2. Volume Homeostasis and Hypo/Hypernatremia Flashcards by Stephanie Powdar

Importance of Hypo/Hypernatremia

Hypo/Hypernatremia are important because sodium interferes with the CNS

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Finish the sentence: Symptoms are related to _______.

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

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

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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Total Body Water in Men vs. Women

Men: 0.6 x body weight (kg)
Women: 0.5 x body weight (kg)

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Measured vs. Calculated Osmolality and Quick Osmolality Estimate

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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Osmolar Gap Calculation and Utility

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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Differentiate between Dehydration and Volume Depletion

Dehydration - cell shrinkage due to osmolar shift
Volume Depletion - depletion in extracellular fluid

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Hypo/Hypernatremia is a disorder of _________

Free water balance
- Too much water dilutes sodium (hyponatremia)
- Too little water concentrates sodium (hypernatremia)

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Hypo/hypervolemia is a disorder of ___________.

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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Effect of Diuretics on Sodium and Extracellular Fluid

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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Name of Loop and Thiazide Diuretics

LOOP
- Furosemide (Lasix)
- Ethacrynic Acid (Edecrin)
- Bumetanide (Bumex)
THIAZIDE
- Hydrochlorothiazide

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Effect of Loop Diuretics

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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Effect of Thiazide Diuretics

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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Diuretic to Avoid in Elderly Females

Thiazide diuretics because they cause hyponatremia

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Normal Na range

135-145 mEq/L

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HYPONATREMIA

Definition

Types

Level when Neurologic Symptoms Appear

Clinical Presentation

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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HYPONATREMIA

Workup

After obtaining a hyponatremic lab value, check serum osmolality to determine tonicity
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
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
In the case of euvolemic hypotonic hyponatremia, check potential causes:
- SIADH
- Hypothyroidism
- Adrenal Failure
- Thiazide Diuretics, ACE Inhibitors
In the case of hypervolemic hypotonic hyponatremia, check for causes of edematous states:
- HF
- Liver Disease
- Nephrotic Syndrome
- Kidney Disease

HYPERTONIC HYPONATREMIA

Definition

Etiology

Pathophysiology

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

ISOTONIC HYPONATREMIA

Definition

Etiology

Pathophysiology

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)

HYPOVOLEMIC HYPOTONIC HYPONATREMIA

Definition

Etiology

Pathophysiology

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

EUVOLEMIC HYPOTONIC HYPONATREMIA

Definition

Etiology

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)

SYNDROME OF INAPPROPRIATE ANTIDIURETIC HORMONE SECRETION

Etiology

Pathophysiology

ETIOLOGY:

CNS
Pulmonary
Neoplasm
Meds

PATHOPHYSIOLOGY:

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

HYPERVOLEMIC HYPOTONIC HYPONATREMIA

Definition

Etiology

DEFINITION:

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

ETIOLOGY:

CHF
Cirrhosis
Nephrotic Syndrome
Renal Failure

HYPONATREMIA

Management

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)

**HYPERNATREMIA** ## Footnote **Definition** **Epidemiology**

**DEFINITION:** Sodium \>145 mEq/L **EPIDEMIOLOGY:** Most common in elderly due to inadequate water intake and water loss.

**HYPERNATREMIA** ## Footnote **Etiology**

**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

**HYPERNATREMIA** ## Footnote **Evaluation**

**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

**HYPERNATREMIA** ## Footnote **Management**

**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

**ACUTE HYPERNATREMIA EFFECTS** ## Footnote **Initially** **After Water Correction**

**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**

**IV Fluids Profile**

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

* Human Plasma Osmolality = 295 * 0.9% NSS

**Bolus vs. Maintenance Therapy**

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

**Definitions of Hypotonic, Isotonic, and Hypertonic**

* **Hypotonic -** osmolality is less than human plasma * **Isotonic -** osmolality close to human plasma * **Hypertonic -** osmolality is more than human plasma

## Footnote **Hypotonic IV Fluids and their Use**

* **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

**Isotonic IV Fluids and their Use**

* 0.9% NSS * Lactated Ringers * Plasma-Lyte A **INDICATIONS:** * Volume Expansion * Dehydration * Shock (with LR, volume expansion and bicarbonate correct acidosis better) * Burns

**Hypertonic IV Fluids and their Use**

* **3% NaCl -** 1000 ml NaCl * Severe Hyponatremia

**Sodium Deficit Calculation and Utility**

**CALCULATION:** Sodium Deficit = TBW x [Na(desired) - Na(meas.)] **INDICATION:** To figure out how much hypertonic saline to give a hyponatremic patient

**Rate and Max Dose of Na Correction in a Hyponatremic Patient**

* 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

## Footnote **#1 Cause of Iatrogenic Hyponatremia**

Writing for hypotonic fluids

**Reason Potassium is added to IV Fluids**

* Increased delivery of sodium increases the potassium excretion rate