more detailed picture is needed before attempting to fix electrolytes levels through PN. Adding right amount of electrolytes can only happen when you identify the causes. Here are some thoughts:
1. Hypomagnesemia: Drug induced i.e. Insulin, Diuretics? Is it hypomagnesemia induced by Hypokalemia? Extra Dextrose? The key is to reduce dextrose in PN and correct hypokalemia.
2. Hypokalemia: Is it due to Alkalosis induced by Diuretics? Extra dextrose/insulin? Excess GI losses? Try ranitidine 100mg in PN. Lower dextrose. Correct acid-base.
3. Hyponatremia: 90% of Hyponatremia is fluid overload. Check blood and urine Osmolarity and identify why Hyponatremia: R/O Hyperglycemia-induced Hyponatremia. Don’t add more than 155mmol/L.
Note: There is no limit on how much Mg and K can be added to PN assuming the patient has massive GI losses. If not, and if the the case is intracellular shift due to acid-base or drug-induced, then be more conservative.
The key to success with electrolytes correction is identifying the of etiologies.