electrolyte imbalances Flashcards
How do we maintain normal plasma osmolality: intake
- Regulated by Osmoreceptors in Anterolateral Hypothalamus that detect Tonicity
- Thirst response activated when Osmolality = 295 mOsm -> happens LATE
- if pt is thristy at ER: really dehydrated
- normal: 275-290
How do we maintain normal plasma osmolality: excretion
- Regulated by Osmoreceptors that detect ADH & Tonicity
- ADH is released when Osmolality = 280-290 mOsm
renal causes of hypovolemia vs extra-renal
renal:
- Diuretics
- Osmotic Diuresis
- Hypoaldosteronism
- Salt-wasting
- DI
extrarenal:
- GI loss
- skin loss: sweating
- respiratory
- hemorrhage: pure blood loss = water loss
osmolarity vs tonicity
Osmolarity: Objective, quantitative value that determines concentration
- what you measure in a test tube
Tonicity: Subjective, comparative value that assess movement of substance between two solutions separated by membrane
- is in relation between membrane and permeability
hypovolemia labs: urine Na+, osmolality, sp gravity
Urine Sodium:
- < 20 mM/L
- Due to increased sodium reabsorption to retain body fluid volumes
Urine Osmolality:
- >450 mOsm
- Due to decreased urine output
Urine Specific Gravity:
- 1.015
- Higher due to decreased urine output
Hypovolemia: the ECF is ________. list 3 categories/causes of hypovolemia
NORMAL OR EXPANDED ECF
Decreased CO: reduces circulating blood volume
- sepsis
Redistribution:
- Hypoalbuminemia: Decreased oncotic pressure = ↓ Intravascular Volume
- Capillary Leakage: Fluid seeping into interstitial spaces
hypovolemia labs: BUN:Cr
BUN: Cr
- normal: 10:1
- prerenal azotemia (decreased renal perfusion) + GI conditions: >20:1
- dehydration: 20:1
Urinary values:
- < 20
- >
hypovolemia tx:
- Based on severity
- Mild: Slow oral rehydration
- IV fluids: based on electrolyte abnormality OR cause of hypovolemia (ie. active GI bleed)
Types of IV Fluids
Normal Saline: ECF replacement due to low osmotic pressure
- mostly distributed to INTERSTITIAL -> could cause third space
D5W: Maintenance fluid that is distributed throughout ALL compartments due to dextrose passing into all compartments
Fresh Frozen Plasma: Colloid that primarily stays intravascular
Hyponatremia: what are the sx dependent on
often associated with hypovolemia
dependent on :
- RATE of decrease: faster decline = more sx
- plasma level of sodium: really low Na+ = more sx
Hyponatremia: cycle of events in the brain
hypotonic state -> water gain causes excess water to move into the brain cells
- swelling: headache, nausea/vomit
rapid adaptation: brain cells respond by active transport to push electrolytes out of cells so water follows
slow adaption: loss of organic osmolytes
too rapid correction of hyponatremia = OSMOTIC DEMYELINATION
- damage to myelin; life threatening
Hyponatremia sx
mostly neurologic sx
Dx hyponatremia
Definition: plasma osmolality under 135
- normal: 135-145
other labs:
- Urine Osmolality
[Na+] Urine and [K+] Urine:
- Potassium is wanted to since both Na+ and K+ influence the body’s tonicity
hyponatremia with high plasma osmolality DDx
- Hyperglycemia: uncontrolled DM
- Mannitol
usually caused by the presence of other osmotically active substances in the blood that can draw water out of cells
hyponatremia with normal plasma osmolality DDx
occur in cases where there is an increase in other plasma components such as protein and lipids - > these conditions can affect the measurement of sodium
- hyperproteinemia: multiple myeloma; neoplasms
- hyperlipidemia
- after bladder irrigation process
hyponatremia with low plasma osmolality DDx first steps
1) check urine osmolality: see if its excess water intake and assess kidney function
Urine osmolality < 100 mOsm:
- primary polydipsia
- osmostat error
- suggests that the kidneys are responding appropriately to the hyponatremia by excreting dilute urine
Urine osmolalilty > 100 mOsm:
- implies that the kidneys are still concentrating urine -> indicates body’s attempt to retain water
- check ECF volume status: ddx SIADH, heart, liver, kidney ds
hyponatremia + low plasma osmolality: Urine Osmolality > 100 mOsm; normal ECF
- SIADH
- Hypothyroidism
- adrenal insufficiency
hyponatremia + low plasma osmolality: Urine Osmolality > 100 mOsm; increased ECF
conditions are often associated with edema and fluid overload
- CHF
- Cirrhosis
- nephrotic syndrome
- renal insufficiency
hyponatremia + low plasma osmolality: Urine Osmolality > 100 mOsm; decreased ECF
1) Check urinary Na+ concentration
urinary sodium (Na+) is less than 10:
- extra-renal loss: past vomiting and diuretic use
urinary sodium (Na+) is greater than 10:
- sodium wasting nephropathy
- hypoaldosteronism
- current diuretic use
- active vomiting
hyponatremia tx
Key in treatment is RATE of sodium infusion
- DO NOT CORRECT > 10-12 mM in first 24 hrs
- too quickly: rapid shift of sodium levels may destroy myelin sheath = Osmotic Demyelination
asymptomatic: 0.5-1.0 mM/hr
emergent sx:
- give hypertonic saline and increase 1-2 mmol/L for 3-4 h OR until sx improvement
- then: 0.5-1.0 mM/hr
Hypernatremia: s + s
Depends on Plasma Na+ levels and rate of Na+ decrease
- brain has mechanisms to protect ICF volume
-Mild: Thirst/Polyuria
- Moderate: Weakness
- Severe: Neurologic Deficits & Altered Mental Status
- Very Severe: Seizure & Coma
Hypernatremia: what would you expect body to do
Renal: Kidneys will try to make maximally concentrated urine with minimal volume
- <500 mL/day
- >800 mOsm
Hypothalamus: THIRST response is activated to maintain adequate intake of free water
Hypernatremia: treatment
Correct underlying cause
Correct water deficit:
- SLOW REHYDRATION- Risk of Osmotic Demyelination
- Plasma Sodium should decrease no more than 0.5 mM/hr or 12 mM/24 hours
- Enteral replacement is ideal
Nephrogenic Diabetes Insipidus: definition and causes
Definition: Renal resistance to ADH
Inherited cause: Genetics
Acquired causes:
- Medications: Lithium (treatment for bipolar ds)
- Hypercalcemia
- Hypokalemia
- Pregnancy
Central Diabetes Insipidus: definition and causes
Definition: Impairment of ADH secretion
Most common cause: Destruction of Pituitary
- Oftentimes nonreversible
DI treatment: central vs nephrogenic
Central:
- intranasal desmopressin
- ADH secreting drugs
- low salt diet
- thiazide diuretics
Nephrogenic:
- treat underlying cause
- NSAIDS
- if taking lithium: amiloride
- low salt diet
- thiazide diuretics
Hyper/Hypokalemia are assessed with fluid draws:
Venous blood *
Arterial Blood
Urine
Blood Draw Tips:
- Avoid drawing from a limb with an IV
- If must, draw the blood distal to IV site
- Use as large bore needle as possible to prevent hemolysis
Potassium: GI system
- we consume 40-120 mM per day and 90% is ABSORBED in GI
- 10% GI loss: increased in renal failure and diarrhea
Potassium summary
most abundant intracellular cation
- ICF: ECF = 38:1
- normal plasma: 3.5-5
- normal intracellular: 150 avg (muscle cells have more)
- normal extracellular: 30-70
Muscle has way more K+ in each cell
- Issue: pt that falls and rhabdo with crush injury -> can release LARGE AMOUNTS OF K+*****
Potassium: renal excretion
- filtered K+: GFR x serum potassium concentration
- passive reabsorption (90%): proximal convoluted tubule and loop of henle
- active secretion: distal convoluted tubule and collecting ducts by PRINCIPAL CELLS
- secretion and reabsorption rates change based on K+ concentration and ALDOSTERONE
How to insulin and Beta 2 agonists affect K+ levels?
Insulin:
- directly and indirectly increases K+ levels through Na+-K+ ATPase
β2 Agonists:
- stimulates Na+-K+ ATPase = ↑ ICF K+
What increases or decreases Na/K ATPase
Increase: higher intracellular Na+
Decrease:
- digoxin toxicity
- CHF
- Chronic renal failure
Hyperkalemia: decreased K+ excretion causes
- renal failure
- interstitial nephritis
- sickle cell ds
- hypoaldosteronism
- durgs: ACEi, trimethoprim, NSAIDs, spironolactone, triamterene
Hyperkalemia: potassium shift causes
Rhabdomyolysis & Hemolysis = Release of ICF K+**
Exercise**
- more exercise = more K+ release
- strenuous + beta blocker: UP TO 4 mmmol/L -> need cardiac rehab
others:
- burns
- sepsis
- hypertonicity
- insulin deficiency
- metabolic acidosis
- drugs: digoxin, beta blockers, succinylcholine, arginine
hyperkalemia sx
Often asymptomatic
If symptomatic:
- MSK: Weakness; K = muscle issues
- Cardio: Palpitations
- GI: Constipation
hyperkalemia tx - acute
Treat underlying cause! - HOWEVER: do not delay treatment to find the cause
As opposed to Sodium, MUST have rapid correction of K+
- Due to risk of Cardiac Abnormalities
acute tx:
- calcium gluconate
- glucose and insulin
- albuterol
- diuretics
- kayexalate
- hemodialysis
hyperkalemia labs + dx
Dx: serum K+ > 5
others:
- BUN/Cr: Determine if renal
- Serum glucose
- EKG: PEAKED t waves
- Urinalysis
hyperkalemia tx - chronic
Dietary Restriction
Removal of Iatrogenic cause
Loop Diuretics
Treat underlying cause:
- ex: Fludrocortisone for hypoaldosteronism
hypokalemia: causes
- renal potassium loss
- potassium shift into ICF
- decreased K+ intake
- extrarenal potassium loss
- sample error
hypokalemia: causes of renal potassium loss
Excess Aldosterone:
- Hyperaldosteronism
- Cushings
- Renovascular HTN
↑ Renal Flow at distal nephron:
- Diuretics
Hypomagnesemia: Mg2+ is needed to transport K+
Renal Tubular Acidosis
Genetic Disorder
- Bartter’s Syndrome
- Liddle’s Syndrome
hypokalemia: causes of K+ shift into the cell
- excess insulin
- alkalosis
- beta adrenergic excess
- hypokalemic periodic paralysis
hypokalemia: extrarenal loss causes
- vomit/diarrhea
- villous adenoma
- zollinger-ellison syndrome
hypokalemia sx
May be asymptomatic
If Symptomatic:
- Muscle cramps
- Fatigue
- Weakness
- Constipation
hypokalemia signs
If Diuretics = ↓ BP
If Gitelman’s Syndrome = ↓ BP
If Hyperaldosteronism = ↑ BP
Irregular HR
Paralysis
Decreased bowel sounds
Serum K+ < 3.5 mM
what other labs/tests to check to help with dx and tx?
hypokalemia
BUN:Cr: To assess renal function
Glucose
Magnesium
EKG: Presence of U WAVES
ABG
hypokalemia tx: who do you give potassium supplements to
Stable: Treat underlying cause; low Na+ diet, d/c meds
Potassium replacement:
- Intolerant to low Na+ diet
- Pt with nausea, vomiting, diarrhea
- Pt unable to stop Diuretics or Laxatives
- Pt with drug-induced hypokalemia
24-Hr Urine: hypokalemia results
If [K+]Urine < 30 mM = Extrarenal
[K+]Urine > 30 mM = Renal
Potassium Replacement
in general: 40-100 mmol/day = effective
- Oral Replacement is preferred
if IV:
- K+ suspended in NS
- No faster than 40 mM/hr -> faster will cause cardiac arrest, K+ is irritating and pts will complain that it is burning
- If 20-40 mM/hr, MUST monitor cardiac
Magnesium replacement in hypokalemia
only indicated if hypokalemia is refractory to tx AND:
- CHF
- Chemo (cisplatin)
- digoxin toxicity
- loop diuretics
hypokalemia f/u
Emergency: check electrolytes every 1-2 h
Stable: check 4-6h after tx; check daily
Outpatient setting: check weekly until stable; then check monthly or quarterly depending on pt compliance
