HYPONATREMIA

Ptns with severe, chronic hypo-Na+ (Na+ <120 mEq/L) and mild/moderate Sms are commonly ttt with either a continuous infusion or intermittent boluses

 

Intermittent bolus vs continuous infusion of hypertonic saline in severe hyponatremia (Nov. 2020)

 

Ptns with severe, chronic hypo-Na⁺  (Na⁺ <120 mEq/L) and mild/moderate Sms are commonly ttt with either a continuous infusion or intermittent boluses of 3 % saline, but these regimens have not been compared in a direct fashion. In an un-blinded trial, nearly 180 such ptns were randomly assigned to continuously infused (0.5 mL/kg/h) or intermittent boluses (2 mL/kg/6 hs) of 3 % saline; these doses are currently higher than recommended. Both regimens, however, were associated with similar rates of Sms relief & correction rate of hyponatremia; nevertheless, rates of the rapidly corrected levels were eventually higher, and almost ½ of cases necessitate intervention to decrease s. Na⁺ again. Experts continue endorsing either approach to 3 % saline infusion (continuous infusion or intermittent boluses) with a more conservative dosage plans to prevent overly rapidly corrected hypo- Na⁺.

Baek SH, Jo YH, Ahn S, et al. Risk of Overcorrection in Rapid Intermittent Bolus vs Slow Continuous Infusion Therapies of Hypertonic Saline for Patients With Symptomatic Hyponatremia: The SALSA Randomized Clinical Trial. JAMA Intern Med 2020.

 

Severe hyponatremia (Na⁺ <120 mEq/L):  ptn with severe, chronic hypo-Na⁺ (s. Na⁺ <120 mEq/L), require IV 3 % saline starting with 0.25 mL/kg/h, infused via a peripheral vein; use 3 % saline (rather than normal saline) in ptns with & without current hypovolemia. Alternatively, is infusing 1 mL/kg boluses of 3 % saline IV/6 hs with modifying the dose accordingly as required. However, some ptns may need desmopressin (dDAVP) to impede the overly rapid correction.  

There is an evidence that 3 % saline can be safely infused in a peripheral vein, but there’s no evidence that it induces > vascular thrombosis or extravasation injuries. However, some centers’ policies starting 3 % saline should be ONLY infused via a central vein. Such policy urges some clinicians to select only  isotonic saline instead of the hypertonic one for hypovolemic ptns; however, isotonic saline should be completely prohibited with severe hypo-Na⁺. If 3 % saline cannot be provided due to center’s policy restriction, then an infusion of 1.5-2 % saline is suggested but with a more rapid rate than that given for 3 % saline.  

 

Scarce data declaring the options among slow, continuous infusion & intermittent boluses of 3 % saline in severe hypo-Na⁺ + mild/moderate Sms. One non blinded trial comparing continuous infusion (0.5 mL/kg/h) with intermittent bolus (s) (2 mL/kg/6 h.s); the dose of 3 % saline are eventually higher than currently recommended. The 2 g. (s) had similar results regarding Sm resolution & overcorrection. However, with these dosages, therapeutic re-lowering with 5 % dextrose in water was currently needed in about ½ of cases, and despite this maneuver, overcorrection has been frequently observed. As most ptns were at very low risk of ODS, safety of these protocols is not established yet. With easily reversible cause (s) of hypo-Na⁺ (e.g., hypovolemia) and likely to develop a water diuresis during treatment, or with higher risk of osmotic demyelination syndrome (ODS), simultaneous desmopressin should be provided to prohibit overly rapid correction.  

 

Risk factors for ODS include:

1)    Very low Na⁺ ≤105 mEq/L

2)    Concomitant hypo-k⁺.

3)    Malnourished subjects

4)    Chronic excessive alcohol abuse

5)    Acute or chronic liver disorders

 

Rapidly reversible causes of hyponatremia include:

1)    Hypo-Na⁺  related to depleted true volume (corrected hypovolemia will inhibit ADH, so, >> water diuresis)

2)    Hypo-Na⁺ related to adrenal insufficiency (providing adrenal steroids will inhibit ADH & induce water diuresis)

3)    Hypo-Na⁺ related to the SIADH; including post-surgical ptns or SIADH related to painful condition or medications).

 

Ptns with severe hypo-Na⁺ are vulnerable to more worse Sms if s. Na⁺ decline more and, on the other hand, they are at risk of ODS if s. Na⁺ corrected very quickly. Ideally, the lower Na⁺ level, the greater this risk. So, it is preferred to give 3 % saline in such ptns to ttt hypo-Na⁺, even among hypovolemic ptns. Isotonic saline can be provided concomitantly (with 3 % saline), if required, to control symptomatic hypovolemia or pre-renal azotemia.