Equations

Question 1

Starling’s forces

Answer 1

Filtration = Kf [(Pc-Pif)- σ (πc- πif)]

Kf – capillary filtration coefficient (capacity of the membrane to filter water at a given net filtration pressure) (ml/min/mmHg)

σ – reflection coefficient (the fraction of the total potential osmotic pressure exerted by the solute in question)

Question 2

Free water deficit (L)

Answer 2

0.6 x BW (kg) x ([patient Na+]/[normal Na+] – 1)

Quick formula: 3.7mls/kg/hr of D5W
*calculated to change Na by 1 mEq/hr

Question 3

Estimated ∆ Na with 1 L fluid

Answer 3

Change in serum [Na]= [Nafluids]-[Naserum]
0.6 (BWkg) + 1

Question 4

Na +deficit in hyponatremia

Answer 4

0.6 x BW (kg) x (Normal Na+ - Pts Na+)

●Sodium deficit should be calculated from the minimum safe sodium : 120 mEq/L

● Do not exceed 0.5 mEq/L/hr or no more than 12 mEq/L/day
● If severe symptoms, may increase sodium more quickly 1.5-2.0 mEq/L/hr for 3-4 hours

Question 5

Corrected Chloride

Answer 5

Pts Chloride x (Norm Na/Pts Na)

Corrects for free water deficit

Question 6

Plasma osmolality

Answer 6

2(Na+ + K+) + (BUN/2.8) + (glucose/18)

Dog: 290-310 mOsm/kg Cat: 290-330 mOsm/kg

Question 7

Effective osmolality

Answer 7

2(Na+K) + (glucose/18)

Question 8

Osmolal gap

Answer 8

Measured osmolality – calculated osmolality

Question 9

GFR (ml/min)

Answer 9

(Uinulin X V )/Pinulin

Either inulin or creatinine clearance rate may be used for GFR