2. Volume Homeostasis and Hypo/Hypernatremia Flashcards
Importance of Hypo/Hypernatremia
Hypo/Hypernatremia are important because sodium interferes with the CNS
Finish the sentence: Symptoms are related to _______.
the RATE OF CHANGE in sodium, not the absolute value.
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)
Total Body Water in Men vs. Women
- Men: 0.6 x body weight (kg)
- Women: 0.5 x body weight (kg)
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)
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
Differentiate between Dehydration and Volume Depletion
- Dehydration - cell shrinkage due to osmolar shift
- Volume Depletion - depletion in extracellular fluid
Hypo/Hypernatremia is a disorder of _________
- Free water balance
- Too much water dilutes sodium (hyponatremia)
- Too little water concentrates sodium (hypernatremia)
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.
- In renal and hepatic patients, volume status is determined by sodium levels.
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
Name of Loop and Thiazide Diuretics
-
LOOP
- Furosemide (Lasix)
- Ethacrynic Acid (Edecrin)
- Bumetanide (Bumex)
-
THIAZIDE
- Hydrochlorothiazide
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
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
Diuretic to Avoid in Elderly Females
Thiazide diuretics because they cause hyponatremia
Normal Na range
135-145 mEq/L
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
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)
- ICU + Hypertonic Saline
HYPERNATREMIA
Definition
Epidemiology
DEFINITION:
Sodium >145 mEq/L
EPIDEMIOLOGY:
Most common in elderly due to inadequate water intake and water loss.
HYPERNATREMIA
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
Evaluation
EVALUATION:
-
Why is there inadequate water intake?
- Stroke, Infection, Neoplasm
- Altered Mental Status
- Impaired Thirst
- No Water
-
Why is there water loss?
- Insensible Losses
- Sweat
- Polyuria (>3 L/24 hours)
- Diarrhea
- Hypertonic Saline
-
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
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
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
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
#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
