electrolytes

what are electrolyte functions

• osmotic pressure

• water distrubution

• acid base balance

• neuromuscular excitability

  • cardiac rhythm

  • muscle contraction

• enzyme cofactors

what are electrolytes

ions capable of carrying electric charge

what do anions move to

anode

what do cations move to

cathode

electrolytes involved in volume and osmotic regulation

Na, Cl, K

electrolytes involved in myocardial rhythm and contractility

K, Mg, Ca

cofactor electrolytes

Mg, Ca, Zn

electrolytes involved in coagulation

Ca, Mg

what percent of the body is water , how does it compare in age and sex

40-75% of body weight

• declines with age and obesity

• less in women than men (higher % of body fat)

how much of water is found in intracellular compartments

2/3

how much of water is found in extracellular components

1/3

what is osmolality

• based on concentration of solutes per kilogram of solvent

• related to changes in properties of solution relative to pure water

what is the clinical significance of osmolality

• parameter to which hypothalamus responds

• regulation of osmolality affects plasma sodium []

• regulation of sodium and water controls blood volume

what specimen is used to determine osmolality

serum or urine

what is preferred test for osmolality

freezing point

what is osmolality testing for research

vapor pressure

what is the major extracellular cation

Na+

what is major intracellular cation

K+

what electrolyte is the largest plasma osmolality contributor

Na+

what does aldosterone do

INC Na reabsorption

promotes K and H secretion

what is the reference range for Na+

136-145 mmol/L

what is hypernatremia? hyponatremia?

high and low Na+ level

what can cause hypernatremia

• dehydration

  • simple

  • DEC ADH ← diabetes insipidus

• INC Na retention

  • INCCC of aldosterone

    • Conn’s disease

• INC Na intake

  • saline administration

what are Na and K regulated by and how

• kidney

  • glomerulus filters

  • proximal tubule reabsorbs

  • distal tubule reabsorbs/secretes

what is depletional hyponatremia

INC Na loss

what causes depletional hyponatremia

• DEC renal Na reabsorption

  • diuretics, tubular disease, DEC aldosterone (ADDISONS), osmotic diuresis, chronic renal failure

• INC skin loss

  • sweating, burns , CF

what is dilutional hyponatremia

water gain

what causes dilutional hyponatremia

• water overload

  • rapid/excess administration

• INC water retention

  • INC ADH (inappropriate ADH/ SIADH)

  • renal failure

  • hypovolemia

    • congesting heart failure

    • hypoalbuminemia

what is the most commonly used routine test for Na

ISE = ion selective electrode analysis

what is Na ordered as a part of

Lytes panel

what ist eh function of K+

neuromuscular excitation, cardiac rhythm

what happens with hyperkalemia

fatigue, numbness, problems breathing, palpitations, paralysis, heart problems, irregular heart beat, death

what happens with hypokalemia

mild arrhythmia, muscle weakness, severe muscle cramps

what things regulate potassium

• renal

• acid base balance

how does renal regulate K+

• most is excreted

• INC aldosterone → INC K+ secretion

how does acid base balance regulate K+

K+ is exchanged with H+ (for renal, cellular compensation)

reference range for K+

3.5-5.1 mmol/L

what can cause hyperkalemia

• DEC K+ secretion

• facetious (pseudo)

• sample type

how does DEC K secretion cause hyperkalemia

• indicates ESRD

• DEC of aldosterone

how can acidosis compensation affect K+

cause INCREASE

what causes pseudohyperkalemia

hemolysis, excessive stasis, transfusion

how does sample type cause hyperkalemia

• serum?plasma

• if exercise forearm→ falsely elevated levels

what causes hypokalemia

• DEC intake

• INC excretion/loss

how does alkalosis compensation affect K+

causes DECREASE

what hormone can affect K+ levels to hypokalemia and HOW

insulin

• promotes entry of K into smooth muscle and lung cells

what can cause INC K excretion / loss

GI/renal

• diuretics

• INC aldosterone

• hypovolemia

what is the first phase of K+ in DKA

transient hyperkalemia phase

what happens in transient hyperkalemia phase

• DEC insulin

  • K+ moves out of cells, into the plasma

• acidosis = ketosis

  • K+ moves out of cells in exchange of H+

what is the second phase of K+ in DKA

hypokalemia phase

what happens in hypokalemia phase

• INC glucose → osmotic diuresis → K+ depletion

  • insulin administration

    • K+ and glucose driven intracellularly

what specimen is used to measure potassium

heparin plasma

what kind of membrane is used for potassium - why?what method?

valinomycin - selectively binds potassium for ISE

what is the major extracellular anion

Cl-

reference range for Cl-

98-107 mmol/L

what is Cl regulation associated with, what is the EXCEPTION

with Na+

• except certain acid-base disorders

how is Cl- involved in acid base balance

chloride shift

what causes hyperchloremia

• metabolic acidosis = 1 degree bicarbonate deficit

• cystic fibrosis

how does metabolic acidosis = bicarbonate deficit cause hyperchloremia

chloride INCREASES in exchange for anion balance

how does CF cause hyperchloremia , how is it measured

• INC sweat chloride

• sweat collected by pilocarpine iontophoresis

what causes hypochloremia

• metabolic alkalosis = 1 degree bicarbonate excess

• gastric HCl loss

what is associated with gastric HCl loss

• prolonged vomiting

• nasogastric suctioning

what specimen is used for chloride measurement

serum or plasma

• lithium heparin

how does hemolysis affect Cl levels

DECREASE

describe magnesium

4th most abundant cation, 2nd intracellularly

• avg human body has.1 mole (24g) of Mg

Mg role in body

• glycolysis

• transcellular ion transport

• neuromuscular transmission

• synthesis of carbohydrates, proteins, lipids, nucleic acids

• release and response to certain hormones

how is magnesium regulated

• diet : raw nuts, dry cereal, hard drinking water, meats, fish, fruit

• processed foods → inadequate intake

• kidneys

  • reabsorb in deficiency

  • excrete in excess

clinical significance of Mg

hypo- hyper- magnesemia

Mg measurement specimen

nonhemolyzed serum / lithium heparin plasma

what methods are used for Mg measurement

• calgamite

• formazen dye

• methylthymol blue

  • bind, color change

describe calcium

• needed for myocardial contraction

• blood ionized calcium is closely regulated , 1.18 mmol/L

• normal ionized levels important during surgery and in critically ill patients

what hormones regulate calcium

PTH, vitD, calcitonin

distribution of calcium

99% of body calcium in bone

1% in blood and other ECF

• 45% is free ions

• 40% is bound to protein

• 15% is bound to anions

clinical application of Ca

• hypo and hyper calcemia

what method determines calcium

dye binding

specimen for calcium

serum, plasma

where is phosphate found

• everywhere in living cells

  • in key biochem processes

how is phosphate regulated

• absrobed in intestine from diet

• released from cells to blood

• lost from bone

phosphate distribution

• 80% in bone

• 20% soft tissue

• <1% in serum/plasma

clinical applications of phospahte

hypo and hyper phosphatemia

specimen for phosphate

serum, lithium heparin plasma

method for phosphate

formation of ammonium pphosphomolybdate complex

what is lactate

byproduct of emergency ATP production

• when O2 is diminished

lactact regulation

• levels rise rapidly when O2 delivery decreases below CRITICAL LEVEL

what is lactate used for clinically

metabolic monitoring in critically ill patients

what to remember for lactate specimen

avoid using tourniquet

method for lactate

enzymatic method

what is indicated when lactate levels are high

• sepsis

• hepatic failure

• cancer

• diabetes mellitus

• decreased heart output

what makes up total CO2 / bicarbonate

95% bicarb = HCO3

5% dissolved CO2 = dCO2

<1% carbonic acid = H2CO3

what is bicarb estimates

[bicarbonate ion]

what are the total CO2 (TCO2) functions

• acid base balance

• transport CO2 form

  • brings CO2 back to lungs = exhale

• renal regualtion

• electroneutrlaity

TCO2 and acid base balance

• renal with lungs

• BLOOD BUFFERING

  • bicarb-carbonic acid

  • weak base and weak acid

what is the MOST important buffering pair in maintaining acid base balance

bicarbonate and carbonic acid

how does TCO2 contribute to electroneutrality

HCO3 and Cl- tend t vary reciprocally

reference range of TCO2

22-28 mEq/L

what is the significance of TCo2

estimates [bicarbonate] / alkali reserve

what is it called when there are acid base imbalances

• metabolic acidosis = 1 degree bicarb deficit

• metabolic alkalosis = 1 degree bicarb excess

what is the diagnosis for acid base imbalances

arterial blood gas )ABG)

electrolyte balance

#plasma cations = #plasma anions

what does the anion gap do, what can it be used for

evaluate electrolyte balance

• estimates unmeasured electrolytes like organic acids or Mg

• QC for analyzer used to measure electrolytes

anion gap equations and their ranges

1. (Na) - (CO2 + Cl) , 7-16 mmol/L

2. (Na + K) - (CO2 + Cl) , 10-20 mmol/L