Tag Archives: hypotonic fluids

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

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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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“We Still Have More to Learn”

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“The most beautiful thing we can experience is the mysterious, it is the source of all true art and science. He to whom this emotion is a stranger, who can no longer pause to wonder and stand rapt in awe, is as good as dead: his eyes are closed.” –Albert Einstein.

I’m not sure the above quote has much direct relevance to today’s blog, but it came to mind after reading “we still have more to learn” in a recent editorial.  The editorial elaborated on another study showing that hypotonic fluids increase the risk of hyponatremia (J Pediatr 2014; 165: 163-9, editorial 14-15).  The editorial cautions that “intravenous fluid therapy is a prescription much like antibiotics or chemotherapy.  What we prescribe for intravenous fluids must fit the patient’s history and condition.”

The article was a systemic review of published studies.  Though 1634 citations were screened, only 10 studies (n=893) were included as independent randomized controlled trials.  Hypotonic fluids were defined as tonicity <250 mmol/L; isotonic fluids were defined as normal saline (0.9%), Ringer lactate, Hartmann solution, and any other fluid with tonicity approaching that of normal serum. The key findings:

  • Hypotonic fluids increase the relative risk (RR) of hyponatremia (Na <135) with RR of 2.37
  • Moderate hyponatremia (Na <130) risk was increased further with RR of 6.1.
  • Sub-group analysis of half-normal saline showed relative risk for hyponatremia was 2.42.

The editorialists comment that much has changed in the 55+ years since Holliday and Segar’s publication in 1957 describing maintenance fluid requirements.  These changes include sicker patients who are at increased risk for non-osmotic ADH release.  Thus, even patients receiving isotonic fluids are at some risk for hyponatremia.  However, the key point is that maintenance fluids are not appropriate for replacement of losses and in the perioperative setting.

Bottomline: Think twice before using a hypotonic fluid especially on admission or after surgery.  While there is no perfect intravenous fluid for all patients at all times, in many patients, isotonic fluids will be more favorable by reducing the risk of hyponatremia.

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Has Your Hospital Restricted Quarter-Normal Saline?

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In a previous post (What’s critical to you | gutsandgrowth), I’ve drawn attention to the problem of hyponatremia.  This particular hospital problem is often iatrogenic and often preventable.  Two recent studies provide more data to support limiting hypotonic fluids.

The first study that took place between 2009-2011, shows that this remains a common problem at Stanford’s pediatric hospital (J Pediatr 2013; 163: 1646-51).  This study was a retrospective study with data extracted from the hospital’s EMR.

From a cohort of 5498 patients receiving intravenous fluids (IVFs) on admission, 1048 were suitable for study due to the availability of serum sodium levels, not having several types of IVFs, and not being neonatal patients.  In addition, patients who had abnormal sodiums on admission (n=753) were excluded.

Hypotonic fluids included: D5W, one-quarter normal saline (1/4 NS), D5 1/4 NS, 1/2 NS, D5 1/2 NS, and total parenteral nutrition.  No patients received D5W as a maintenance fluid, but its use with medications contributed to total free water delivery.

Isotonic fluids were D5 NS, NS, and Lactated Ringer’s.

Results:

  • Hyponatremia (Na <135 mEq/L) developed in 260 of 674 (38.6%) who received hypotonic fluids and in 104 of 374 (27.8%) who received isotonic fluids. OR 1.63
  • The overall incidence of hyponatremia was 34.7% in this cohort.
  • Other factors associated with developing hyponatremia: surgical admission (adjusted OR 1.44), cardiac admitting diagnosis (aOR 2.08), and hematology/oncology admission (aOR 2.37)

The fact that hyponatremia occurred in a large number on isotonic fluids indicates that additional factors like total fluid volume and uncorrected volume deficits contribute as well. Preferential water retention can still occur in the setting of increased ADH levels. This study, like all retrospective studies, has several limitations.  However, the basic finding that hypotonic fluids increase the risk of hyponatremia remains solid.

The second study was a recent meta-analysis (Pediatrics 2014; 133: 105-113 -thanks to Seth Marcus for this reference) which included ten randomized controlled trials. It showed that hypotonic maintenance IV fluids were associated with a much higher risk of hyponatremia (RR 2.24) and severe hyponatremia (Na <130) (RR=5.29).

Bottomline from both studies: Isotonic fluids are safer than hypotonic fluids in hospitalized children for maintenance IV fluids in terms of decreasing the risk of hyponatremia.

 

What’s critical to you

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Over the past ten years, there has been increasing scrutiny with regard to iatrogenic hyponatremia.  Specifically, one of the concerns has been that the administration of hypotonic fluids will result in hyponatremia and potential complications.

In our hospital system, several years ago the hospital administration circulated a list of the new critical laboratory values that would be used to notify physicians of severe derangements.  The goal of selecting a critical value is to improve the outcome of patients by allowing a more rapid and direct communication of an abnormality.  At the same time, it takes time to contact physicians and most physicians do not want to be called too often.

I carefully reviewed the critical values list and was very concerned that the value to call for hyponatremia was <120.  When I protested, I was informed that in fact the sodium critical value had not been changed and had been in place “without a problem” for more than ten years.  In addition, the critical value cutoff at several other children’s hospitals was similar (range was between 120-130).

Despite these reassurances, I remained concerned that this was not the right policy, particularly as alterations in sodium are frequently due to physician error and need to be addressed promptly.  This led to a number of discussions with the laboratory and ultimately to a retrospective review (Guarner, J; Hochman, J; Kurbatova, E; Mullins, R.  Study of outcomes associated with hyponatremia and hypernatremia in children.
Pediatric and developmental pathology 2011;14(2):117-23.)  During a six month period, 53,099 sodium tests were reviewed with 166 having sodium values of 124 or less.  Some of the important findings include the following:

  • Mortality was 42% in patients with sodium values <120mmol/L
  • Treatment was instituted more rapidly when physicians were notified
  • Half of the patients with hyponatremia were receiving hypotonic fluids.

At this time, our critical value for sodium has changed so that physicians are now notified if sodium is less than 125.  Do you know your institution’s critical value?  Are your patients receiving hypotonic fluids?  Something to think about.

Another article in Pediatrics adds more insight into the prevention of hyponatremia (Pediatrics 2011; 128: 980 -983).  Moritz and Ayus reiterate their arguments from 2003 that hypotonic fluids should not be used routinely in children due to the risk of hyponatremia and associated complications.  They cite 20 studies completed over the last seven years which indicate that isotonic fluids are safe and prevent hyponatremia.  “There can no longer be any justification for the routine administration of hypotonic fluids in hospitalized children….On the basis of today’s standards, hypotonic fluids would not receive FDA approval for routine use.”  The main concern about hyponatremia is hyponatremic encephalopathy –this remains a common medical emergency (Pediatrics 2008; 121 (6): www.pediatrics.org/cgi/contnet/full/121/e1577).  Early in the hospital course and in the immediate postoperative period are timeframes that have been noted to have increased incidence of hyponatremia.  However, hyponatremia (<135) is common at all times and affects ~25% of hospitalized patients (Arch Dis Child 2008; 93: 285-287).  So, with your next admission, think about lactated ringer’s or normal saline instead of half-normal.

Additional References:

  • -Pediatrics 2011; 128: 857.
  • -J Peds 2008; 153: 444-447 (letters and references on this topic).
  • -Am J Clin Pathol 2007; 127: 56-59.  Critical Na values.
  • -J Pediatr 2008; 152: 33 & 4.  Frequent p-op hyponatremia.
  • -NEJM 2008; 359: 1018.  Hyponatremia associated with poor prognosis in patients awaitng OLT.
  • -Hepatology 2006; 44: 1535.  Hyponatremia (Na <130) associated with increased mortality & ascites reaccumulation.
  • -J Pediatr 2004; 145: 584. Recs 20-80ml/kg of isotonic fluid to correct hypovolemia prior to typical maintenance fluids (to avoid hyponatremia due to hypovolemia).  Says that isotonic fluids for maintenance may be problematic if cardiopulmonary or renal dz.
  • -Pediatrics 2004; 113; 1395.  Advocates use of isotonic saline (0.9%).  States that hypotonic fluids lead to hyponatremia in many cases b/c of excessive ADH in many patients.
  • -NEJM 2005; 352: 1550 & 1613. Hyponatremia related to Boston Marathon & London Marathon