1. Dr. M. A. SOFI MD; FRCP (London); FRCPEdin; FRCSEdin
HYPONATREMIA
Dr. M. A. SOFI MD; FRCP (London); FRCPEdin; FRCSEdin

2. HYPONATREMIA
Hyponatremia is commonly defined as a serum sodium
concentration below 135 meq/L but can vary to a small
degree in different clinical laboratories.
The dilutional fall in serum sodium is in most patients
associated with a proportional reduction in the serum
osmolality (i.e., to a level below 275 mosmol/kg), but there
are some exceptions
Hyponatremia represents a relative excess of water in
relation to sodium. It can be induced by a marked increase
in water intake (primary polydipsia) and/or by impaired
water excretion resulting from advanced renal failure or
from persistent release of antidiuretic hormone (ADH).

3. Disorders in which ADH levels are elevated or appropriately suppressed
Effective circulating volume depletion
True volume depletion
Heart failure
Cirrhosis
Thiazide diuretics
Inappropriate ADH secretion
Hormonal changes
Adrenal insufficiency
Hypothyroidism
Pregnancy
ADH levels appropriately suppressed
Advanced renal failure
Primary polydipsia
Beer drinker's potomania
Hyponatremia with elevated or normal plasma osmolality
High plasma osmolality (effective osmols)
Hyperglycemia
Mannitol
High plasma osmolality (ineffective osmols)
Renal failure
Alcohol intoxication
Normal plasma osmolality
Pseudohyponatremia (laboratory artifact)
High triglycerides
Cholestatic and obstructive jaundice (lipoprotein X)
Multiple myeloma
Absorption of irrigant solutions
Glycine
Sorbitol

4. Acute or hyperacute hyponatremia:
developed within the previous 24 hours, it is called "acute."
developed over just a few hours due to a marked increase in water intake (self-induced water intoxication, as may be seen in marathon runners, psychotic patients, and users of ecstasy), it is called "hyperacute."
Chronic hyponatremia:
present for more than 48 hours, or if the duration is unknown (such as in patients who develop hyponatremia at home), it is called "chronic."
Sub-acute :
developed within the previous 24 to 48 hours, it is called "subacute."
Mild to moderate hyponatremia:
defined as a serum sodium concentration between 130 and 135 meq/L; moderate hyponatremia is often defined as a serum sodium concentration between 121 and 129 meq/L.
Severe hyponatremia:
defined as a serum sodium of 120 meq/L or less.

5. EVALUATION — The diagnostic approach consists of a directed history and physical examination, appropriate laboratory tests.
A history of fluid loss (e.g., vomiting, diarrhea, diuretic
therapy) and, on examination, signs of volume depletion,
such as decreased skin turgor, a low jugular venous pressure,
or orthostatic or persistent hypotension.
A history of low protein intake and/or high fluid intake.
A history consistent with one of the causes of SIADH.
Use of medications associated with hyponatremia.
Signs of peripheral edema and/or ascites, which can be due to
heart failure, cirrhosis, or renal failure.
Symptoms and signs suggestive of adrenal insufficiency or
hypothyroidism.

6. Symptoms : Hyponatremia
Absent symptoms – Patients are frequently asymptomatic, if the hyponatremia is chronic and of mild or moderate severity (i.e., serum sodium >120 meq/L). However, such patients may have subclinical impairments in mentation and gait.
Mild to moderate symptoms –Relatively nonspecific and include headache, nausea, vomiting, fatigue, gait
disturbances, and confusion in patients with chronic hyponatremia (i.e., >48 hours duration).
However, in patients with more acute hyponatremia, such symptoms should be considered ominous and may evolve without warning to seizures, respiratory arrest, and herniation.
Severe symptoms – Severe symptoms of hyponatremia include seizures, obtundation, coma, and respiratory arrest.

7. Laboratory tests :
Three laboratory tests provide important initial information in the differential diagnosis of hyponatremia :
Serum osmolality
Urine osmolality
Urine sodium, potassium, and chloride concentrations
Serum osmolality (Sosm), (NR 275 to 290 mosmol/kg) is reduced in most hyponatremic patients.
In some patients Sosm is high or normal.
The three most common causes of hyponatremia with a high or normal Sosm
Marked hyperglycemia
Severe azotemia
Alcohol intoxication

8. Hyponatremia causes:
Hyperglycemia – In patients with marked hyperglycemia, which is almost always a manifestation of uncontrolled diabetes, the increase in serum glucose raises the Sosm, which pulls water out of the cells and lowers the serum sodium concentration
Azotemia – In patients with advanced renal failure, the hyponatremia is due to an inability to excrete water resulting from the impairment in renal function. Although this will tend to lower the Sosm, this effect is counterbalanced to a variable degree by the associated elevation in blood urea nitrogen (BUN), resulting in an Sosm that may be normal or elevated. Alcohol intoxication – True hyponatremia is common in patients with alcoholism. The reduction in the Sosm associated with hyponatremia can be offset in some patients by high circulating levels of ethanol.

9. Less common causes of hyponatremia with a high or normal Sosm include:
Administration of either hypertonic mannitol or maltose or sucrose in conjunction with intravenous immune globulin will cause hyponatremia in patients with renal failure.
Irrigant absorption – The absorption of nonconductive glycine, sorbitol, or mannitol irrigation solutions during TURP (called the transurethral resection syndrome) or during hysteroscopy or laparoscopic surgery can lower the serum sodium by increasing the extracellular fluid volume with these sodium free solutions.
Pseudohyponatremia – Hyperlipidemia or hyperproteinemia lower the serum sodium concentration (and therefore the calculated Sosm) without changing the measured Sosm. This laboratory artifact is called pseudohyponatremia

10. Treatment Hyponatremia
Patients with acute or hyper-acute hyponatremia, most patients with severe hyponatremia, and many symptomatic patients with moderate hyponatremia should be treated in the hospital
Emergency therapy
Patients with severe symptoms such as seizures or obtundation.
Patients symptomatic with acute hyponatremia. even if such symptoms are mild.
Patients with hyperacute hyponatremia due to self-induced water intoxication, even if there are no symptoms at the time of initial evaluation.
Symptomatic patients who have either acute postoperative hyponatremia or hyponatremia associated with intracranial pathology.

11. Treatment Hyponatremia
Patients with acute or hyper-acute hyponatremia, most patients with severe hyponatremia, and many symptomatic patients with moderate hyponatremia should be treated in the hospital
Patients with severe hyponatremia (i.e., serum sodium ≤120 meq/L) who have either absent or mild to moderate symptoms. initial treatment with hypertonic saline
Patients with moderate hyponatremia who have mild to moderate symptoms. Initial therapy depends in large part upon the underlying etiology.
Non-emergency therapy
Asymptomatic patients with acute or sub-acute hyponatremia: Initial treatment with hypertonic saline rather than other therapies.

12. Treatment
In all hyponatremic patients the serum sodium initially be increased by 4 to 6 meq/L during the first 24
hours and by less than 9 meq/L over any given 24-hour period.
In patients who require non-emergency therapy, this goal can be achieved slowly.
Patients receiving emergency therapy their serum sodium measured every two hours to ensure increase at the desired rate.
Other patients who are treated for chronic hyponatremia in the hospital should have their serum sodium measured often enough to ensure an appropriate rate of correction and to allow the clinician to react quickly to impending overly rapid correction (e.g., every four hours).
The urine output should also be monitored

13. Figure 3
Recommendations for relowering of serum sodium concentration ([Na+]) to goals (green) for patients presenting with serum [Na+] <120 mmol/L who exceed the recommended limits of correction (red) in the first 24 hours. Abbreviations: L = liter; mmol = millimole; ODS = osmotic demyelination syndrome.

14. Severe symptomatic hyponatremia
If the patient is making large volumes of urine, serum sodium may be rising too quickly.
This can be accomplished by giving desmopressin to slow urinary free water loss while simultaneously giving hypotonic fluids.
An intravenous bolus of 100 mL of 3% saline is given and repeated if symptoms persist after 10 minutes.
Once symptoms improve, the rate of sodium correction in 24 hours with this regimen should not exceed 6 to 8 mEq/L in 24 hours or 12 to 14 mEq/L in 48 hours.
Check serum sodium every two hours and monitor urine output closely

15. Asymptomatic or mildly symptomatic hyponatremia:
Hypovolemic hyponatremia: Treatment is aimed at correcting volume status
ADH secretion will always choose to preserve volume over osmolarity.
In most cases, normal saline will restore intravascular volume.
Rapid correction of serum Na, so hypotonic solutions (½ NS) should be used.
Once volume is replete, ADH release will cease.
Vaptans should not be used in hypovolemic hyponatremia, or in conjunction with other treatments for hyponatremia.

16. Asymptomatic or mildly symptomatic hyponatremia
Euvolemic Hyponatremia: Typically caused by SIADH- high Uosm (>100 mosm/L) and a high UNa (>30 mEq/L).
Free water restriction, and fluid at least 500 mL below a patient’s urine output.
If this is ineffective, salt tabs can be given to increase the solute load.
Nine grams of salt tabs in 3 divided doses (equivalent to 1 L of NS).
Patients with highly concentrated urine (Uosm >500 mosm/L) will not respond to the salt load.
In such patients, a loop diuretic can be used to help excrete free water.

17. Asymptomatic or mildly symptomatic hyponatremia
In addition, ACEI can improve hyponatremia in CHF by reducing ADH levels and improving cardiac output via after-load reduction.
Recent interest in the use of vasopressin V2 receptor antagonists or “vaptans.”
The latest AHA guidelines for CHF recommend (class IIb) vaptans in patients with “hyponatremia that may be causing cognitive symptoms when standard measures have failed.
Hypervolemic Hyponatremia: caused by CHF, cirrhosis, or NS.
ADH is in all cases.
In CHF and cirrhosis, the degree of hyponatremia is a marker of disease.
Fluid restriction is the cornerstone of therapy
If the patient’s volume status is not optimized, then loop diuretics may improve hyponatremia through excretion of diluted urine.

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