Abstract: SA-OR066

Mobilization of Nonosmotically Stored Sodium after Water Loading in Healthy Individuals

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 704 Fluid, Electrolyte, Acid-Base Disorders


  • Wouda, Rosa Diana, Academic Medical Center, Amsterdam, Amsterdam, Netherlands
  • Dekker, Shosha, AMC Amsterdam, Amsterdam, Netherlands
  • Reijm, Joelle, Academic medical center, Amsterdam, Netherlands
  • Olde Engberink, Rik Hg, Academic Medical Center, Amsterdam, Netherlands
  • Vogt, Liffert, Academic Medical Center, Amsterdam, Netherlands

Recently it was discovered that significant amounts of sodium (Na+) can be stored without concurrent water retention. These observations indicate the presence of a third compartment for Na+ distribution. The role of this compartment under hypotonic conditions is not known. In this study we investigated whether Na+ can be released from its nonosmotic stores after a hypotonic fluid load.


Twelve healthy male subjects had a water loading test (WL; 20 ml water/kg in 20 min). During a 240 min follow-up, we compared the observed plasma [Na+], fluid and cation excretion with values predicted by the Barsoum-Levine and Nguyen-Kurtz formula. These formulas are used for guidance of fluid therapy during dysnatraemia and do not account for nonosmotic Na+ stores.


30 min after WL plasma [Na+] was decreased with -3.2±0.5 mmol/L (mean (SE)), after which plasma [Na+] increased gradually. The observed maximal decrease in plasma [Na+] after WL was significantly overestimated by the Barsoum-Levine (-4.4±0.3 mmol/L) and Nguyen-Kurtz formula (-5.2±0.4 mmol/L)(p<0.05). In addition, 120 min after WL the Barsoum-Levine and Nguyen-Kurtz formula overestimated urine volume, while cation excretion was significantly underestimated with a cation gap of 51±18 mmol and 60±19 mmol, respectively (p<0.05). At 240 min, this gap was 29±18 mmol and 5±23 mmol, respectively (p=NS).


These data demonstrate that healthy individuals are able to mobilize osmotically inactivated Na+ after a hypotonic fluid load. Further research is needed to expand knowledge on the Na+ buffer and asses its impact on therapy of dysnatremia.