HYPONATREMIA By Nastane Le Bec, MD

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

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 126. On that visit patient did not have any particular complaint except for mild fatigue that she has been experienced. Denies any nausea, muscle pain.

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.

Definition An electrolyte disturbance in which the sodium concentration in the serum is lower than normal. Normal serum sodium levels are between 135-145 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

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 (280-300 mOsm/kg) stimulate hypothalamic osmoreceptors, which, in turn, cause an increase in thirst and in circulating levels of ADH.

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.

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

Type of Hyponatremia Hypervolemic hyponatremia Euvolemic hyponatremia Hypovolemic hyponatremia Pseudohyponatremia

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

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

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

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

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

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.

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

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.

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 (120-110)= 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

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 120-125.

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.