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MS2 Renal > 9/11- Dysnatremias > Flashcards

9/11- Dysnatremias Flashcards

1
Q

Hypo and hypernatremia are defined by what?

A

Serum sodium CONCENTRATION

(NOT CONTENT!!!!!!)

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2
Q

What is the equation for serum Na?

A

Edelman Equation

Serum Na (mEq/L) = (Na + K)/TBW

(Na and K here are “exchangeable”- the ones available across the cell for movement)

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3
Q

What are the CONCENTRATION ranges for hypo and hypernatremia?

A

Hyponatremia: less than 135 mEq/L

  • Relatively more TBW compared to total body Na

Hypernatremia: > 145 mEq/L

  • Relatively less TBW compared to total body Na

(thus, normal range = 135-145)

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4
Q

Dysnatremia is caused predominantly by what?

A

Dysnatremia is predominantly caused by changes in TBW (total body water)

  • Think back to Edelma equation and small denominator (TBW)
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5
Q

What is the predictor of volume status in a person?

A

Salt intake

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6
Q

How may high salt intake present clinically?

A

Volume overlaod

  • Increased JVP
  • Edema
  • Lung crackles
  • HTN
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7
Q

How may low salt intake present clinically?

A

Volume depletion

  • Decreased BP
  • Poor skin turgor
  • Dry mucus membranes
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8
Q

How may high water intake present clinically?

A

Hyponatremia

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9
Q

How may low water intake present clinically?

A

Hypernatremia

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10
Q

KEY: Dysnatremic patients can present with volume overload, volume depletion, or euvolemia!!

A

yay

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11
Q

Case

  • 37 yo man with Na 159 (normal 135-`145)
  • He was out in the sun all day long and did not eat/drink much
  • His BP is 90/50 (hypotensive)
  • He has tenting of his skin
  • Urine Na is under 10 mEq/L

Diagnosis?

What is you initial choice of IV fluids?

A. Salt water [normal saline] (0.9%)

B. Dextrose water (D5W)

C. Blood transfusion

A

Hypovolemic hypernatremia

  • Total body Na is decreased
  • Total body water is very decreased What is you initial choice of IV fluids:

A. Salt water [normal saline] (0.9%)

B. Dextrose water (D5W)

C. Blood transfusion

You want to fix depleted water status (hypotension and whatnot)

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12
Q

T/F: Normal saline (0.9%) is hypotonic?

A

False! It is isotonic

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13
Q

What is normal saline?

A

Isotonic saline (0.9% concentration)

  • 0.9g salt in 100cc water
  • Na is 154 mEq/L (approximates plasma sodium of 140)
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14
Q

What is dextrose water (D5W)?

A

Concentration is 5%

  • 5g sugar in 100cc water
  • Na content is 0!

Given because:

  • Avoids hemolysis (entry of water into the cells)
  • Dextrose will move into the cells (insulin effect), leaving “free” water
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15
Q

What fluid should be given to a hypovolemic patient?

A

Normal saline should be used to expand ECF volume

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16
Q

What fluid should be given to patient with relatively low TBW?

Example of this case?

A

Give oral water or IV D5W to patients with relatively low TBW

  • Ex) hypernatremia
17
Q

What equation is used in calculating water deficit?

A

Water deficit = TBW x (pt Na - 140)/140

TBW for man ~ 60% of weight (70kg)

Water deficit = 0.6 x 70 x (pt Na - 140)/140

Always add ongoing losses when replacing water, including insensible losses and ongoing urinary losses

18
Q

Case

  • 23 yo med student has polyruia and polydipsia
  • While cramming for the renal exam, he sits in the library and forgets to drink water for > 15 hrs
  • This is the 1st time he has gone so long without water
  • He continues to urinate as he normally does
  • He presents to the ER with altered mentation
  • Serum sodium is 161 and he weighs 60 kg

Water deficit calculation?

Treatment?

While in the ER, his mother calls and says he left a certain prescription medication at home

  • “He sustained head trauma as a child and takes this nasal spray several times a day” to decrease his urine output

Diagnosis?

A. Nephrogenic diabetes insipidus

B. Diabetes mellitus

C. Central diabetes insipidus

D. Osmotic diuresis

A

Water deficit = 0.6 x 60 x (161-140)/140 = 5.4 L

Tx: Replace water deficit over 48 hours to avoid sudden changes in serum Na concentration

Diagnosis:

A. Nephrogenic diabetes insipidus

B. Diabetes mellitus

C. Central diabetes insipidus

D. Osmotic diuresis Kid was taking vasopressin

- DO NOT stop vasopressin in these pts (can decrease load, but stopping would cause swing FAR to the other side, with much urine excretion and hypernatremia)

19
Q

What does “gently” imply in treatment?

A

Over 48 hours

20
Q

What is diabetes insipidus? Subtypes?

A

Production of large volumes of very dilute urine (polyuria)

  • > 3 L per 24 hrs
  • < 300 mOsm/L

There are four major subtypes (2 involve defect in ADH)

  1. Central DI
  2. Nephrogenic DI
  3. Gestational DI
  4. Primary Polydipsia (Dipsogenic DI)
21
Q

What differentiates between diabetes mellitus and insipidus?

A

Glycosuria (hyperglycemia)

22
Q

What is the mechanism of central DI?

  • Genetics?
  • Causes?
A

Central DI = deficiency in ADH production/release

Acquired:

  • Brain tumor
  • Head trauma
  • Granulomatous disease
  • Autoimmunity

Inherited:

  • AD/AR mutation in AVP gene or X-linked mutation in ? gene
23
Q

What is the mechanism of nephrogenic DI?

  • Genetics
  • Causes?
A

Nephrogenic DI = defective kidney response to ADH

  • Genetic: mutations in V2 receptor or AQP2
  • Drugs: Lithium
  • Electrolytes: hypokalemia, hypercalcemia

Pathologies:

  • Obstruction
  • Chronic kidney disease
  • Sickle cell anemia
24
Q

What is the mechanism of gestational DI?

A

Vasopressinase produced by placenta degrades arginine vasopressin (ADH)

25
Q

Diagnosis of DI by urine osmolality after dehydration/exogenous vasopressin and plasma vasopression?

A
26
Q

How to treat central DI?

A

Give synthetic vasopressin (DDAVP)– often intranasal

27
Q

How to treat nephrogenic DI?

A
  • Find and treat the underlying disease
  • HCTZ (diuretic) induces a mild volume depletion and tricks kidney into reabsorbing salt/water at proximal tubule (the result that less water is sent distally for ADH to reabsorb)
28
Q

Hydrochlorthiazide causes __natremia?

A

Hydrochlorthiazide causes HYPOnatremia

29
Q

What is SIADH?

  • Serum osmolality?
  • Urine osmolality?
  • Kidney function?
  • Volume status?
  • Na excretion up/down?
A

Syndrome of Inappropriate ADH

  • Low serum osmolality (< 275 mOsm/kg water)
  • Inappropriate Uosm > 100 with NORMAL kidney function
  • Clinical EUVOLEMIA
  • Increased urinary Na excretion when on normal salt/water intake
  • NORMAL thyroid, adrenal, and kidney function
30
Q

What may cause SIADH?

A

CNS disorders

  • Tumors
  • Mening-encephalitis
  • Pituitary stalk lesion
  • Subdural hematoma

Pulmonary/pleural disorders:

  • Pneumonia
  • TB
  • Empyema
  • Tumor

Drugs

  • Depression
  • Tricyclics
  • SSR
  • Ecstasy
  • Carbamezapine
  • Omeprazole
31
Q

Treatment for SIADH by cause and volume status?

A
32
Q

What is the definition for chronic hyponatremia?

A

MORE THAN 48 HOURS

33
Q

What is osmotic demyelination syndrome?

A

Aka central pontine myelinolysis (CPM)

Due to rapid correction of chronic hyponatremia; correct gradually!!

  • Happens when SrNa is under 120

Symptoms:

  • Confusion
  • Seizures
  • Respiratory arrest
  • Myelinolysis
  • Coma
  • Death

Symptoms of myelinolysis

  • UMN disorders
  • Spastic quadraparesis
  • Pseudobulbar palsy
  • Coma MRI diagnostic
34
Q

What is gradual correction for chronic hyponatremia?

A

Hyponatremia for > 38 hours or patient presents with hyponatremia

Correction rate:

  • 8 mEq/L correction in 1st 24 hours
  • Under 18 mEq/L in 48 hours
  • If symptomatic, rapid correction of 6 mEq/L in the first 4-6 hours is recommended

If overcorrected:

  • Give water and DDAVP to keep within target
35
Q

T/F: Acute hyponatremia can be corrected quickly?

A

True! Brain changes haven’t occurred

36
Q

Case

  • 45 yo pt has not seen doctor for several yrs
  • He was brought to the ER with a seizure and the ER doctor calls you for a sodium of 110 mEq/L
  • Due to altered mentation and seizure, you want to give 3% saline (513 mEq Na/L) for rapid correction of hyponatremia
  • How much volume (mL) should you give?
A

400 mL hypertonic saline

  • Goal is 4-6 mEq/L in 4-6 hours (if symptoms) and ~8 mEq/L/day
  • Na is 110; goal is to raise to 116

Calculation:

  • Sodium deficit = TBW x (Na desired - Na of pt)

= 0.5 x 70 x (116-110) = 210 mEq/Na

  • 210 mEq/513 mEq/L = 0.4 L

MS2 Renal (25 decks)

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