Hyponatremia and Hypernatremia

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 Hypovolemic Hyponatremia – Diarrhea,Vomiting – Adrenal insufficiency(Addison disease( – Thiazide overdose..loss of Na. – Decrease intake of Na, Excessive sweating → increased thirst → intake of excessive amounts of pure water only without Na.

4 (Delusional Hyponat.) Euvolemic SIADH Primary Polydipsia Hypervolemia Cirrhosis and CHF, Nephrotic Synd

5 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 Normal ADH response to low sodium is to be suppressed to allow maximally dilute urine to be excreted thereby raising serum sodium level Causes of Hyponatremia can be classified based on ADH level _ Hyponatremia with ADH inappropriately elevated (SIADH) _appropriately suppressed eg. Primary polydypsia

ADH elevation Conditions which ADH is elevated – Volume Depletion True volume depletion (i.e. bleeding) Effective circulating volume depletion (i.e. heart failure and cirrhosis) – Increase plasma Osmolality(NR mOsm/kg) – SIADH

Main diagnostic criteria for SIADH Clinical Euvolemia Hyponatremia below 130 mmol/l Urine osmolality isnot minimally low(as one expect ( Usually more than 150 mOmol/kg,though generally greater than mOsm/kg in setting of low serum osmolality (below 270 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 Or it may present with more severe symptoms such as seizures, coma or respiratory arrest

WHAT NEXT? With no severe symptoms : fluid restriction started, next step is to assess volume status to help determine cause Hypovolemic – urine output, dry mucous membranes, sunken eyes Euvolemic – normal appearing Hypervolemic – Edema, past medical history, Jaundice (cirrhosis), S3 (CHF)

Workup for Hyponatremia 3 mandatory lab tests – Serum Osmolality – Urine Osmolality – Urine Sodium Concentration Additional labs depending on clinical suspicion – TSH, cortisol (Hypothryoidism or Adrenal insufficiency) – Albumin, LFTs, B.glucose,Keton in urine,and S.Protein electrphoresis (psuedohyponatremia…..DKA,MM) Chest Xray (small cell carcinoma ؟

Treatment is based on symptoms &type of Hyponatremia Patients with serum sodium above 120 are generally asymptomatic Symptoms tend to occur at serum sodium levels lower than 120 or when a rapid decline in sodium levels occur Patients can have mild symptoms at sodium concentrations of mEq/L when this level is reached gradually

If Hyponat. Develops over hours or days..morbidity high due to cerebral oedema relatively rapid correction with starting bolus of 100 ml of 3% hypertonic saline which generally raise serum sodium level by 2-3 mEq/L Goals for correction : gradual correction – 2 mEq/L per hour for first 3-4 hours until symptoms resolve – Increase by no more than mEq/L in first 24 hrs – Increase by no more than 18 mEq/L in first 48 hrs

What if little to no symptoms are present : For Delusional Hyponatremia Oral fluid restriction is the first step – No more than mL per day – Removal of cause of SIADH, – Demeclocycline mg If volume depletion (Deplesional Hypovolemic) is present, isotonic (0.9%) saline can be given intravenously Hypervolemic Hyponatremia : treat underlying cause,Causious Duiretics with fluid restriction. K sparing duiretics are especially benificial in states of Secondary Hyperaldoseronism *Serum sodium levels should be drawn every 4-6 hours or more frequently if hypertonic saline is used

Hypertonic saline contains 500 mEq/L of sodium Normal saline contains 154 mEq/L of sodium

What if the sodium increases too fast? The serious complication of replacing 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

Summary of Hyponatremia Hyponatremia has variety of causes Treatment is based on symptoms – Severe symptoms = Hypertonic Saline – Mild or no symptoms = Fluid restriction Overcorrection, more than 12 mEq increase in 24 hours must be avoided with monitoring Serum Osmolality, Urine Osmolality and Urine sodium concentration are initial tests to order

Hypernatremia – Produced by either administration of hypertonic fluids or much more frequently, loss of thirst or failure of ADH mechanisms – Water moves from ICF → ECF &Cells dehydrate Because of extremely efficient regulatory mechanisms such as ADH and thirst, hypernatremia generally occurs only in people with prolonged lack of thirst mechanism Patients with loss of ADH - Diabetes Insipidus(DI(usually can compensate with increased fluid intake

Causes of Hypernatremia sweat losses in prolonged fever…..loss of pure water. Insufficient intake of water (hypodipsia( GIT losses Diabetes Insipidus (both central and nephrogenic( Osmotic Diuresis – DKA Hypothalamic lesions which affect thirst function – Causes include tumors, granulomatous diseases or vascular disease Sodium Overload – Infusion of Hypertonic sodium bicarbonate for metabolic acidosis

Hypernatremia I nitial symptoms include lethargy, weakness and irritability Can progress to twitching, seizures, obtundation or coma Resulting decrease in brain volume can lead to rupture of cerebral veins leading to hemorrhage Severe symptoms usually occur with rapid increase to sodium concentration Sodium concentration greater than 180 mEq are associated with high mortality

Diagnosis of Hypernatremia Same labs as workup for hyponatremia: Serum osmolality, urine osmolality and urine sodium If urine osmolality is lower than serum osmolality then DI is suspected – Administration of Desmopressin-DDAVP will differentiate types of DI * Urine osmolality will increase in central DI, no response in nephrogenic DI

Treatment of hypernatremia Typical fluids given in form of Dextrose 5% Same as hyponatremia, sodium should not be lowered by more than 12 mEq/L in 24 hours Overcorrection can lead to cerebral edema which can lead to encephalopathy, seizures or death