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Calculating Osmolarity of an IV Admixture
There are any number of ways to calculate the osmolarity of an I.V. admixture, here is one method:
- For each component of the admixture, multiply the volume in milliliters of that component times the value of mOsm per ml of the component.
- Add the mOsm obtained in step [1] for each of the components in order to determine the total number of milliosmoles in the admixture.
- Add together the volumes of each component in order to obtain the total volume of the admixture.
- Divide the total number of milliosmoles from step [2] by the total volume from step [3], then multiply by 1,000 to obtain an estimate of the osmolarity of the admixture in units of milliosmoles per liter.
Example Calculation
| Description | Volume | x | mOsm/mL | = | mOsm |
| Sterile Water for Injection |
500mL |
x |
0.00 |
= |
0.00 |
| Sodium Bicarbonate 8.4% |
50mL |
x |
2.00 |
= |
100.00 |
| Potassium Chloride |
10mL |
x |
4.00 |
= |
40.00 |
| Heparin 5,000 units |
0.5mL |
x |
0.46 |
= |
.23 |
| Pyridoxine |
1mL |
x |
1.11 |
= |
1.11 |
| Thiamine |
1mL |
x |
0.62 |
= |
0.62 |
| Totals |
[3] 553.50mL |
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[2] 141.96 |
[Step 4] Osmolarity of Admixture (141.96 / 553.50) x 1,000 = 256 mOsm / L
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