# Calculations

harshd's version from 2017-02-16 03:38

## Common Calcs

Corrected Ca (if Albumin <3.5)Ca.c = Ca.r + [(4.0 - Albumin) * (0.8)]
Phenytoin Correction (if Albumin <3.5)True Level = (Phenytoin measure (mcg/ml)) / (0.1 + (0.2 * Albumin))
Anion Gap (>12mEq/L is high)Ag = Na - (Cl + HCO3)
Absolute Neutrophil Count(ANC cells/mm3) = (%Segs + %Bands) / 100
Renal Clearance(CrCl ml/min) = (140 - age) / (72 x SCr) * (wt kg) * (0.85 if Fem)
BMI (standard --> Metric)BMI = (lbs / in^2) * 703
IBW Male(IBW kg) = 50kg + 2.3 * (inches >60)
IBW Fem(IBW kg) = 45.5 + 2.3 * (inches >60)
BMI (units)kg/m^2
BMI underweightBMI < 18.5
BMI overweightBMI ≥ 25 to 29.9
BMI ObeseBMI ≥ 30
BMI normalBMI 18.6 to 24.9
Fluid Management(35mL/kg/day) -OR- 1,500ml + (20ml) * (kg -20)
Nitrogen Balance(Nitrogen grams) = (Protein grams) / (6.25)
Harris Benedict Eq - MaleBEE = 66.5 + (13.7 * (wt kg)) + (5 * (ht cm)) - (6.75 * (age))
Harris Benedict Eq - FemBEE = 655 + (9.6 * (wt kg)) + (1.85 * (ht cm)) - ( 4.7 * (age))
Total Energy ExpenditureTEE = BEE * (stress factor) * (activity factor)
LDL levelLDL = TC - HDL - (TG / 5)
Body Surface AreaBSA (m^2) = sq root [ (TBW kg) * (ht cm) / 3,600 ]
Dubois BSABSA (m^2) = 0.007184 * (ht cm)^0.725 * (wt kg)^0.425
Specific GravitySG (g/ml) = (weight of substance (g)) / (equal weight of water)

## Ions, Valence, and mols

MilliequivalancemEq = (mg * valance) / mw
Acetate valance-1
Sulfate valance-2
Phosphate valance-2
Carbonate valance-2
Citrate valance-3
Ionization factor# of ions a substance dissociates into = (i)
Isotonicity (e-value)E = (58.5 * i) / ((mw of drug) * 1.8)
E-valueSodium equivalent, E * (drug quantity) = (Sodium Equiv)
Molsmol = (g / mw)
mmolsmmol = (mg / mw)
mOsmol/L(mOsmol/L) = (wt g/L) / (mw) * (# of particles) * (1,000)

## Nutrition

Dehydration(BUN / SCr) > 20
Fat Kcal9 kcal/g
Fat 10% IVFE1.1 kcal/ml
Fat 20% IVFE2 kcal/ml
Fat 30% IVFE3 kcal/ml
Carbs Kcal4 kcal/g
Dextrose kcal3.4 kcal/g
Glycerol kcal4.3 kcal/g
Protein kcal4 kcal/g
Fluid Management(35mL/kg/day) -OR- 1,500ml + (20ml) * (kg -20)
Nitrogen Balance(Nitrogen grams) = (Protein grams) / (6.25)
Harris Benedict Eq - MaleBEE = 66.5 + (13.7 * (wt kg)) + (5 * (ht cm)) - (6.75 * (age))
Harris Benedict Eq - FemBEE = 655 + (9.6 * (wt kg)) + (1.85 * (ht cm)) - ( 4.7 * (age))
Total Energy ExpenditureTEE = BEE * (stress factor) * (activity factor)

## Acid Base

pKa from pKbpKa = 1 - pKb
Henderson-Hasselbach AcidpH = pKa + log [salt / acid]
Henderson-Hasselbach BasepH = pKa + log [base / salt]
% ionization weak acid(weak acid) = 100 / (1 + 10^(pKa - pH))
% ionization weak base(weak base) = 100 / (1 + 10^(pH - pKa))

## Biostats

Type 1 ErrorFalse Positive (a), "Drug doesn't work, but it is accepted in error", (reject the null hypothesis in error)
Type 2 ErrorFalse Negative (b), "Drug works, but is rejected in error", (fail to reject null hypothesis)
Powerpower = 1 - b
risk (r)r = (# of subjects w/ event in arm) / (total # of subjects in arm)
relative risk (rr)rr = (r in Tx) / (r in control)
relative risk reduction (rrr)rrr = 1 - rr -OR- (ARR) / (risk of control)
absolute risk reduction (arr)arr = (risk of control) - (risk of Tx)
# needed to treat (NNT) (# needed to harm (NNH))NNT = 1 / arr
NNTAlways round UP
NNHAlways round Down
oddsodds = (event #) / (nonEvent #)
Odds Ratio (OR)OR = (Tx event) * (control nonEvent) / (control event) * (Tx nonEvent)
Hazard Ratio (HR)HR = (hazard rate in Tx) / (hazard rate in control)
Sensitivitytest of inclusion, = (1 - b), (True +) / (True +) + (False -)
Specificitytest of exclusion, = (1 - a), (True -) / (True -) + (False +)

## Kinetics

Bioavailibility (F)F = 100 x (AUC extravascular) / (AUC IV) * (Dose IV) / (Dose Extravascular)
Dose ConversionNew Dose (D) = (Current dose (current formulation)) / (F of new formulation)
Volume of Distribution (Vd)Vd = (Amount of drug in body (mg)) / (Concentration of drug in plasma (mg/L))
Clearance (CL)CL = (Rate of Elimination (mg/min)) / (concentration (mg/L))
variable relationshipF * Dose = CL * AUC
Elimination constant (Ke)(Ke (hr^-1)) = CL / Vd
Half-Life (t.1/2)(t.1/2) = 0.693 / Ke