Brown Pediatrics

Brown's Pediatric Residency Blog

Category: #FOAMpeds

Pass the salt…

Post Created by: Dani Halpern, MD

Case: 5yo M comes into the ED with nausea, confusion, and headache. On exam, he is sleepy but noticeable uncomfortable. He has moist mucous membranes, pupils are reactive and he has no noticeable edema. Suddenly, he begins to have a generalized tonic-clonic seizures. Amid the chaos and his mother’s crying you check a BMP and lo and behold his Na comes back as 125!

 

Image credit: http://westeastonpa.com/wp-content/uploads/2015/03/no-salt.jpg

What is the pathophysiology of hyponatremia?

When there is an acute drop in sodium in the blood, water is pulled into the intracellular fluid so cells, especially brain cells, begin to swell. This causes meningeal irritation and the manifested symptoms of nausea, confusion, headache, vomiting and eventually, seizures.

Effects of Hyponatremia on the Brain and Adaptive Responses

Image from: Adrogue HJ et al, 2000

What is the workup of hyponatremia?

Choice of diagnostic algorithms:

  • Classic algorithm begins with an evaluation of patient’s fluid status.
    • Hypovolemic hyponatremia: ↓↓Na/↓H20 Euvolemic hyponatremia: ↔Na/↑H20   Hypervolemic hyponatremia: ↑ Na/↑↑H20
    • This is notoriously difficult to do accurately and clinicians have been shown to be very inaccurate in their assessment with sensitivities ranging from 0.5-0.8 and specificities 0.3-0.5 (Chung HM et al, 1987)
  • Alternative algorithm: (Milionis HJ et al, 2002).

Application of Alternative Algorithm

(Adapted from Milionis HJ et al, 2002)

Step 1: Verify this is an accurate level and is not spuriously low

Step 2: Obtain serum osmolality: (normal 275-290)

  • Low serum osmolality: True hyponatremia
  • Normal serum osmolality: Results from either large volumes of isotonic fluid lacking sodium (most common = mannitol), or in cases of hyperparaproteinemia or hyperlipidemia/triglyceridemia, that latter cases being referred to as “pseudohyponatremia” (see below for illustration). This is only seen in labs that use flame photometry; newer methods using ion-specific electrode have nearly eliminated this entity (Androgue HJ et al, 2000).

  • Increased osmolality: Osmotically active substances (most commonly glucose), draw water out of cells, effectively diluting serum sodium
    • Correction is approximately 2 mEq Na for every 100 glucose is >100

Step 3: Obtain urine Osm and Urine Sodium

  • <100 mOsm/kg = Appropriate water Excretion
    • Primary polydipsia/ psychogenic water drinking
      • Adult needs to drink about 18L for noticeable decrease in Na
    • Low solute intake (e.g. malnutrition, “beer potomania”)
  • >100 mOsm/kg = impaired water excretion. Can be due to problems in 3 different locations in process of diluting urine (this is where urine sodium comes in):
    • <20 mEq/L: hypovolemia (most common cause) and other states of decreased effective arterial blood volume (e.g. cirrhosis, congestive heart failure, nephrotic syndrome (rare in the absence of concurrent renal failure or volume depletion))
    • >40 mEq/L: SIADH vs renal salt wasting (e.g. renal dysplasia, post-obstructive diuresis, post-ATN diuresis), diuretics [mostly thiazide diuretics, uncommon with loop diuretics], adrenal insufficiency, metabolic alkalosis) THIS IS WHERE CLINICAL ASSESSMENT OF VOLUME STATUS ACTUALLY MATTERS (SIADH: restrict water.  Salt wasting: give salt or stop drugs)

In summary, a diagnosis of SIADH requires SOsm < 275, Uosm >100, UNa >30 (Because the fact that urine sodium is not low suggests that the patient is not volume depleted)

Treatment

Image Credit: pixabay.com

In general, treatment of hyponatremia must weigh the benefits of therapy against the risks of overcorrecting, namely, osmotic demyelination (Adrogue HJ et al, 2000).

General Principles

  1.  If the patient has severe symptoms (e.g. seizures, CNS depression), hypertonic saline (3-5cc/kg) should be administered (Brenkert TE et al, 2013)
  2. When correcting hyponatemia, the rate of correction should not exceed 8mmol/L on any day of treatment  (Adrogue HJ et al, 2000).
  3. Treat the underlying condition, as detailed above

 

And now a table for all the conditions that often get confused for one another: 

First test yourself:

SIADH Renal salt wasting Hypovolemia
Volume Status
Serum Na
Urine Na
Serum Osm
Urine Osm
Urine output
ADH

 

Answers: 

 

SIADH Renal salt wasting Hypovolemia
Volume Status Euvolemic Hypovolemic hypovolemic
Serum Na low low Low
Urine Na > 40 >>40 <20
Serum Osm low low low
Urine Osm > plasma Osm > plasma Osm >plasma Osm
Urine output Low high low
ADH high high high

Faculty Reviewer: R. Kremsdorf, MD


References

Adrogué HJ, Madias NE, and Madias NE. “Hyponatremia.” N Engl J Med. 2000;342:1581-1589

Brenkert TE et al. “Intravenous hypertonic saline use in the pediatric emergency department.” Pediatr Emerg Care. 2013 Jan;29(1):71-3.

Chung HM, Kluge R, Schrier RW, Anderson RJ. “Clinical assessment of extracellular fluid volume in hyponatremia.” Am J Med. 1987;83: 905-908

Milionis HJ, Liamis GL, Elisaf MS. “The hyponatremic patient: a systematic approach to laboratory diagnosis.” Canadian Medical Association Journal. 2002;166(8):1056-1062.

OPENPediatrics

We are so excited to launch the OPENPediatrics Critical Care Curriculum! The OPENPediatrics platform will have two purposes.
  1. The Guided Learning Pathway is designed to teach you the bread and butter of critical care.
  2.  The second component is a Group page that will have additional educational material outside the OPENPediatrics curriculum. We will invite each resident to the group page. We encourage residents to send any interesting data or learning material to us. We will review the material with the critical care team and then uploaded onto the group page.

How to gain accesses to the material:

  1. Go to https://www.openpediatrics.org
  2. Create a username and password. Please create a username with the email the residency uses. We will be searching for your email when designing the group page.
  3.  Click the learning tab
  4. Click Guided Learning Pathways
  5. Click on Brown Pediatric Critical Care Resident Curriculum
  6. Enroll!
Our goal is asynchronous learning that provides a solid foundation for clinical management of patients.  As such, the material can be approached in a nonlinear fashion.

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