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Contents Fluid compartment & Osmolality Sodium control Definition of hyponatremia Epidemiology Types clinical manifestation Diagnosis Treatment Definition of hypernatremia Clinical manifestation Diagnosis Treatment
Total body water 60% of lean body weight in men and 50% in women. 2/3 comprises ICF & 1/3 ECF. 25% of ECF is intravascular & 75% in
interstitial spaces.Sodium is the main solute in Ecf where is potassium is main in Icf.
Disturbances in TBW manifest primarily as changes in osmolality of fluid compartments.
Osmolality Solute concentration is measured by osmolality i.e osmoles/kg
water. 285-295 mosm/kg Tonicity – osmolytes impermeable to cell membrane, they are
effective osmolyte. e.g: Na, gluccose. Ineffective osmolytes – permeate cell membrane. e.g:
urea,ethanol.
Plasma osmolality= 2Na + glucose/18 +BUN/2.8
Effective plasma osm= 2Na It is obvious that Na is intimately related to osmolality. Because of their relation to osmolality ,hyponatremia &
hypernatremia are primarily disorders of water balance & water distribution across fluid compartment.
Since 85-90% total body Na is in ECF,alterations manifest clinically as ECF volume depletion(hypotension,tachycardia) or ECF volume overload(peripheral/pulmonary edema).
Sodium control
Serum sodium conc is regulated by:
1. Stimulation of thirst
2. Secretion of ADH
3. Renin-Angiotensin-Aldosterone
4. Renal handling of Na.
Stimulation of thirst
○ Osmolality increasesMain driving forceOnly requires an increase of 2% - 3%
○ Blood volume or pressure is reducedRequires a decrease of 10% - 15%
○ Thirst center is located in the anteriolateral center of the hypothalamus Respond to NaCL and angiotensin II
Secretion of ADH
• Synthesized by the neuroendocrine cells in the supraoptic and paraventricular nuclei of the hypothalamus
• Triggers:– Osmolality of body fluids
» A change of about 1%– Volume and pressure of the vascular system
Actions of ADH 1. Increases the water permeability of
the collecting tubule2. Mildly increases vascular resistance
Renin-Angiotensin-Aldosterone• Renin
– Stimuli are perfusion pressure, sympathetic activity, and NaCl delivery to the macula densa
– Increase in NaCl delivery to the macula decreases the GFR by decrease in the renin secretion
• Aldosterone– Reduces NaCl excretion by stimulating it’s resorption
» Ascending loop of Henle» Distal tubule» Collecting duct
HYPONATREMIA
DEFINITION: Defined as sodium concentration < 135 mEq/L Generally considered a disorder of water as opposed to disorder of
salt Most often due to retention of free water
2ndary to impaired excretion of free water
Occ. due to Na loss exceeding water loss i.e. thiazide-induced hypoNa (elderly women)
EPIDEMIOLOGY
○ Hyponatremia is the most common electrolyte disorder○ incidence of approximately 1%○ prevalence of approximately 2.5%
Mortality/Morbidity○ Acute hyponatremia (developing over 48 h or less) are
subject to more severe degrees of cerebral edemasodium level is less than 105 mEq/L, the mortality is over
50%○ Chronic hyponatremia (developing over more than 48 h)
experience milder degrees of cerebral edema Brainstem herniation has not been observed in patients
with chronic hyponatremia
TYPES
HYPOOSMOLAR Hypovolumic Renal or Non-Renal
Thiazide diuretics,cerebral salt wasting.
Vomiting,diarrhea.
EuvolumicSIADH, hypothyroidism, psychogenic polydipsia.
HypervolumicCHF,Hepatic cirrhosis,severe nephrotic syn.
HYPEROSMOLAR EUOSMOLAR PSEUDONATREMIA
Clinical manifestation most patients with a serum sodium concentration exceeding 125
mEq/L are asymptomatic Patients with acutely developing hyponatremia are typically
symptomatic at a level of approximately 120 mEq/L Most abnormal findings on physical examination are
characteristically neurologic in origin and are related to osmotic intracellular water shift leading to cerebral edema.
Depends on the severity of fall of plasma Na conc and rate of development.
Acute (<48 hrz),chronic (>76 hrz) Mild ( =125mEq/L): anorexia, nausea, lethargy Mod (115-125mEq/L): disoriented, agitated, neuro deficit Sev (<115mEq/L): seizures, coma, death
Algorithm for Diagnosis
Step 1 Sna > 145 => Hypernatremia Sna< 135 => Hyponatremia Step 2 Calculate Serum Osmolarity Hyponatremia = Is it Hypoosmolar, Isoosmolar or
Hyperosmolar Step 3 Does calculated serum osmolarity agree with
measured serum osmolarity to within 10 meq/l. Step 4 Determine ECV status euvolemic, hypovolemic, or
hypervolemic (ECV status) Step 5 Obtain Urine Sodium and Urine Osmolarity. Is Urine sodium <or> 20 meq/l ? Is Urine osmolarity <or> 400 meq/l ?
Mandatory Lab Test
Serum OsmolalityUrine OsmolalityUrine Sodium Concentration
Additional tests:TSH, cortisol (Hypothryoidism or Adrenal
insufficiency)Albumin, BMP, triglycerides and SPEP
(psuedohyponatremia, cirrhosis, MM)
Interpretation of Test
Serum Osmolality Can differentiate between true hyponatremia,
pseudohyponatremia and hypertonic hyponatremia Urine Osmolality
Can differentiate between primary polydipsia and impaired free water excretion
Urine Sodium concentration Can differentiate between hypovolemia hyponatremia and
SIADH
DIFFERENTIAL DIAGNOSIS
First test to obtain: serum osmolality Helps exclude two easier to remember causes of
hyponatremia 1. Hyperosmolar hypoNa (osmo > 290)
Hyperglycemia, mannitol 2. Iso-osmolar hypoNa (nl serum osmo)
Severe hyperlipidemia or hyperproteinemia “pseudohyponatremia” not a true hypoNa
Ddx(contd)
2nd test to obtain: urine osmolalityPlasma osmolality < 275 mosmol/kg+ urine osmolality
>100 mosm/l○ Increased volume,
CHF, cirrhosis, nephrotic syndrome○ Euvolemic
SIADH, hypothyroidism, psychogenic polydipsia, beer potomania, postoperative states
○ Decreased volumeGI loss, skin, 3rd spacing, diuretics
Ddx(contd)
3rd test:Urine sodium for dehydrated patients UNa < 20 ,i.e Na and water are lost other then via kidneys
Diarrhea,vomiting,burns,trauma,heat exposure. UNa > 20 ,i.e Na is lost via kidneys
Renal failure,diuretic excess,addison’s disease.
Uric Acid Level○ < 4 mg/dl consider SIADH
FeNa○ Help to determine pre-renal from renal causes
Treatment
Four issues must be addressed○ Asymptomatic vs. symptomatic○ acute (within 48 hours)○ chronic (>48 hours)○ Volume status
Treatment (contd) 1st step is to calculate the total body water:
○ total body water (TBW) = 0.6 × body weight
2nd step is to decide what our desired correction rate should be:
Symptomatic:
1. 1.5 to 2 mEq/L per hour for first 3-4 hours until symptoms resolve
2. Increase by no more than 10 mEq/L in first 24 hrs
3. Increase by no more than 18 mEq/L in first 48 hrs
The risks of correcting hyponatremia too rapidly are volume overload and development of central pomtine myelinolysis(CPM),due to shrinkage of neuron away from their myelin sheaths.The risk of precipitaing cpm is increased with correction of Na >12 meq/l in 24 hrz.
The absolute magnitude of correction in 24 hrz is more important then the rate.
Treatment(contd)o Na deficit = TBW x (desired [Na] - actual [Na]) (mmol)Change in sodium from 1 litre of fluid:o Change in Na={(Na I)+(k i) –(Na s)} /TBW
When do you need to Rx quickly? Acute (<24h) severe (< 120 mEq/L) Hyponatremia
○ Prevent brain swelling or Rx brain swelling Symptomatic Hyponatremia (Seizures, coma, etc.)
○ Alleviate symptoms
“Quickly”: 3% NS, 1-2 mEq/L/h until:○ Symptoms stop○ 3-4h elapsed and/or Serum Na has reached 120 mEq/L
Then SLOW down correction to 0.5 mEq/L/h with 0.9% NS or simply fluid restriction. Aim for overall 24h correction to be < 10-12 mEq/L/d to prevent myelinolysis
Treatment(contd) When to Rx slowly (correct < 0.5 mEq/L/h, 10-
12 mEq/L/d)
Symptomatic/Acute: rapid Rx has resolved symptoms and brought serum Na up to 120 mEq/L
Asymptomatic, mild, chronic hyponatremia Want to prevent myelinolysis(Symptoms include:
dysarthria, dysphagia, paraparesis, quadriparesis, lethargy, coma or even seizures)Increased risk: Women, alcoholics, malnourished
Treatment (contd)
Treatment in asymptomatics:
Correct the underlying cause in the DDx Hypovolemic → give volume Hypervolemic → Na & water restriction
Loop diuretics if CHF or nephrotic syndrome Euvolemic → water restriction (because excretion can’t
match it) Specifics: if it’s hypothyroid → give thyroxine Also use loops or, rarely, demeclocycline - causes
opposite problem (diabetes insipidus
Treatment (contd) IV Fluids
One liter of Lactated Ringer's Solution contains:○ 130 mEq of sodium ion = 130 mmol/L○ 109 mEq of chloride ion = 109 mmol/L ○ 28 mEq of lactate = 28 mmol/L○ 4 mEq of potassium ion = 4 mmol/L ○ 3 mEq of calcium ion = 1.5 mmol/L
One liter of Normal Saline contains:○ 154 mEq/L of Na+ and Cl− (total osm=308)
One liter of 3% saline contains:○ 514 mEq/L of Na+ and Cl− (total osm=1028)
Example 60 kg woman with sodium level of 116 How much sodium will bring him up to 124 in the next 24 hours? Sodium needed = 0.5 x 60 x (124-116) = 240 Hypertonic saline contains 500 mEq/L of sodium Normal saline contains 154 mEq/L of sodium The patient needs 240 mEq in next 24 hours That averages to 10 mEq per hour or 20 mL of hypertonic saline per hour However, this will only raise the serum sodium by 0.33 per hour therefore, increasing
the rate 60 mL to 90 mL will produce the desired rate of serum sodium increase of 1.0 to 1.5 mEq per hour until symptoms resolve
Take Home Points
If asked to work-up hypoNa, first: H&PHistory of fluid loss (vomit/diarrh) or diuretics.On exam: mucous membranes, skin turgor, peripheral
edema/ascites (CHF or cirrhosis) Labs: ask for serum osmolality FIRST
Rule out the hyper & iso-osmolar forms #2: assess volume status if hypo-osmolar
Determine if it’s Hyper- / Eu- / Hypovolemic form Ask for urine osmolality & urine sodium
Identify the cause of hypoNa, then treat
Treatment is based on symptomsSevere symptoms = Hypertonic SalineMild or no symptoms = Fluid restriction
HYPERNATREMIADEFINITION
Hypernatremia is defined as sa plasma Na >145 mEq/L and represents a state of hyperosmolality.
TYPES May be caused by a primary water deficit or Na gain.
Primary water deficit:
1. Impaired thirst response
2. Non renal water losses( diarrhea,sweating,burns)
3. Renal water loss( osmotic diuresis or diabetes inspidus).
Na gain:
4. Mineralocortecoid excess
5. NaHco3 excess
CLINICAL MANIFESTATION
Initial symptoms include lethargy, weakness and irritability Can progress to twitching, seizures, obtundation or coma Resulting decrease in brain volume can lead to rupture of
cerebral veins leading to hemorrhage Severe symptoms usually occur with rapid increase to
sodium concentration of 158 mEq or more Sodium concentration greater than 180 mEq are associated
with high mortality
ALGORITHM FOR DIAGNOSIS
First asses Ecf volume Second to asses urine volume. Third to measure the urine osmolality If urine osmolality >800,then 4th test to do Urine Na level if urine osmolality 300-800 ,then 4th to measeure Urine osmole excretion per day If urine osmolality <300,then 4th to do Response to dDAVP
DIFFERENTIAL DIAGNOSIS
First check Ecf volume. Hypervolemic
Helps exclude 2 common causes:
1. Hypertonic Na load
2. Cushing syndrome
Ddx (contd)
If hypovolemic or euvolemic then check urine volume and measure urine osmolality:
If urine volume <800 and urine osmolality >800 mosm/l
1. Insensible losses
2. Gi losses
3. Loop diuretic
4. Primary hupodipsia If urine volume >1000 ml and urine osmolality 300-800 Urine osmole excretion per day > 900 mosm/day
1. Osmotic diuresis( glucosuria,mannitol,high solute loads,) If urine volume >1000ml and urine osmolality <300 and
response to dDAVP :
1. Complete CDI(if +)
2. Partial CDI(if-)
TREATMENT
Therapeutic goals are:
1. Reduce serum sodium concentration to 145 mmol/L
2. Determine rate of correction
3. Correct the water deficit
4. Correct the underlying disorder
TREATMENT (CONTD)
Hypernatremia that developed over a period of hours (accidental loading) Rapid correction improves prognosis without cerebral
edema Accumulated electrolytes in brain rapidly extruded Reducing Na+ by 1 mmol/L/hr appropriate
Hypernatremia of prolonged or unknown duration a slow pace of correction prudent full dissipation of brain solutes occurs over several days maximum rate 0.5 mmol/L/hr to prevent cerebral edema A targeted fall in Na+ of 10 mmol/L/24 hr
TREATMENT (CONTD)
Administration of Fluids: Preferred route: oral or feeding tube IV fluids if oral not feasible Except in cases of frank circulatory compromise,
isotonic saline is unsuitable Only hypotonic fluids are appropriate-pure water,
5% dextrose, 0.2 % saline, 0.45% saline-the more hypotonic the infusate, the lower the infusion rate required
Recommended