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

1. Hypovolemic
   1. Extrarenal losses (UNa <20)
      1. Sweating
      2. Vomiting
      3. Diarrhea
      4. Third-spacing
         1. Burns
         2. Peritonitis
         3. Pancreatitis
   2. Renal losses (UNa >20)
      1. Diruetics
      2. Addison's
      3. Ketonuria
      4. RTA
      5. Osmotic diruresis
2. Euvolemic (UNa >20 meq/L)
   1. SIADH
      1. CNS
      2. Lung
      3. CA
      4. Pain
      5. Drugs
   2. H2O intoxication
3. Hypervolemic
   1. Renal failure (UNa >20)
   2. Cirrhosis, CHF, RF (UNa < 20)
4. Pseudo
   1. Hyperprotein
   2. Hyperlipid
   3. Hyperglyc
   4. Mannitol

Treatment

1. Correct volume deficit (NS)
2. For severe (<120 with CNS changes):
   1. 3% NS @ 100 cc/hr x 3 hrs (70kg person)
3. For non-70kg person:
   1. (kg X 0.6)/513 = cc/hr 3%
4. For seizure, benzos + bolus 1.5cc/kg of 3% over 10min; repeat Q10min until sz stops (max total = 6cc/kg)

NA DEFICIT

1. Na Deficit (meq) = kg x 0.6 x (140 - Na)
2. Give 1/3 total def rapidly in severe sx
3. 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)