Hypernatremia Pathophysiology
what the difference between dehydration & depletion?
Dehydration: Loss of total body water in the form of pure water (NO SALT LOSS), lead to hypertonicity, kidney works to increase water reabsorption by increasing ADH and thirst drive/water intake
Depletion: loss of body water AND salt, leads to volume contraction. kidney works to increase water & salt reabsorption by increasing ADH, Aldosterone, and afferent & efferent arteriolar tone.
What central DI/AVP-D (arginine-vasopressin deficiency)?
pituitary doesn't release/make ADH, 1of 2 cause of DI
what is the 1st part of assessment for hypernatremia? Describe its types w/corresponding lab values & possible causes
Volume status!
Hypovolemia, Euvolemia, Hypervolemia
what is the first thing assessed and what are the 3 types w/ criteria?
Tonicity/Osmolality!
Hypertonic- serum osm >295
Isotonic- serum osm 280-295
Hypotonic- serum osm <280
What serum Na+ is Hyponatremia and what are complications and symptoms of Hyponatremia?
Serum Na+ <135
cerebral edema is worse complication, other symptoms: In early disease: Nausea and malaise. With progression: headache, lethargy, obtundation, seizures, coma, respiratory arrest When levels <115-120.
What is the formula for free water deficit?
Female= 0.5 [if old .45] x Weight in kg x (Measured Na-140 / Ideal Na)
Male= 0.6 [if old .5] x Weight in kg x (Measured Na-140 / Ideal Na)
What is nephrogenic DI/AVP-R ( arginine-vasopressin resistance) ?
Kidney doesn't respond to ADH, 1 of 2 causes of DI.
What are the corresponding lab values & possible causes to each of the 3types of volume status?
Hypovolemia- low body water & Na+, Urine Na+ >20 indicates renal losses (meds, post-obstruction, renal d/os), Urine Na+<20 indicates extra renal losses (sweating, burn, diarrhea, fistula)
Euvolemia- low body water & variable body & urine Na+ Renal loss (DI, hypodipsia), extrarenal loss (respiratory, dermal)
Hypervolemia- high body water & Na+, Urine Na+ >20- sodium retention (1 hyperaldosteronism, cushing's, hypertonic dialysis, NaCl tablets)
Possible causes of Isotonic & hypertonic hyponatremia?
Isotonic Hyponatremia- hyperproteinemia (myeloma), hyperlipidemia (chylomicrons & TGs, rarely choelsterol)
Hypertonic Hyponatremia- 1. hyperglycemia, 2. mannitol, sorbitol, glycerol, maltose, 3. radiocontrast agents, 4. ethylene glycol, methanol
What are features on PE for Hypo & Hyper -volemic Hypotonic hyponatremia?
Hypovolemic PE: low JVP, no edema, dry axilla, dry underneath tongue
Hypervolemic PE: pitting edema, lung crackles as bases, high JVP, ascites, Pulmonary edema on CXR
What is Central Pontine Myelinolysis?
complication of acute hypernatremia, is a demyelinating brain lesions likely from an overcorrection of hyponatremia.
3 key symptoms and urine volume in DI pt presentation?
3Ps- polydipsia, polyuria, maybe polyphagia
24hr urine > 3L output, can have up to 20L
what is the big picture Tx of hypernatremia?
WATER!
-different concentrations depending on volume status and other things
What is assessed further in Hypotonic Hyponatremia?
Volume status, Urine Na+ (determines renal response), Urine osmolality (U Osm- only for Euvolemic hypotonic hypoNa+ determines ADH response)
Hypovolemia- U Na+>20: renal loss, U Na+<20: extra renal loss
Euvolemia- High U Osm: high ADH state
Hypervolumia- U Na+>20: renal causes (inside tubules), U Na+<20: extra renal/outside tubules Edematous states
What are some causes of Hypovolemia Hypotonic hyponatremia w/U Na+ >20 & Hypervolemia Hypotonic hyponatremia U Na+ <10?
Hypovolemia Hypotonic hyponatremia w/U Na+ >20 - RENAL SALT LOSS: 1. diuretics, 2. ACEIs, 3. Nephropathies, 4. Mineralocorticoid deficiency/Addision's,
Hypervolemia Hypotonic hyponatremia U Na+ <10 - Edematous states: 1. CHF, 2. Liver disease, 3. Nephrotic syndrome/Renal Na+ retention
what are symptoms of hypernatremia?
Lethargy, weakness, and irritability lead to (including brain shrinkage): Twitching, Seizures, Coma
what are the three main causes of polydipsia/polyuria?
AVP-D, AVP-R, primary (lifestyle choices, pt is actively drinking a lot of water)
What part of patient presentation determines the speed of correction? describe it too!
time of onset!
Rapid correction done when pt present with acute hypernatremia lasting <48hrs and are symptomatic!
Slow correction done when pt presents with chronic hypernatremia lasting >48hrs
How does hyperglycemia cause hyponatremia?
SIKE! it's a PSEUDOHYPONATREMIA and is hypertonic. No change in body Na+, it shifts due to osmotic pressure. It can eventually cause hypernatremia due to osmotic diuresis
What are some causes of Euvolemic Hypotonic Hyponatremia w/ U Na+ 20?
High ADH states! ADH can be increased by increased serotonin, and increased Prostaglandin inhibition (NSAIDs)
1. SIADH, U Osm > 200, 2. Meds: thiazide, ACEIs, NSAIDs, SSRIs, 3. adrenocorticotropin deficiency- decreased cortisol thus decreased water clearance, 4. hypothyroidism.
Other Unique ones: HIV, Exercise endurance, stress, idiopathic low Na+ of elderly, psychogenic, beer potomania.
What is the function of ADH?
secreted from hypothalamus, acts on collecting ducts to reabsorb water, increase Urine Osmolality, increased water in the body that dilutes body Na+
How to tell the difference between 3 types/causes of polydipsia/polyuria?
Look at vasopressin(AVP)!
AVP-D- pituitary isn't making ADH so low/deficient levels of AVP
AVP-R- pituitary is making ADH but no reaction from kidney so it keeps making it to compensate, high AVP levels.
Primary- patient is drinking a lot so ADH and AVP levels are suppressed.
How do you treat the various volume states in hypernatremia?
Hypovolemia- fluid rescue w/ballanced cristalloid then switch to half 5% dextrose & isotonic saline
Euvolemia- 5% dextrose may or may not need loop diuretics
Hypervolemia- 5% dextrose w/ loop diuretics
What is the biggest rule to correction Tx & what can go bad?
Slow correction! Do not exceed Na+ correction rate of more than 112/24hrs
CPM- not inflammatory, osmotic demyelination that damages descending motor tracts to cause spastic tetraparesis, pseudobulbar paralysis, locked-in syndrome.
what are some causes of SIADH?
Neuro/psych causes, ectopic production of ADH from tumors, drugs, pulmonary disease, post-op!!, prolonged nausea, Vasopressin (ADH) or oxytocin administration