CARDIO-TOPIC E

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CARDIO-TOPIC E
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MRS FF

• Mrs FF Clinical Chemistry profile
• -Creatinine 115 mmol/L (55-120)
• -Urea 6.5mmol/L (2.5-6.5)
• -Na 133mmol/L (132-144)
• -K 3.0mmol/L (3.3-4.7)
• -Mg 0.7mmol/L (0.8-1.0)

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CREATININE AND UREA

• The patient chemistry profile indicates she has a
  normal to high creatinine and a high urea level.
• The renal function is unable to be accurately
  determined as the patients height and weight is
  unavailable.
• A relatively normal creatinine in combination
  with a high urea level usually indicates the
  abnormal urea value is related to a non-renal
  cause.

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RENAL FUNCTION

• . Despite a creatinine within the recommended
  range the patient may have decreased renal
  function.
• Sodium and potassium levels are also at or below
  the lowest desired level.
• This is uncommon in renal impairment as renal
  clearance of these electrolytes is commonly
  reduced when GFR is lowered.

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DIURETICS

• The electrolyte profile indicates there may be a
  non-renal cause of increased urea
• Creatinine clearance and other more specific
  tests discussed last week should be performed as
  it can not be discounted.
• Current thiazide therapy may be responsible for
  lower electrolyte levels in a renally impaired
  patient.

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GASTROINTESTINAL

• The possible non-renal causes of uraemia include
  gastrointestinal bleed or a hyper-catabolic
  state.
• The patient currently takes aspirin 100mg daily
  and may be causing gastrointestinal bleeding
  resulting in an above normal urea level.
• Asses GI status to eliminate bleed as possible
  cause of elevated urea

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OTHER ELECTROYLTES?

• The low potassium levels may be a result of
  diuretic use or low dietary intake.
• Vomiting has not been reported.
• Hyponatremia usually results from excess
  fluid/oedema which occurs in conditions such as
  heart failure.
• But what about Magnesium???

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MAGNESIUM DEFICIENCY
Magnesium Deficiency
Reduced Intake
Increased Excretion
Reduced Absorption
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REDUCED INTAKE

• Foods high in magnesium include cereals and nuts
  which may be eaten less frequently in todays
  diet.
• Meat, dairy and foods low in magnesium are
  consumed more often in the current environment as
  fresh produce is readily available.

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REDUCED ABSORPTION

• 20-40 of chronic heart failure sufferers are
  magnesium deficient primarily due to a decreased
  magnesium absorption as a result of
  gastrointestinal oedema .
• One third of magnesium is absorbed primarily in
  the proximal small bowel
• This area is particularly prone to oedema in
  congestive heart failure.

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INCREASED EXCRETION

• Two thirds of magnesium is filtered at glomerular
  and one third is bound to albumin.
• Of the filtered magnesium 20-30 is reabsorbed
  proximally in the ascending limb of the loop of
  Henle.
• Loop diuretics at on the ascending limb which
  causes loss of magnesium, sodium and water.
• Thiazide diuretics result is a less marked loss
  of magnesium.

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CONSEQUENCES

• Potential consequences of magnesium deficiency
  include
• -arrhythmia
• -hypertension
• -decreased cardiac contractility
• -hypokalemia

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SUBCELLULAR

• At the subcellular level Mg regulates contractile
  proteins, acts as a cofactor in the activation of
  ATPase, controls metabolic regulation of
  energy-dependent cytoplasmic and mitochondrial
  pathways, influences DNA and protein synthesis
  and modulates transmembrane transport of Ca, Na
  and K.
• In this way Mg has the potential to influence
  intracellular free s of these cations.

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ELECTROLYTE RELATIONSHIPS

• Hypomagnesemia is associated with other
  electrolyte disorders. For hypomagnesemic
  patients, 23 were hypophosphatemic, 23 were
  hypocalcemic, 29 were hyponatremic and 42 were
  hypokalemic.
• The relationship of Mg to the other ions is such
  that if abnormalities are seen in one, the others
  should be screened for potential problems.

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Mg AND POTASSIUM

• Potassium deficiency in particular should
  indicate the potential for Mg deficit - K
  depletion is accelerated and repletion made more
  difficult by concurrent Mg deficit.
• The ability to move K into the cell is dependent
  on adequate Mg stores if Mg deficiency exists it
  may need to be corrected before therapy to
  ameliorate hypokalemia will be effective.

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SERUM MAGNESIUM

• Mg is distributed in 3 major body compartments
  65 in the mineral phase of bone, 34 in muscle
  and 1 in plasma and interstitial fluid. It is
  the free intracellular fraction of Mg that is
  responsible for its physiological effects.

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A GOOD INDICATOR?

• Serum Mg assays measure total serum Mg levels
  but these are kept remarkably stable even in the
  presence of intracellular Mg depletion or
  overload.
• Because serum Mg levels are not in equilibrium
  with intracellular Mg they are not good
  indicators of total body Mg stores.

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CLINICAL ASPECTS

• Generally, if serum Mg is low a deficiency state
  probably exists
• If serum Mg is high body stores are probably
  adequate
• Serum Mg levels that fall within the reference
  range communicate little about total Mg stores A
  normal serum Mg level can mask a deficiency state

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FLAME PHOTOMETRY

• Flame photometry involves the use of spectral
  data to identify and quantify substances.
• An emission spectrum, such as the hydrogen atom
  line spectrum, is produced when atoms that have
  been excited to higher energy levels emit photons
  characteristic of the element as they return to
  the lower energy levels.
• Some elements produce a very intense spectral
  line which is the basis for flame tests.

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METALS

• This method is suitable for many metallic
  elements, especially for those metals which are
  easily excited to higher energy levels at flame
  temperature
• these include sodium, potassium, calcium and
  copper.

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PHOTOMETRY CONT

• Measurement of the intensity of coloured light
  emitted in the flame involves the use of a flame
  photometer.
• The wavelength at which the light is emitted is
  isolated with an interference filter.
• Light from the flame is focused onto the end of a
  fibre optic cable which transmits the light onto
  a photodiode in a small electronics box by the
  flame photometer.
• The electronics therein convert the diodes
  output into a digital display.

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STANDARAD CURVE

• To determine the concentration of an element in
  solution, first you need to create a standard
  curve of known concentrations as a reference with
  which to compare.

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STRENGTHS

• fast,
• simple and
• sensitive method
• free from interference from other elements

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WEAKNESSES

• This method requires careful calibration to
  provide accurate results. Calibration must be
  done carefully and frequently.

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ION SELECTIVE ELECTRODES

• ISE are part of a group of relatively simple and
  inexpensive analytical tools which are commonly
  referred to as sensors. An ISE produces a
  potential that is proportional to the
  concentration of an analyte.
• Making measurements with an ISE is therefore a
  form of potentiometry. The most common ISE is the
  pH electrode, which contains a thin glass
  membrane that responds to the H concentration in
  a solution.

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WHERE ARE ISEs USED?

• ISE are used in a wide variety of applications
  for determining the concentration of various ions
  in aqueous solutions. The following is a list of
  some of the main areas in which ISEs have been
  used.
• Pollution Monitoring CN, F, S, Cl, NO3 etc., in
  effluents, and natural waters.
• Agriculture NO3, Cl, NH4, K, Ca, I, CN in soils,
  plant material, fertilisers and feedstuffs.
• Food Processing NO3, NO2 in meat preservatives.
• Salt content of meat, fish, dairy products, fruit
  juices, brewing solutions.

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HOW DO THEY WORK?

• An Ion Selective Electrode measures the potential
  of a specific ion in solution. (The pH electrode
  is an ISE for the Hydrogen ion.)
• This potential is measured against a stable
  reference electrode of constant potential. The
  potential difference between the two electrodes
  will depend upon the activity of the specific ion
  in solution.
• This activity is related to the concentration of
  that specific ion, therefore allowing the
  end-user to make an analytical measurement of
  that specific ion. Several ISE's have been
  developed for a variety of different ions.

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CLINICAL USE

• In clinical laboratories they can be used to
  measure Ca, K, and Cl- in body fluids (blood,
  plasma, serum,sweat) and F- in skeletal and
  dental studies. ISE determinations are not
  subject to interferences such as color in the
  sample. There are few matrix modifications needed
  to conduct these analyses. This makes them ideal
  for clinical use (blood gas analysis) where they
  are most popular.

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DIFFERENCES TO FLAME PHOTOMETER

• Unlike the flame photometer, they have a linear
  response over a wide concentration range.
  However, they have some disadvantages
• they are not entirely ion-specific. Eg, the
  sodium electrode will also respond to potassium,
  although not with the same sensitivity. This
  means that Na will be overestimated if a high
  concentration of K is present.

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DIFFERENCES CONTINUED

• they underestimate high concentrations because of
  crowding of the ions at the membrane- some just
  dont get seen. The activity coefficient is a
  measure of this activity equals concentration at
  low values, but is less than concentrated at high
  values. ISEs measures activity.

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REFERENCES

• Quamme G, Renal magnesium handling New insights
  in understanding old problems, Kidney
  International, vol. 52(5), 1997, pp1180-1195
• Innerarity S, Hypomagnesemia in Acute and Chronic
  Illness, Critical Care Nursing Quarterly, vol.
  23(2), 2000, p1-19
• Laurant P, Touyz R, Physiological and
  pathophysiological role of magnesium in the
  cardiovascular system implications in
  hypertension, Journal of Hypertension, vol.
  18(9), 2000, pp1177-1191
• Yu A, Evolving concepts in epithelial magnesium
  transport, Current Opinion in Nephrology and
  Hypertension, vol. 10(5), 2001, pp649-653