Electrolytes, Electrochemistry, Co-Oximetry & Acid Base Balance

What is the renin-angiotensin-aldosterone system?

Body's response to low BP.

Renin, which is released primarily by the kidneys, stimulates the formation of angiotensin in blood and tissues, which in turn stimulates the release of aldosterone from the adrenal cortex.

This causes the body to retain water and increase BP.

What does ADH do?

Facilitates reabsorption of water in nephron of kidney

ADH ADores H20

What does aldosterone do?

Increases reabsorption of sodium and increases secretion of potassium

dilutes urine

Aldosterone saves sodium and pees potassium

What is the major cation in the ECF?

Sodium

What are the two kinds of hyponatremia?

Dilutional - sodium is diluted un plasma due to excess fluid. edema is present

Depletional- sodium is lost from plasma. edema not present

What is the major anion of ECF?

Chloride

What is the role of chloride?

maintains osmotic pressure and buffers CO2

How is cystic fibrosis diagnosed?

Sweat chloride test

High chloride levels are seen in

metabolic acidosis

Low chloride levels are seen in

metabolic alkalosis

How does bacterial meningitis impact ECF electrolyes?

Raises protein levels which reduces concentration of chloride anions in the fluid

What interferes with chloride assays?

Other halides like fluoride, bromine

What interferes with sodium assays?

lipemia

causes falsely low Na

What electrolyte test is known to have diurnal variation

Urine Na+ - lower at night

What needs to be done when taking an electrolyte sample from a catheter?

remove 5.5x the dead space and discard the blood

catheters are flushed with saline which can falsely increase Na and Cl

How does insulin impact electrolytes?

Lowers potassium

What diseases cause hypokalemia?

Fanconi syndrome

SIADH

Addison's disease

Cushing's disease

How does licorice impact electrolytes?

mimics aldosterone - lowers potassium

What conditions can cause hyperkalemia

renal failure

uncontrolled type I diabetes

crush injury

what causes hypernatremia?

dehydration

drowning in salt water

What causes hyponatremia?

Too much water, SIADH,

What are the potassium critical values?

<2.5 mmol/L

>6.0 mmol/L

T/F: Samples to be analyzed for a full lytes panel should be kept on ice

FALSE!!!!

This will cause a false increase of K+ and decrease of Na+

What interferes with potassium assays?

Hemolysis

cold temperature

evaporation

delayed centrifugation

hot trucks

Why do we recommend patients to NOT pump their fist while getting blood drawn?

Increases potassium

What is the formula for TCO2

TCO2 = HCO3 + Carbonic acid + dissolved CO2

What happens when tubes are left uncapped

Evaporation

falsely increases potassium and chloride

falsely decreases TCO2

A patient has critically low electrolytes and incredibly high glucose. What does this indicate?

Sample was taken from an IV

How does diabetes insipidus effect electrolytes?

Lack of ADH causes extreme water loss

plasma: increased Na and Cl

urine: decreased Na and osmolal

How does syndrome of inappropriate antidiuretic hormone (SIADH) effect electrolytes?

Overproduction of ADH causes excessive water retention

plasma: decreased Na, K+, Cl-

urine: Increased Na+, K+, Cl-

How does addisson's disease effect electrolytes?

Hypoaldosteronism causes reduced Na reabsorption

plasma: decreased Na. Cl, OSM increased K

urine: increased Na, Cl, OSM decreased K

How does Conn's disease effect electrolytes?

Hyperaldosterone causes excessive Na reabsorption

Plasma: increased Na, Cl, OSM and decreased K

urine: decreased Na, Cl, OSM and increased K

What is included in the "Lytes" panel?

Na+ K+ Cl- TCO2 Anion gap

There are more unmeasured ___ than ___

There are more unmeasured anions than cations

There are more measured ___ than ___

There are more measured cations than anions

How is anion gap calculated?

Na - (Cl + TCO2)

What is the anion gap?

Difference between anions & cations

represents anions other than Cl- and TCO3 that are needed to balance cations

What causes an increased anion gap?

metabolic acidosis

Alcohol poisoning

lactic acidosis

Uremia

Toxins

albumin (dehydration)

IgA

What causes a decreased anion gap?

hypoalbuminemia

IgG

Treatment with Lithium

Can patients with a normal anion gap still be in metabolic acidosis?

YES

this is known as hyperchloremic metabolic acidosis

caused by a loss of plasma bicarbonate

What is an implausible anion gap?

0>

How does PTH effect electrolytes?

Increases calcium

Decreases phosphorus

How does calcitriol effect electrolytes?

Increases plasma calcium and phosphorus

How does calcitonin effect electrolytes?

Decreases calcium

What would electrolytes look like in a patient with primary hyperparathyroidism?

High serum calcium

Low serum phosphorus

High urine Cal

High urine phosphorus

What would electrolytes look like in a patient with hypoparathyroidism?

Low serum calcium

High serum phosphorus

Low urine calcium

Low urine phosphorus

Calcium and Phosphorus have an _ relationship

Inverse

What calcium is considered physiologically active?

Ionized calcium

What does PTH regulate?

Ionized calcium

T/F: PTH regulates bound calcium

False.

it regulates ionized calcium

What causes hypercalcemia?

Hyperparathyroidism

Malignancy

Paget's Disease ( increased ALP)

What are the critical values for calcium?

>2.80

<2.20

What causes hypocalcemia?

Hyperparathyroidism

Chronic renal failure

Magnesium deficiency

Why does magnesium deficiency cause hypocalcemia?

Magnesium is needed for PTH

How do we measure TCAL?

Colorimetric reaction using o-cresolphthalein complexone which acts as a dye

ICAL and pH have an _ relationship

Inverse

Why does pH effect Ionized calcium levels?

H+ competes with Ca+ for albumin's binding slot

high pH = lower calcium

low pH = higher calcium

T/F: pH does not effect TCAL

True

pH effects ICAL

T/F: pH does not effect ICAL

False

pH and ICAL have an inverse relationship

How does albumin effect TCAL?

High albumin: increases TCAL

more albumin available to bind calcium in blood. less excreted into urine

Low albumin: decreases TCAL

more free calcium to excrete into urine

Albumin has a _ relationship with TCAL

Direct

What is the formula used to correct TCAL for albumin levels?

CorrCA = TCAL + [0.02 (47 - ALB in g/L)]

What causes hyperphosphatemia?

Low PTH hypoparathyroidism

Renal Failure

What causes hypophosphatemia?

Hugh PTH Hyperparathyroidism

alcoholism

insulin

How is phosphorus measured?

Molybate colorimetric reaction

What are some phosphorus interferents?

Hemolysis

How much magnesium does the human body contain?

25g

PTH _ Magnesium

Increases

PTH _ calcium

increases

PTH _ Phosphorus

Decreases

What is a complication of hypomagnesemia?

magnesium is needed to make PTH

Leads to hypoparathyroidism and hypocalcemia

How does diabetes cause hypomagnesemia ?

Magnesium is excreted alongside glucose

How is total magnesium measured?

Calgamite

Formazen

Methylthymol blue

What electrolyte is given to pregnant women to treat pre term convulsions and pre eclampsia?

Magnesium

What is the critical value for magnesium

>4mmol/L

Cord blood contains what substance that is known to damage analyzers?

Wharton's Jelly

What is average body pH?

7.35-7.45

What pH levels are incompatible with life?

<6.8 or >8.0

How would a pH of 7.39 be reported?

Normal

How would a pH of 9.2 be reported?

Reject the sample this is impossible

At the tissues, RBC's exchange HCO3- for

Chloride

What represents the metabolic component?

Bicarb

What represents the respiratory component?

co2

What base:Acid ratio is needed to maintain a normal pH?

20:1

What is respiratory acidosis?

Low pH caused by excessive H+ due to insufficient gas exchange resulting in increased PCO2

Hypoventilation results in Hypercapnia

What is respiratory alkalosis?

High pH caused by a decrease in H+ due to excessive gas exchange resulting in decreased PCO2

Hyperventilation results in hypocapnia

What is metabolic acidosis?

Low pH caused by an accumulation of H+ resulting in decreased HCO3

caused by increased acid production (ketoacidosis) decreased excretion in kidney failure and diarrhea

What is metabolic alkalosis?

High pH caused by a decrease in H+ resulting in increased HCO3

caused by severe vomiting and bicarb ingestion

What is milk-alkali syndrome?

A condition in which the chronic ingestion of milk and/ or calcium carbonate antacids leads to hypercalcemia and metabolic alkalosis.

When is compensation evident?

When PCO2 and HCO3 are either both decreased or both increased

How doe the body compensate for respiratory acidosis?

kidneys retain bicarb

How does the body compensate for respiratory alkalosis?

kidneys excrete bicarb

How does the body compensate for metabolic acidosis?

Hyperventilation

How does the body compensate for metabolic alkalosis?

Hypoventilation

pH is inversely proportional to

the acid PCO2

pH is directly proportional to

the base HCO3

pH =

HCO3/PCO2

What is SBE?

Base excess

-2 - 2+ is normal

What does an SBE >2+ indicate?

metabolic alkalosis due to high bicarb

What does an SBE >-2 indicate?

metabolic acidosis due to low bicarb