# Calculations

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

## Common Calcs

Question | Answer |
---|---|

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) |

Adj.40 BW | (Adj 40 BW) = IBW + 0.4 (TBW - IBW) |

BMI (units) | kg/m^2 |

BMI underweight | BMI < 18.5 |

BMI overweight | BMI ≥ 25 to 29.9 |

BMI Obese | BMI ≥ 30 |

BMI normal | BMI 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 - Male | BEE = 66.5 + (13.7 * (wt kg)) + (5 * (ht cm)) - (6.75 * (age)) |

Harris Benedict Eq - Fem | BEE = 655 + (9.6 * (wt kg)) + (1.85 * (ht cm)) - ( 4.7 * (age)) |

Total Energy Expenditure | TEE = BEE * (stress factor) * (activity factor) |

LDL level | LDL = TC - HDL - (TG / 5) |

Body Surface Area | BSA (m^2) = sq root [ (TBW kg) * (ht cm) / 3,600 ] |

Dubois BSA | BSA (m^2) = 0.007184 * (ht cm)^0.725 * (wt kg)^0.425 |

Specific Gravity | SG (g/ml) = (weight of substance (g)) / (equal weight of water) |

## Ions, Valence, and mols

Question | Answer |
---|---|

Milliequivalance | mEq = (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-value | Sodium equivalent, E * (drug quantity) = (Sodium Equiv) |

Mols | mol = (g / mw) |

mmols | mmol = (mg / mw) |

mOsmol/L | (mOsmol/L) = (wt g/L) / (mw) * (# of particles) * (1,000) |

## Nutrition

Question | Answer |
---|---|

Dehydration | (BUN / SCr) > 20 |

Fat Kcal | 9 kcal/g |

Fat 10% IVFE | 1.1 kcal/ml |

Fat 20% IVFE | 2 kcal/ml |

Fat 30% IVFE | 3 kcal/ml |

Carbs Kcal | 4 kcal/g |

Dextrose kcal | 3.4 kcal/g |

Glycerol kcal | 4.3 kcal/g |

Protein kcal | 4 kcal/g |

Fluid Management | (35mL/kg/day) -OR- 1,500ml + (20ml) * (kg -20) |

Nitrogen Balance | (Nitrogen grams) = (Protein grams) / (6.25) |

Harris Benedict Eq - Male | BEE = 66.5 + (13.7 * (wt kg)) + (5 * (ht cm)) - (6.75 * (age)) |

Harris Benedict Eq - Fem | BEE = 655 + (9.6 * (wt kg)) + (1.85 * (ht cm)) - ( 4.7 * (age)) |

Total Energy Expenditure | TEE = BEE * (stress factor) * (activity factor) |

## Acid Base

Question | Answer |
---|---|

pKa from pKb | pKa = 1 - pKb |

Henderson-Hasselbach Acid | pH = pKa + log [salt / acid] |

Henderson-Hasselbach Base | pH = 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

Question | Answer |
---|---|

Type 1 Error | False Positive (a), "Drug doesn't work, but it is accepted in error", (reject the null hypothesis in error) |

Type 2 Error | False Negative (b), "Drug works, but is rejected in error", (fail to reject null hypothesis) |

Power | power = 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 |

NNT | Always round UP |

NNH | Always round Down |

odds | odds = (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) |

Sensitivity | test of inclusion, = (1 - b), (True +) / (True +) + (False -) |

Specificity | test of exclusion, = (1 - a), (True -) / (True -) + (False +) |

## Kinetics

Question | Answer |
---|---|

Bioavailibility (F) | F = 100 x (AUC extravascular) / (AUC IV) * (Dose IV) / (Dose Extravascular) |

Dose Conversion | New 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 relationship | F * Dose = CL * AUC |

Elimination constant (Ke) | (Ke (hr^-1)) = CL / Vd |

Half-Life (t.1/2) | (t.1/2) = 0.693 / Ke |

Steady state | after 5 half-lives |

Loading Dose (LD) | LD = ((desired conc) * Vd) / F |

Vmax | Maximum rate of metabolism |

Km | 1/2 of Vmax |

## Misc Eq

Question | Answer |
---|---|

Rule of 500 (for Rapid Insulin) | 500 / (total daily dose) = grams of Carbs covered by 1 unit of rapid insulin |

Rule of 450 (for Regular Insulin) | 450 / (total daily dose) = grams of Carbs covered by 1 unit of regular insulin |

Insulin Correction Dose | (current BG) - (target BG) / (correction factor) = correction dose |

Correction Factor (define) | # of points that each insulin unut will decrease BG |

CF (rapid) | 1,800 / (total daily dose) = CF for 1 rapid unit |

CF (regular) | 1,500 / (total daily dose) = CF for 1 regular unit |

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