Background: Severe Hypotonic Hyponatremia (SHH, defined as a plasma Sodium ≤ 120 mmol/L) may induce fluid shifts causing cerebral edema and neurological symptoms. This usually requires immediate correction with NaCl 3.0%, to induce a rapid initial rise in plasma sodium of 5 mmol/L to reduce cerebral cell swelling. However, overcorrection may lead to central demyelination. The optimal infusion volume is still under debate,

Objectives: To compare the efficacy and safety of an initial bolus regimen with 100 and 250 ml NaCl 3.0%.

Methods: All patients admitted between March 2017 and March 2018 with a plasma sodium ≤ 120mmol/L were included. Patient information was collected retrospectively, including diagnosis at admission, initial treatment, sodium concentrations during treatment, etc.  

Results: 95 patients were included. Mean sodium at admission was 116+-4 mmol/L. SIADH (n = 32) and sodium depletion (n = 32) were the most common diagnoses. NaCl 3.0% bolus treatment was given to 69 patients: 100 ml in 31 patients, 250 ml in 28, and a variety of other doses in 10. Twenty-six patients received other treatments (NaCl 0.9%, fluid restriction, or no treatment). Mean plasma sodium increased by 3.9 ± 2.2 mmol/L in the ‘250’ group, and by 2.4 ± 2.1 mmol/L in the ‘100’ group (p = 0.017). Overcorrection of plasma sodium, defined as a rise > 10 mmol/L within the first 24 hours was not observed.

Conclusions: Severe hyponatremia can be safely treated with 250 ml NaCl 3.0%, and this is more effective then treatment with 100 ml. Cases of overcorrection were not observed.