HYPONATREMIA (electrolyte imbalance)

HYPONATREMIA 

  • Hyponatremia is a low sodium concentration in the blood
  • It is generally defined as a sodium concentration of less than 135 mmol/L                  (135 mEq/L), with severe hyponatremia being below 125mEq/L
  • Affects plasma osmolality
  • changes in plasma sodium levels will affects plasma osmolality that will cause fluid shift across the brain cells and cause life threatening seizures
PLASMA OSMOLALITY = 2( sodium + potassium ) +BUN/2.8 + GLUCOSE/18

 BUN = BLOOD UREA NITROGEN

NORMAL PLASMA OSMOLALITY = 285 -295 mOsm/L

URINE OSMOLALITY  = 100 - 900 mOsm/L.it usually fluctuates a lot and helps to maintain plasma osmolality in a narrow range of 10 mOsm/L

  • Normal sodium - 135 -145 meq
  • Mild Hypo sodium - 130 - 135 meq
  • Moderate Hypo sodium - 125 - 135 meq
  • severe hypo sodium - < 125 meq - high risk of causing the fluid shift across the brain predisposing - Life threatening seizures


HYPOTONIC HYPONATREMIA - Abnormal plasma osmolality - <285 mOsm/L subsequent types of  Hyponatremia depending- on volume status of patient



- In Diarrhoea/vomiting - TBW( total body water) lesser and TBS( total body salt) lesser = HYPOVOLEMIC HYPONATREMIA - treatment - FLUIDS(ORS OR IV FLUIDS)



- SIADH ( syndrome of inappropriate antidiuretic hormone secrection ) - increases ADH (anti diuretic hormone) acts on V2 receptor and causes more reabsorption of water - TBW increase and TBS normal is DILUTIONAL HYPONATREMIA (Euvolemic Hyponatremia)


case scenario
- Patient with massive ascites - decrease circulation fluid volume - decrease GFR (glomerular filtration rate) which activate RAAS (renin angiotensin aldosterone system) causing secondary hyperaldosteronism which cause activation of  epithelium sodium channel (ENac)  =  result in increase TBW and increase TBS causing HYPERVOLEMIC HYPONATREMIA



case scenario
- In patient of SAH (sub arachnoid hemorrhage)(worst headache of life , thunderclap headache), (after rupture of Berry Aneurysm or trauma ) there is a release of B.N.P(brain natriuretic peptide) causing Natriuresis  =  result in TBW increase and TBS increase causing   HYPOVOLEMIC HYPONATREMIA(cerebral salt wasting syndrome)


DIFFERENT TYPES OF HYPONATREMIA



HYPOVOLEMIC
( TBW↓ and TBS↓ )

- GI CAUSES (urinary sodium ↓)
  • Diarrhoea
  • vomiting
treatment - ORS , RL(Ringer's lactate)

- RENAL CAUSES (urinary sodium ↑)
  • cerebral salt wasting syndrome
  • Excess diuretics
  • Addison disease


EUVOLEMIC
( TBW↑ and TBS  normal)

  • SIADH
  • Post- operative(nausea and vomiting due to anaesthetic)
  • Endurance sports
  • Psychogenic polydipsia
  • Beer potomania
  • Hypothyroidism
treatment - fluid restriction
vaptans - V2 blockers


HYPERVOLEMIC
(TBW↑ and TBS↑)

  • CHF(congestive heart failure)
  • Cirrhosis
  • Nephrotic syndrome
  • CKD(chronic kidney disease) 


treatment - Diuretics

- HYPERTONIC HYPONATREMIA - Increase in the osmolality of plasma >295mOsm/L
Eg:Hyperosmolar coma,Mannitol,radiocontrast

- ISOTONIC HYPONATREMIA - PSEUDO HYPONATREMIA - because sodium is normal but values are low
Eg:Hyperlipidemia,hyperproteinemia








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