Hyponatremia

Background

Low = <135meq/L

Symptomatic = <120meq/L (or higher than this if drop occurs abruptly)

Rapid correction can cause CHF & CPM (AMS, dysphagia, dysarthria, paresis)

Diagnosis

• Correct for glu/lipid/protein

• see med calc 'Change in plasma Na'

DDX

A. Hypovolemic

    1. Extrarenal losses (UNa <20)

         a. Sweating

         b. Vomiting

         c. Diarrhea

         d. Third-spacing

              i. Burns

              ii. Peritonitis

              iii. Pancreatitis

    2. Renal losses (UNa >20)

         a. Diruetics

         b. Addison's

         c. Ketonuria

         d. RTA

         e. Osmotic diruresis

B. Euvolemic (UNa >20 meq/L)

    1. SIADH

         a. CNS

         b. Lung

         c. CA

         d. Pain

         e. Drugs

    2. H2O intoxication

C. Hypervolemic

    1. Renal failure (UNa >20)

    2. Cirrhosis, CHF, RF (UNa < 20)

D. Pseudo

    1. Hyperprotein

    2. Hyperlipid

    3. Hyperglyc

    4. Mannitol

Treatment

• Correct volume deficit (NS)
• For severe (<120 with CNS changes):
• 3% NS @ 100 cc/hr x 3 hrs (70kg person)
• For non-70kg person:
• (kg X 0.6)/513 = cc/hr 3%
• For seizure, benzos + bolus 1.5cc/kg of 3% over 10min; repeat Q10min until sz stops (max total = 6cc/kg)

NA DEFICIT (for later replacement)

Na Deficit (meq) = kg x 0.6 x (140 - Na)

Give 1/3 total def rapidly in severe sx

• OR (Desired Na - Measured Na)(0.6)(wt in kg)= mEq Na administered

NS = 154 meq/L

3% = 513 meq/L

EXAMPLE:

desired Na- 120

measure Na- 100

(120-100)(.6)(70kg)=840 meq

• if 513meq in 1L, then 840 meq in 1.6L. Correct over 24hr, so 68cc hypertonic Na/ hr for 24 hrs

Asympt = max inc 0.5meq/L/hr (12meq/L/dy)

Sympt = 1-2 meq/L/hr

• Do not correct to >120 meq/l or >20 meq/l in 24 hr

Disposition

Admit Na < 125

Source

2/4/06 DONALDSON (adapted from Tintinalli, Mistry)