Ch01-2-4-9781975113285

Useful Formulae   1 3

• FE Na <1% in prerenal states, early acute tubular necrosis, contrast or heme-pigment nephropathy, and acute glomerulonephritis. • Not valid when diuretics have been given. • See “Acute Kidney Injury” section in Chapter 12, Top 10 Workups.

FRACTIONAL EXCRETION OF UREA

FE

 = [(U

 × P

)/(P

 × U

)] × 100

urea

[urea]

[Cr]

[urea]

[Cr]

( all units in mg/dL )

• FE

<35% in prerenal states.

urea

• Not affected by diuretics. • See “Acute Kidney Injury” section in Chapter 12, Top 10 Workups.

MEAN ARTERIAL PRESSURE

Mean arterial pressure = [SBP + (2 × DBP)]/3

MODEL FOR END-STAGE LIVER DISEASE

MELD = (3.78 × Ln[bilirubin]) + (11.2 × Ln INR) + (9.57 × Ln[SCr]) + 6.43 ( [bilirubin] and [Cr] in mg/dL ) • Who remembers what a nature log is? Rhetorical… Only included to provide the interpretation (Table 4-1).

OSMOLALITY (SERUM, ESTIMATED)

Calculated serum osm = (2 × [Na + ]) + ([glucose]/18) + ([BUN]/2.8)

( [Na + ] in mmol/L; [glucose] and [BUN] in mg/dL )

• To correct for methanol + ([MeOH]/3.2). • To correct for ethanol + ([EtOH]/4.6).