electrolytes 1 Flashcards

1
Q

references ranges for osmolality

  • serum
  • osmolar gap
  • critical values
A

serum : 275-295 mOsm/kg
*urine has a wider range than serum
osmolar gap : 5-10 mOsm/kg
critical serum values : <250 & > 325 mOsm/kg

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2
Q

what is the ultimate regulator of water in the body

A

Kidneys

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3
Q

hormones and water balance

A

Arginine Vasopressin Hormone (AVP )

  • antidiuretic hormone(ADH)
  • increases water reabsorption
  • secreted by the hypothalamus

Aldosterone

  • increases Na+ reabsorption
  • produced by adrenal cortex
  • increased aldosterone= more Na+( and Cl-) reabsorbed in exchange for H= (or K+) secretion into urine
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4
Q

body weight % of water

amount that is intracellular & extracellular

A

40-75% water

2/3 is intracellular
-40-50%

1/3 is extracellular

  • intravascular (plasma) 5%
  • interstitial (lymph & tissue) 15%
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5
Q

anions and anode

cations and cathode

A

anions (-) move toward the anode (+)
cations (+) move towards the cathode (-)

electrolytes are substances that split into ions

total anions =total cations
- an increase in one anion means another anion must decrease or a cation must increase to keep balance

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6
Q

main anion and cation of intracellular fluid & extracellular fluid

A

ICF

  • main cation is K+
  • main anion is HPO4(2-) aka phosphate

ECF

  • main cation is Na+
  • main anion is Cl-
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7
Q

what should you do if you have a high K+ result on a patient

A

first check for hemolysis ( hemolysis falsely increase K+)
then rerun
then report

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8
Q

what has osmolality replaced for testing

A

it has replaced specific gravity as the test to assess renal concentration

SG includes number & size of molecules

osmolality is a measure of concentration based only on the number of small molecules present in solution ( not weight or size )

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9
Q

Colligative properties

A

solution properties related to the number if molecules ( particles present in the solvent

increasing the number of particles in a solution will

  • lower freezing point
  • higher boiling point
  • increased osmotic pressure
  • lower vapor pressure

if 1 Osmol of any solute is added to 1 kg of water the freezing point is decreased by 1.86 degrees Celsius

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10
Q

Na+ accounts fro what % of osmotic activity in plasma

A

• The concentration of Na+ in plasma is affected by:

  • The regulation of osmolality
  • The regulation of blood volume

• Osmoreceptors in the hypothalamus respond to small changes in
osmolality.
- An increase in osmolality causes an increase in AVP concentration.
- A decrease in osmolality shuts off AVP production.

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11
Q

water deficit

A
  • Thirst is important in preventing water deficit.
  • Deficit of H2O will increase plasma osmolality.
  • AVP and thirst will be activated
  • AVP will cause H2O to be reabsorbed

• Thirst is the major defense against hyperosmolality and hypernatremia
• Hyperosmolality and hypernatremia is a concern for:
- Infants
- Unconscious patients
- Older patients
- Those with diminished mental status

• For these patients, dehydration is a concern

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12
Q

water excess

A

• Excess intake of H2O (polydipsia) will lower plasma osmolality.
• AVP and thirst will be suppressed
• H2O will not be reabsorbed
• Large volume of dilute urine excreted (10 - 20 L)
• Hypoosmolality and hyponatremia usually only occur if there is an
impairment with the renal excretion of water

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13
Q

diabetes insipidus

A

• No AVP production or no ability to respond to circulating AVP
• Excessive thirst
• Increased urine output (up to 10 L/day)
• Water intake = water output
• Plasma osmolality remains normal
• Because thirst response is normal in these patients, dehydration is
prevented.

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14
Q

Regulation of blood volume - decreased blood volume or pressure (hypovolemia)

A

Renin converts angiotensinogen to angiotensin l
angiotensisn converting enzyme ( ACE) converts Angiotensin l to angiotensin ll
angiotensin ll causes vasoconstriction
- blood pressure is increased
Aldosterone is excreted which increases retention of Na+ ( and the H2O that accompanies it )

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15
Q

Regulation of blood volume - increased blood volume/ pressure ( hypervolemia )

A
  • Atrial natriuretic peptide (ANP) is released from myocardial atria
  • Promotes Na+ excretion in kidney
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16
Q

specimens for osmolality

A

• Measured on serum or urine (not plasma)

  • Plasma may have osmotically active particles from the anticoagulant
  • Sample must be free of particles or centrifuged prior to testing

• Clinical unit of measure is the milliosmole (mOsm/kg)

17
Q

common methods for analysis of osmolality

A
  • Freezing point depression
  • Vapor Pressure decrease

-Freezing point osmometers use sodium chloride as reference
solutions (calibrators).

18
Q

Osmolality Measurement: Freezing Point Depression Osmometer

A
  • Sample is supercooled to -7 degrees C
  • Supercooling - cooling below the freezing point but remaining in a liquid state

• Mechanical agitation ‘seeds’ crystal formation
• As crystals form, the heat of fusion is released and the solution warms to its
freezing temperature and freezes

  • Probe measures freezing point
  • Final reading is taken reflecting the freezing point of the solution

• The more particles present in a sample, the more the freezing point is depressed
(lowered)

19
Q

Calculated Osmolality

A
  • Based on the major contributors to serum osmolality: glucose, urea and sodium
  • Sodium is always with chloride (therefore 2 ions upon dissociation)

1.86*(Na+ mmol/L) + glucose (mmol/L) + urea (mmol/L)

20
Q

Oamolal Gap

A

Difference between the measured and the calculated osmolality

• An increased osmolal gap may indicate the presence of other
osmotically active substances:
• Ethanol, methanol, ethylene glycol, isopropanol, lactate or β-hydroxybutyrate

- ex. an increase in lactate may occur due to increased anaerobic metabolism 
of glucose (pyruvate → lactate) during an AMI
  • an increase in β-hydroxybutyrate ( a ketone body ) is increased if someone is diabetic

• The osmolal gap should be 5 - 10 mOsm/kg

21
Q

Electrolyte functions

  • maintains osmotic pressure & water distribution
  • maintains pH
  • regulates the function of heart & other muscles
  • oxidation- reduction rxns
A
  • Maintain osmotic pressure and water distribution (Na+)
  • Maintain pH (HCO3-/H+)
  • Regulate the function of heart and other muscles (K+, Ca++)
  • Involved in oxidation-reduction reactions (H+)

• Act as cofactors for enzymes

22
Q

Ion-Selective Electrode Potentiometry - Key Words

oxidation , reduction , anode, cathode, electrochemical cell

A

Oxidation - loss of electrons at the anode

Reduction - gain of electrons at the cathode

Anode - positive electrode; where oxidation takes place

Cathode - negative electrode; where reduction takes place

Electrochemical cell - combination of 2 half cells (oxidation and reduction),
connected by a salt bridge

23
Q

potentiometry & principle

A
measures voltage (mV) generated by an electrochemical cell at 
zero current

Difference between potential from the reference electrode and the indicator (ISE) electrode

24
Q

electrochemical cell

A

• Electrochemical cell - 2 half cells or electrodes connected by a salt bridge

  • Indicator (ISE) Electrode - detects the ion of interest
  • Reference Electrode - provides constant potential

Note: ISE’s used in instruments have all the components (indicator electrode,
reference electrode and salt bridge) in one unit.

25
indicator electrode
• Measuring electrode constructed to detect a specific ion of interest • Generates electrical potential when placed in a solution containing the ion to be measured. • The potential generated is proportional to the concentration of the ion (activity)
26
reference electrode
* Surrounded by a solution of constant composition * At constant pH; generates constant potential; compensates for changes in temp., electrical noise, age of electrodes, etc. * Common reference electrodes: * Silver/ silver chloride (Ag/AgCl) * Calomel (mercury/ mercury chloride) Hg/HgCl
27
Nernst Equation
𝐸= (𝐸𝑜+2.39𝑅𝑇 / 𝑛𝐹 ) log𝑎 in brackets is the constant slope = 2.3 RF/ nF reduced equation = E~log a i.e. measuring potential (mV) ~ activity (concentration) of the ion
28
sloping of an electrode ( calibrating using 2 standards )
when conc & potential are plotted against each other on a semi log paper - straight line For a monovalent ion (eg. K+) Calibration Standards with tenfold difference have voltage difference of 59.1mV When the sample is analyzed, the mV reading is used to extrapolate the concentration of ion from the slope
29
Ion-Selective Electrodes selectivity
* ISEs are selective but not specific * Other interfering ions are also measured to a slight degree • Each ion has a selectivity factor to determine the amount of interference it will cause • Electrodes are designed to have the lowest possible selectivity factors for interfering ions.
30
classes of electrodes
* Solid material (eg. Glass)• Specific types of glass used (eg. H+, Na+) * Can be modified using a gas-permeable membrane (eg. CO2) * Liquid (Ion-exchange)• Binds with ion being measured (eg. K⁺) * Solid state• Insoluble inorganic salts in a membrane; potential due to the ion exchange process. (eg. Cl⁻) * Enzyme• Enzyme bound to surface; reacts with a non-ion to produce ionic species which can then be measured (urea/urease = NH₄+)