Learn: Chapter 12: Calculations IV. Clinical

BMI calculation (kg/m^2)

(weight in kg)/(height in m^2)

Normal Weight BMI

18.5-24.9

IBW

m = 50 + 2.3xinches over 5ft

f = 45.5 + 2.3xinches over 5ft

AdjBW

IBW +0.4(TBW-IBW)

When should IBW, TBW, and AdjBW be used for dosing?

IBW

• Aminophylline, theophylline

• Acyclovir

• Levothyroxine

TBW

• LMWH

• UFH

• Vancomycin

AdjBW

• Aminoglycosides (IF OBESE)

If underweight, always use TBW

% above IBW

TBW/IBW x 100

What BUN:SCr ratio indicates dehydration?

> 20:1

When should AdjBW be used to calculate eGFR?

If BMI ≥ 25

What is on an ABG?

pH/PCO2/PO2/HCO3/O2 sat

How to calculate anion gap?

AG = Na - Cl - HCO3

How to remember causes of Anion Gap acidosis?

CUTE DIMPLES

Cyanide

Uremia

Toluene

Ethanol (alcoholic ketoacidosis)

Diabetic ketoacidosis

Isoniazid

Methanol

Propylene glycol

Lactic Acidosis

Ethylene Glycol

Salicylates

When might an anion gap be seen?

Metabolic acidosis (>12 meq/l)

Interpretation of pKa

• pH > pKa = more acid is ionized

• pH = pKa = about equal ionization/unionization

• pH < pKa = more acid un-ionized

how to calculate pH of solution with hendersen hasselbach

Weak Acid

pKa + log (salt/acid)

Weak Base

pKa + log (base/salt)

Percent ionization of drug

Weak Acid

100/(1 + 10^(pKa-pH))

Weak Base

100/(1 + 10^(pH-pKa))

Calcium Salts

Calcium Carbonate (Tums)

• acid-dependent absorption; take w meal

• 40% elemental calcium

Calcium citrate

• acid-independent absorption

• 21% elemental calcium

*calcium acetate not for calcium replacement

ANC calculation

WBCs x [(segs+bands)/10]