HYPONATREMIA

Dr.Avinash gupta DNB General medicine

Sri Action Balaji Hospital ,New Delhi

INTRODUCTION• Hyponatremia is one of the most common biochemical abnormalities in clinical

practice.

• Hyponatremia, which is defined as a plasma concentration less than 135mM, occuring in upto 22% of hospitalised patients.

• Hyponatremia ia a common fluid electrolyte disturbance , particularly in patients with ICU setting. For general hospital admissions, about 15% have sodium levels <135 mmol/l[5], 3-4% have <130 mmol/l[6,7], and 1-2% have <125 mmol/l[8,9] (often considered as 'severe' hyponatremia).

• Hyponatremia can be associated with poor outcomes, if left untreated. Several complications and adverse outcomes including an increase risk of death can occur.

MECHANISM AND CAUSES

• Mechanism of hyponatremia is almost always the result of an increase in circulating Arginine Vasopressin and/or increase renal sensitivity to Arginine Vasopressin , combined with any intake of free water .

• Mech of Hypovolemic hyponatremia-: HYPOVOLEMIA ------->>>> CAUSED NUEROHUMERAL ACTIVATION ---- INCREASING LEVEL OF AVP -------INCREASE AVP LEADS TO BP PRESERVATION VIA VASCULAR AND BARORECEPTORS V1A RECEPTORS AND INCREASE WATER REABSORPTION VIA RENAL V2 RECEPTORS ; ACTIVATION OF V2 RECEPTOR CAN LEAD TO HYPONATREMIA IN SETTING OF INCREASED FREE WATER INTAKE .

HYPOVOLEMIA HYPONATREMIA Dec TBW and Dec Total body sodiumCAUSES when urinary sodium is more than 20 1.Renal loses ,excess diuretics 2.Mineralocorticoid deficiency(Addision)3.Salt losing deficiency4.Bicarbonaturia with renal tubular acidosis and metabolic alkalosis5.osmotic diuresis6.Cerebral salt syndrome.CAUSES when urinary sodium is less than 20..Diarrhoea ,Vomiting , Third space loss ,Burn ,Pancreatitis ,Trauma

• Mechanism of HYPERVOLEMIC HYPONATREMIA :-It leads to increase in body water as compare to total body sodium , leading to a reduced plasma Na Concentration.

• CAUSES:- when urine Na is less than 20 meq• Nephrotic syndrome• Chirrhosis • Cardiac failure • Acute or chronic renal failure (Urine Na is more than20 )

EUVOLEMIC HYPONATREMIA

• Most common cause is SIADH.• Four disticnt pattern of ADH secreation has been recognised in patients

with SIAD , independent for the most part of the underlying cause.• Unregulated and erratic AVP secreation is seen in one third with no

obvious corelation between serum osmalarity and circulating AVP levels.

• Some patients fails to suppress AVP secreation at lower osmolaries with normal response curve to hyperosmoler conditions.

• Others have a reset osmostat ,with a lower threshold osmolarity and a left shifted osmotic response curve, i.e ADH and thirst responses although functional ,maintain plasma osmolarity to this new level,lower level.

eg .In almost all pregnant women ..

• Hypothyroidism

• Other causes includes low salt intake eg in chronic beer drinkers also called as Beer Potomania .

• Bcz beer is very low in salt conc 1-2 meq per litre.

• Other causes of SIADH includes Pulmonary TB ,pneumonia ,Drugs induced.

Diagnostic Algorithm

Hypovolemia – Measure Urine Na

Isovolemia – Measure Urine Na

Hypervolemia – Measure Urine Na

Urine Na <10 mEq/LExtrarenal loss:- GI loss: vomiting, NG suction, diarrhea- Skin loss: fever, burns- 3rd spacing - pancreatitis

Urine Na > 20 mEq/LRenal Loss:- Diuretics- Salt-wasting nephropathy- Low aldosterone

Urine Na < 20 mEq/L- Water intoxication- Psychogenic polydipsia- Urine is very dilute (Urine Osm < 100 mEq/L)

Urine Na > 20 mEq/L- SIADH- Hypothyroidism- Adrenal insufficiency- Drugs (NSAIDS, thiazides)- Renal failure- Urine is less dilute (Urine Osm > 100 mEq/L)

Urine Na < 10 mEq/L- CHF- Nephrotic syndrome- Cirrhosis

Urine Na > 20 mEq/L- Renal failure

Hypo-osmolar < 275 mOsm/L

Causes of Acute Hyponatremia

• Polydypsia

• MDMA ingestion

• Exercise induced • Multifactorial eg thiazide and polydypsia

• Iatrogenic -Postoperative premenopausal women– Hypotonic fluids with cause of increase vasopresin- Glycine irigation during TURP- Colonoscopy preparation– Recent institution of thiazide

CLINICAL SIGN AND SYMPTOMS

• Clinical signs and symptoms of hyponatremia are primarily neurologic, reflecting the development of cerebral edema with a rigid skull.

• Early symptoms include- NAUSEA HEDACHE VOMITING IRRITABLITY CONFUSION Other symptoms include DIZZINESS ,MUSCE CRAMPS,CONVULSIONS, POSTURAL HYPOTENSION , DRY MUCUS MEMBRANE ,COLD AND CLAMMY SKIN,TREMORS AND SEIZURES.

Severe complications can evolve rapidly, including seizure activity, brainstem herniation, coma and death.[4]

Diagnostic AlgorithmHyponatremia Serum Na < 135 mEq/L Measure serum

Osmolarity

Hypo-osmolar < 275 mOsm/L Hyper-osmolar > 295 mOsm/L Normal 275-290 mOsm/L

Pseudohyponatremia:- Hyperlipidemia- paraproteinemia

Factitious hyponatremia 2˚ hyperglycemia (1.6 mEq/L dec. Na for every 100 mg/dL inc. in glucose > 150 mg/dL- Manitol

Assess volume status

Hypovolemia – Measure Urine Na

Isovolemia – Measure Urine Na

Hypervolemia – Measure Urine Na

DIAGNOSIS-Important points

• PLASMA OSMOLARITY more than 275 indicate psuedohypoNa .

• URINE OSMOLARITY to r/o hypo ,eu or hypervolemia.

• BLOOD SUGAR –EVERY RISE IN 100 mg/dl in sugar there is Na falls by 1.6 to 2.4 meq. Bcz of glucose induce water efflux from cells.

• SERUM POTTASIUM -increase level suggest hypoaldosteronism or adrenal insufficiency.

• SERUM URIC ACID is usually less than 4 meq in SIADH,

• Smoking ,beer history • Chest xrays to r/o small cell ca for SIaDh.• Other history…

TREATMENT• Three major considerations guide therapy for hyponatremia .• First ,the presence and/ or severity of symptoms ,determine the urgency

and goals of therapy.

• Acute Hyponatremia less than 48hrs more sever symptoms• Chronic hyponatremia more than 48 hrs, less severe symptoms

• Increase risk of development of cerebral pontine demyelination in chronic Hyponatremia if it is treated more aggressive i.e more den 10-12 meq /day.

• Treat reversible causes like stop culprit drug , hypothyroidism ,glucose controls.

Treatment

• Treatment involves restricting water intake and promoting its loss, replacing any Na deficit, and treating the cause. • When hypovolemic - 0.9% saline• When hypervolemic - fluid restriction and sometimes a diuretic• When euvolemic - treatment of cause• Rarely, cautious correction with hypertonic (3%) saline

• Water Deprivation is the main stay of treatment for chronic Hyponatremia and hypervolemic hyponatremia .

• This can be calculated by Urine: plasma electrolyte ratio (urinary [Na] + [K] / Plasma [Na] ,

If it is more than 1 den fluid can be aggressively restrict upto less than 500 ml / day . For approx 1 than fluid can be restrict upto 500-700ml For ratio less than 1 ,fluids can be restrict upto 1 litres.

Sodium Deficit Formula

• (Desired change in Na) × TBW• TBW is 0.6 × body weight in kg in men and 0.5 ×

body weight in kg in women.

Example: The amount of Na needed to raise the Na from 106 to 112 in a 70-kg man can be calculated as follows:

(112 mEq/L − 106 mEq/L) × (0.6 L/kg × 70 kg) = 252 mEq

Treatment - Severe hyponatremia

• Hypertonic (3%) saline (containing 513 mEq Na/L) may be used, but only with frequent (q 2 to 4 h) electrolyte determinations.

• For patients with seizures or coma, ≤ 100 mL/h may be administered over 4 to 6 h in amounts sufficient to raise the serum Na 4 to 6 mEq/L. This amount (in mEq) may be calculated using the Na deficit formula.

• Initial NaSerum per L infusate = NaInfusate – NaSerum

-------------------------------

TBW + 1

Here TBW is 0.6x body weight for male 0.5 x body weight for female

• Rate of corrected Na should not exceed 10 – 12 mEq/L to avoid osmotic demyelination syndrome (spastic/flaccid quadriplegia, dysarthria, dysphagia)

Review Questions - Treatment• What is the first step in management?

• Determining volume status• How do you treat hyponatremia with

• Hypovolemia?• Administration of normal saline IV

• Hypervolemia?• Diuretics and fluid restriction

• Euvolemia (SIADH)?• Fluid restriction. If the patient is symptomatic, correction

of serum Na with hypertonic saline may be indicated• What are the indications for hypertonic saline

with or without diuretics?• Serum Na < 120 mEq/L, particularly when CNS

symptoms are present

Reivew Questions

• What is the appropriate rate for administration of IV NaCl in the treatment of hyponatremia?• Rate is calculated as that necessary to increase serum

Na by 0.5 – 1.0 mEq/L per hour (ex: raise serum Na from 115 to 125 mEq/L over 24 hours)

• What can result from rapid correction of hyponatremia?• Osmotic demyelination syndrome with spastic/flaccid

quadriplegia or other neurological symptoms

Review Questions - Physiology

• How is serum or Posm calculated?• Posm = 2 * Na + Glucose / 18 + BUN / 2.8

THANk you ….