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Formulae
Cardiology
Digoxin Dose (mg/day) = (((0.2 x CrCl) + 14)
x (wgt in kg))/ 10,000 QT
corrected = QT/ (√RR (seconds)
)
Infectious Disease
Aminoglycoside Dosing
| Step 1: Select loading dose in mg/kg (lean weight)
based on peak level desired as below |
| Loading dose |
Expected peak serum level based on 30' IV infusion |
| 2.0 mg/kg |
6-8 mcg/ml |
| 1.75
mg/kg |
5-7 mcg/ml |
| 1.5 mg/kg |
4-6 mcg/ml |
| 1.25
mg/kg |
3-5 mcg/ml |
| 1.0 mg/kg |
2-4 mcg/ml |
| Step 2: Select maintenance dose as a percentage of
the total loading dose, to continue the above noted peak serum
levels, based on the patient's creatinine clearance and desired
dosing interval |
|
% of Loading Dose required for dosage interval
selected |
| Creatinine clearance |
8 hours |
12 hours |
24 hours |
| 90 |
90 |
- |
- |
| 80 |
88 |
- |
- |
| 70 |
84 |
- |
- |
| 60 |
79 |
91 |
- |
| 50 |
71 |
87 |
- |
| 40 |
66 |
80 |
- |
| 30 |
57 |
72 |
92 |
| 25 |
51 |
66 |
86 |
| 20 |
45 |
59 |
80 |
| 15 |
37 |
50 |
75 |
| 10 |
29 |
40 |
64 |
| 7 |
24 |
33 |
55 |
| 5 |
20 |
23 |
42 |
| 2 |
14 |
20 |
35 |
| 0 |
9 |
13 |
25 |
Metabolism
BSA(m2)=
Wgt (kg)0.245 x Hgt (cm)0.275
x 0.007184
Estimated Serum Osmolality = (2
x (Na+ + K+)
) + (glucose/18) + (BUN/2.8)
Pulmonary
H+ = 24 X (PCO2/HCO3)
ΔP(A-a)O2=((PAtm
- 47)FIO2) - ((PACO2/RQ)
- PaO2
pH= 6.1 + log
(HCO3/(0.03 x PCO2))
|
Acid Base
see also Acid Base page |
| |
Acidosis |
Alkalosis |
| Metabolic |
ΔPCO2/ΔHCO3=
1-1.5 |
0.5-1.0 |
| |
1.2 X ΔHCO3=
PCO2 |
0.5 X ΔHCO3=
PCO2 |
| Respiratory |
|
| Acute |
ΔHCO3/ΔPCO2=
1/10 or 1/8 |
0.1-0.3 |
| Chronic |
ΔHCO3/ΔPCO2=
3/10 to 4/10 |
0.2-0.5 |
Renal
Anion Gap= Sodium - (chloride +
bicarbonate) normal (8-12)
Creatinine Clearance
Estimated Creatinine Clearance:
Male: (140-age in years) X weight (kg)
serum
creatinine (mg/dL) X 72
Female: (140-age in years) X weight (kg) X0.85
serum
creatinine (mg/dL) X 72
Measured Creatinine Clearance:
urine creatinine (mg/dL) X 24° urine volume (liters)
1.44 X serum
creatinine (mg/dL)
Fractional Excretion of Sodium
urine sodium (mg/dL) X serum creatinine
X100
serum sodium (mg/dL) X urine creatinine
Milliequivalents
1 gram sodium = 43 meq
1 gram potassium = 27 meq
Potassium
Total body Potassium:
Male: 45 meq/kg
Female: 35 meq/kg
Effect of pH:
ΔK/
ΔpH = 0.7/0.1 Total body
deficit ( in meq) = (4.0 - K) X (wgt in kg) X 5.3
Renal Failure Indices
| Index |
Units/Formula |
Prerenal |
Renal |
| Urine osmolality |
mOsm/kg H2O |
>500 |
<350 |
| Urine Sodium |
mEq/Liter |
<20 |
>40 |
| Urine/Plasma urea nitrogen |
|
>8 |
<3 |
| Urine/Plasma creatinine ratio |
|
>40 |
<20 |
| Renal Failure Index |
UNa/(U/PCr) |
<1 |
>1 |
| Fractional Excretion of Filtered Sodium |
(U/PNa)/(U/PCr)
x100 |
<1 |
>1 |
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