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NEPHROLOGY/UROLOGY > 2. Volume Homeostasis and Hypo/Hypernatremia > Flashcards

2. Volume Homeostasis and Hypo/Hypernatremia Flashcards

1
Q

Importance of Hypo/Hypernatremia

A

Hypo/Hypernatremia are important because sodium interferes with the CNS

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2
Q

Finish the sentence: Symptoms are related to _______.

A

the RATE OF CHANGE in sodium, not the absolute value.

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3
Q

Body’s Fluid Compartments and their Fraction of Total Body Water

A

Total Body Water (60% in males, 50% in females)

  • Intracellular Fluid (2/3)
  • Extracellular Fluid (1/3)
    • ​Interstitial Fluid (3/4)
    • Plasma (1/4)
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4
Q

Total Body Water in Men vs. Women

A
  • Men: 0.6 x body weight (kg)
  • Women: 0.5 x body weight (kg)
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5
Q

Measured vs. Calculated Osmolality and Quick Osmolality Estimate

A
  • Osmolality - number of solute particles / kg of solvent
  • Measured Osmolality - obtained by drawing blood
  • Calculated Osmolality - [2(Na) + Glu)] / 18 + BUN / 2.8
  • Estimated Osmolality - 2(Na)
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6
Q

Osmolar Gap Calculation and Utility

A
  • Calculation: Osmolar Gap = Osm(meas.) - Osm(calc.)
  • With a patient who’s intoxicated and/or unconscious, an osmolar gap (> 10 mmol/L) indicates toxidromes (like due to anti-freeze and isopropyl alcohol) and overdose
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7
Q

Differentiate between Dehydration and Volume Depletion

A
  • Dehydration - cell shrinkage due to osmolar shift
  • Volume Depletion - depletion in extracellular fluid
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8
Q

Hypo/Hypernatremia is a disorder of _________

A
  • Free water balance
    • Too much water dilutes sodium (hyponatremia)
    • Too little water concentrates sodium (hypernatremia)
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9
Q

Hypo/hypervolemia is a disorder of ___________.

A
  • Sodium control
    • In renal and hepatic patients, volume status is determined by sodium levels.
      • Ordinarily, kidney reabsorbs sodium, and because water follows sodium, you retain water.
    • In healthy patients, hypo/hypervolemia is a disorder of volume. You’re either vomiting, excessively bleeding, or have diarrhea.
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10
Q

Effect of Diuretics on Sodium and Extracellular Fluid

A
  • Diuretics block sodium reabsorption in the renal tubules, so the body loses sodium
  • Sodium loss causes a decrease in extracellular fluid
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11
Q

Name of Loop and Thiazide Diuretics

A
  • LOOP
    • ​Furosemide (Lasix)
    • Ethacrynic Acid (Edecrin)
    • Bumetanide (Bumex)
  • THIAZIDE
    • ​Hydrochlorothiazide
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12
Q

Effect of Loop Diuretics

A
  • Acts as a POWERFUL diuretic, blocking Na reabsorption at the Ascending Loop of Henle (Loop of Henle is where 20-30% of Na is reabsorped)
  • An equal amount of sodium and water is lost so sodium concentration is UNCHANGED
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13
Q

Effect of Thiazide Diuretics

A
  • Blocks Na reabsorption at the Distal Convoluted Tubule (Where 5-10% of Na reabsorption occurs)
  • More Na is lost than water
  • With water retained, ECF sodium concentration lowers and you get hyponatremia
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14
Q

Diuretic to Avoid in Elderly Females

A

Thiazide diuretics because they cause hyponatremia

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15
Q

Normal Na range

A

135-145 mEq/L

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16
Q

HYPONATREMIA

Definition

Types

Level when Neurologic Symptoms Appear

Clinical Presentation

A

DEFINITION:

Sodium <130 mEq/L

TYPES:

  • Hypertonic (Osm > 295)
    • Hyperglycemia
  • Isotonic (Osm 275-295)
    • Hyperlipidemia
    • Hyperprotinemia
  • Hypotonic (Osm < 275)
    • Hypervolemic - cirrhosis, renal failure
    • Euvolemic - Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)
    • Hypovolemic - vomiting

LEVEL WHEN NEUROLOGIC SYMPTOMS APPEAR:

Sodium <120 mEq/L

CLINICAL PRESENTATION:

  • Weakness
  • Confusion
  • Coma
  • Seizures
  • Decreased Deep Tendon Reflexes
  • Cramps
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17
Q

HYPONATREMIA

Workup

A
  1. After obtaining a hyponatremic lab value, check serum osmolality to determine tonicity
  2. In the case of hypotonic hyponatremia, assess volume status
    • Vital Signs: Blood Pressure, Heart Rate
    • Skin Turgor
    • Mucous Membranes
    • Signs of HF: Crackles in lungs, Pitting Edema
  3. In the case of hypovolemic hypotonic hyponatremia, obtain urinary sodium
    • U Na > 20 mEq/L = renal salt loss
    • U Na < 10 mEq/L = extrarenal salt loss
  4. In the case of euvolemic hypotonic hyponatremia, check potential causes:
    • SIADH
    • Hypothyroidism
    • Adrenal Failure
    • Thiazide Diuretics, ACE Inhibitors
  5. In the case of hypervolemic hypotonic hyponatremia, check for causes of edematous states:
    • HF
    • Liver Disease
    • Nephrotic Syndrome
    • Kidney Disease
18
Q

HYPERTONIC HYPONATREMIA

Definition

Etiology

Pathophysiology

A

DEFINITION:

  • Plasma Osmolality > 295 mmol/L
  • Sodium < 130 mEq/L

ETIOLOGY:

  • Hyperglycemia
  • Radiocontrast

PATHOPHYSIOLOGY:

  • High concentration of osmotically active solutes in ECF causes net movement of water out of ICF and into ECF
  • Plasma osmolality increases (due to solutes)
  • Sodium concentration diluted
19
Q

ISOTONIC HYPONATREMIA

Definition

Etiology

Pathophysiology

A

DEFINITION:

  • Plasma osmolality 275-295 mmol/L
  • Sodium concentration <130 mEq/L

ETIOLOGY:

  • Hyperlipidemia
  • Hyperproteinemia

PATHOPHYSIOLOGY:

  • High levels of lipids and proteins cause a factitious lower sodium value (even though sodium and osmolality are normal)
20
Q

HYPOVOLEMIC HYPOTONIC HYPONATREMIA

Definition

Etiology

Pathophysiology

A

DEFINITION:

  • Plasma osmolality <275 mmol/L
  • Sodium concentration < 130 mEq/L
  • Volume depletion

ETIOLOGY:

  • Renal Causes
    • Diuretics
    • Renal Tubular Acidosis
    • Interstitial Nephritis
    • Nephropathies
  • Extrarenal Causes
    • Volume Replacement with Isotonic Fluids (0.9% NSS)
    • Vomiting
    • Diarrhea
    • Enteric Fistulas
    • NG Tube Suctioning
    • Third Space Loss - Burns, Peritonitis
    • Sweating
    • Adrenal Insufficiency

PATHOPHYSIOLOGY:

  • Sodium and water is lost without adequate oral rehydration
21
Q

EUVOLEMIC HYPOTONIC HYPONATREMIA

Definition

Etiology

A

DEFINITION:

  • Plasma osmolality <275 mmol/L
  • Sodium concentration <130 mEq/L
  • Normal volume status

ETIOLOGY:

  • SIADH is the #1 cause
  • Hypothyroidism
  • Adrenal Failure
  • Thiazide Diuretics, ACE Inhibitors
  • Porphyria
  • Psychogenic Polydypsia (water intoxication)
22
Q

SYNDROME OF INAPPROPRIATE ANTIDIURETIC HORMONE SECRETION

Etiology

Pathophysiology

A

ETIOLOGY:

  • CNS
  • Pulmonary
  • Neoplasm
  • Meds

PATHOPHYSIOLOGY:

ADH is secreted independently of the body’s need to conserve water

23
Q

HYPERVOLEMIC HYPOTONIC HYPONATREMIA

Definition

Etiology

A

DEFINITION:

  • Plasma osmolality <275 mmol/L
  • Sodium concentration <130 mEq/L
  • Volume overload

ETIOLOGY:

  • CHF
  • Cirrhosis
  • Nephrotic Syndrome
  • Renal Failure
24
Q

HYPONATREMIA

Management

A

MANAGEMENT:

  • Asymptomatic or Mildly Symptomatic
    • Water restriction of 800 ml/24 hours
  • Critical Hyponatremia
    • ICU + Hypertonic Saline
      • Sodium must be corrected SLOWLY (no more than 0.5-1 mEq/hr to avoid Osmotic Demyelination Syndrome)
25
Q

HYPERNATREMIA

Definition

Epidemiology

A

DEFINITION:

Sodium >145 mEq/L

EPIDEMIOLOGY:

Most common in elderly due to inadequate water intake and water loss.

26
Q

HYPERNATREMIA

Etiology

A

ETIOLOGY:

  • Extrarenal Water Loss with impaired thirst
    • Fever
    • Sweat
    • Diarrhea
  • Renal Water Loss with impaired thirst
    • Osmotic Diuresis - highly osmotically active solutes (glucose, mannitol - to treat glaucoma or reduce ICP in a head injury patient, or tube feedings) promote diuresis
    • Central Diabetes Insipidus - deficiency of ADH secretion
      • Etiology: Head Trauma, Idiopathic, Neoplasm
      • Clinical Presentation: Polyuria >5-10 L/24 hr
      • Diagnosis: Administer Vasopressin and urine volume will decrease and osmolality will increase
    • Nephrogenic DIabetes Insipidus - kidney unresponsive to ADH secretion happening
      • Etiology: Hypocalcemia, Hyperkalemia, Interstitial Kidney Disease, Medications
      • Clinical Presentation: Polyuria (not as high volume)
      • Diagnosis: Administration of Vasopressin will not change/concentrate urine
27
Q

HYPERNATREMIA

Evaluation

A

EVALUATION:

  1. Why is there inadequate water intake?
    • Stroke, Infection, Neoplasm
    • Altered Mental Status
    • Impaired Thirst
    • No Water
  2. Why is there water loss?
    • Insensible Losses
    • Sweat
    • Polyuria (>3 L/24 hours)
    • Diarrhea
    • Hypertonic Saline
  3. Polyuria (>3 L/34 hours)? Measure urine osmolality
    • >300 mOsm/L = Osmotic Diuresis
    • <150 mOsm/L = Diabetes Insipidus
      • Response to Vasopressin = Central
      • No Response to Vasopressin = Nephrogenic
28
Q

HYPERNATREMIA

Management

A

MANAGEMENT:

  • Calculate Free Water Deficit - how many L the patient is down
    • TBW x [Na(meas.) - Na(desired)] / [Na(desired)]
  • IV 0.45% NSS or D5W depending on severity of hypernatremia
    • If you use D5W, monitor sodium and glucose
29
Q

ACUTE HYPERNATREMIA EFFECTS

Initially

After Water Correction

A

INITIALLY:

  • Water shifts out of ICF and into ECF
  • Brain shrinks
  • Shrunken brain hangs from meninges
  • High risk of intercranial bleeds

AFTER WATER CORRECTION:

  • Rapid overcorrection results in cerebral edema
30
Q

IV Fluids Profile

31
Q

Human Plasma Osmolality & Best IV Fluid to Increase Volume without Changing it

A
  • Human Plasma Osmolality = 295
  • 0.9% NSS
32
Q

Bolus vs. Maintenance Therapy

A
  • Bolus - large doses of IV fluids for volume replacement
  • Maintenance - small amounts of fluids to cover metabolic demands and insensible losses
33
Q

Definitions of Hypotonic, Isotonic, and Hypertonic

A
  • Hypotonic - osmolality is less than human plasma
  • Isotonic - osmolality close to human plasma
  • Hypertonic - osmolality is more than human plasma
34
Q

Hypotonic IV Fluids and their Use

A
  • D5W - all free water
    • To Keep Vein Open
    • Severe Hypernatremia
    • Avoid in Diabetics due to Hyperglycemia
  • 0.45% NSS - 500 ml NaCl + 500 ml Water
    • Volume Depeted, with Hypernatremia
35
Q

Isotonic IV Fluids and their Use

A
  • 0.9% NSS
  • Lactated Ringers
  • Plasma-Lyte A

INDICATIONS:

  • Volume Expansion
  • Dehydration
  • Shock (with LR, volume expansion and bicarbonate correct acidosis better)
  • Burns
36
Q

Hypertonic IV Fluids and their Use

A
  • 3% NaCl - 1000 ml NaCl
    • Severe Hyponatremia
37
Q

Sodium Deficit Calculation and Utility

A

CALCULATION:

Sodium Deficit = TBW x [Na(desired) - Na(meas.)]

INDICATION:

To figure out how much hypertonic saline to give a hyponatremic patient

38
Q

Rate and Max Dose of Na Correction in a Hyponatremic Patient

A
  • Rate: 1 mEq/hr x 8 hours then slow to 0.5 mEq/hr
  • Max Dose: 6-8 mEq over 8 hrs

This is all to prevent Osmotic Demyelination Syndrome

39
Q

#1 Cause of Iatrogenic Hyponatremia

A

Writing for hypotonic fluids

40
Q

Reason Potassium is added to IV Fluids

A
  • Increased delivery of sodium increases the potassium excretion rate

NEPHROLOGY/UROLOGY (3 decks)

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