Memory Joggers: Helpful Equations
ANION GAP: Na - (Cl + HCO3)
OSMOLALITY:
2xNa + glucose/18 + BUN/2.8
FRACTIONAL Na EXCRETION:
urine Na x serum creatinine serum Na x urine Creatinine
BODY WATER DEFICIT: (liters)
0.6 x weight(kg) x (pt Na-normal Na)
normal Na
MAINTENANCE HOURLY FLUIDS:
4 mL for each kg 1-10
plus 2 mL for each kg 11-30
plus 1 mL for each kg > 30
ex: 70 kg pt. = 120 mL/hr
CREATININE CLEARANCE:
(estimate of GFR)
urine creatinine x urine volume(mL)
serum creatinine x time (min)
(140-age)xWeight(kg)(x.85 for fmls)
72 x serum creatinine(mg/dL)
CORRECTED Na:
Na + [(glucose - 100) x 0.016)]
CORRECTED TOTAL Ca:
[0.8x(norm. albumin-pt. albumin)]+Ca
Aa GRADIENT:
[(713 x FIO2) - (PCO2 / 0.8)] - PO2
MEAN ARTERIAL PRESSURE:
diastolic BP + [(systolic BP - diastolic BP) / 3]
BODY SURFACE AREA: (m2)
square root of:
height(cm) x weight(kg) / 3600
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