Metric System and Conversions

Basic Metric System Conversions

• Metric system relies on powers of 10 for straightforward conversions
• Kilo (k) means thousand (1,000), with a factor of ×1,000; e.g., 1 kg = 1,000 g
• Hecto (h) means hundred (100), with a factor of ×100; e.g., 1 hL = 100 L
• Deca (da) means ten (10), with a factor of ×10; e.g., 1 dag = 10 g
• Gram (g), Liter (L), and Meter (m) are Base Units, with a factor of 1
• Deci (d) means tenth (0.1), with a factor of ÷10; e.g., 1 dL = 0.1 L
• Centi (c) means hundredth (0.01), with a factor of ÷100; e.g., 1 cm = 0.01 m
• Milli (m) means thousandth (0.001), with a factor of ÷1,000; e.g., 1 mg = 0.001 g
• Micro (µ) means millionth (0.000001), with a factor of ÷1,000,000; e.g., 1 µg = 0.000001 g
• Mnemonic to remember the order: "King Henry Died By Drinking Chocolate Milk" (Kilo, Hecto, Deca, Base, Deci, Centi, Milli)
• To go to a larger unit, divide by 10 per step
• To go to a smaller unit, multiply by 10 per step

Medical Math Mnemonics & Shortcuts

• "Move Three Rule" simplifies common conversions
• kg to g: Move decimal three places to the right (1 kg = 1,000 g)
• g to mg: Move decimal three places to the right (1 g = 1,000 mg)
• mg to mcg: Move decimal three places to the right (1 mg = 1,000 mcg)
• Reverse direction to convert mcg to mg (move decimal three places to the left)

"Dr. D.A." for Medication Dosage Calculations

• Desired Dose: The required amount
• Reference Dose: What is available
• Dose Available: Concentration on hand
• Amount to Give: The final calculated answer

Medication Dosage Calculation Formula

• (Desired Dose ÷ Dose on Hand) × Volume = Amount to Give
• Example: For an order of 500 mg with 250 mg per 5 mL on hand, use (500 mg ÷ 250 mg) × 5 mL to get 10 mL

IV Drip Rate Calculation

• "Vicious Dogs Bite" helps determine IV drip rate
• To calculate drops per minute (gtt/min): (Volume (mL) × Drop Factor (gtt/mL)) ÷ Time (min) = gtt/min
• Example: 1,000 mL NS over 4 hours with a 15 gtt/mL set is (1000 × 15) ÷ 240 = 63 gtt/min

IV Flow Rate Calculation

• "Volume Over Time" determines IV flow rate
• To calculate IV flow rate: Volume (mL) ÷ Time (hr) = mL/hr
• Example: 500 mL over 4 hours is 500 ÷ 4 = 125 mL/hr

Pounds to Kilograms Conversion

• Method: "Divide by Two, Subtract a Tenth”
• Halve the weight in pounds
• Subtract 10% of the halved number
• Example: For 180 lbs, half is 90, 10% of 90 is 9, so 90 - 9 = 81 kg (actual is 81.6 kg)
• Quick estimate: Divide pounds by 2.2 (180 ÷ 2.2 = 81.8 kg)

Pediatric Weight Estimation

• Use for children ages 1-10 years: (Age × 2) + 8 = weight in kg
• Example: A 5-year-old's weight is estimated by (5 × 2) + 8 = 18 kg

Pediatric Medication Dosing Shortcut

• "One-Fifty-Fifty" assists in dosing
• 1 mg/kg for Epinephrine 1:10,000 in cardiac arrest cases
• 50 mg/kg for Dextrose administration
• 50 mg/kg for Diphenhydramine administration

Parkland Formula for Burn Patients

• Formula: 4 × TBSA% × Weight (kg) = total fluid in first 24 hours
• Administer half of the total fluid in the first 8 hours
• Administer the remaining half over the next 16 hours
• Example: For 40% burns on a 70 kg patient, 4 × 40 × 70 = 11,200 mL total fluid
• Give 5,600 mL in the first 8 hours, then 5,600 mL in the next 16 hours

"Rule of 9s" for Burn Percentage

• Head = 9%
• Each arm = 9% (4.5% front, 4.5% back)
• Each leg = 18% (9% front, 9% back)
• Torso (front) = 18%
• Torso (back) = 18%
• Perineum = 1%

Oxygen Tank Duration Calculation

• Formula: ((PSI - Safe Residual) × Cylinder Factor) ÷ Flow Rate (L/min) = Minutes Remaining
• Cylinder Factors:
  • D tank = 0.16
  • E tank = 0.28
  • M tank = 1.56
• Example: E tank at 2,000 psi, running at 10 L/min: ((2000 - 200) × 0.28) ÷ 10 = 50.4 minutes