Hyponatremia

Hyponatremia – Kaitlyn Reasoner

Background

  • Definition: Serum Na+ <135 mEq/L. A problem of excess free water.
  • Can be due to water intake or ADH release
  • ADH is released in response to serum osm or volume (low cardiac output can also look like low volume to the body, e.g. heart failure exacerbation)
  • The body will protect volume over preserving a normal osmolarity and ADH will be released for low volume/low CO despite a low osm
  • Herniation almost exclusively occurs in acute settings including large volume H2O ingestion (ecstasy usage, runners, psychogenic), post-op, intracranial pathology
  • Severity:
    • Mild: Na+ 130-134
    • Moderate: Na+ 125-129
    • Severe: Na+ <125

 

 

Presentation

  • Mild to moderate symptoms include lethargy, N/V, dizziness, confusion, fatigue, cramping
  • Severe symptoms include obtundation, coma, respiratory arrest, seizure.

 

Evaluation/Management

  • Rule out pseudohyponatremia, review meds and infusions (often hypotonic)
    • If pt also has hypokalemia, correcting the K+ will also increase the Na+ and this must be taken into account when calculating the amount of Na+ needed
  • Step 1: Rule out pseudohyponatremia
    • Causes of pseudohyponatremia include hyperglycemia (most common), sorbitol, mannitol, sucrose, elevated lipids, TSH, or protein
    • Check glucose, TSH, lipids, and protein level
    • If hyperglycemic, corrected serum Na+ = measured Na+ + 1.6*[(glucose – 100)/100]
        • If corrected Na+ is normal, treat hyperglycemia; there is not a water balance problem
        • If corrected Na+ is low, there is hypotonic hyponatremia + coexisting hyperglycemia
  • Step 2: Determine if ADH is high or low and treat accordingly
    • Send urine osm and urine Na+ at the same time you send serum osm
    • High ADH = urine osm or urine osm>serum osm
    • Low ADH, high free water intake = urine osm or urine osm< serum osm
        • Causes: primary polydipsia, beer potomania, tea & toast
        • Treatment: restrict free water
  • Step 3: If ADH is high, determine if it is appropriate versus inappropriate elevation
    • Appropriate ADH is due to actual/perceived circulatory volume or cardiac output
        • Causes:  hypovolemia, cirrhosis, heart failure/ CO, nephrotic syndrome, salt wasting (HCTZ, cerebral, SSRIs, etc.)
        • Urine Na+ usually <30 mmol
        • Treatment: Stop offending medications & Correct volume perturbation
    • Inappropriate ADH , euvolemic or ADH out of proportion to stimulus, urine Na+>30
        • Causes: SIADH (malignancy, meds, surgery, pulmonary disease, hormones, pain, or bladder distension)
        • Treatment: water restriction, can add NaCl tabs or urea if fluid restriction is severe
        • Calculate Water restriction for SIADH (L per day) = 600 / Urine osm
          • 600 is the average salt meq in an American diet per day

 

 

 

Additional Information

 

Consider nephrology consult if:

  • Considering ddAVP clamp for overcorrection, or suspect this will happen, PO urea (a non-sodium osmole), Lasix if appropriate, vaptans, salt tablets
  • ICU care for pts with serum Na+<120
  • Pts at high risk for osmotic demyelination: chronic liver disease, chronic alcohol use, concurrent hypokalemia, malnourishment, serum sodium <105

 

Acute (<48 hrs)

  • If severe or symptomatic + not autocorrecting, give 50 cc bolus 3% NaCl (HTS)
  • Monitor Na+ q1-2 hr
  • Goal is an initial rapid 4-6 mEq/L correction and then hold
    • May require Hypertonic Saline infusion

 

Chronic (>48 hrs or unknown, higher risk for osmotic demyelination if corrected too quickly):

  • Goal Na+ correction rate 4-6 mEq/L over 24 hrs (Max 8mEq/L)
    • 8 mEq/L per 24 hrs thereafter
  • If severe, proceed as under acute above