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I’ve seen several free online resources recently that claim to teach dietitians and pharmacists how to order TPN electrolytes. Unfortunately, these are all incomplete, confusing, and at times incorrect! Here’s what I teach in my Nutrition Support Skills Course:
Electrolyte Dosing for Custom PN: The Basics
- When writing a custom parenteral nutrition (PN) order, you don’t just order “sodium.” You order a sodium salt. Sodium comes in a few forms: sodium chloride, sodium acetate, or sodium phosphate. Potassium can be provided as potassium chloride, potassium acetate, or potassium phosphate. Calcium is typically provided as calcium gluconate, and magnesium as magnesium sulfate.
- When you see “adjust chloride and acetate” or “adjust acid/base balance”, you need to know that chloride and acetate are not ordered on their own. Parenteral amino acid solutions contain acetate, which is metabolized into bicarbonate in the liver. Chloride comes in the form of sodium chloride, or potassium chloride. In other words, chloride “rides along” when you order electrolyte salts. When you adjust the chloride to acetate ratio, what you’re typically doing is controlling how much sodium acetate versus sodium chloride you’re providing. You might provide more sodium acetate for patients with metabolic acidosis, and more sodium chloride for patients with metabolic alkalosis (this is notoriously complex and many clinicians get this wrong. Learn exactly when, why, and how to do this correctly in the Acid/Base Balance Lectures in my Nutrition Support Skills Course).
The following information, unless otherwise specificized, is for adult patients.
Step 1: Determine daily fluid goal for your PN order.
Be sure to consider all IV fluids the patient is receiving when you determine this goal. A few things to keep in mind:
- Vomiting, diarrhea, NG tube suction, and other GI losses raise sodium and potassium needs
- Refeeding syndrome raises potassium and phosphorous needs
- Replete magnesium with potassium, as they work in tandem
Many students ask me if fluid and electrolyte losses should be replaced 1:1. In other words, if the patient loses 2 liters out of their NG tube, would you add an additional 2 liters of water into the PN? The answer is: it depends. Fluid balance is complicated; learn how to finesse this in the Fluid and Electrolyte Balance modules in my Nutrition Support Skills course.
The tables below are helpful when considering electrolyte losses. The highlighted sections are “heavy hitters” in terms of output. For example, ileal contents are heavy in sodium, so you may need to add more sodium to a PN if a patient is having high ileostomy loss.
I’m going to work with this example from the 4th edition of the ASPEN Core, chapter 17 (I’ve taken the liberty of adding onto it a bit):
A 53-year-old male is admitted with an ileus following small bowel resection. He has have been NPO for 5 days. You have been consulted to start parenteral nutrition. The patient weighs 80 kg, and has estimated requirements of 25-30 kcal/kg/day, and 1.5 g protein/kg/day. SO,MCT,OO,FO-ILE will be provided as 20-30% of total energy. The primary team has requested that the PN be maximally concentrated. Stock solutions used by the pharmacy are: 10% or 15% amino acid, 70% dextrose, and 20% lipid. The patient is receiving ½ NS IVF at 100 ml/hr. The patient has no emesis, and no stool x3 days.
The patient’s labs are as follows:
Step 2: Look at ASPEN’s dosing guidelines to determine appropriate ranges for each electrolyte
You can find this information in my PN Calculation Cheat Sheet, which is included in my Nutrition Support Skills Course and CNSC Exam Study Guide Bundle, or by downloading my free Nutrition Support Toolkit.
Step 3: Calculate daily electrolyte goals for sodium (mEq), potassium (mEq), phosphorous (mmol), calcium (mEq), and magnesium (mEq).
Be sure to consider any losses when you determine daily goals.
Sodium
The patient’s IV fluid is running at 100 mL/hr continuous (2400 mL/day). Typically, IV fluid will stop when PN starts. A nice “hack” is to match fluid and sodium in the IV fluid.
Normal saline contains 154 mEq sodium per liter, ½ normal saline contains 77 mEq sodium per liter
So, our fluid goal would be 2400 mL/day, and our sodium goal would be: 77 mEq/L x 2.4 L = 185 mEq sodium goal
The patient is not losing chloride via emesis or NGT output. The patient’s electrolytes are currently within normal limits, though he is at risk of refeeding syndrome due to being NPO x5 days.
Potassium
1-2 mEq/kg or 60-100 mEq/day (note although sodium and potassium can both be dosed at 1-2 mEq/kg, we almost always provide more sodium than potassium in a PN order). Let’s dose on the higher end, for refeeding syndrome risk: 80 mEq potassium goal
Phosphate
20-40 mmol/day (dose on the higher end for refeeding syndrome risk): 40 mmol phosphate goal
Magnesium
Dose on the higher end for refeeding syndrome risk: 15 mEq magnesium goal
Calcium
⚠️Watch calcium/phosphate solubility: the goal is to add as much as we can, while keeping the mixture stable
Step 4: Pull out your calculator or spreadsheet, and get to work!
In real life, you’ll use a facility-approved calculator. The math is dependent on which specific types of salts you have. The ones I listed above are relatively standard, but some compounding pharmacies have different salts to work with. The brand and concentration of lipid, amino acid and dextrose, will also matter.
For practicing purposes, you can use this online calculator, and to get exact numbers of potassium and phosphate, use the Electrolyte Salt Calculator included in the Nutrition Support Skills Course.
- Enter your macronutrients and volume first (if you don’t know how to take grams of each macronutrient and convert it to mL of a stock solution, watch this video). For sterile water, add as much as you need to get to your desired volume. For this example, I’m using the following:
- Start with sodium. Load all the sodium in as sodium chloride. Skip sodium acetate and sodium phosphate for now.
- Next, add all the phosphate in the way of potassium phosphate
- Next, add remaining potassium* as potassium chloride, or potassium acetate (it truly doesn’t matter which)
- Next, add magnesium as magnesium sulfate
- Next, add calcium as calcium gluconate (start with 10 mEq, go up to 15 or 20 mEq if you can. The red dot must be below and to the left of the curve).
- Click “calculate” and click “create curve”
*In order to get this number, use a calculator or spreadsheet. In my Nutrition Support Skills Course, I provide a practice calculator. To do the math by hand, take mmol potassium phosphate and multiply by 1.47. This equals mEq potassium. Subtract that from your daily potassium goal. That’s the number you put in the Potassium Chloride or Potassium Acetate box.
The curve will show you whether your mixture is safe to administer or not, based on calcium phosphate solubility. The red dot should be below and to the left of the curve. If it is above or on the curve, calcium and phosphate are likely to form a dangerous precipitate.
⚠️ Keep in mind, this curve is specific to Travasol, which is a brand of amino acid. It does not apply to all brands of amino acid solutions. Calcium phosphate solubility is dependent on several variables, including amino acid concentration, presence of lipid in the PN solution, pH of the final solution, and temperature.
Step 5: Adjust chloride to acetate ratio
In the Nutrition Support Skills Course, I provide a calculator which you can use to practice this. The ratio of our solution is currently 1.72:1.
For most PNs, we’d balance chloride:acetate 1:1. But, there are a few reasons you might want to add more chloride or more acetate to the PN bag (learn why in the Nutrition Support Skills Course).
You can’t see this on the RxKinetics calculator, but in the calculator I provide, you can easily adjust chloride and acetate and see the ratio change. The best way to do this is to play around with sodium chloride and sodium acetate. I rarely mess with potassium chloride vs. potassium acetate, as the numbers are much lower, and have less of an effect on the final ratio. We want to keep sodium at a total of 185 mEq, but we can provide that in the way of sodium chloride or sodium acetate.
See what I mean:
Now, the chloride:acetate ratio is 1:1. The calculator does the hard work for you, but the acetate number is based on acetate from amino acid + acetate from sodium acetate.
Here are some general tips to keep in mind:
- You can’t put bicarbonate in the PN bag; the liver converts acetate to bicarbonate
- For metabolic acidosis, provide more acetate
- For metabolic alkalosis, provide more chloride
- Don’t adjust acid/base balance for respiratory disorders
Again, this is not something you’ll ever have to do from scratch. If you write custom PNs, your facility will have a calculator for you.
Common mistakes I see
- Removing all sodium from a PN order because sodium is high.
Hypernatremia is usually a fluid balance issue, not a sodium excess. Sodium-free PN provides free water, but does little to restore intravascular (blood vessel) volume.
- Providing less chloride in the PN because the patient’s chloride lab is high.
Balance chloride:acetate (acid:base) 1:1, unless you have a good reason to do otherwise. There absolutely are indications to use a 2:1 or 1:2 ratio, but you need to have an indication. High chloride is not an indication to reduce chloride in the PN bag. If the patient’s serum potassium is low, we’d add more potassium. Not so with chloride. Acid/base balance is complicated and dependent on multiple factors. Chloride doesn’t rise and fall due to chloride “excess” or “deficiency” like potassium does. This is very complex; learn all about it in my Nutrition Support Skills Course.
- Removing calcium from the PN order because it’s too difficult.
In one study (Kramer, et al. P21), calcium was the #1 most frequently forgotten additive in home PN orders, which is really scary. Yes, we have a storage form of calcium (our bones), but if we continually pull from our calcium bank without replenishing stores, we can get osteoporosis. This is why DEXA scans are recommended annually for long-term PN patients. Calcium is difficult and can be a bother, but you don’t want your patients getting squishy bones! Use the calcium phosphate solubility curve in your compounding pharmacy software to add as much calcium to your PN order as you can. Often, this involves playing around with the numbers a bit (start with 5 or 10 mEq of calcium, increase to 15 or 20 if you can). As a very rough rule, calcium x phosphate should be <200 per liter (for example, 10 mEq calcium and 40 mEq phosphate in a 2.4 liter bag). But, don’t stop here! It’s different for each PN you are writing. If you don’t enter custom PN orders into the compounding pharmacy computer, this is a great opportunity to collaborate with your pharmacy colleagues. It’s ideal to be able to see the curve for each PN you are writing.
How much to adjust?
Trend the patient’s labs and adjust electrolytes as needed. Many students ask me, but how do I know how much to adjust? This is where PN order writing becomes more of an art than a science. With the exception of potassium, where ± 10 mEq typically results in 0.1 mEq/L change in serum potassium, there aren’t specific guidelines on how much to adjust. Here are some general guidelines:
- Don’t be too timid. If the patient’s serum phosphorous is <2 mg/dL, increasing phosphate in the PN from 10 to 15 mmol isn’t going to do much. Take a look at your facility’s electrolyte replacement protocol to get a sense of how much is given for low labs.
- You can always replete IV electrolytes outside of the bag.
- Collaborate with the MD and pharmacist to come up with a plan.
What about refeeding syndrome?
ASPEN guidelines say, “If electrolytes become more difficult to manage or drop precipitously during initiation of nutrition support, decrease to 50% of caloric goal.” In practice, this depends on your clinical judgement. For example, if you’re replacing phosphorous per protocol and it’s still <2 mg/dL, decrease to 50% of calorie goal.
Previously, guidelines were to delay initiation of nutrition support until electrolytes stabilize, but this only worsened feeding deficits. Now, unless the patient has “electrolyte derangements”, you can start low-dose nutrition support while repleting electrolytes. Often, I’ll replete immediately (for example, order phosphorous repletion in the AM, check again 4 hours later, order another repletion, and re-check before the PN even starts that evening). In other words, you usually have some time between deciding on nutrition support and the actual bag (or formula) running.
“Electrolyte derangements” isn’t well-defined, but if it’s looking like a hot mess (for example, if K, phosphorous and Mg are all low), I’d hold off. Phosphorous <2 mg/dL has always been a red flag (though you still can start nutrition support with a phosphorous <2, I’d be sure to replete prior, add thiamine, and increase phosphorous in the PN).
As you get more comfortable with this, you’ll get a good “spidey sense” of when to start, and when to hold off. I definitely have pushed back against starting nutrition support right away, even if the doctor consults for it, because I am worried about the patient’s labs.
If electrolytes are severely low (potassium <2.5 mmol/L, phosphorous <1.5 mg/dL, magnesium <1 mg/dL, calcium <1 mmol/L), do not initiate nutrition support until electrolyte levels are stabilized. IV electrolyte repletion is more effective than PO, and is preferred for severely low electrolytes.
Add a multivitamin to the PN order. Add 100 mg thiamine prior to feeding, and 100 mg thiamine to the PN order for 5-7 days. Many journal articles recommend 200-300 mg of thiamine as an initial “loading dose” prior to initiation of nutrition support.
Pediatric Refeeding Syndrome Guidelines
- Patients at greatest risk: weight loss at or below 70% ideal body weight and/or weight loss of ≥ 10% within 2-3 months
- Malnourished patients need to be monitored closely when initiating and advancing nutrition support
- Initial calories are limited to 50% of goal, not exceeding 20-25 kcal/kg/day
- After electrolytes have stabilized and patient has received ≥ 72 hours of nutrition at 50% goal, calories can be gradually increased every 3 days by 200-300 kcal
- Aggressive electrolyte repletions of phosphorous, potassium and magnesium may be required
- Patients should also receive a daily multivitamin/mineral supplement and may also require thiamine supplementation of 200-300 mg/day for 10 days
TPN electrolytes include sodium, potassium, phosphorus, magnesium, and calcium, plus chloride and acetate. Each one is added as a salt, such as sodium chloride, potassium phosphate, magnesium sulfate, or calcium gluconate. Chloride and acetate aren't ordered on their own; they come in with the sodium and potassium salts and the amino acid solution.
Phosphate is ordered in millimoles because its electrical charge changes with pH, so its mEq value isn't fixed. Millimoles stay constant. Every other TPN electrolyte (sodium, potassium, calcium, and magnesium) is ordered in mEq.
Each mmol of potassium phosphate provides 1.47 mEq of potassium. So 40 mmol of potassium phosphate delivers 59 mEq of potassium.
ASPEN's standard daily requirements for adults are sodium 1-2 mEq/kg, potassium 1-2 mEq/kg, phosphorus 20-40 mmol, magnesium 8-20 mEq, and calcium 10-15 mEq. Chloride and acetate are given as needed to maintain acid-base balance. Needs increase with GI losses, refeeding risk, and high dextrose intake. Check out ASPEN's Appropriate Dosing for Parenteral Nutrition
Most TPN orders use a balanced chloride:acetate ratio of 1:1. If the patient has confirmed metabolic alkalosis or acidosis, you may shift this ratio. Learn how to do this in my Nutrition Support Skills Course.
No. Bicarbonate isn't added to TPN because it's unstable in the solution and can precipitate with calcium. Acetate is used instead, because the liver converts acetate to bicarbonate.
Acetate in TPN comes from two sources: acetate salts (sodium acetate and potassium acetate) and the amino acid solution itself. The amount contributed by amino acids varies by product, and some amino acid products also contain chloride. Check the product insert, or rely on your compounding software, when calculating the final chloride:acetate ratio.
The chloride:acetate ratio compares how much chloride and acetate are in a TPN bag, from both the electrolyte salts and the amino acid solution. A 1:1 ratio is the usual starting point. Ratios closer to 2:1 or 1:2 are used when there's a clear indication, such as metabolic alkalosis or metabolic acidosis.
Adjust the chloride:acetate ratio in TPN only when the medical team has identified a metabolic acid-base disorder, not because a single lab is out of range. That requires a pH from a blood gas, plus the bicarbonate and clinical picture. If there's no clear indication, keep chloride and acetate balanced at about 1:1. I teach a step-by-step approach to this in the Acid/Base Balance lectures in my Nutrition Support Skills Course.
Usually not. Hypernatremia is most often a water deficit, not a sodium excess, especially in patients with vomiting, diarrhea, or other fluid losses. Sodium-free TPN provides free water but does little to restore intravascular volume. Assess volume status and trends like the BUN:creatinine ratio before changing sodium.
Not automatically. A high serum chloride isn't, by itself, a reason to lower chloride in the TPN bag. Chloride reflects acid-base and fluid status, not a simple excess or deficiency the way potassium does. Identify the underlying cause first, and keep chloride:acetate balanced unless there's a specific indication.
Calcium gluconate is the preferred calcium salt in TPN because it dissociates less than calcium chloride, leaving fewer free calcium ions available to bind phosphate. That lowers the risk of calcium phosphate precipitation. Solubility curves developed for calcium gluconate don't apply to calcium chloride.
Check every TPN order against a calcium phosphate solubility curve for the specific amino acid product being used. Solubility depends on amino acid concentration, pH, temperature, and whether lipid is in the bag. Work with your pharmacist, and don't simply leave calcium out, since long-term omission can harm bone health.
Normal saline contains 154 mEq of sodium per liter, and half normal saline contains 77 mEq per liter. Matching a new TPN order's sodium concentration to the patient's current IV fluid is a common starting point, as long as that fluid is clinically appropriate.
Meet The Author
Sara Griffin, MS, RD-AP, CNSC is a currently practicing clinical dietitian specializing in critical care and nutrition support.
She has precepted dozens of interns, and has received accolades for her precepting work. Sara was selected as Colorado Dietitian of the Year, has been nominated for an Academy of Nutrition and Dietetics Excellence in Practice award, and holds her ASHP/ASPEN Nutrition Support Certificate. She is a CDR-certified CPEU provider.
Learn more about what sets Sara apart from other clinical instructors here.
Citations:
Electrolyte Composition of Bodily Fluids (Adult): Kumpf VJ, Lord LM, Marian M, McCarthy MS, McClave SA, Miller SJ, Pimiento JM, Roberts KM, eds. ASPEN Adult Nutrition Support Core Curriculum. 4th ed. Silver Spring, MD: American Society for Parenteral and Enteral Nutrition; 2025.
Electrolyte Composition of Bodily Fluids (Pediatric): Larson-Nath C. Pediatric Nutrition. 3rd ed. 2024.
Boland Kramer E, Monczka J, Laglenne T, Voyles A, Dietz S, Martinez K. Identifying and correcting missing parenteral nutrition order components during transitions of care [abstract P20]. JPEN J Parenter Enteral Nutr. 2025;49(suppl 1):S90-S308. doi:10.1002/jpen.2735
Reber E, Friedli N, Vasiloglou MF, Schuetz P, Stanga Z. Management of Refeeding Syndrome in Medical Inpatients. J Clin Med. 2019 Dec 13;8(12):2202.
da Silva, et al. Parenteral Nutrition Safety and Clinical Practice Committees, American Society for Parenteral and Enteral Nutrition. ASPEN Consensus Recommendations for Refeeding Syndrome. Nutr Clin Pract. 2020 Apr;35(2):178-195.