Calculations *** Flashcards
1 tsp (t) =
5 mL
1 tbsp (T) =
15 mL
1 fl oz =
30 mL
1 cup =
8 oz, 240 mL
1 pint =
16 oz, 480 mL
1 quart =
2 pints, 960 mL
1 gallon =
4 quarts, 3,840 mL
1 kg =
2.2 lbs
1 oz =
28.4 g
1 lb =
454g
1 grain (gr) =
65 mg
1 inch =
2.54 cm
1 meter =
100 cm
ratio relationships
4:8 = 4/8 = 1/2
ex: 2:3 = 2 parts + 3 parts = 5 total parts, use ratios to fine out what 1 part is and then multiply by 2 and 3 to find the amount of drug in each ratio segment
Order of Operations
B-PEMDAS
-brackets –> parenthesis –> exponents –> multiplication and division –> addition and subtraction
corrected phenytoin level formula
(total phenytoin) / (0.2 * albumin) + 0.1
Precent Strength *
–> % W/V = g/100 mL (solid mixed into a liquid)
–> % V/V = mL/100 mL (liquid mixed into a liquid)
–> % W/W = g/100 g (solid mixed into a solid
Common IV Fluids
–> NA = 0.9% (W/V) NaCl
- 1/2 NS = 0.45% (W/V) NaCl
- 1/4 NS = 0.225 (W/V) NaCl
–> D5W = 5% (W/V) dextrose in water
–> D20W = 20% dextrose in water
Ratio Strength
-most multi-step calculations will require converting ratio strength to percentage strength. If a ratio strength is presented in a problem, convert it to a percentage strength and convert it back if needed
-Ratio strength –> percentage strength
% strength = 100/ratio strength
-Percentage strength –> ratio strength
ratio strength = 100/% strength
Parts per million
PPM –> Percentage strength
- move the decimal left 4 places
Percentage strength –> PPM
-move the decimal right 4 places
Specific gravity
-ratio of the density of a substance to the density of water
–> water has a specific gravity of 1
–> < 1 = lighter than water
–> > 1 = heavier than water
SG = g/mL
Dilutions and Concentrations equation
Q1C1 = Q2C2
Osmolarity formula
(wt (g/L)/MW (g/mole) * # of particles * 1,000
Isotonicity, E value equation
E = (58.5) (i) / (MW of drug)(1.8)
once the E value is determined, what are the 3 steps to follow when doing isotonicity problems
1) calculate the total amount of Nacl needed to make the final product/rx isotonic by multiplying 0.9% NS by desired volume of the rx
2) calculate the amount of NaCL represented by the drug. - multiply the total drug amount (in ml or grams) by the E value
3) subtract step 2 from step 1 to determine the total amount of NaCl needed to prepare an isotonic rx
moles and millimoles equations
mols: g/MW
mmols: mg/MW
Milliequivalents formula
mEq = mg* valence/MW
calorie sources in enteral and parenteral admin*
Carbs:
-Enteral: 4 kcal/gram
-Parenteral: 3.4 kcal/gram (glycerol: 4.3)
Fat:
-Enteral: 9 kcal/gram
-Parenteral: product specific ( 10% = 1.1, 20%=2, 30% =3)
Protein:
-Enteral: 4 kcal/gram
-Parenteral: 4 kcal/gram
Fluid requirement determination when pt is > 20 kg
fluid requirement = 1500 mL + [(20 mL)(weight in kg - 20)]
Determining Caloric needs: BEE and TEE
BEE (males) = 66,37 + 13.75(wt in kg) + 5(ht in cm) - 6.76(age)
BEE (females) = 655.1 + 9.6(wt in kg) + 1.85(ht in cm) - 4.68(age)
TEE= BEE * activity factor * stress factor
Protein Requirements
Non-hospitilized/non-stressed: 0.8-1 g/kg/day
Hospitalized/malnourished: 1.2-2 g/kg/day
Nitrogen intake formula
= grams of protein / 6.25
Non-protein Calories to Nitrogen Ratio
1) calculate the grams of nitrogen supplied per day ( 1 g N = 6.25 g of protein)
2) then divide the total non-protein calories (dextrose + lipids) by the grams of nitrogen
Desirable NPC:N ratios:
- 80:1: the most severely stressed patients
-100:1: severely stressed patients
-150:1: unstressed patients
Amino Acid Calculation
protein source = 4 kcal/gram
Carbohydrates calculation
Eternal: 4 kcal/gram
Parenteral: 3.4 kcal/gram
Fat Calculations
EN: 9 kcal/gram
PN: 10% = 1.1 kcal, 20% = 2 kcal, 30% = 3 kcal
Corrected Calcium formula
*calculate when albumin is LOW
= calcium + [(4-albumin)(0.8)]
Calcium and phosphate solubility
-choose calcium gluconate over calcium chloride b/c it has a lower risk of precipitation with phosphates
-add phosphate first, after the dextrose and amino acids
—> the calcium and phosphate added together should not exceed 45 meq/L
Drug + nutrient interactions with enteral feeding
–> hold feedings 1 hr before and 1-2 hrs after feedings
-Warfarin: enteral products bind to warfarin = dec INR, hold feedings 1 hr before and 1-2 hrs after feedings
-Tetracyclines, quinolones, levothyroxine: will chelate with cations; separate from tube feeds
-Ciprofloxacin: oral suspension is oil based + not compatible; crush IR tabs and mix that way
-Phenytoin: levels are reduced when drug binds to feeding solution, separate from tube feeds by 2 hrs
Body Mass Index (BMI) equations
= [weight (kg)] / [height (m)^2]
=[weight (lbs)] / [height(in)^2] * 703
25-29.9 = overweight
>/ 30 = obese
Formulas for Ideal Body Weight
Males: 50 kg + (2.3 kg)(# inches over 5 feet
Female: 45.5 kg + (2.3)(# inches over 5 feet)
Adjusted Body Weight formula
= IBW + 0.4(TBW- IBW)
Which weight to use for drug dosing: underweight
-TBX < IBW
–> use TBW for ALL medications
Which weight to use for drug dosing: normal weight
TBW = IBW (or < 120% of IBW)
–> use TBW for MOST medications
–> *use IBW for aminophylline, thepphyline and acyclovir
Which weight to use for drug dosing: Obese
TBW >/ 120% of IBW
–> *use IBW for aminophylline, thepphyline and acyclovir
–> use TBW for LMWHs, UFH, and vancomycin
–> use adjusted body weight for aminoglycosides
Flow rates step by step example
1) 1st fraction is the drug concentration (400 mg/250 mL)- since we are usually solving for ml/hr –> put the ml on top
2) 2nd fraction converts the drug weight from mg to mcg (1 mg/ 1000 mcg)
3) 3rd fraction is the rate of administration (x mcg/min or hr)
4) 4th fraction is to convert min to hr if needed
Renal function and Crcl estimation
-as kidney function declines, the level of Scr increases
–> BUN: Scr ratio > 20:1 = dehydration
(figure out by BUN/Scr = X:1)
Interpreting ABGs*
1: is it an acidosis or alkalosis?
–> low ph: acidosis
–> high ph: alkalosis
2: What other lab values are abnormal?
–> Respiratory:
- low Co2 = alkalosis
-high Co2 = acidosis
–> Metabolic:
-high HCO3: alkalosis
-low HCO3: acidosis
3: Match pH with abnormal lab value in step 2:
EX: loc pH, high CO2 & normal HCO3: respiratory acidosis
4: ex: low pH, low CO2 and low HCO3
–> match w/ pH and the other one is the compensated part)
= metabolic acidosis with respiratory compensation
respiratory opposite, metabolic equal
Anion gap formula and interpretation
AG: Na- Cl- HCO3
AG > 12 = + anion gap acidosis
–> CUTE DIMPLES (cyanide, uremia, toluene, ethanol, diabetic ketoacidosis, isoniazid, methanol, propylene glycol, lactic acidosis, ethylene glycol, salicylates) = causes of a gap acidosis
Buffer Systems and Ionization
-if the pH > pKa, more of the acid is ionized, and more of the conjugate based is UN-ionized
-if the pH = pKa, the ionized and un-ionized forms are equal
-if the pH < pKa, more of the acid is un-ionized, and more of the conjugated base is ionized.
Weak acid and weak base formulas*
Weak acid:
-pH = pKa + log (salt/acid)
Weak base:
-pH = (14- pKb) + log (base/salt)
Percent Ionization equations*
Weak acid:
= 100 / 1 + 10 ^ (pka - ph)
Weak base:
100 / 1+ 10 ^ (ph- pka)
Drug conversions: calcium carbonate and calcium citrate*
-calcium carbonate: 40% elemental Ca
-calcium citrate: 21% elemental Ca
Drug conversions: Aminophyline to theophylline *
A –> T : Multiply by 0.8
T –> A: Divide by 0.8
Absolute Neutrophil Count (ANC) formula*
ANC = WBC * [(% neut + % bands) / 100]
Normal ANC = 2200 - 8000
Neutropenia = < 1000
Severe Neutropenia = < 500
Profound neutropenia = < 100
