Hyponatremia

Hyponatremia:

•        Defined as sodium concentration < 135 mEq/L

•        Generally considered a disorder of water as opposed to disorder of salt

•        Results from increased water retention

•        Normal physiologic measures allow a person to excrete up to 10 liters of water per day which

protects against hyponatremia

•        Thus, in most cases, some impairment of renal excretion of water is present.

•        Volume status helps predict cause:

•  

         (Deplesional Hyponat.)

•        1 *  Hypovolemic Hyponatremia

•        Diarrhea ,Vomiting

•          Adrenal insufficiency(Addison disease)

•        Diuretic Thiazide overdose..loss of Na.

•        Decrease intake of Na, Excessive sweating→ increased thirst → intake of excessive amounts of pure water only without Na.

•     

   (Delusional Hyponat.)

•

        2*  Euvolemic

•        SIADH

•        Primary Polydipsia

•        3*  Hypervolemia

•        Cirrhosis and CHF, Nephrotic. Synd.

•       Clinical manifestations of Hyponatremia

•        Neurological symptoms

•        Lethargy, headache, confusion, apprehension, depressed reflexes, seizures and coma

•        Muscle symptoms

•        Cramps, weakness, fatigue

•        Gastrointestinal symptoms

•        Nausea, vomiting, abdominal cramps, and diarrhea.

Psuedohyponatremia :

•        High blood sugar (DKA) or protein level (multiple myeloma) can cause falsely depressed sodium levels.

Causes of Hyponatremia can be classified based on ADH level:

Hyponatremia with ADH inappropriately elevated

(SIADH)

_ Hyponatremia with appropriately suppressed ADH eg. Primary polydipsia.

ADH elevation:

•        Following Conditions stimulate ADH

     1. Volume Depletion

•        True volume depletion (i.e. bleeding)

•        Effective circulating volume depletion (i.e. heart failure and cirrhosis)

    2. Increase plasma Osmolality  (NR..275-290 mOsm/kg)

      in SIADH , ADH IS ELEVATED BUT INAPPROPRIATLY

•        low sodium level can cause ADH  suppression to allow maximally dilute urine to be excreted thereby raising serum sodium level.

•       Main diagnostic criteria for SIADH

•        Hyponatremia below 130 mmol/l

•        Clinical Euvolemia

•         low serum osmolality (below 270 mOsm/kg)

•        Urine osmolality is not minimally low 

     Usually more  than 150 mOmol/kg, though generally greater than 400-500 mOsm/kg

•        Urine sodium is not minimally low ie greater than 30 mEq/L

•        Normal hepatic, renal and cardiac function

•        Normal thyroid and adrenal function.

SIADH:

       Caused by

•        CNS disease – tumor, infection, CVA, SAH,

•        Pulmonary disease – TB, pneumonia, positive pressure ventilation

•        Cancer – Lung, pancreas, thymoma, ovary, lymphoma

•        Drugs – NSAIDs, SSRIs, diuretics, TCAs

•        Surgery - Postoperative

•        Idopathic – most common.

First step in Assessment: Are symptoms present?

•        Hyponatremia can be asymptomatic and found by routine lab testing

•        It may present with mild symptoms such as nausea and malaise (earliest) or headache and lethargy

•        Mild symptoms or asymptomatic Hyponatremia: fluid restriction

•        next step is to assess volume status to help determine cause

•        Hypovolemic – decrese urine output, dry mucous membranes, sunken eyes

•        Euvolemic – normal appearing

•       Hypervolemic – Edema?, features of cirrhosis?, features of heart failure?

•        more severe symptoms such as seizures, coma or respiratory arrest

•        Hypertonic Saline

•        Overcorrection, more than 12 mEq/L per 24 hours must be avoided .

•         monitoring of Serum Osmolality, Urine Osmolality and Urine sodium concentration are initial tests to order

•        Hypertonic saline contains 500 mEq/L of sodium

•        Normal saline contains 154 mEq/L of sodium

•       What if the sodium increased too fast?

•        The dreaded complication of increasing sodium too fast is Central Pontine Myelinolysis which is a form of osmotic demyelination

•        Symptoms generally occur 2-6 days after elevation of sodium and usually either irreversible or only partially reversible

•        Symptoms include: dysarthria, dysphagia, paraparesis, quadriparesis, lethargy, coma or even death.