Dr. Adeeb Zaer Hyponatremia: An Overview

If in extremis:

• Symptoms: Seizures, AMS, brain herniation, cerebral edema
• Treatment: 100cc 3% hypertonic saline over 20 minutes – reevaluate and repeat x 3 if necessary until neurologic signs are gone

How to evaluate Hyponatremia:

1^st step – Determine which of the 3 kinds it is by calculating the serum Osms.

• Hypertonic – (serum Osm >295) 2/2 hyperglycemia or mannitol
• Isotonic – (serum Osm 280-295) “pseudohyponatremia” 2/2 hypertrygliceridemia or paraproteinemia
• Hypotonic – (serum Osm <280) – most common

2^nd step – If the patient is hypotonic, determine what kind of hypotonic hyponatremia it is, as there are 3 kinds.  Use history, physical exam findings of volume status, and urine electrolytes to assist you.

• Hypervolemic
  • Causes
    • Extrarenal– CHF, cirrhosis, nephritic syndrome
      • UNa < 20
    • Chronic renal failure
      • UNa > 20
    • Tx – correction of underlying cause and water restriction
• Hypovolemic
  • Causes
    • Extra renal – vomiting, diarrhea, GI drainage tubes, burns, third spacing
      • UNa < 20
    • Renal – diuretics and salt wasting nephropathies
      • UNa > 20
    • Tx – NS at rate as calculated below
• Euvolemic
  • Causes
    • Exogenous water load – psychogenic polydipsia, hypotonic fluids, hypothyroidism, cortisol deficiency
    • SIADH – ADH causes urine to be concentrated by absorbing water back into the blood stream
      • Cause – CNS or pulmonary malignancy, meds (chlorpropamide)
      • Labs
        • UNa > 20
        • Urine Osm > 100
    • Tx – water restriction. Demeclocycline if water restriction has failed

How to raise Na with fluids:  

• If you correct it too quickly you may get central pontine myelinolysis
• Can raise it 2 mEq/L/hr during seizure and after seizure only by 1mEq/L/hr max – some say 0.5
• Infusate rate = (1000*change in Na per hour desired * ((0.6*kg)+1))/(IVNa + IVK – Serum Na)
  • HTS has 513mEq/L of Na while NS has 154mEq/L
  • Using an online calculator is easier

A recent EMCrit podcast recommends ordering labs but not giving any fluids to hyponatremic patients who do not have neurologic deficits.  They suggest that the admitting team can determine treatment and fluid rates once the results of urine electrolytes have returned.

If with stable vital signs, how do you personally treat hyponatremia in the ED?  Fluids? And if so, how much?