IV Administration – Dosage Calculation

1. IV Administration – Dosage Calculation Keith Rischer, RN

2. Alternate Methods Dosage Calc. Formula Ratio proportion Dimensional analysis

3. IV solutions Administered in plastic bags/bottles Administered continuously and/or intermittently Components: Water Glucose(dextrose) Saline Electrolytes Salts

4. 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

5. IV Solution Label • Calculate components: • D5 0.45% NS in 1000 mL • D10 ¼ NS in 500 mL

6. 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 Tonicity of IV Solutions

7. 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

8. 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 • Order: • Give Amiodarone 150mg in 100 ml of D5W over 10 minutes

9. Setting Flow Rates for Manually Regulated IVs Adjusting the rate by hand Counts drops per minute Use the roller clamp to adjust rate

10. Calculating flow rates - Manually Formulamethod 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. The IV infusion set is calibrated with a drop factor of 10 gtt/mL. Calculate the IV flow rate

11. 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

12. 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

13. Drop Factor Constants

14. Drop Factor Constants • Physician orders: D5W IV at 125 mL/hr • 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= 6

15. 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

16. Adjusting IV flow rates 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

17. 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

18. 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

19. Calculation of IV Flow Rate Adjustment Adjusted flow rate 1 1

20. Calculation of IV Flow Rate Adjustment Adjusted gtt per min – ordered gtt per min Ordered gtt per min 40 – 50 = -10 = -0.2 = - 20% 50 50

21. Adjusting IV flow rates • 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?

22. IV Push Injections Use same calculations as other parenteral injections IMPORTANT – Follow manufacturer or hospital guidelines for rate of administration

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

24. 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”

25. 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

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

27. 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

28. 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) Volume4 mL=0.5 mL push every 15 seconds Push Factor 8

29. 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?