Why D5 1/2NS was the Right Choice in the 1950s!

For many, a frequent practice is to order D5 1/2NS intravenous fluids for maintenance IVFs.  An expert review (ML Moritz, JC Ayus. NEJM 2015; 2015: 373: 1350-60) of this topic explains why this was right in the 1950s but is usually the wrong choice today.

Key points:

  • Use of hypotonic maintenance fluids (sodium concentration <130 mmol per liter), “has been associated with a high incidence of hospital-acquired hyponatremia and more than 100 reports of iatrogenic deaths or permanent neurologic impairment related to hyponatremic encephalopathy.”
  • Acutely ill patients have “disease states associated with excess arginine vasopressin.”
  • Recommendations on the use of hypotonic fluids were “based on theoretical calculations from the 1950s, before the syndrome of inappropriate antidiuresis was recognized as a common clinical entity.”
  • “More than 15 randomized, prospective trials involving more than 2000 patients have evaluated the safety and efficacy of isotonic fluids…most of these studies involved children…isotonic fluids were superior.” Limitations: these studies were typically <72 hours and excluded patients with renal disease, heart failure, and cirrhosis.
  • The authors also note potential problems with 0.9% NS for rapid infusion, perhaps related in part to the polyvinyl chloride bags which lowers the pH.  “0.9% saline, as compared with balance salt solutions, may produce a hyperchloremic metabolic acidosis, renal vasoconstriction, an increased incidence of acute kidney injury requiring renal-replacement therapy, and hyperkalemia.”
  • Hypotonic fluids may be appropriate in the setting of established hypernatremia or a clinically significant renal concentrating defect (with free-water losses).

My take: D5 1/2 NS and other hypotonic fluids should not be used commonly as a maintenance fluid.

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2 thoughts on “Why D5 1/2NS was the Right Choice in the 1950s!

  1. Interesting… tho, in truth, nothing new. Back when I was a resident routinely ordering fluids, it was obvious that many kids on what we then considered maint. would get mildly hyponatremic. One fix: was to stop ordering labs and pull the IV!

    This may come across as unnecessarily crusty, but I blame a fundamental flaw in medical education. How many residents know the difference between dehydration (that is, not enough free water, as reflected by a high serum sodium, which should be treated if necessary with free water), and a volume deficit (which is a clinical diagnosis based on vitals, lack of tears, decr UOP, etc, and should be treated with isotonic fluids)? Yes, in peds, sometimes kids have both at the same time– then you can be sloppy and half the difference to treat with 1/2 NS. But that’s still not MAINTENANCE, that’s therapeutic.

    //end nerdy rant

    • What I don’t understand is why hypotonic fluids remain so popular when it is known that there are increased risks. Since many patients are carefully monitored, very few develop complications. Yet, given the high frequency usage of hypotonic fluids, iatrogenic complications will continue. A particular group at risk are post-operative patients and these patients also tend to be monitored with bloodwork less frequently.

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