4 Electrolytes and Osmometry Flashcards
What does water do for the body?
- Helps transport nutrients.
- Used to removes waste products via urination.
- Regulates body temperature through sweating.
40-75% of your total body weight is water.
What are electrolytes?
- Charged minerals that help to control the body’s fluid (osmotic pressure & water) and acid-base balance.
- Connected to muscle and nerve activity, heart rhythm, etc.
- Oxidation-reduction reactions and enzyme cofacters.
Common electrolytes include Na+, k+, Cl- TCO2 (or HCO3-).
What component in the body regulates thirst?
Hypothalamus in response to increased plasma osmolality.
What regulates our water output through the kidneys?
ADH (antidiuretic hormone) and aldosterone action in the kidney.
- ADH causes the kidneys to reabsorb water, decrease urine.
- Aldosterone conserves Na+ and Cl- levels in bloodstream (water follows and gets retained in body) and promotes the elimination of K in urine.
Overall plasma osmolality starts to return normal (as well as blood volume and pressure) until ADH and aldosterone are suppressed.
Where is the water in our bodies (intra versus extracellular)? What separates these two bodies of water?
Intracellular Fluid –> 2/3 of total body water (inside cells)
Extracellular Fluid –> 1/3 remaining. Includes interstitial fluid spaces, plasma, lymph, GI fluids, synovial fluids, pleural fluids, CSF, etc.
Separated by semipermeable membranes.
What three mechanisms maintain water’s equilibrium in the body?
Controlled by maintaining concentrations of electrolytes and proteins in individual compartments (cells) using these three modes:
- Active Transport - ATP (energy) moves solutes from low to high concentration areas
- Passive Diffusion - Solutes move from high to low concentration without energy input. Random.
- Osmosis - semipermeable membrane allows water (not solutes) to move from low osmotic pressure to areas of high osmotic pressure. No energy input.
What are the specimen blood collection requirements for electrolytes? Precautions?
Lithium heparin anticoagulant tubes (used most often).
Precautions:
- Sodium heparin anticoagulant will falsely increase Na values.
- Avoid hemolysis & separate cells from plasma/serum ASAP.
- Intracellular K+ will be released into plasma/serum. Falsely increases results.
- Samples for ionized calcium must remained unopened.
How long do urine electrolyte samples need to be collected for?
May need 24 hour collection.
A 100 mL random sample may be acceptable.
What may the patient do that can affect potassium results?
Strenuous exercise can cause potassium values to be increased as much as 20%.
What is the adult reference range for sodium for plasma and urine samples respectively?
Sodium - Adult
Plasma 135-147 mmol/L
Urine 40-200 mmol/d
What is the adult reference range for potassium for plasma and urine samples respectively?
Potassium - Adult:
Plasma 3.5 - 5.1 mmol/L
Urine 40-80 mmol/d
What is the adult reference range for chloride for plasma and urine samples respectively?
Chloride - Adult:
Plasma 97-106 mmol/L
Urine 110-250 mmol/d
What is the adult reference range for TCO2 for plasma samples?
Total Carbon Dioxide (CO2)
22-30 mmol/L
What is the adult reference range for calcium (total) for plasma?
Total Calcium - Adult:
Plasma 2.10 - 2.60 mmol/L
What is the adult reference range for glucose, albumin, and urea for plasma samples?
Plasma samples - adults:
Glucose 3.6-6.0 mmol/L
Albumin - 33-45 g/L
Urea 2.8 - 7.1 mmol/L
What is the function of sodium in the body?
Sodium functions:
- Maintains
a) fluid distribution
b) Osmotic pressure - Role in nerve and muscle function.
Recall that Na went through the channels that were opened ACh in the NMJ then traveled as a muscle action impulse! Plus it operates in nerves as a voltage gated channel.
What happens if there is imbalances in sodium in the body?
Imbalances in Sodium –> Can lead to brain swelling and coma.
What is the clinical relevance of sodium?
Clinical:
- Acid base balance, water balance.
- Dehydration.
- Renal threshold 110-120 mmol/L.
What function does potassium (K+) play in the body?
Potassium (K+):
- Nerve impulse transmission
- Muscle contractility.
Recall that when a nerve impulse depolarizes (charge goes up), K+ channels open to bring the signal back down to repolarize.
What is the clinical relevance of potassium?
- Electrolyte imbalance.
- Muscle weakness
- Cardiac arrhythmia.
- renal failure
- Hemolysis falsely increases lab value.
What is the function of chloride?
- Maintains fluid balance with Na+
- Cl- values change with Na+ (i.e. NaCl, salt)
- Acid-base regulation.
What is the clinical relevance of chloride?
- Sweat chloride test is used to detect cystic fibrosis.
- Stomach is unable to secrete digestive enzyme
- Acid base balance, water balance and dehydration.
Note: re2 in ppt she said it was pancreas.
What is the function of total carbon dioxide (includes HCO3-)?
- Acid base regulation
- Released and reabsorbed by kidneys to maintain pH
- Electrical neutrality.
4 Chloride shift - Transport of CO2 (via HCO3- and that acid/base equation with carbonate.)
What is the clinical relevance of total carbon dioxide?
Total CO2:
- Acid base imbalance in respiratory & metabolic systems.
- Increased TCO2 in metabolic alkalosis.
- Decreased TCO2 in metabolic acidosis.
How much calcium is free or ionized calcium in the body and what amount is bound (to what protein), in %?
Calcium:
50% is free or ionized calcium, active form
40% is bound to albumin.
What is the function of calcium in the body?
Calcium:
- Activator for coagulation factors.
- Decreases neuromuscular excitability.
- Membrane permeability.
- Cell motility.
- Bone and teeth (but she doesn’t have it listed as function, but 99% of total body calcium is in bones as hydroxyapatite.
Note: Intake of vitamin D for GI absorption of calcium.
What other molecule affects the total calcium that can be measured in the body? What are all the components of total calcium?
Measured calcium, total, is affected by albumin concentration.
If albumin concentration is lower, so is the calcium.
Total calcium = ionized + bound + complexed.
What hormones in the body regulate calcium?
Parathyroid hormone (PTH) and Calcitonin.
- PTH increases levels of calcium and phosphate in the blood from your bones. (by stimulating osteoclasts to break down bone).
- Calcitonin decreases calcium levels in the blood.
FYI
Calcitonin from Thyroid gland from parafollicular cells.
PTH from Parathyroid gland from chief cells.
What is the clinical relevance of calcium and phosphate?
Calcium:
Bone, parathyroid, and renal disease assessment.
What is the function of phosphate in the body?
Phosphate functions:
- Bone and teeth formation, maintenance and repair.
- Carbohydrate metabolism.
- Constituent of phospholipids, nucleic acids and ATP.
What is magnesium’s function in the body?
Magnesium’s function:
- Enzyme activator
- Influences nerve conduction and neuromuscular contractions.
- Formation of bones and teeth.
What is the clinical relevance of magnesium?
Clinical relevance of magnesium:
Hypomagnesemia - magnesium deficiency
Hypermagnesemia - magnesium excess
What are the intracellular and extracellular ions we are studying?
Intracellular:
*Potassium (K+)
Phosphate
Magnesium
Extracellular:
- Sodium (Na+), primary
- Chloride (Cl-)
*major
What is chloride shift?
When CO2 enters red blood cells, it combines with water to form H2CO3 (carbonate) then that splits into H+ and HCO3-. H+ is buffered by deoxyhemoglobin and HCO3- diffuses into plasma.
Because HCO3- leaves the cell, to maintain neutrality, Cl- enters the RBC.
That is the chloride shift!
What is the purpose of calculating the anion gap?
Anion gap indicates the differences between anions and cations.
- This can indicate:
a. Presence of unmeasured anions in metabolic or respiratory disorders (Ketones, lactic acids, toxic substances, etc.)
b. Low albumin (can be in patients w/ kidney failure, heart disease, cancer, etc.). - QC purposes. In healthy patients the anion gap is within a certain range and may indicate an instrument problem if out of range.
What conditions ion conditions are associated with vomiting and diarrhea?
Conditions associated with vomiting and diarrhea:
- Hyponatremia - low sodium
- Hypokalemia - low potassium.
- Hypochloremia - low chloride
- Hypomagnesemia - low magnesium
What is osmolality?
Osmolality:
Measure of the concentration of solute particles that contribute to osmotic pressure (solutes/kg of solute).
Measured in plasma/serum and urine using an osmometer.
Why would the lab get a request for osmality?
Assessment of:
- Electrolyte balance
- Acid-base disorders
- Toxin ingestion, etc.
Reference ranges:
Plasma: 285-305 mOsm/kg
Urine: 50 -1200 mOSm/kg, depending on fluid intake.
What does the osmometer measure?
Measures colligative properties –> freezing point depression.
This is related to solute concentration.
1 osmole of solute lowers freezing point by 1.86C.
What are the interferences for the osmometer to be concerned with in the lab?
Osmometer interferences are:
- Improper cleaning a) carry over b) alcohol residue (false lowers results)
- Hemolyzed or lipemic samples to be avoided.
- Samples contaminated with bacteria or other particulate matter.
What is osmo gap and its clinical relevance?
The osmo gap is the difference between measured and calculated osmolality.
It may indicate:
- Presence of osmotically active substances other than sodium, urea or glucose such as:
a) Ingestion of poison such as ethylene glycol, methanol or isopropanol.
b) Presence of lactic acid or beta-hydroxybutyrate.
A gap greater than 10 mOsm/kg indicates poisoning or acidosis.
