconds?... Divide the gtts determined by 15 (seconds) This will be the seconds between each gtt 5 gtts every 15 seconds 15/5= x seconds 3 gtts every 15 seconds 15/3= x seconds

Calculation of Drops per min: Microdrip Drop Factor
Volume (mL) X drop factor (gtt per mL)= Rate Time (min) Order: D5 NS IV at 50 mL per h Drop factor is 60 drops per mL Calculate gtt/min Notice order, 50 mL per hour, is the same as the flow rate of 50 drops per min when drop factor is 60 drops per mL

Drop Factor Constants Drop Factor Drop Factor Constant 10 drops per mL

Drop Factor Constants Physician orders: D5W IV at 125 mL/hr 6
10 gtts/mL manual infusion set 125 mL=20.8 gtt/minute or 21 gtts 6 Physician orders: 0.9 NS IV at 75 mL/hr. 75mL= Only works with hourly rates not less than 1 hour

Adjusting IV Flow Rate Check for institutional policy regarding correcting off-schedule IV rates and the percentage of variation allowed Variation should not exceed 25 percent % variation will be positive (+) if administration is slow and rate has to be increased Negative () if administration is too fast and rate has to be decreased Sometimes rate is changed due to: gravity, condition of patient or movement. It helps to avoid problems with IV being off schedule if the IV is monitored every 30 min to 1hour. Tape bag with where it should be every hour to assess if on track Safe rule of thumb when adjustment is necessary: rate per minute can be adjusted by 25% or less. (percent variation) Check with MD, hospital policy, and use good nursing judgment. You do not want to overhydrate or underhydrate your patient or significantly alter the electrolyte balance in a negative manner

Follow three steps: Remaining volume = recalculated mL/h Remaining hours V X C (gtt factor) = R T Adjusted gtt per min – ordered gtt per min = % variation Ordered gtt per min If adjustment of the rate is permitted, then use the following formulas to recalculate the flow rate of an IV and determine the percent of variation: Next, the new rate is used to recalculate the drops per minute. Last, to figure out the percent of variation, which is how much the IV is off schedule, the original drops per minute rate is subtracted from the new drops per minute rate. NS 125 ml/hr over 8 hours (1000ml) After 4 hours 600ml remaining

Calculation of IV Flow Rate Adjustment
Order: 500 mL LR to run over 10 hours at 50 mL per hour Drop factor is 60 drops per mL and IV is correctly infusing at 50 drops per min After 2 hours, 300 mL is remaining Almost half of total volume infused in one-quarter the time

Calculation of IV Flow Rate Adjustment
IV infusion is ahead of schedule Compute a new rate of 300 mL to complete IV fluid order in remaining 7 hours Patient would require close assessment for fluid overload

Calculation of IV Flow Rate Adjustment

Calculation of IV Flow Rate Adjustment
Adjusted gtt per min – ordered gtt per min Ordered gtt per min 40 – 50 = = = - 20%

The physician orders 1000 mL of D5 0.45% NS at 100 mL per hour over 10 hours. Drop factor-10 gtt per mL What is the initial correct gtt/minute How many gtts/15 seconds…1 gtt every __ secs. After 5 hours only 300 mL has infused. The IV is behind schedule. Calculate the new flow rate. Is this new rate acceptable? Gtts/minute-16.6-round to 16/minute 4 gtts every 15 seconds…appx 1 gtt 4 seconds 700ml/5 remaining hours=140 ml 140/6 gtt factor=23.3 or 24 gtts/minute 24gtts-16gtts=8 16 gtts original rate…..8/16=50% difference…too high

IV Push Injections Use same calculations as other parenteral injections IMPORTANT – Follow manufacturer or hospital guidelines for rate of administration Dosage calculations for IV push injections are the same as calculations for other parenteral injections. When giving medications IV push, it is important to follow the manufacturer or hospital guidelines for the rate of administration.

IV Push Rate Calculation
Dosage Desired Quantity (available form) IV Push Rate Time Supply Dosage Recommended

Calculation of IV Push Rate
Order: Furosemide (Lasix) 40 mg IV Push stat x1 Supply: Furosemide 10 mg per mL with drug literature guidelines of “IV infusion not to exceed 20 mg over 1 minute”

Calculation of IV Push Rate
How much Furosemide should you prepare? Step 1. Convert No conversion is necessary Step 2. Think You want to give more than 1 mL

Calculation of IV Push Rate
How much Furosemide should you prepare? Step 3. Calculate

Calculation of IV Push Rate
What is a safe infusion time? Use the formula: D X Q = X H 40 mg X 1 min = 2 minutes 20 mg 2 minutes

Calculation of IV Push Rate
How much should you infuse every 15 seconds? Push Factor Constant 4 per minute 15 seconds = 1/4 60 seconds 4 mL over 2” Push factor is 8 (4x2”=8) Volume mL=0.5 mL push every 15 seconds Push Factor

Calculation of IV Push Rate
Order: Dilantin 100 mg IV now Supply: Dilantin 50 mg per mL with drug literature guidelines of “the infusion rate should not exceed 50 mg per min”. How much should you prepare? What is safe infusion time? How much should you infuse every 15 seconds? 2 ml 2 minutes 0.25 ml every 15 seconds