Abnormalities in serum sodium. David Metz Paediatric Nephrology

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1 Abnormalities in serum sodium David Metz Paediatric Nephrology

2 Basics Total body sodium regulated by aldosterone and ANP Mediated by intravascular volume (not sodium) RAAS and intrarenal determines Na excretion Hence sodium regulation determines plasma volume / ECF volume (not serum sodium) Excess hypertension, oedema Total body water regulated by ADH Mediated by serum Na, osmolarity Abnormal serum Na ADH response change in water balance Hence water regulation determines serum sodium (in normal state) However ADH activity is overridden by hemodynamic stimuli (eg hypovolemia), Body will attempt to preserve the ECF volume at expense of the serum sodium; a hemodynamic stimulus for ADH production will override any inhibitory hypoosmolar effect of hyponatremia.

3 Hyponatremia or is it? Is it factitious? Fluid shift btw ICF and ECF from solute (eg glucose, mannitol) acting as effective osmole Hence check serum osmolarity Is it pseudohyponatremia? Reduced plasma water fraction due to marked hyperlipidemia or hyperproteinemia Most labs use assay that doesn t make this error any more

4 Hyponatremia 1 st step = volume status (as different aetiology and Rx) Really about differentiating 1 vs 2 (3 generally clear) 1. Hypovolemia Loss of Na in excess of loss of water Rx Rehydration (eg isotonic saline) 2. Euvolemia (eg SIADH) Excess TBW, relative normal TBNa Rx Water restriction 3. Hypervolemia (ECF excess - oedema) Gain of water in excess of Na (though gain of both) Rx Salt and water restriction 2 nd step = urine Na (and urine osmolarity)

5 ~ rel. water > Na Na<135 Na dilution (Na /, TBW ) Hypervolemic (oedema) Euvolemic Na depletion (Na TBW ) Hypovolemic Urine Na <20* Urine Na >20* Urine Na >20* Urine Na <20* Urine Na >20* Heart failure Cirrhosis Nephrotic syndrome Kidney disease SIADH Hypothyroid ACTH-def Water intox Extra-renal losses: GIT Skin Lungs Renal losses: Tubular defect CSW MCC deficiency *mmol/l

6 Symptoms hypona Initial: headache, lethargy, irritability, confusion Severe: LOC, seizures, brainstem herniation Treatment of hypona Rapid if severe neurological symptoms, else slow

7 Principles of treatment Whatever the cause (hypo/euvol/hyper) If Na < 125 and severe symptoms (seizures, depressed conscious state / evidence brainstem herniation, respiratory arrest) Treat with 3% NaCl IV 4ml/kg over 15-30m (will raise by ~ 3mmol/L) Repeat if necessary, until asymptomatic or Na 125 (above from RCH CPG s) If above doesn t apply Mandates slow correction else may cause central pontine demyelinolysis irreversible brain damage Close monitoring of serum Na (and wgt, fluid balance) 2hrly Na in symptomatic/severe, 4-6hrly if asymp 6hrly weight

8 Equations exist to guide Mx Eg hypov hypona: Na deficit = (desired Na actual Na) x TBW* (NB need to add maintenance requirements and ongoing losses) *(TBW = 0.6 x wgt)

9 However in practice Body is not a closed / fixed system Equations don t account for (potentially changing) renal water handling, endocrine responses, treatment of condition Hence frequent monitoring more important than careful equation 2hrly in symptomatic/severe, 4-6hrly if asymp

10 Situations where consideration of renal response important Likely change in renal water handling Diarrhoeal dehydration, psychogenic polydipsia, DDAVP, thiazides Free-water diuresis once volume status restored or medication ceased (leading to rapid rise Na) Hence may need change to 0.45% saline or less to prevent this (based on serum Na) Natriuresis with 0.9% saline volume expansion, leading to further drop in serum Na as urine sodium concentration greater than 0.9% saline, will excrete more Na than water CSW SIADH

11 HypoV hypona Rx (w/o severe sx) Salt and water deficit, Salt deficit > water deficit Thus needs salt and water replacement Consider ORT, Na 60-90mmol/L if feasible If IV Bolus 0.9% saline if required for reperfusion then SLOW correction of Na abnormality <0.5mmol/hr; (<10mmol in 24hrs, <18mmol in 48hrs) 2hrly serum Na in symptomatic/severe, 4-6hrly if asymp Slow rehydration eg maintenance + deficit (+/- losses) over 24-48hrs

12 Which fluid? (hypov hypona) 0.9% saline (bolus) if required for reperfusion, then 0.45% to 0.9% (with D5W) guided by serum Na If losses extra-renal (eg D+V / skin / lung) or reversible renal cause (eg thiazides) 0.45% after reperfusion (else rapid Na rise as ADH drive stops, kidneys get rid of water excess) If renal losses Suspected MC defect (eg Type 4 RTA, CAH) % saline; NB should have high K, acidosis Cerebral salt wasting, proximal renal salt wasting (v rare) Start with 0.9%; may need > 0.9% saline if serum Na not rising (eg addition of 3% saline IV or 6% saline oral) Thus in practice if aetiology unclear Order urgent urine Na (& osmo) After reperfusion with 0.9% saline Start rehydration with 0.45%+D5W Start with 0.9%+D5W if strong suspicion CSW or RSW Either way repeat serum Na in 2hrs to ensure heading in right direction

13 SIADH Rx (w/o severe sx) Water excess, salt ~ neutral (Treat cause) Fluid restrict (eg 50-75% maintenance) Sometimes (rare) addition of NaCl oral (hypertonic), +/- addition of loop diuretic (if Uosm >2x Posm) 0.9% saline (+D5W) if IVT used

14 Water and salt excess HyperV hypona (w/o severe sx) Rx = Restrict Na and water Consider frusemide 0.5-1mg/kg if happy patient is intravascularly replete In setting intravascular depletion and hypoalbuminemia Saline or 4% Alb for shock 20% Albumin with frusemide half-way

15 Hypernatremia

16 Symptoms HyperNa Headache, nausea, lethargy Severe = impaired conscious state, seizures Fever Examination Doughy skin, lack common signs of dehydration (wrinkled skin, poor peripheral perfusion) Well perfused and hypertensive (in hypervolemic hypernatremia)

17 Na > 145 Hypovolemic Hypervolemic Urine Osmo <300 Urine Na < 20, Urine Osmo >500 Urine Na > 20 Urine Osmo >300 Urine Na usu < 20 Diabetes insipidus: Central Nephrogenic Urine Na > 20 Osmotic diuretics Renal dysplasia Diabetes mellitus Extra-renal losses: Insensible/Sweat Diarrhoea Lack of access to water (including inability to express thirst premmie / neonate, neurological impair, critical illness) Excess NaCl intake Conn syndrome Cushing syndomre

18 Treatment Be even more slow / cautious than hypona! Again, max rate of change = 0.5mmol/hr If Na >170 mmol/l, should not be corrected to below 150 mmol/l in the first h If severe neurological symptoms develop with correction 3% NaCl IV (as per hypona orders) to bring Na back up, prevent sudden cerebral oedema Type of IV fluid depends on cause (hence urine Na and osmo critical)

19 HypoV hyperna Correct shock with 0.9% saline Then rehydrate over 48 to 72hrs Estimate free water deficit Water deficit = TBW x [(Na measured Na desired) / Na desired] Use this to calculate volume needed to get Na to target (eg 10mmol/L reduction in 24hrs) Also need to consider maintenance, ongoing losses IVT: 0.9% saline (+D5W) a good start Often then changed to 0.45%, if needed, based on rate of change of serum Na, ongoing losses, etc

20 DI Rx Deficit is water Hence D5W rehydration generally best choice (SLOW over 48-72hrs) change rate of rehydration depending on serum Na If partial DI may need some salt also (eg 0.45% saline) If neurologically stable, enteral water is a good option

21 DI Rx cont Central DI DDAVP Nephrogenic DI Ongoing high volumes of fluid once Na corrected Low Na diet (reduce solute load) HCT or amiloride (increase proximal Na/H20 reabsorption) Indomethacin (reduce renal blood flow)