Some quick observations that made my life a bit easier when trying to calculate weight based dosages. Really pretty simple but once you reframe your mind this way it does tend to make life a bit easier.

Tip one: Use percentages instead of an absolute number.

• Example 1: 0.1mg/kg of a drug is really the same thing as saying 10% of patient’s weight in kg. So for example – you are ordered to give 0.1mg/kg of Morphine to a patient weighing 70 kilos – 10% of that is 7mg – simple.
• Example 2: 0.01mg/kg of a drug is the same as saying 1% of the patient’s body weight, which is also the same as saying 10% of 10% . So if you are ordered to give 0.01mg/kg of epinephrine to a 25 kilo patient yields… 10% is 2.5mg and 10% of that is 0.25mg – your dose.
• Example 3: 0.25mg/kg is the same as saying 25% of the patient’s weight. So if ordered to give 0.25mg/kg of diltiazem to an 80 kilo patient – your dose is simply 20mg

Tip two – drip rates

When you are trying to calculate your how fast to infuse your fluids, the following may be handy

• A 10gtts/ml drip set, set to one drip per second will yield 6ml per minute or 360 ml per hour,
• Increase the rate to two gtts per second and you are now running at 12ml per minute or 720ml/hr –

• (KVO rate is approximately one drip every two seconds which yields 3ml/min or 180ml/hr)

• You are ordered to give 2gm of mag sulfate in 50ml of NS over ten minutes. After adding the 2gm to the bag, you calculate as follows…I need to give the 50 ml over ten minutes which requires that I give 5ml per minute (50/10) so if one gtt/sec gets you 1ml/min – easy, you need 5 times that rate – or 5 gtts/sec to give your 50ml over ten minutes.

Pretty basic stuff that you may find helpful.

Sunday, October 26, 2008
Intro to Med Math

Order of operations

PEMDAS
Parenthesis
Exponents
Mult
Div
Add
Sub

(Please Excuse My Dear Aunt Sally)

——————-
lb/2.2= KG so 125lbs = 125/2.2=56.81

1ml = 1cc

% Solutions

% = G/100ml

Eg.
3% = 3G/100ml
First convert to your dose (mg in this case)
So… 3000mg/100ml reduce to 30mg/1ml


Bolus Calcs
Desired Dose/Dose On Hand = Volume to Admin or DD/DOH=VTA

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Some Conversions

• °C = (°F – 32) ÷ 1.8 For example: (68°F-32) ÷ 1.8 = (36) ÷ 1.8 = 20°C
• °F = (°C x 1.8) + 32 For example: (20°C x 1.8) + 32 = (36) + 32 = 68°F

g = gram
kg = kilogram (1,000g)
mg = milligram (¹/_1,000g)
mcg or µg = microgram (¹/_1,000,000g)

L or l = litre (or liter in US)
cl = centilitre (¹/₁₀₀ L)
ml = millilitre (¹/₁₀₀₀ L)
µl = microlitre (¹/_1,000,000 L)

2. kilo- hecto- deka- [unit] deci- centi- milli-

3. Each step is ten times or one-tenth as much as the step on either side

4. So… kilo(1000)- hector(100)- deka(10)- [unit] deci (1/10)- centi (100)- milli(1/1000)- micro(¹/_1,000,000)

See the rest here… http://www.purplemath.com/modules/metric.htm

Another good way to remember metric units

• King Henry Doesn’t [Usually] Drink Chocolate Milk