I am confused about calcium and phosphate solubility curve.
As per glycophos compatibility…
Additions should be made aseptically.
Up to 120 ml of Glycophos and 48 mmol of calcium (as CaCl2) can be added to 1000 ml Vamin Glucose, Vamin 9 Electrolyte Free, Vamin 14, Vamin 14 Electrolyte Free, Vamin 18 Electrolyte Free and Vaminolact.
Up to 10 ml of Glycophos and 10 mmol of calcium (as CaCl2) can be added to 1000 ml Glucose 50 mg/ml.
Up to 20 ml of Glycophos and 20 mmol of calcium (as CaCl2) can be added to 1000 ml Glucose 200 mg/ml.
Up to 60 mmol of Glycophos and 24 mmol of calcium (as CaCl2) can be added to 1000 ml Glucose 500 mg/ml.
So to make calcium – phosphate compatibility, shall I consider tpn total volume OR only volume of amino acids solution or volume of dextrose only.
Waiting for your precious guidance.
I don’t have a definite evidence for your inquiry but I would recommend the maximum solubility option, in other words; choose maximum calcium and phosphate based on dextrose or Amino acid used whichever is higher. Below is my interpretation: –
1- Solubility of Calcium phosphate depends on the availability of soluble form of phosphate (monobasic phosphate) which tends to be available with increased acidity of TPN solution.
2- Referring to the equation of PH calculation in typical situation (excluding other factors such as inherent buffering capacity and dissociation constants): –
A) PH= – log [H+]
B) Assuming PH of (X) with the said volume (1000 ml) of the chosen solution (AA, D5W, D20W or D50W)
C) Assuming total volume of (3000ml), i.e (3) times the volume of the chosen acidic solution; then the PH would increase by the value of [- log (1/3) = 0.477].
3- The increase in PH would be lower than assumed in (C) as a part of the added solutions is usually acidic considering either amino acid or dextrose as additive with referral to their role as main determinants of the final PH as well as inherent buffering capacity.
Attached is a theoretical numerical example for the recommended allowed amounts of glycophos and calcium based on the final concentration of the said used components. Referring to the said example, kindly observe that using higher dextrose concentration would allow higher amounts of phosphate and calcium to be incorporated as well as lower volumes to be used.
Generally speaking, risk of precipitation with organic phosphate is lower than that with inorganic phosphate.
Again, this is a theoretical interpretation which I hope to be reviewed and assured as appropriate.
Hope this help with your query.
1- The manufacturer reports that up to 120 mmol/L Sodium glycerophosphate and 48 mmol/L calcium chloride in one liter PN volume
2- It was reported that PN containing up to 50 mEq/L calcium gluconate and 50 mmol/L Sodium glycerophosphate was compatible. This information allows prescriber to go for higher amounts of calcium and phosphorus especially in neonates. (MacKay M, Anderson C. Physical compatibility of sodium glycerophosphate and calcium gluconate in pediatric parenteral nutrition solutions. April 2, 2014. JPEN J Parenter Enteral Nutr)
3- One unintended consequence of increasing the calcium gluconate in PN, due to the favorable solubility when compounded with Sodium glycerophosphate, is the potential for aluminum toxicity.
4- The FDA guideline recommends not to exceed intake of aluminum above 5 mcg/kg/d.
5- When calcium gluconate injection 10 mL glass ampoules is used in the preparation of parenteral nutrition, the aluminium content of the bag from the ampoule could be up to 220 µg/L. Due to the higher need for calcium and phosphate in neonatal PN, these patients may exceed the recommended limit of Aluminum.
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