Sodium Abnormalities

what is sodium and its main function?

dominant cation in ECF and necessary for maintenance of intravascular volume

what are the 3 methods the body uses to maintain Na+ and water homeostasis?

-aldosterone regulates Na+ gradient in the nephron to increase or decrease water reabsorption

-ADH concentrates urine by water reabsorption

-thirst influencing fluid intake by response to serum osmolality

what prevents hyponatremia?

prevented by thirst and ADH, which is released in response to hypovolemia and decreased effective circulating volume

what are 2 main causes of hyponatremia?

-increased free water intake (>18 L/day)

-decreased free water excretion due to high ADH, low GFR, or low solute intake

what are 2 types of clinical presentation of hyponatremia and the levels that they happen at?

-altered mental status, agitation (115-120)

-seizures and coma (<115)

what are 2 degrees of hyponatremia and their results?

-severe: less than 120, may lead to permanent neurologic damage if not treated promptly

-mild-moderate: greater than 120, minimal symptoms

what are the 2 timing categories of hyponatremia?

-acute: <48 hr

-chronic: >48 hr or duration unknown

what are the 3 serum osmolality classifications of hyponatremia?

-hypotonic (most common)

-isotonic (pseudo-hyponatremia): caused by hypertriglyceridemia

-hypertonic: caused by hyperglycemia

what are the 3 types of hypotonic hyponatremia and their causes?

-hypovolemic: loss of ECF volume and Na+ due to diarrhea/vomiting or diuretics

-hypervolemic: increase in ECF volume but not intravascular volume due to cirrhosis, AKI, CHF, CKD

-euvolemic: decreased ECF sodium and increased TBW caused by SIADH

what are the 4 main evaluation steps of hyponatremia?

-plasma osmolality: true hyponatremic patients are hypotonic

-urine osmolality: >100 mOsm/kg suggest high ADH state

-volume status: hypovolemic

-urine Na+ concentration: urine Na+ <10 mmol/L suggests extrarenal loss of fluid

what is the normal range for plasma osmolality?

275 mOsm-290 mOsm/kg

what are the treatments for 2 types of acute symptomatic hyponatremia?

-severe: administer 3% NaCl, 100 mL IV @ 15-30 mL/hr

-mild to moderate: 3% NaCl, slow infusion

what are the treatments for 3 types of chronic asymptomatic hyponatremia?

-hypovolemic: isotonic fluids and hold diuretics

-hypervolemic: treat underlying condition, restrict salt and fluids, loop diuretics, vaptans

-euvolemic: fluid restriction (<1 L/day) or vaptans

what are vaptans and their MOA?

-selective vasopressin 2 receptor antagonists

-increase water excretion and serum Na+ concentration, decrease urine osmolality

what are the indications and contraindications for vaptans?

-indicated for chronic hypervolemic and euvolemic hyponatremia

-contraindicated for hypovolemia hyponatremia

-not recommended for treatment of acute hyponatremia

what is the dosing for tolvaptan (samsca) and its suggestions?

-15 mg PO qd

-do not use for more than 30 days due to hepatotoxicity risk

-achieve increase in serum Na+ by 4-6 mEq/L

-CYP3A4 drug interactions

what is the dosing for conivaptan (vaprisol) and its suggestions?

-loading dose of 20 mg over 30 minutes then continuous infusion of 20 mg over 24 hr

-not to exceed 4 days of therapy

-achieve increase in serum Na+ by 4-6 mEq/L

-CYP3A4 drug interactions

what are 3 suggestions for treatment safety for hyponatremia?

-correct hypokalemia first

-avoid rapid Na+ correction which can cause osmotic demyelination syndrome (ODS) that can lead to permanent neurologic damage

-correct Na+ by <10 mEq/L in any 24 hr period

what is the value for overcorrection of hyponatremia and what are the exceptions?

->10 mEq/L in 24 hr

-exceptions for patients with severe symptoms and rapidly decreased sodium levels

what are 2 mechanisms for hypernatremia?

-water deficit: common

-excess Na+ solute: rare

what are 5 contributing factors to hypernatremia?

-unreplaced losses of hypotonic fluids

-diabetes insipidus

-drugs

-head trauma

-hyperaldosteronism

what are 5 drugs that can contribute to hypernatremia?

-lithium

-phenytoin

-ethanol

-amphotericin B

-foscarnet

what are 3 characteristics of the clinical presentation of hypernatremia?

-rapid change or Na+ over 160 mmol/L

-symptoms suggestive of fluid loss

-clinical signs of dehydration

what are the 2 results of assessing urine output and potential causes?

-<3000 mL/day: excessive Na+ intake, hypodipsia

->3000 mL/day, assess urine osmolality (Uosm): <300 mosm/kg, challenge with synthetic ADH; >300 mosm/kg, likely osmotic diuresis

what is the main treatment goal of hypernatremia?

correct serum Na+ concentration at a rate that restores and maintains brain cell volume; rapid correction of chronic asymptomatic hypernatremia is a potentially fatal error

what are the 3 main suggestions for treatment of hypernatremia?

-correction rate should be about 0.5 mmol/L/hr, correct by no more than 10-12 mmol/L/day

-calculate volume deficit to replace

-monitor plasma Na+ every 2-4 hrs in acute phase, then every 4-6 hr

what are the 4 main underlying issues of hypernatremia and their treatments?

-hypovolemic: give isotonic crystalloids, preferably NS

-central DI: give intranasal dDAVP due to oral formulations having poor bioavailbility

-nephrogenic DI: dietary Na+ restriction and thiazide diuretic

-Na+ overload: give loop diuretics and D5W

what are 2 populations that commonly experience hypernatremia?

-infants

-elderly population with neurological or physical impairment