Electrolytes Flashcards
what are the major electrolytes and where are they found (intracellular or extracellular)
Extracellular Electrolytes
Sodium (major cation) Na+
- approx. 140 mmol in the serum
- major determinent of serum osmolality
- normal concentration : 135-145
Chloride (major anion) Cl-
- exisits as 100 mmol in serum
- hyperchloremia & hypochloremia are rarely isolated instances = they usually indicate a Na+ or bicarb shift as they attempt to offset any changes in electricity
Intracellular Electrolytes
Potassium (major cation) K+
- in small (3.5-5 mmol) can be found in the serum
- but large (150 mmol) within the cells (approx. equal to the amount of sodium on the outside)
- during a hemolyzed sample: may have falsely elevated K+ because the cells burst and spill into blood
posphates & protiens can be intracelluluar too
Other Solutes
- CO2 (anion)
- BUN
- Creatinine
- Glucose
What is the Anion Gap
when is it calculated
how is it calculated
what is a normal gap acidosis v elevated gap
Anion Gap: the gap in the difference between calculated cations and anions within the serum
major cation: Na+
major anions: Cl- & HCO3-
AG = (Na+) - (Cl- + HCO3-)
the gap is the “unaccounted” for other anions (acids) which exist in the body normal = 8-12
Anion Gap = calculated in determining the cause of a metabolic acidosis
Normal Gap Metabolic Acidosis: occurs when the amount of “other anions” or acids within the body do not change; but there is a loss in HCO3-; thus a gain in Cl- occured to keep the gap the same
Increased Gap Metablic Acidosis: occurs within the cration of new “anions” or acids within the body; a decreased HCO3- which is not compenstate for by an increas in Cl-
- the acids soaked up all the bicarb
Carbon Dioxide relationship with HCO3-
CO2 + H2O = H2CO3 = HCO3- + H+
- the CO2 content of the body is measured from the free CO2, the H2CO3 & the HCO3- within the body
the amount of H2CO3 and dissolved CO2 is so small within the body that its understood that the CO2 level within a BMP is the estimated level of HCO3-
what is the BUN
where does urea come from
Blood urea nitrogen = measures the amount of urea within the blood
where does urea come from
- urea is an end product of protein breakdown made in the liver, transported and excreted in the kidneys
- when there is kidney disease, the excretion of urea is impacted and then there is a build up of BUN levels within the blood as a result
- BUN is normally understood in the context and relationship with creatitine
What is the Creatitine Measurement on a BMP
what is creatitine
- creatitine is a catabolic product of the creatine phosphate breakdown which occurs in skeletal muscle breakdown
- creatitine is excreted entirely by the kidneys from the blood **thus: it is proportional to renal function in that the level in the blood (should be low) gives a good idea about how well the kidneys are able to filter
Level of Glucose and its significance
glucose measurements should always be evaluated in the context of a patients meal (either fasting or after eating
elevated glucose = indicative of DM
how is osmolalitiy calculated? what does it tell
osmolality = 2 x Na+ + (glucose/18) + (BUN/2.8)
osmolality = the soulte concentration per amount of solution
normal osmolatiy = 290-295within serum
Fluid within the body
amount in intercellular
amount in extracellular (interstital v plasma circulation)
how is fluid moved
the body is made of approx. 60% fluid (less in females because muscle = water and males ahve more muscle)
of the 60% –> approx. 2/3 of that is INTRAcellular & 1/3 is EXTRAcellular
of the extracellular –> 80% is in the interstitum and 20% is circulating as plasma within the blood
Fluid Movement
- is determined by hydrostatic pressure defferences and by osmotic (protein) pressure differences
- membranes are permiable to water –> such that it can flow freely while solutes cannot
of the water taken into the body (water consumed) its about equal to the amount out (urine)
The Balance of Fluid within the Body is dependent on what factors
what are the solutes/electrolytes we care about
forces of flow
- volume of the fluid (hydrostatic pressures)
- solute charges (osmotic load)
Solutes
cations = Na+, K+, Ca2+, H+
anions = Cl-, HCO3-, PO43- (phospahte)
uncharged particles: protein, urea, glucose, O2 and
CO2
Function = keep homeostasis
electrically neutral & osmotically stable (particles per volume of fluid)
kept homeostasis by…
- ion channels and trasnport
- osmosis of water
- kidney function
remeber the forces of osmosis, diffusion, active transport in maintaining hydrostatic and oncotic pressures
When the the body is regulating its water contents
- what is the natural drive
- what controls water content (and what drives these mechanisms
defult is to excrete water
controlled by…
1. ADH release
2. Thirst stimuli (from hypertonic (high osmolaltiy) serum, low volume, hypotension, AGII, increased Na+)
Thirst Stimul =
1. trigger osmoreceptors which trigger the neeed to drink water
2. trigger ADH release
Types of Volume Abnormalities
- isotonice loss
- isotonic gain
- edema
isotonic loss
- a decrease in extracellular fluid volume, weight loss, dry skin, decreased urine output
- think hypovolemic shock
- losing the fluid and the solutes all together
isotonic gain
- an increase in extracellular fluid volume, weight gain, decreased hematocrit (hemodilutaion), diluted plamsa proteins, distended neck veins, increased BP
- think : anasarca fluid overload (HF) (fluid in areas of the body which are not just the dependent areas
edema
- accumultaion of fluid within the interstital spaces
- can be a cause of…
1. increased hydrostatic pressure (fluid pressure) = obstruction in the venous system, lymphedema, CHF, renal failure
2. a lowered plasma oncotic pressure (no pull of the proteins to bring the fluid back into plasma) = liver failure, malnutrition, burns, renal failure
3. increased capillary membrane permiability = inflammation, SIRS, sepsis
Edem can result in….
- a further distance for diffusion to happen
- impaired blood flow (because theres a higher pressure now in the interstital space)
- slower healing (takes longer to get to places)
- increased infection
- pressure sores in boney areas
- impaired organ function (cant work with the fluid in the interstitum that well)
Sodium (Na+)
- concentration within the plasma
- importance in function
- how it is reabsorbed/regulated in the kidneys
(the high level of sodium outside the cell & the low amout inside, contrasted with teh high amoutn of potassium inside the cell and low amoutns outside is maintained due to the 3Na+ out and 2K+ in the cell ATP cellular transporter on cells surface)
Sodium: Na+
- main extracellular cation : most important role in water balance because where sodium goes water follows
- pairs with Cl- and HCO3- to neutralize
- 135-145
sodiums role in function
- plays arole in nerve and muscle function
reabsored in kidneys
- majority of Na+ reabsored from the PCT, later some in the DCT/collecting duct
- due to the effects of aldosterone, renin & ANP
Potassium (K+)
- concentrations in the cell and plasma
- role in teh body
- regulated through the kidneys
Potassium (K+)
- major INTRAcellular cation (kept in there via the Na+/K+ ATP pump)
- approx. 150-160 mEq
function
- helps regulate the resting membrane potential
- regulates fluid, ion balance within the cell
Kidney regulation
- aldosterone
- insulin (insulin forces K+ into the cell and H+ out)
Chloride (Cl-)
- concentration within the plasma v cells
- role in the body
- regulated by the kidneys
Chloride (Cl-)
- major extracellular (plasma) anion
- approx. 105 mEq
- (there is a Na+/Cl-/K+ pump within the kidneys)
role in the body
- regulates tonicity
Kidneys
- reabsorbed with sodium (K+/Cl-/Na+ pump in LoH)
- relationship is reciprocale with HCO3-
Hypernatremia
- what is the cut off
- due to what
- clinical manifestations
Plasma Na+: > 145
- water is moving from the intracellular space to the extracellular spaces
- can be due to an increase in sodium or a decrease in water (because less water = more concentrated plasma because the same amounts of solutes remain)
- cells will push their water outside to try to dilute (thus dehydrating the cells)
Due to
- excess Na+ intake (like an IV)
- excess Na+ retention (due to aldosterone oversecretion)
- loss of pure water (due to sweating, respiratory infections or DM)
- insufficent intake of water
Symptoms of hypernatremia
- thirst
- lethargy
- irritability
- seizures
- fever
- olgouria (kidnye holding onto water in order to dilute the sodium)
