1. HYPONATREMIA By
Nastane Le Bec, MD

2. Objective To Understand the physiology of Sodium and fluid balance
To learn the 4 most common causes of Hyponatremia
How to appropriately manage fluid in hyponatremia
Treatment guideline and complications

3. Case
HPI: 65 y/o female with PMH of HTN and bipolar disorder presented to the clinic for her f/u visit. Upon reviewing her labs. Patient was found to have a sodium level of On that visit patient did not have any particular complaint except for mild fatigue that she has been experienced. Denies any nausea, muscle pain.

4. Frequency
Hyponatremia is a commonly encountered electrolyte abnormality in hospitalized patients and is associated with significant morbidity and mortality.
Prevalence rates of 0.97% and 2.48% respectively
It occurs in one out of 65 US admissions and adds significant costs.

5. Definition
An electrolyte disturbance in which the sodium concentration in the serum is lower than normal.
Normal serum sodium levels are between mEq/L.
Hyponatremia is defined as a serum level of less than 135 mEq/L and is considered severe when the serum level is below 125 mEq/L

6. Pathophysiology
Serum sodium concentration is regulated by stimulation of thirst, secretion of ADH, feedback mechanisms of the renin-angiotensin-aldosterone system.
Increases in serum osmolarity above the normal range ( mOsm/kg) stimulate hypothalamic osmoreceptors, which, in turn, cause an increase in thirst and in circulating levels of ADH.

7. Pathophysiology (con’t)
ADH increases free water reabsorption from the urine, yielding urine of low volume and relatively high osmolarity and, as a result, returning serum osmolarity to normal.

8. Pathophysiology (con’t)
No ADH:
ADH Present:

9. Type of Hyponatremia Hypervolemic hyponatremia Euvolemic hyponatremia
Hypovolemic hyponatremia
Pseudohyponatremia

11. Hypovolemic Hyponatremia
Sodium and free water are lost and/or replaced by inappropriately hypotonic fluids

12. Causes Nonrenal loss Renal Loss GI losses Excessive sweating
Vomiting, Diarrhea, fistulas, pancreatitis
Excessive sweating
Third spacing of fluids
ascites, peritonitis, pancreatitis, and burns
Renal Loss
Acute or chronic renal insufficiency
Diuretics

13. Euvolemic Hyponatremia
Normal sodium stores and a total body excess of free water
Psychogenic polydypsia, often in psychiatric patients
Administration of hypotonic intravenous or irrigation fluids in the immediate postoperative period

14. Causes SIADH Medications Small cell, pneumonia, TB, sarcoidosis
SSRI, Antipsychotics, Opiates, Depakote, Tegratol

15. Hypervolemic Hyponatremia
Total body sodium increases, and TBW increases to a greater extent.
Can be renal or non-renal
-acute or chronic renal failure
-dysfunctional kidneys are unable to excrete the ingested sodium load
- cirrhosis, congestive heart failure, or nephrotic syndrome

16. Pseudohyponatremia
The aqueous phase is diluted by excessive proteins or lipids. The TBW and total body sodium are unchanged. This condition is seen with hypertriglyceridemia and multiple myeloma.

17. Clinical Manifestation
Most patients with a serum sodium concentration exceeding 125 mEq/L are asymptomatic
Patients with acutely developing hyponatremia are typically symptomatic at a level of approximately 120 mEq/L
Most abnormal findings on physical examination are characteristically neurologic in origin
patients may exhibit signs of hypovolemia or hypervolemia

19. Treatment
In an asymptomatic or has only subtle Symptoms, water restriction may be required.
In a setting of volume depletion, intravenous administration of normal saline may be effective.
Vasopressin Receptor Blocker can be used in the treatment of hyponatremia, especially in patients with congestive heart failure or liver cirrhosis.

20. Fluid Replacement Example:
a 80 kg man with a plasma sodium of 110 meq/L
(total body water [TBW]× [desired serum sodium – current serum sodium])
80 kg patient; serum sodium=110 meq\L ; male; desired target= 120 meq/L.     1)   0.6 x 80kg x ( )= 480 meq  (total needed)     2)  Amount needed to increase serum level by 0.5 meq/L/hr =            0.6 x 80 x 0.5= 24 meq.  (rate should be 24 meq/hr)     3)  3% hypertonic saline contains 513 meq/Liter          [desired rate/hr]/513 x 1000= # ml/hr  //      Total meq/rate/hr                                                                             =infusion time. 24 meq/hr  x 1000= 47 ml/hr         513

21. Take Home point Determine Volume status: Hypo, hyper isovolemic
What labs work would you order (Urine Na, Serum osmolality)
Treatment depending of the volume status : Fluid restriction, Fluid replacement.
How to correct hyponatremia
total body water [TBW]× [desired serum sodium – current serum sodium])
serum sodium=110 meq\L ; male; desired target= 120 meq/L. Female

22. Complications
Neurological impairments which can affect gait and attention and can lead to falls, osteoporosis, and decreased reaction time.
Acute hyponatremia can lead to much more serious complications including brain disease, brain herniation, cardiopulmonary arrest, cerebral edema, seizures, coma, and death.