CLINICAL CALCULATIONS NURS 1510

Equivalents of Measurements Metric: decimal system, most logically organized. Each unit is organized into units of 10. In X the decimal moves to the “R”; in division it moves “L” Basic measurement=meter(L), liter(volume), gram(weight) In medication calculations only volume and weight are used. Each unit is organized into units of 10 . In multiplication the decimal moves to the r , in division it moves to the left

Basic units: Deci 1/10 or 0.1 Centi 1/100 or 0.01 Milli 1/1000 or 0.001 500mg or 0.5g, not 1/2g 10ml or 0.01L, not 1/100L With fractions the zero is always place in front of the decimal to prevent error

Conversion in One System In metric system, division or multiplication are used, ie, to change mg to g. divide by 1000 or move the decimal 3 points to the left To convert liters to ml, multiply by 1000 or move the decimal 3 points to the right

To convert units of measurement within the apothecary or household system, must know the equivalent. Example: To convert ounces to quarts must know 32 oz is = to 1 quart To convert 8 oz to a quart measurement, divide 8 by 32 to get the equivalent, ¼ or 0.25 quart

Setting Up the Calculations When looking at a medication order, ask yourself 3 questions: What did the MD order? (desired quantity) What do I have on hand? (dose available) What conversion factor (conversion do I need? factor)

The desired quantity is the MD order, (10mg, v gr) The dose available is found on the drug label, (tablet, number of capsules, ml) *Remember, the quantity of tablets, capsules, or ml is always the numerator of the dose available; the amount (or dosage) is in the denominator

To decide which equivalent measure should be in the numerator and which should be in the denominator, look at the units of measure in the desired quantity. The units of measure in the desired quantity should be in the denominator of the conversion factor (i.e.,if the desired quantity is 100 mg and the equivalent conversion factor is 1000 mg = 1 g, then the conversion factor in fraction form should be 1 g / 1000mg

Formula Desired quantity x Dose available X Conversion (if factor needed) = Amount to Administer This is a simple formula that uses ratio and proportions which will help you both correctly set up and solve dosage calculation problems Set up your problem first then perform the arithmetic. I n the end, always remember to go back and assess your answers when you’re finished: does it make logical sense? Double check with others.

MD order: ASA 300 mg q4h prn pain Drug label: ASA 1 tab = v gr Conversion factor: 1 gr = 60 mg 5gr x 1 tab x 60 mg = x 300mg 1 gr 5 x 1 tab x 60 = 300 tab = x 300 300

continued 300 tab = x 300 x = 1 tab

More Formulas Another basic formula that can be used when preparing solid or liquid forms: Desire dose X Amt on hand = Amt to give dose Have Demerol 50 mg ordered comes in 100 mg vial in I cc Dose ordered over Dose on hand x amount on hand = amount to give

Rate of infusions Amount in cc’s X drip factor = gtt/min time in minutes

Conversions to know 1 gram (G) = 1000 milligrams (mg) 1000 micrograms (mcg) = 1 mg 60-65 mg = 1 grain (gr) 1 fluid ounce = 30 ml or 2 tablespoons 1 teaspoon = 5 ml 1000 ml = 1 quart or 1 liter 1 kg = 2.2 pounds (lb) 1 inch = 2.54 cm