There are any number of ways to calculate the osmolarity of an I.V. admixture, here is one method:
|Sterile Water for Injection||500mL||x||0.00||=||0.00|
|Sodium Bicarbonate 8.4%||50mL||x||2.00||=||100.00|
|Heparin 5,000 units||0.5mL||x||0.46||=||0.23|
|Totals|| 562.50mL|| 141.96|
[Step 4] Osmolarity of Admixture
(141.96 / 562.5) x 1,000 = 252 mOsm / L
The following table lists the values of mOsm per ml for common IV admixture components
(values obtained from package inserts for each product except where noted):
|Description||mOsm per Ml|
|Multi-trace Elements (MTE-4)||0.36|
|Multivitamin injection (Adult)||4.11 1|
|Pyridoxine HCl (B-6)||1.11|
|Sodium Bicarbonate 4.2%||1.00|
|Sodium Bicarbonate 8.4%||2.00|
|Sodium Chloride 14.6%||5|
|Thiamine HCl (B-1)||0.62|
|Water for Injection||0.00|
Pediatric MVI, on the other hand, is formulated with an aqueous polysorbate vehicle. Because of this difference
in formulation, the osmolarity of Pediatric MVI is significantly lower, approximately 0.5 mOsmol/ml.
The following table lists the values of mOsm per ml for common IV solutions
(values obtained from package inserts for each product):
|Description||mOsm per Ml|
|Sodium Chloride 0.45%||0.154|
|Sodium Chloride 0.9%||0.31|
|Amino Acid 3.5%||0.357|
|Amino Acid 8.5%||0.85|
|Amino Acid 10%||1.0|
|Liposyn III 30%||0.293|
Normal osmolarity of blood/serum is about 300-310 mOsm/L. The tonicity of an IV fluid dictates whether the solution should be delivered via the peripheral or central venous route. Hypotonic and hypertonic solutions may be infused in small volumes and into large vessels, where dilution and distribution are rapid.
Solutions differing greatly from the normal range may cause tissue irritation, pain on injection, and electrolyte shifts. When solutions with extremes of tonicity are infused, fluids shift into or out of cells, including endothelial cells of the tunica intima near the catheter tip and blood cells. The resulting changes in the cell size of the vein wall causes the inflammatory and clotting processes to occur, leading to phlebitis and thrombophlebitis.
The generally accepted upper limit for a peripheral IV is 900 mOsm/L. When the osmolarity exceeds 900 mOsm/L, the ability of the peripheral veins to dilute parenteral infusions sufficiently is compromised, and chemical irritation of the vein intima occurs. Admixtures greater than 600 to 900 mOsm/L are associated with a dramatic increase in phlebitis and should be administered via a central line.
In a brief review of the literature, I couldn't find a 'magic' number regarding the lowest acceptable osmolarity or tonicity of an IV solution. Most people have been taught 0.45% sodium chloride, at 154 mOsm/L, is the lowest osmolarity that should be used via any IV route. Very hypotonic IV solutions such as 1/4 NS (NaCl 0.2%) cause red blood cells to swell and burst. If a sufficient number of RBC's are so affected, the patient may develop anemia. This condition is usually referred to as hemolytic anemia.
To use the following osmolarity calculator:
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