Electrolytes, Acid Base

Question 1

Sodium Regulation: osmoregulation vs. Volume regulation

Answer 1

See image.

ANP - atrial natriuretic peptide
AVP - arginine vasopressin
BNP - brain natriuretic peptide

Question 2

Symptoms of hyponatremia

Answer 2

Nausea, Vomiting, Confusion, lethargy, disorientation, seizures, herniation, coma, death

Question 3

Hyponatremia causes

Answer 3

• ↑ AVP (almost always)
  (Exceptions: beer potomania)
  Non-osmotic ↑AVP: drugs, pain, nausea, strenuous exercise.

AVP atrial natriuretic peptide.

Question 4

How does beer potomania cause hyponatremia?

Answer 4

↓↓ urinary solute excretion is inadequate to support the excretion of sufficient H2O.

Question 5

Hyponatremia - lab investigations?

Answer 5

S-osmol; Glucose; Potassium, BUN, Creatinine, urine electrolytes and osmol; Thyroid functions, Adrenal & Pituitary functions.

__ S-osmol (exclude pseudohyponatremia due to hyperlipidemia, hyperproteinemia).
__↑K+ suggest adrenal insufficiency or hypoaldosteronism
__ Urine electrolytes + osmol

U-Na < 20 mEq/litre = hypovolemic hyponatremia in absence of oedematous state

U-osmol < 100 mosmol/kg suggestive of polydipsia, or less likely decrease solute intake.

U-osmol
• > 400 mosmol/kg AVP excess
• Intermediate values, multifactorial pathophysiology

Question 6

Hyponatremia classification (3)

Answer 6

Hypovolemic; Hypervolemic; Euvolemic

Question 7

Hypovolemic Hyponatremia - causes

Answer 7

___ RENAL cause:
Primary adrenal insufficiency
hypoaldosteronism
salt losing nephropathies (reflux nephropathy, non-oliguric ATN)
diuretics
osmotic diuresis

___ NON-RENAL cause:
GI loss (V&D, tube drainage)
Integumentary loss (sweat, burns)

Question 8

How does urine Na help to differentiate causes of hypovolemic hyponatremia?

Answer 8

___ RENAL cause:
urine Na > 20 mEq/L (usually);
may be <20 in diuretic associated long after administration of drug.

___ NON-RENAL cause:
urine sodium < 20 mEq/L (usually)

Question 9

How do you treat the different kinds of hyponatremia?

Answer 9

___ HYPO volemic:
volume, usually isotonic crystalloid.

___ HYPER volemic:
Treat underlying disorder
Sodium restriction
Diuretic Therapy
sometimes water restriction
Vasopressin antagonists effective in CHF

___ EU volemic:
Water restriction
Vasopressin antagonists
Loop diuretics + oral salt tablets
Urea po

Question 10

Hypervolemic hyponatremia - causes

Answer 10

Oedematous states (CHF, Cirrhosis, Nephrotic)

Neurohumoral activation.
Decreased arterial filling and circulatory integrity.
Peripheral Vasodilatation.
Hypoalbuminemia.

Question 11

Euvolemic hyponatremia - causes (6)

Answer 11

___ SIADH
___ LUNG (pneumonia, TB, effusions)
___ CNS (tumor, SAH, meningitis)
___ CANCER (small cell lung CA)
___ DRUGS (SSRI, TCA, Nicotine, Vincristine, carbamazepine, narcotic analgesics, antipsychotics, cyclophosphamide, ifosfamide)
___ ENDOCRINE (hypothyroidism, pituitary adrenal insufficiency)