HYPERNATREMIA MADE EASY (1).pptx

Hyponatremia notes

1. Hypernatremia management made easy! Bashir Admani Paediatric Nephrology

2. Hypernatremia Hypernatremia is defined as a serum sodium concentration of more than 145 mEq /L. ( NORMAL SODIUM 140 MMOL/L) It is characterized by a deficit of total body water (TBW) relative to total body sodium levels due to either loss of free water, or infrequently, the administration of hypertonic sodium solutions. 1 In healthy subjects, the body's 2 main defense mechanisms against hypernatremia are thirst and the stimulation of vasopressin release.

3. Pathophysiology The following 3 mechanisms may lead to hypernatremia, alone or in concert: Pure water depletion Water depletion exceeding sodium depletion Sodium excess

4. Pathophysiology Sustained hypernatremia can occur only when thirst or access to water is impaired. Therefore, the groups at highest risk are infants and intubated patients.

5. Why infants?? Because of certain physiologic characteristics, infants are predisposed to dehydration. They have a large surface area in relation to their height or weight compared with adults and have relatively large evaporative water losses. In infants, hypernatremia usually results from diarrhea and sometimes from improperly prepared infant formula or inadequate mother-infant interaction during breastfeeding

6. Why should we discuss hypernatremia in children???? It is very common Hypernatremia itself is associated with high morbidity and mortality If poorly managed, the management can lead to morbidity and mortality

7. Epidemiology Estimated at about 1% of all admissions In developing countries it is estimated around 1.5-20% Associated with poor breastfeeding and rehydration Diarrhea contributes to about 20%

8. Consequences Hypernatremia causes decreased cellular volume as a result of water efflux from the cells to maintain equal osmolality inside and outside the cell. Brain cells are especially vulnerable to complications resulting from cell contraction. Severe hypernatremic dehydration induces brain shrinkage, which can tear cerebral blood vessels, leading to cerebral hemorrhage, seizures, paralysis, and encephalopathy.

9. Pathophysiology In patients with prolonged hypernatremia, rapid rehydration with hypotonic fluids may cause cerebral edema, which can lead to coma, convulsions, and death.

10. Clinical features Physical Skin turgor is a physical finding in patients with hypernatremia. Extracellular and plasma volumes tend to be maintained in hypernatremic dehydration until dehydration is severe (ie, when the patient loses >10% of body weight). When dehydration is severe, skin turgor is reduced, and the skin develops a characteristic doughy appearance

11. Investigations Serum tests of sodium, osmolality, BUN, and creatinine levels Urine tests of sodium concentration and osmolality In cases of hypovolemic hypernatremia, extrarenal losses show urine sodium levels of less than 20 mEq/L, and in cases of renal losses, urine sodium values are more than 20 mEq/L. In euvolemic hypernatremia, urine sodium data vary. In hypervolemic hypernatremia, the urine sodium level is more than 20 mEq/L.

12. U/E/Cr Serum Na+*: > 190 mEq/L – chronic salt ingestion >170 mEq/l – Diabetes Insipidus 150- 170 mEq/l – dehydration Serum K+: reduced in incr aldosterone Urea: Dehydration Urea driven hypernatraemia- osmotic diuresis * Emedicine article Hypernatraemia Steven L Stephanides, MD, Attending Physician, Department of Emergency Medicine, Eisenhower Medical Center Aug, 2007

13. Serum Osmolality Def: osmolality determined by the No. of particles in solution Relatively stable despite changes in fluid intake Calculated by: 2 (Na + + K + ) + Urea + Glucose Normal*: 275 – 290 mOsm/L

14. Urine Osmolality Determined by No. of particles ( size of particles in urine- SpGr) Highly Variable in relation to fluid intake. Urine osmolality : serum osmolality ratio <2 = highly suggestive of Diabetes insipidus* Correlates with Specific Gravity**: 0.001 in SpGr = 30 – 40 mOsm *oxford textbook of medicine 3 rd edition, Oxford University Press ** Up to date 2009

15. Relationship of serum to urine osmolality in dehydration

16. Urine Electrolytes Sodium: concentration can be used to estimate volume status and conc< 20mEq/l suggests volume depletion. (Dependant on water reabsorption, will be falsely reduced in DI) FeNa: U.Na x P. Creat x 100 P. Na U. Creat <1% suggests hypovolaemia Chloride: mainly useful in acid-base disturbances Potassium: useful in hypo/hyper –kalaemia

17. Management of Hypernatraemia Based on cause: Replace water lost Free fluid deficit replacement Reducing loss of free water –diabetes insipidus Remove excess sodium Water + diuretics Haemodialysis

18. Dr Bashir Admani

19. Management 2 Administered sodium with feeds/drugs* *the BNF for children gives sodium amounts in added to all intravenous drugs

20. Free Fluid Deficit Formula: K x BdWt measured [Na+] expected [Na+] K = dependant on TBW = 0.6 Expected [Na+] = 140 mmol /L -1

21. Administration of Fluid FFD + fluid for isonatraemic dehydration + maintenance fluid Aim to reduce sodium by 0.5 mmol/hr* Use of commercially prepared fluids *Kahn, A, Brachet, E, Blum, D. Controlled fall in natremia and risk of seizures in hypertonic dehydration. Intensive Care Med 1979; 5:27. *Blum, D, Brasseur, D, Kahn, A, Brachet, E. Safe oral rehydration of hypertonic dehydration. J Pediatr Gastroenterol Nutr 1986; 5:232.

22. Fluid for Isonatremic Dehydration Assume more than 10% dehydration in children with hypernatraemia . Calculate free fluid, add sodium calculated by formula below: FID = 0.6 x 135 x fluid deficit x weight in Kg

23. Example 10 kg, 1 year old child with diarrhoea and serum sodium 160 meq/l FFD : 0.6 x 10 160 = 0.85 L 140 Assumption of 10% dehydration: so isotonic losses .15 litres Maintenance fluid in 24 hrs = 1.0L/24 hrs -1

24. Correction would should not be faster than 0.5 mmol /hr So to correct to 140 mmol/l from 160 mmol/l you need 20 x 2 hrs=40 hrs First 24 hrs: 24/40 x 1000ml=600ml Plus maintence fluid: 1000ml Total in 24 hrs: 1600ml

25. If the serum sodium was 170mmol/l Free fluid deficit: 0.6 x 10 (170/140-1) 1285 ml Total dehydration: 15% Isotonic losses 215ml Correction over 60hrs In 24 hrs; 24/60 x 1500ml: 600ml plus maintenance

26. If the serum sodium was 180mmol/l Free fluid deficit: 0.6 x 10 (180/140-1) 1715 ml Total dehydration: 20% Isotonic losses 285ml Correction over 80hrs In 24 hrs; 24/80 x 2000ml: 600ml plus maintenance

27. SO WHY IS NEPHROLOGY SO DIFFICULT?

28. OBSERVATIONS WITH FORMULA Difficult to remember so usually not used properly Free fluid deficit is used to calculate the whole replacement and children and fluids are undercalculated Extremely dilute fluids used bringing down the sodium level too fast leading to brain oedema

29. No magic

30. Simple formula… Bashir’s formula From the understanding from our calculations of free fluid deficit and dehydration The assumption is made that children with hypernatremia would be dehydrated increasingly with the level of sodium 150 mmol/l-5% 160mmol/l- 10% 170mmol/l-15% 180mmol/l-20%

31. From the calculations for free fluid deficit and amount of fluid to be given I have come up with a single equation to calculate fluid management in hypernatremic dehydration 60ml/kg +maintenance fluid every 24 hrs As long as required to calculate sodium excess

32. If sodium is at 160mmol/l Using free fluid deficit calculation If the serum sodium was 160mmol/l Free fluid deficit: 0.6 x 10 (160/140-1) 850 ml Total dehydration: 10% Isotonic losses 150ml Correction over 40hrs In 24 hrs; 24/40 x 1000ml: 600ml plus maintenance 1600 ml in 24 hrs My formula 60 ml/kg + maintenance fluid (60 x 10) + 1000 ml 1600 ml in first 24 hrs