Learning Objectives - Hyponatremia Flashcards
Define hyponatremia.
Plasma sodium concentration <135 mmol/L
Symptoms of hyponatremia usually begin once Na levels fall to ___. What happens?
<120;
There is too much water relative to sodium. This causes osmotic water shifts, leading to increased ICF, brain swelling, and cerebral edema
Signs and symptoms of hyponatremia?
Headache, increased ICP, seizure, HTN Delirium, coma Irritability Muscle twitching/cramps Weakness Hypoactive DTRs N/V, ileus, watery diarrhea Increased salivation/lacrimation Oliguria -> anuria
First step in evaluating hyponatremia?
Unlike hypernatremia, which is always hypertonic, hyponatremia may be hypo/iso/hypertonic. The first step is to determine serum osmolality.
Effective osmolality?
Measured osmolality - BUN/2.8 (corrects for urea, which is an ineffective osmole)
What is pseudohyponatremia?
If the assay measures sodium indirectly, elevated levels of serum lipids or proteins may cause the level to be falsely lowered
Proteins and lipids expand the non-aqueous portion of plasma
What happens in hypertonic hyponatremia?
Osmotically active solutes like mannitol or glucose draw water out of the cells and into the serum, therefore lowering the sodium concentration of the serum (dilutional hyponatremia). For every 100 mg/dL increase in glucose, the serum sodium decreases by 1.6-2.4 mmol/L
NO CHANGE in the actual sodium content of the ECF
What happens in hypotonic hyponatremia?
Patients may be hypovolemic, euvolemic, or hypervolemic.
Very common causes of hypotonic hyponatremia?
Diuretic use (especially thiazides) SIADH
After determining the serum osmolality, ruling out pseudohyponatremia or hypertonic hyponatremia, what is the next step?
Assess volume status
History and physical supporting hypovolemia?
Vomiting, diarrhea, diuretic use, bleeding, postural dizziness
Low JVP, orthostatics, decreased skin turgor
Urine sodium concentration to determine volume status?
If urine sodium is <25, hypovolemia
If >40, euvolemic
Exceptions: renal salt-wasting due to diurietcs, Addison’s, or cerebral salt-wasting (urine sodium may be elevated, but patient is hypovolemic)
History and physical supporting hypervolemia?
History of CHF, renal failure, cirrhosis
Anasarca, pulmonary edema
What is the third step after assessing volume status?
Assess urine osmolality to determine the presence of ADH
ADH present: UOsm >150 (ADH concentrating urine)
UOsm <100 (primary polydipsia - ADH secretion shut down, kidneys respond by maximally diluting urine), malnutrition, beer potomania (solute intake and stores are low, decreased solute excretion), reset “osmostat”-> serum sodium level at which ADH release occurs is lowered
Low serum osmolality + high urine osmolality?
Inappropriate presence of ADH (ADH should not be present if serum osmolality is low)
DDx - hypotonic hyponatremia associated with impaired renal water excretion - hypovolemic
Diuresis (medication or osmotically induced)
Thiazides
Adrenal insufficiency
Salt-wasting nephropathy
Bicarbonaturia
Ketonuria
Diarrrhea/votmiing/blood loss/excess sweating/fluid sequestration (third spacing)
High urine sodium (>20) suggests renal salt loss
Low urine sodium (<10) suggests extrarenal losses
DDx - hypotonic hyponatremia associated with impaired renal water excretion - euvolemic
SIADH Thiazides Hypothyroidism Adrenal insufficiency Decreased solute intake (beer potomania, tea and toast) Oxytocin use Drugs (haloperidol, cyclophosphomide, anti-neoplastics) Post-operative
DDx - hypotonic hyponatremia associated with impaired renal water excretion - hypervolemic
CHF Cirrhosis Renal failure Nephrotic syndrome Pregnancy
DDx - hypotonic hyponatremia associated with impaired water intake
Primary polydipsia
Irrigation of the bladder or uterus with sodium-free solutions during hysteroscopy, cystoscopy, or transurethral resection of the prostate
Most common causes of SIADH?
- Disorders of the lung (small-cell carcinoma, infections, PPV, acute respiratory failure)
- Disorders of the CNS (mass lesions, trauma, inflammatory or demyelinating disorders, stroke, hemorrhage, acute psychosis)
Management of hyponatremia?
IV fluids (if SIAD is a consideration, restrict oral intake of free water to 1 L daily)
Correct sodium NO FASTER than 8-12 mEq/L over 24 hours
If chronic hyponatremia (higher risk for demyelination), serum sodium should be raised by 0.5-1 mEq/L per hour.
If severe symptoms/severe hyponatremia known to have developed within 48 hours, rapid correction - 3% saline to raise serum sodium level by 1-2 mEq/L per hour, but no more than 8-10 in the first 24 hours
___ may be caused by severe hyponatremia. They are not caused by rapid correction, but they are an indication for rapid initial correction.
Seizures
How should patients with alcohol use disorder be given IV solutions?
Thiamine BEFORE dextrose IV solutions
Presentation of osmotic demyelination or central pontine myelinolysis?
Confusion Quadriplegia Pseudobulbar palsy Catatonia Locked-in syndrome Parkinsonism Mutism Dystonia
Several days after hyponatremia correction
