Hyponatremia

Dr.Methaq A.M.Hussein

MRCP(UK), Endocrine ,D.M (LONDON) ,ASSIST.PROF.

Hyponatremia

• Hyponatremia defines as serum sodium concentration <135meq/L.
• Most frequent electrolyte abnormality in the hospitalized pt.
• Essentially common in critical care units. In addition to being a potentially life-threatening condition, hyponatremia is an independent predictor of death among intensive care unit and geriatric patients and those with heart failure, and cirrhosis.

Hyponatremia

• Changes in serum sodium concentration results from derangements in water balance.
• Low serum sodium concentration denotes a relative deficit of sodium and /or a relative excess of water.
• As seen in the formula, hyponatremia may result from either a decrease in the numerator or an increase in the denominator.
Serum sodium = total body sodium
total body water

Approach to the pt with hyponatremia

Decreased serum osmolality --check volume status. It could be:


Hypovolumeic,
Hypervolumeic or
Euvolumeic.

Approach to the patient with Hyponatremia

• Hypovolumeic Hyponatremia (Dehydartion)
• Decrease Sodium
• Decrease water
• Causes:
• Diarrhea
• Diuretic use
• Mineralcorticoid defeciency
• Osmotic diuresis like mannitol

Approach to the patient with Hyponatremia

• Hypervolumeic Hyponatremia
• Sodium content unchanged
• Increase water
• Causes:
• Heart Failure
• Cirrhosis
• Nephrotic syndrome


Approach to the patient with Hyponatremia
Euvolumeic Hyponatremia

Sodium content unchanged

Relative increase in water

Cause:

Syndrome of inappropriate diuretic hormone
(SIADH)

Approach to the patient with Hyponatremia

Hyponatremia with decreases serum osmolality

ECF volume ECF volume ECF volume

decreased normal (euvolumic) increased (edema)

Renal Extrarenal SIADH CHF

Diuretics GI losses Cirrhosis
Nephrotic syndrome



Urine Na Urine Na Urine Na Urine Na

TB Na

TB water
TB Na
TB water
TB Na
TB water

SIADH

Inappropriate release of ADH causes siadh.
It is diagnosed by checking :
Serum sodium <135
Serum osmolality <280
Urine osmolality >100
Urine sodium >30
also low serum uric acid <4.0

Causes of SIADH

• Central nervous system;
• meningitis, brain abcess,
• stroke, acute psycosis
• Pulmonary
• pneumonia, lung abcess,
• tuberculosis
• Endocrine
• Addison's disease, hypothyroidisim ,
• hypopituitarism
• Neoplastic
• pancreatic or lung cancers.


Drugs induced SIADH
• Increased ADH ADH potentiation
• Anti-depressant carbamazepine
• anti-psycotics chlopropamide
• carbamazepine cyclophosphamide
• platinum alkaloids Nsaids
• alkylating agents ADH like activity
• interferon vasopressin
• levimasole ddavp
• oxytocin

Clinical manifestation of siadh

• Acute: (<48 hours)
• Stupor/coma
• Convulsions Treatment with
• Respiratory arrest 3% NaCl
• Chronic; (>48 hours)
• Headache
• Irritability Treat with medicines
• Nausea & vomiting like Vaptans
• Confusion & Disorientation
• Gait disturbance



SIADH
Treatment
Fluid Restriction
Oral Salt, Hi-protein diet or Urea (30 g/d): promote solute diuresis
Lasix 20 mg po od-bid: Loop direct diminishes medullary gradient
Demeclocycline 300-600 mg bid (can be nephrotoxic)
Lithium (induces NDI)
IV salt solution:
Rarely if ever needed (i.e. only if symptomatic with SZ/coma)

Rx Hyponatremia

Na deficit = 0.6 x wt(kg) x (desired [Na] - actual [Na])
(mmol)

When do you need to Rx quickly?

Acute (<24h) severe (< 120 mEq/L) Hyponatremia
Prevent brain swelling or Rx brain swelling
Symptomatic Hyponatremia (Seizures, coma, etc.)
Alleviate symptoms
“Quickly”: 3% NS, 1-2 mEq/L/h until:
Symptoms stop
3-4h elapsed and/or Serum Na has reached 120 mEq/L
Then SLOW down correction to 0.5 mEq/L/h with 0.9% NS or simply fluid restriction. Aim for overall 24h correction to be < 10-12 mEq/L/d to prevent myelinolysis


Rx Hyponatremia (Example)
Na deficit (mmol) = 0.6 x wt(kg) x (desired [Na] - actual [Na])

60 kg women, serum Na 107, seizure recalcitrant to benzodiazepines.

Na defecit = 0.6 x (60) x (120 – 107) = 468 mEq
Want to correct at rate 1.5 mEq/L/h: 13/1.5 = 8.7h
468 mEq / 8.7h = 54 mEq/h
3% NaCl has 513 mEq/L of Na
54 mEq/h = x
513 mEq 1L
x = rate of 3% NaCl = 105 cc/h over 8.7h to correct serum Na to 120 mEq/h

Note: Calculations are always at best estimates, and anyone getting hyponatremia corrected by IV saline (0.9% or 3%) needs frequent serum electrolyte monitoring (q1h if on 3% NS).

Correcting hyponatremia

traditional approach;

add to the

numerator

Serum sodium = Total body sodium

Total body water


Correcting hyponatremia
Current approach;

Serum sodium = Total body sodium

Total body water

Subtract from the

the denominator

Treatment strategies for Acute hyponatremic emergencies

3% NaCl: 100ml bolus for severe symptoms.
3% NaCl@1 to 2ml/kg/hr for 2 to 4 hours plus furosemide.
Goal: correction by 4 to 6 mEq/L in first few hours.
Monitor closely to avoid excessive correction.

Treatment strategies for chronic hyponatremia

Treatment
Mechanism
Advantages
Limitations
Fluid restriction
(0.5- 1 liter/day)
Water intake
Effective, inexpensive
Poor compliance
Demeclocycline
(600-1200mg/d)
Inhibits action of adh
Easily available
3-4 days for onset,
nephrotoxicity
Urea
(30mg/d)
Osmotic diuresis
Decreased risk
Poor palatability,
Avoid in ckd
Lithium
(up to 900mg/d)
Inhibits action of adh
Easily available
Slow onset,
toxicity


Rate of correction
• Acute symptomatic :
• 4 to 6 mEq/L in first 4 hours
• Target <12 mEq/L in first 24 hours.
• Chronic:
• Target correction at <8 mEq/L in first 24 hours
• Goal not to exceed;
• 12 mEq/L in first 24 hr
• 18 mEq/L in first 48 hr

Importance of appropriate serum sodium correction

• Too-rapid correction of hyponatremia (e.g., >12 mEq/L/24 hours) can cause osmotic demyelination syndrome (ODS) resulting in:
• dysarthria, dysphagia,
• seizures, coma and death
• spastic quadriparesis.
• Risk factors for ODS:
• severe malnutrition,
• alcoholism,
• advanced liver disease

Non-peptide AVP receptor antagonist (Vaptans)

• Aquaretic nonpeptide arginine vasopressin receptor (AVPR) antagonists are safe and effective hyponatremia therapies.
• Vaptans lead to aquaresis, an electrolyte-sparing excretion of free water, that results in the correction of serum sodium concentration.