Hyponatremia
Background
- Defined as sodium concentration <135meq/L
- Patients often not symptomatic until <120meq/L although this level varies by patients and may be higher if the change occurred abruptly[1]
Clinical Features
- Nausea and Vomiting
- Anorexia
- Muscle cramps
- AMS
- Seizure (esp if Na < 113)
- Coma
- Rapid correction can cause CHF & CPM (AMS, dysphagia, dysarthria, paresis)
Diagnosis
- Must determine volume status and calculated osm
- In true hyponatremia the osm is reduced
Work-Up
Prior to giving treatment
- Urine
- UA
- Urine electrolytes
- Urine urea
- urine uric acid
- urine osmolality
- urine creatinine
- Serum
- Chemistry
- Serum osmolality
- Uric acid
- TSH
- Cortisol
Types and Causes
- Often described in terms of tonicity and volume status of the patient [2]
Hypertonic Hyponatremia
- Defined as osmolarity > 295mmol/L with the following causes:
- Hyperglycemia
- Traditional teaching: [Na+] decreases by 1.6-1.8mEq/L for each 100mg/dL increase in glucose over 100mg/dL
- 2.4mEq/L may be a more accurate correction factor (Hillier 1999)
- Mannitol excess
Isotonic (pseudo) hyponatremia
- Defined as osmolarity > 275-295mmol/L. Often referred to as pseudo hyponatremia because the elevated lipids or proteins interfere with the laboratory sodium reading. The following are common causes:
- Hyperlipidemia
- Hyperproteinemia
Hypotonic Hyponatremia
- Defined as an osmolarity < 275 mmol/L and categorized as hypovolemic, hypervolemic or euvolemic
Hypovolemic
- Renal Causes
- Thiazide diuretic use
- Na-wasting nephroathy (RTA, CRF)
- Osmotic diuresis (glucose, urea)
- Aldosterone deficiency
- Extra-renal Causes
- GI loss
- 3rd space loss
- Burns
- Pancreatitis
- Peritonitis
Hypervolemic
- [[Urinary Na >20]]
- Renal failure
- [[Urinary Na <20]]
Euvolemic
- SIADH
- urine sodium is greater than 20-40 mEq/L
- Pain, stress, nausea
- Hypothyroidism
- Drugs[3]
- NSAIDs, sulfonylureas
- H20 intoxication
- Glucocorticoid deficiency
Treatment
Hypertonic hyponatremia
- Correct underlying disorder which is often hyperglycemia[4]
- Often volume depleted due to osmotic diuresis and normal saline provides adequate volume repletion
Isotonic (pseudo) hyponatremia
- No treatment needed [4]
Hypotonic hyponatremia
- Hypovolemic
- Give NS but be cautious of total daily repletion of Na so you avoid causing central pontine demylinosis
- Euvolemic[4]
- Water restrict
- Treat underlying cause
- Hypervolemic
- Water restriction
- Diuresis
- Treat underlying cause
Na Therapy
- Max correction 10mEq/L in 24hr (avoids central pontine demylinosis)
Fluid type | Sodium Concentration |
1/2 Normal Saline | 77 mEq/L |
Normal Saline | 154 mEq/L |
Lactated Ringers | 130 mEq/L |
3% Saline | 513 mEq/L |
Asymptomatic
- Step 1: Calculate total body water[5]
- TBW(kg) = Wt(kg) x 0.6 = [Wt(lb) x 0.45] x 0.6 = Wt(lb) x 0.27
- Step 2: Calculate mEq deficit
- (Desired Na - Measured Na) ~ must be ≤ 10
- Step 3: Calculate NS rate to be given over 24hr
- NS rate (cc/hr) = TBW x mEq deficit x 0.27
- If using 3% NS (to avoid volume overload) divide above rate by 3.33
- NS rate (cc/hr) = TBW x mEq deficit x 0.27
Symptomatic
Template:Symptomatic Hyponatremia Treatment
- Fluid restrict
Disposition
- Admit if Na <125
See Also
Sources
- ↑ Spasovski G. et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Nephrol Dial Transplant. 2014
- ↑ Understanding Lab Testing for Hyponatremia. Clin J Am Soc Nephrol 2008;3:1175
- ↑ Review of Drug-Induced Hyponatremia. Am J Kidney Dis 2008;52:144
- ↑ 4.0 4.1 4.2 Schrier RW, Bansal S. Diagnosis and management of hyponatremia in acute illness. Curr Opin Crit Care 2008;14:627-34
- ↑ The hyponatremia formulas do not work so well (Clin J Am Soc Nephrol 2007;2:1110 and Nephrol Dial Transplant 2006;21:1564)
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction
factor for hyperglycemia. Am J Med. 1999 Apr;106(4):399-403. PubMed PMID: 10225241.