hyponatremia

1. Dr. Simon Prince, FACP, FASN Assistant Professor of Medicine NYU School of Medicine North Shore Nephrology Hyponatremia

2. SodiumThe problems with sodium has little to do with direct effects of the ion. Disregulation of sodium causes changes in cell volume. WATER PROBLEM 3. OSMOSIS 4. Why we care about osmolality Alterations in cell size disrupt tissue function. 5. Sodium is an indicator of osmolality The clinically important variable is tonicity . 6. Tonicity vs. Osmolality

Osmolality

Total concentration of all particles

Tonicity

Only impermeable particles contribute to tonicity.

Only impermeable particles cause changes in cell volume. 7. Why are we interested in TONICITY?

When elevated, water leaves the cells causing cellshrinkageand dysfunction.

When decreased water moves into the cells causing cellularswellingand dysfunction.

We are interested insodiumbecause it usually tells us the plasmatonicity .

8. Pseudohyponatremia:high osmolality

Elevated glucose raise plasma tonicity which draws water from the intracellular compartment diluting plasma sodium.

Hillier TA, Abbott RD, Barrett EJ. Am J Med 1999; 106: 399-403. 9. Pseudohyponatremia:high osmolality

Correcting the sodium for hyperglycemia.

Add 1.6 to the sodium for every 100 mg/dL the glucose is over 100.

Example: Na = 126 mEq/L. Glucose = 600 mg/dL:

600 - 100 = 500. So the glucose is five 100s over 100

5 x 1.6 = 8

126 + 8 =134

True sodium equals 134 mEq/L

To remember 1.6 thinkSweet 16

If a person drinks more water than the kidney is capable of clearing the excess water will dilute the plasma.

Causes of hyponatremia: Increased fluid intake

To exceed the maximal renal clearance of water an adult needs to drink about18 liters a day .

11. True hyponatremia

Hyponatremiadoes notoccur when sodium excretion exceeds sodium intake.

Negative salt balancecauses hypovolemia 12. Causes of Hyponatremia: Defect in Free H2O clearance

13. Etiology of Hyponatremia: 3 steps to generating dilute urine

1. Delivery of water to the diluting segments of the nephron.

2. Functional diluting segments.

3. Collecting tubule impermeable to water (lack of ADH)

1400 285 100 50 14. Failure to Generate dilute urine Lack of water delivery to the diluting segments.

Renal Failure

Volume deficiency

Cirrhosis

Heart failure

Nephrotic syndrome

15. Failure to Generate dilute urine

Ineffective solute reabsorption diluting segments:

Thick ascending limb of the loop of Henle (TALH)

Distal convolutedtubule.

Diuretics

Non-oliguric ATN

16. Failure to Generate dilute urine

Permeable collecting ducts (ADH)

Volume related ADH

Drug induced

Paraneoplastic

Pulmonary disease

Adrenal insufficiency

Hypothyroidism

17. AD dsH ydration to the body. ADH Osmolality 18. ADH is normally used to regulate osmolality We start with an increase in the plasma osmolality This is detected by the brain The brain releases ADH ADH acts on the kidney The kidney reacts by retaining water and producing a small amount of concentrated urine. The retained water goes here not here 19. Clinical Approach 20. What Studies Are Needed? 21. Tests to send...

UA, Urine: Na and Osmolality

Serum osmolality, TSH, uric acid, BNP, cortisol

Head CT

22. What is the Volume Status?

Hypovolemic

Euvolemic

Hypervolemic

23. Hypovolemic Hyponatremia

Volume expansion with SALINE

24. Hypervolemic Hyponatremia

Fluid restrict

Diurese

25. EUVOLEMIC HYPONATREMIA

Excess intake in Free Water

Defect in Free Water Clearance

ADH problem

26. ADH ShouldNOTBe Present When...

Euvolemic / Hypervolemic states

Serum Osmolality is low - normal range

If ADH is elevated... that would beINAPPROPRIATE

27. Diagnostic Criteria forSIADH

Hypoosmolar hyponatremia

Euvolemic

Urine Na >25

Urine Osmolality elevated

>350 mOsm

>200 higher than Serum Osmolality

28. Causes ofSIADH

Neurological:

Meningitis

Tumors

Trauma

Pulmonary disease:

Asthma

Mechanical ventilation

Pneumonia

Stress

Vomiting

Post-surgical

Medication

Antipsychotics

First generation sulfonylureas

Pitocin/Oxytocin

Narcotics

Cyclophosphamide

Ecstasy

29. TREATMENT

Conservative vs. Aggressive

Who should get treated and why?

30. Symptomatic Hyponatremia

Mental status changes

Nausea

Vomitting

Head ache

Movement abnormalities

Seizures

Hypoxia / respiratory failure

31. Symptomatic vs. Asymptomatic

Symptomatic

HYPERTONIC SALINE

Asymptomatic

Conservative approach is best

32. Acute symptomatic hyponatremia

In patients with neurologic symptoms due to hyponatremia: 3%.

Increase sodium until symptoms abate or 6 mmol/L, which ever comes first.

Increase Na < 24 mEq/L in the first 24 hours.

Goal is not more than 0.5 mEq/L/hour

33. The problem with compensation The starting point is after compensation has reduced the amount of intracellular solute and the ICP Now, an over-eager intern sees the low sodium and starts an infusion of 3% NaCl to raise the sodium to normal. Sodium 108 Sodium 134 The sodium draws water from the inside of the cells causing the brain to shrivel. 34. C entralP ontineM yelinolysis

Brain Shrinkage

Quadriplegia

Respiratory paralysis

Mental status changes

Usually fatal within three to five weeks

Risk factors:

Hyponatremia for > 24 hours

Over-correction of hyponatremia (> 24 mEq/L/day)

Rapid correction (greater than 12 meq/hr)

Alcoholism

Malnutrition

Liver disease

35. Damned if you do. Damned if you dont

Without treatment patients have cerebral edema.

With mistreatment patients are at risk of CPM.

36. TAKE HOME POINTS

Hyponatremia is a WATER problem, not sodium problem

In general best strategy in ER if not symptomatic...DO NOTHING(Primum non nocere) ... including holding NS unless dehydrated

Repeat blood tests to confirm and watch for psuedohyponatremia, send off urine studies

Careful hypertonic saline (3%) if symptomatic

rule of thumb start hourly rate @0.5 LBM (kg)

37. CASE REPORTS

hyponatremia

Documents

generate dilute urine

diluting segments

cell volume

pulmonary disease

mental status

high osmolality

serum osmolality

water