Commonly Used Formulas

A-a gradient = [(PB-PH2O) FiO2 - PCO2/R] - PO2 arterial

PB = 760 mmHg; PH2O = 47 mmHg ; R = 0.8 normal Aa gradient <10-15 mmHg (room air)

Arterial oxygen capacity =(Hgb(gm)/100 mL) x 1.36 mL O2/gm Hgb

Arterial O2 content = 1.36(Hgb)(SaO2)+0.003(PaO2)= NL 20 vol%

O2 delivery = CO x arterial O2 content = NL 640-1000 mL O2/min

Cardiac output = HR x stroke volume

Na (mEq) deficit = 0.6 x (wt kg) x (desired [Na] - actual [Na]) SVR = MAP-CVP x 80 = NL 800-1200 dyne/sec/cm2

COL/min

CO L/min

72 (males) x serum creatinine (mg/dL) 85 (females) x serum creatinine (mg/dL)

Creatinine clearance = U creatinine (mg/100 mL) x U vol (mL) _

P creatinine (mg/100 mL) x time (1440 min for 24h)

Normal creatinine clearance = 100-125 mL/min(males), 85-105(females)

Body water deficit (L) = 0.6(weight kg)([measured serum Na]-140) 140

Serum Osmolality = 2 [Na] + BUN + Glucose = 270-290 2.8 18

Na (mEq) deficit = 0.6 x (wt kg)x(desired [Na] - actual [Na])

Fractional excreted Na = U Na/ Serum Na x 100 = NL<1% U creatinine/ Serum creatinine

For each 100 mg/dL increase in glucose, Na decreases by 1.6 mEq/L.

Corrected = measured Ca mg/dL + 0.8 x (4 - albumin g/dL)

Predicted Maximal Heart Rate = 220 - age

PR QRS

Heart rate/min

60 70 80 90 100

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