Electrolytes Flashcards
What regulates serum sodium?
thirst
ADH
RAAS system
What’s included on an electrolyte panel?
Na K Cl CO2 Ca
*Mg and phosphate need to be ordered separately
What is the most common electrolytes abn. in hospitalized pt?
hyponatremia
danger zone Na below 125
can be acute or chronic
can be seen in assoc. with pulmonary disease of CNS disorder
What are some clinical manifestations of hyponatremia?
Headache, dizziness Nausea, vomiting Lethargy Weakness Confusion Hypoventilation, respiratory arrest Seizures Coma
What are some causes for hyponatremia?
Pseudohyponatremia
Redistributive hyponatremia
Hypovolemic hyponatermia
Hypervolemic hyponatremia
Euvolemic hyponatremia
What is pseudohyponatremia?
Falsely low serum sodium
Serum Na<135 but NORMAL osmolality
When does pseduohyponatremia occur?
Occurs with hyperlipidemia and hyperproteinemia
-Can also occur with obstructive jaundice & multiple myeloma
lab artifact!! call lab to confirm
What is redistributive hyponatremia?
Hyperosmolar state; “relative hyponatremia”
Caused by osmotically active solutes in extracellular space that draw H2O from cell diluting
What is a common cause of redistributive hyponatremia?
hyperglycemia
How do you calculate redistributive hyponatremia?
Add 1.5mEq/L to sodium value for every 100mg/dl serum glucose > 100mg/dl
What are some renal losses responsible for Hypovolemic Hyponatremia?
diuretics
osmotic diuresis
addison’s disease
What are some non-renal losses responsible for Hypovolemic Hyponatremia?
External GI: vomiting, diarrhea, NG suction, fistula
Internal GI: pancreatitis, peritonitis
Burns
Tx for hypovolemic hyponatremia?
replace fluid losses (with isotonic fluid, ie. NS), and treat the underlying cause
Causes for hypervolemic hyponatremia? tx?
Hepatic cirrhosis, CHF, Renal failure
diuretics, dialysis, fluid restriction
Causes for euvolemic hyponatremia?
SIADH
Primary polydipsia
Often psychogenic
Urine maximally dilute
Hypothyroidism
Adrenal Insufficiency
Tx for euvolemic hyponatremia?
fluid restriction,
treat underlying cause.
Describe SIADH
Syndrome of Inappropriate Antidiuretic Hormone Secretion
This impairs free water excretion but sodium continues to be excreted normally
Hallmark findings in SIADH?
Concentrated urine (>100mOsm/kg) with low serum osmolality and euvolemia
SIADH usually occurs in…
hospital setting
Tx for SIADH?
Fluid restriction
Treatment of underlying pathology
For refractory cases +/- Hypertonic saline Demeclocycline Urea Lithium “Vaptans”
How do we eval for hyponatremia?
good H &P
labs: UA- Na and osmolarity, serum osmolarity, CMP
secondary labs: TSH, serum cortisol
Tx for hyponatremia?
Depends on underlying cause
If Na<125 or symptomatic hospitalize!
Chronic hyponatremia must be managed with extreme care
-slow cautious correction
Why do we need to be careful about correcting Na?
Rapid increase in serum sodium can lead to cerebral pontine myelinolysis (CPM)
What can be used to tx hyponatremia?
hypertonic solutions
traditional tx: chronic hyponatremia =demeclocycline
How often should you check serum Na while correcting?
q2hrs
What is Central pontine myelinolysis?
CPM is a poorly understood entity characterized by focal demyelination in the pons and extra- pontine areas – it is irreversible!!
Sxs of central pontine myelinolysis?
Dysarthria, dysphagia, seizures, altered mental status, quadriparesis, hypotension
Work up for hyponatremia?
Check serum osmolarity
- if high»_space; hyperglycemia
- if low»_space; check urine osmolarity
if urine osmolarity is low»_space; water intoxication
if high»_space;need to check volume status
What is hypernatremia?
A hypertonic disorder due to serum sodium >145mEq/L
“Too little water relative to salt”
Clinical features of hypernatremia?
Often asymptomatic Thirst, signs of volume depletion AMS, weakness Neuromuscular irritability Focal neurologic deficits Seizures or coma
Causes for hypernatremia?
Too little dietary water
Too much dietary salt
Excessive water loss from the body
Work up for hypernatremia?
check urine osmolality!
if less than plasma osmolality (<300) = central or nephrogenic DI
If intermediate (300-600) = osmotic diuresis or DI
If high (>600) : dehydration most likely secondary to extrarenal water loss
Normal response to hypernatremia?
thirst, increase fluid intake
concentrates urine
What is diabetes insipidus?
Nonosmotic urinary water loss in setting of elevated serum sodium: urine is dilute when it should be concentrated
Describe central DI
due to impaired secretion of antidiuretic hormone (ADH)
Describe Nephrogenic DI
lack of kidney response to ADH, causing continued water loss even though patient is low on water. Adequate ADH is present.
Tx for nephrogenic DI?
Thiazide diuretic
Amiloride (potassium sparing diuretic)
Chlorpropamide (antidiabetic oral agent)
NSAIDs have been tried (including Indomethacin)
Tx for hypernatremia?
hospitalize if severe
stop water loss
replace water deficit
-but not too quickly!
How can you calculate water deficit? What is this used for?
normal TBW-Current TBW
Normal: .6 x body weight in kg
current: normal serum x normal TBW
to replace free water in hypernatremia
Serum Potassium is a…
major IC cation
hypokalemia is common in…
pts receiving diuretics
Clinical presentation of hypokalemia?
Weakness, fatigue Muscle cramps Hyporeflexia Flaccid paralysis (ascending) Cardiac arrhythmia Hypercapnia
ECG findings for hypokalemia?
Flattened T waves
Prominent U waves
Premature Ventricular
Contractions (PVC’s)
Depressed ST segments
What are the 3 dif. mechanisms that can causes hypokalemia?
transcellular shifts- drugs, delirium tremens…
renal losses - diuretics MC cause
extra-renal losses- V/D, burns, Mg deficiency
Tx for hypokalemia?
replace K (oral preferred!) and underlying cause
telemetry monitoring if inpt
IV for those not able to eat/emergencies
Can you push IV K?
NO, should be given slowly
give with lido if using peripheral IV
How do you replace K?
For every 0.1 mEq/L below 4mEq/L,
Give 10 mEq/L
(10 for ever .1 you want to increase)
What is hyperkalemia?
Defined as K > 5 mEq/L, severe > 6.5 mEq/L
In the absence of renal failure or other identifiable cause, actually quite rare
Clinical presentation for hyperkalemia?
Relatively asymptomatic
Muscle weakness
Begins in legs and ascends to trunk and arms
“ascending flaccid paralysis”
ECG changes: potentially life threatening arrhythmias
ECG findings in hyperkalemia?
Peaked T waves >
widen QRS >
junctional rhythm> ventricular fibrillation
K > 6 more likely to cause severe cardiac arrhythmias
Causes of hyperkalemia?
Factitious-hemolysis
Impaired K excretion- renal failure
Drugs- K sparing diuretics, ACE/ARBs,NSAIDS, Bactrim
Increased intake
Other causes for hyperkalemia?
conditions which move K+ from intracellular to extracellular space:
-tissue damage, acidosis, decreased insulin
Tx for emergent hyperkalemia?
- IV calcium
- Maneuvers to shift K from ECF to ICF
- -sodium bicarb
- -Insulin IV + D50W - other potential options: nebulized albuterol, IV lasix, dialysis
Less urgent tx for hyperkalemia?
Kayexalate
- exchanges Na for K in the gut
- causes lots of diarrhea
Lasix
correct underlying cause
How is serum calcium measured?
otal Ca = free (ionized) + protein-bound
Used to evaluate metabolism and monitor patients with hyperparathyroidism, malignancies and renal failure
There is an inverse relationship btwn Ca and…
phosphate
Most Ca is in the…
bone
What are the dif. Ca forms?
ionized
complexed
protein-bound (albumin)
A decreased in serum Ca triggers the release of….
A increase in serum Ca triggers the release of…
PTH from parathyroid gland, which acts to increase Ca in the blood by:
calcitonin from the thyroid gland, which acts to decrease Ca in blood by: Inhibiting bone resorption
hypercalcemia..
Calcium > 10.1
Relatively common, most cases are mild and self-limiting
presentation for hypercalcemia?
Stones, Bones, Abdominal Moans,
and Psychiatric Groans”
Primary causes for hypercalcemia?
malignancy and hyperparathyroidism
other causes: meds
What labs should you check for hypercalcemia?
Serum Ca
PTH and rPTH
TSH
Protein electrophoresis
Tx for hypercalcemia?
***volume expansion
- Calcitonin > lowers levels rapidly
- Pamidronate
- Zoleronic Acid
Others: fallium nitrate, prednisone, dialysis
Presentation for hypocalcemia?
Increased neuromuscular: excitability (tetany) Paresthesias (peri-oral, extremities) Hyperactive reflexes, carpopedal spasms Chvostek’s sign Trousseau’s sign
Cardiovascular effects:
ECG changes (prolonged QT interval); arrhythmia
Hypotension
What is tetany?
involuntary sustained contractions
Chvostek’s sign?
tapping facial nerve against the bone just anterior to the ear results in contraction of facial muscles
Trousseau’s sign?
occluding brachial artery for 3 minutes with BP cuff induces carpal spasms.
Causes for hypocalcemia?
hypoalbuminemia, large blood tranfusion, hypomagnesemia, hypoparathyroidism, renal failure, intestinal malabsorption/Vit D def.
Neuromuscular changes in hyper v. hypocalcemia
decreased excitability (weakness)
increases excitability (tetany)
Phosphate
used to investigate parathyroid and calcium abnormalities
Causes for hyperphosphatemia
Renal failure Hypoparathyroidism Hypocalcaemia Rhabdomyolysis Exogenous Phosphorus
causes for hypophosphatemia?
Decreased intestinal absorption Hyperparathyroidism Chronic alcoholism Severe diarrhea Cellular shift -Insulin -Refeeding Syndrome
Describe Mg
Normal value: 1.3 – 2.1 mEq/L (adult)
Involved in neuromuscular and cardiac function
bound to ATP, excreted by kidneys
Mg is intimately tied to…
Ca and K
Hypomagnesium inhibits…
and impairs…
PTH activity which can cause hypocalcemia
and impairs ability of the kidneys to conserve K
