formulas

Question 1

Winter’s Formula

Answer 1

expected pCO2 = 1.5(HCO3) + 8 (+/-2)

expected compensation in metabolic acidosis

Question 2

Anion Gap

Answer 2

Unmeasured anions - unmeasured cations
Na - (HCO3+Cl)
Normal is 10

Question 3

Clearance

Answer 3

(Urine concentration * Urine Volume)/Plasma concentration

Question 4

Electrolyte Free Water Clearance

Answer 4

Electrolyte free water clearance = Urine volume (1- urine electrolytes/plasma electrolytes)

Question 5

Free Water Clearance

Answer 5

Free water clearance = Urine volume (1 - Urine osm/plasma osm)

Question 6

Water Deficit

Answer 6

TBW = 0.6 * wt(kg) - Men
TBW = 0.5 * wt(kg) - Women
TBW normal = TBW * (Serum Na/140)
Water deficit = TBWnormal - TBW present

Question 7

Fractional Excretion

Answer 7

Fe = (UrineX/SerumX) / (UrineCr/SerumCr)

Question 8

Filtered Load

Answer 8

Filtered Load = GFR * serum [X]

Question 9

Plasma Osmolarity

Answer 9

Posm = 2*Na + Gluc/18 + BUN/2.8

Question 10

Plasma Tonicity

Answer 10

Pton = 2*Na + Gluc/18

Question 11

Henderson-Hasselbach

Answer 11

Ph = pka + log ([HCO3]/0.03*PCO2)

Note: 0.03*PCO2 = [H2CO3]

Question 12

Body Fluid Compartments

Answer 12

ICF = 2/3
ECF = 1/3
1/4 ECF = plasma
3/4 ECF = interstitial fluid