Electrolytes

1
Chapter 13

• Electrolytes

2
Electrolytes

• Ions capable of carrying an electrical charge.
• Anion () ? Anode
• Cation () ? Cathode
• Processes necessary for electrolyte involvement
  in the body.
• Volume and Osmotic pressure (Na, K, Cl)
• Myocardial rhythm and contraction (K, Mg, Ca)

3

• 3. Cofactors in enzyme activation (Mg, Ca, Zn).
• 4. Regulation of ATPase ion pump (Mg)
• 5. Acid/Base balance (pH)- HCO3, K, Cl)
• 6. Coagulation (Mg, Ca)
• 7. Neuromuscular (K, Mg, Ca)
• 8. Production and Utilization of ATP from glucose
  (Mg, PO4)
• All activities work together to keep an
  electrolyte balance in the body.

4

• Water
• Average water content 40-70 total body weight.
• Solvent for all body processes
• Transport system for all nutrients
• Regulates cell volume
• Removes waste products
• Coolant
• All occurs intracellular and extracellular of the
  cells.

5

• Normal plasma 93 H2O, rest is mixture of
  Lipids and proteins.
• Concentration of ions within the cells and plasma
  maintained by
• Energy consumption
• Diffusion Passive movement of ions across the
  membrane.
• Passive transport
• Active transport ( Mechanism that requires energy
  to move ions across the cellular membrane.)

6

• Osmolality Physical property of a solution based
  on the concentration of solutes per kilograms of
  solvent.
• Related to changes in the properties of a
  solution relative to pure H2O
• ADH ( Antidiuretic Hormone) Induces thirst by
  the secretion of ADH, stimulated by the
  hypothalmus in response to increase in body
  osmolality.

7

• ADH increase fluid intake increase H2O content,
  diluting the Na level in the blood which
  decreases the osmolality turning the ADH off.
• Clinical significance (osmolality)
• Sets parameters that the hypothalmus must
  responds to maintain fluid intake.
• Effects Na concentration in plasma
• Regulates blood volume through Na concentration.

8

• 1-2 increase in osmolality 4 fold increase in
  ADH secretion.
• 1-2 decrease in osmolality no ADH secreted.
• Renal function relate to Osmolality
• 1. Kidneys respond to H2O intake decrease in
  osmolality
• 2. ADH and thirst suppressed excess urine
  produced and excreted.

9

• H2O deficit
• Increase water intake increases plasma
  osmolality, as a result ADH increase secretion
  and induces thirst.
• Thirst is the major defense against
  hyperosmolality and hyponatremia.
• Hyponatruemia (low sodium), concern with infants
  and unconscious patients.

10

• Regulation of blood volume
• Blood volume essential in maintaining blood
  pressure and ensure perfusion to all cells and
  tissue.
• Renin-angiotensin-aldosterone system of hormones
  that respond to decrease in blood volume and help
  maintain the correct blood volume.

11

• Changes in blood volume regulated by receptors in
  the cardiopulmonary circulation , carotid sinus,
  aortic arch and glomerular arterioles- they
  activates effectors that restore volume.
• Factors effecting blood volume
• Anti natriuretic Peptide (ANP)
• Volume receptors
• Glomerulus filtrate rate (GFR)

12
Determination of Osmolality

• Serum or urine sample (plasma not recommended due
  to the use of anticoagulants.
• Based on properties of a solution related to the
  number of molecules per kilogram of solvent
  present in sample.

13
Measured by

• Freezing Point Osmometer
• Standardized method using NaCl reference
  solution.
• Specimen is super cooled to -7ºC, to determine
  freezing point. More solutes present the longer
  the specimen will take to freeze.

14
Electrolytes

• Sodium
• Most abundant extracellular cation- 90
• ATPase ion pump the way the body moves sodium
  and potassium in and out of cells.
• 3 sodium ions pump out of the cell for every 2
  potassium ions pumped in to convert ATP to ADP.

15

• Renal regulation of sodium balance
• Thirst to increase intake of water
• Excretion of water
• Blood volume
• 60-75 of sodium that is filtered is reabsorbed
  by or in proximal tubules.

16

• Hyponatremia
• Associated with the regulation of blood volume
• Assessed by patients skin turgor, venous
  pressure, and urine Na concentration.
• Hypovolemic Hyponatremia result of excess Na
  loss due to excess H2O loss by
• Diuretics, loss of fluid, potassium depletion,
  aldosterone deficiency, salt wasting nephropathy.

17

• Hypernatremia increased sodium concentration.
• Result of excess water loss in the presence of
  sodium excess.
• Loss of fluid by kidneys, sweating or intestinal
  loss, fever, burns, heat exposure, diseases
  (Diabetes insipidus)
• Chronic hypernatremia involves hypothalamic
  disease

18
Sodium determination

• Specimen Serum, plasma or Urine (24 hr)
• Methods
• Chemical
• Flame emission spectrophotometry
• Atomic absorption spectrophotometry
• Ion Selective electrode (2 electrode method)

19
Potassium

• Major intracellular cation
• 20X greater concentration in the cell vs. outside
  the cell.
• 2 of the bodies potassium circulates within the
  plasma.
• Function
• Regulates neuromuscular excitability
• Hydrogen ion concentration.
• Intracellular fluid volume.

20
Effects on Cardiac muscle

• Increase plasma potassium slows the heart rate
  by decreasing the resting membrane potential of
  the heart.
• Decrease extracellular potassium increase
  myocardial excitability-cause arrhythemia.

21
Potassium role in hydrogen concentration

• Decrease serum potassium potassium ions loss
  from the body then sodium and hydrogen ions move
  into the cells this results in a decrease of
  hydrogen ions in the extracellular fluid (ECF)
  resulting in alkalosis.

22
Regulation of potassium

• Kidneys regulate the potassium balance.
• Reabsorption of potassium occurs in the proximal
  tubules
• Influenced by aldosterone- potassium secreted in
  the urine exchange for sodium.
• Cellular breakdown potassium released.

23
Hypokalemia

• Decrease of serum potassium caused by
• GI loss
• Renal Loss
• Cellular shift
• Decrease intake
• Symptoms muscle weakness, cardiac arrhythmia,
  paralysis
• Treat potassium replacement.

24
Hyperkalemia

• Increase potassium serum levels
• Associated with diseases such as renal, diabetes
  and metabolic acidosis
• Results of inability to remove potassium
  sufficiently.
• Caused by
• Decreased renal excretion
• Cellular shift
• Increased intake
• Artificial
• Symptoms weakness and cardiac arrhythmia
• Treatment calcium given to reduce the threshold
  potential of the myocardial cells.

25
Potassium monitored by

• Monitor Patient sodium bicarbonate, glucose and
  insulin.
• Sample serum or plasma, fasting preferred
• Assay method
• ISE use valinomycin membrane
• Flame emission

26
Chloride

• Major extracellular anion
• Component of NaCl- essential in water balance,
  osmotic pressure acid base balance and electric
  neutrality within the body.
• Cl ion shift is secondary to sodium and
  bicarbonate movement in and out of cells
• Ingested in diet and absorbed in the intestines-
  become part of HCl.

27
Electric Neutrality

• Sodium/chloride shift maintains equilibrium
  within the body.
• Na reabsorbed with Cl in proximal tubules.
• Chloride shift
• CO2 generated in RBC from carbonic acid. Splits
  to hydrogen and bicarbonate, the bicarbonate
  diffuses out into cells to maintain electrical
  balance within the body an cells.
• Reciprocal relationship between HCO3 and CL

28
Disorders

• Hyperchloremia increased loss of bicarbonate
  increased loss of Cl.
• Hypocholremia decreased level of Cl

29
Assay

• Amperometric-Coulmetric titration (ref. method)
• generator?Ag Cl? AgCl
• Looks for a decrease in free chloride.
• Ag (silver) produces a change in potential which
  shuts off timer looks for the end product
  silver chloride.
• 2. Ion selective electrode method for
  instrumentation and sweat chloride test for
  infants to diagnose cystic fibrosis.

30
Assay cont.

• 3. Mercuric titration ( Schales- Schales method)
• Titrate Cl with mercury forming mercuric
  chloride- violet blue color indicator.
• 4. Colormetric utilizes thiocynate and ferric
  nitrate to for red color product that is measured
  at 480nm.

31
Bicarbonate

• 2nd most abundant anion of ECF.
• Major component of the buffering system.
• Buffering system NaHCO3/H2CO3, Phosphate,
  hemoglobin and plasma proteins.
• Balanced by the conversion of O2 CO2 ? H2O ?
  HCO3

32
Regulation

• Kidneys 85 of bicarbonate ion reabsorbed by
  the proximal tubules 15 reabsorbed by the
  distal tubules as CO2.
• Excess bicarbonate ion or hydrogen ions results
  in
• Alkalosis
• Acidosis

33
Clinical application

• Acid-base imbalance causes changes in bicarbonate
  and CO2 levels.
• Decrease in bicarbonate may occur from metabolic
  acidosis.
• Increase in total CO2 concentration occurs in
  metabolic alkalosis

34
Assay

• Specimen lithium heparin plasma or serum is
  preferred.
• Two common methods
• Ion selective electrode
• Enzymatic converts all forms of CO2 to HCO3
  HCO3 is used to caboxylate phosphoenolpyruvate.
  Coupled enzyme reaction that measures the amount
  of NADH is consumed. The rate of absorbance
  change is proportional to amount of CO2 present.

35
Magnesium

• 4th most abundant cation in the body and most
  abundant intracellular ion.
• 53 of Mg found in the bone, 46 in muscle and
  tissue, lt1 is present in the serum.
• The Mg circulating in serum is in the bound form
  ( one third-bound to albumin), of the remaining
  two thirds- (61) is in the free or ionized form,
  5 bound to phosphate and citrate.
• Free form is physiologically active.

36

• Role in the body is of an essential cofactor.
• Abnormal levels related to cardiovascular,
  metabolic, and neuromuscular disorders.
• Regulated by dietary intake, sm. intestine may
  absorb 20-65 of dietary intake and body needs.
• Kidneys regulate absorption and excretion of Mg.
• Related to that of calcium and sodium.
• PTH increases the renal reabsorption of Mg

37

• Hypomagnesaemia most frequently observe in
  hospital patients, especially those receiving
  diuretics or digitalis therapy.
• Result of
• Reduce intake
• Decreased absorption
• Increased excretion

38

• Hypomagnesaemia less frequently seen.
• Caused by
• Decreased excretion
• Increased intake

39
Assay

• Specimen nonhemolyzed, 10X more Mg in RBC than
  in ECF.
• Methods (colormetric)
• Calmagite
• Formazen dye
• Methylthymol blue

40
Phosphate H2PO4

• Element found everywhere, participates in various
  biochemical processes.
• Most significant ATP, Creatine Phosphate,
  phosphoenolpyruvate reactions.
• Important compound in the release of O2 from Hgb.

41
Regulation

• Absorbed in the intestine through diet, released
  from cells regulated by renal excretion or
  reabsorbtion.
• Renal regulation is effected by factors such as
  Vit. D, calcitonin, growth hormone, acid-base
  balance and PTH.
• Distribution two forms
• Organic
• inorganic

42
Clinical application

• Hypophosphatemia decreased level of phosphate
  in blood
• Hyperphoahatemia patients with acute and chronic
  renal failure are at the greatest risk for
  condition.

43
Assay

• Specimen subject to circadian levels (highest in
  the AM)
• Avoid hemolysis
• Method photometric method utilizing molybdenum
  blue formed by the reduction of phosphomolydenum
  to form ammonium phosphomolydbate complex.

44
Lactate

• Is the by-product of emergency mechanism that
  produces a small amount of ATP when O2 delivery
  is diminished- leads to accumulation of excess
  NADH.
• Regulated by the liver- through gluconeogenesis

45
Clinical Application

• Monitors the severity of an illness through
  metabolic process.
• Checks for O2 delivery or O2 consumption.
• Vasodilators

46
Assay

• Serum or plasma, collected on ice
• Enzymatic method use lactate dehydrogenase with
  cofactors NAD to convert Lactate to Pyruvate with
  the formation of NADH.

47
Anion Gap

• Use to evaluate electrolytes ( Na, K, Cl, HCO3.
• Difference between unmeasured anions and
  unmeasured cations.
• Formula AG(Na K)- (Cl HCO3)

48
Electrolytes and Renal function

• Kidney is the central regulator
• Electrolyte excretion occurs in the following
• Glomerulus
• Renal tubule (phosphate, calcium, magnesium,
  sodium, chloride, potassium, bicarbonate.

49
Chapter 14 Blood Gases, pH, and Buffer system.

• Through the maintenance of the body exchanging
  CO2 and O2 it keeps the acid-base balance.
• Acid substances that yields a H ion or hydronium
  in H2O.
• Base yields a hydroxyl ion (OH).
• Substance ability to dissociate is based on
  strength of acids and base (ionizaton constant-K
  value)

50

• Acid have a larger K value greater ability to
  dissociate into ions in H2O
• Base smaller K value lee affinity to dissociate
  into ions in H2O.
• pK defined as the negative log of the ionization
  constant is that pH where the protonated and
  unprotonated forms are present in equal
  concentration.

51
Strong acids vs. Strong Base

• Strong acids have pK value of less than 3.0
• Strong base have a pK value greater than 9.0
• Buffer is dependent on the pK of the buffering
  system and the pH of the surrounding environment.

52
Acid-Base balance

• Maintenance of hydrogen ions Body produces
  15-20 mol of H/day, normal concentration of H in
  ECF ranges from 36-4 mol if hydrogen ion. Any
  deviation from the values the body will try to
  compensate.
• gt44 mol/L altered consciousness, coma- death
• lt36 mol/L neuromuscular irritability, tetany,
  loss of consciousness- death.

53

• Hydrogen ion concentration expressed as pH
  formula (Henderson-Hasselbalch equation)
• Reciprocal relationship in the concentration of H
  ions and pH
• Increase pH decrease in H ion
• Decrease pH increase H ions
• Arterial blood pH is controlled by the production
  of acid and base by
• Buffers
• Respiratory System
• Kidneys

54
Buffer System

• Phosphate
• Hemoglobulin
• Plasma Proteins
• Carbonic Acid (H2CO3-Weak Acid)
• Bicarbonate (HCO3)
• All work together to dissociate hydrogen ions.

55
Example

• Add acid to the bicarbonate-carbonic acid system-
  the HCO3 combines with H from the acid to form
  H2CO3.
• Add a base to the system, H2CO3 combines with OH
  to form H2O and HCO3
• Keeps the body at the correct pH (7.35-7.45)

56
Kidneys System Buffer

• Rapid exchange of CO2 between the tissue and
  blood- the lungs compensate the effect of pH to
  make bicarbonate- carbonic acid system- control
  the excretion of hydrogen ions in the kidneys.
• Hemoglobulin system hydrogen ions neutralized by
  its ability to oxygenate and release of Hgb.
  Oxygenated which binds to H yields H20.

57

• Phosphate system regulates the plasma and RBC
  exchange of sodium ions for hydrogen ions in the
  urine filtrate.
• Hydrogen binds to HPO2 to form H2PO4.
• Plasma proteins bind hydrogen by the imidazole
  group of histidine, yield a net () charge.

58
Respiratory system

• Regulates carbonic acid
• End product of aerobic metabolic process is CO2,
  this diffuses out the tissue into plasma and RBC.
• In plasma it combines with H2O to form H2CO3 (
  carbonic acid), then dissociates into hydrogen
  ions which is buffered by plasma proteins.

59
RBC regulation

• CO2 and O2 exchange, some CO2 remains in the RBC
  in combination to HGB (carboxyhemoglobin)
• CO2 combines to water to form carbonic acid and
  is transported in the blood.
• Carbonic anhydrase enzymes in the RBC accelerate
  this process (CO2 H2O?H2CO3

60
Chloride Shift- (lungs)

• Hydrogen ions dissociate to HCO3 then picked up
  by O2 in the lungs- unloads oxyhemoglobulin
  (O2Hgb) in tissue. Hgb accepts hydrogen ion to
  form deoxyhemoglobulin.
• HCO3 increases in RBC it will diffuse out into
  the plasma, to keep electrically neutral plasma,
  chloride diffuses into the cells.

61
Respiratory effects

• Hydrogen ions carried on the deoxyhemoglobulin in
  blood circulation (H2CO3?H2O CO2)
• CO2 is released in the lungs
• If CO2 cont remove sufficiently there is an
  increase in hydrogen ions-causes a decrease in
  pH.
• If CO2 removed to quickly there is a decrease in
  hydrogen ions, causes a increase in pH.

62
Kidney system

• Kidneys respond to increase or decrease in
  hydrogen ions by selectively excreting or
  reabsorbing
• Hydrogen ions
• Sodium
• Chloride
• Phosphate potassium
• Ammonia
• Bicarbonate

63

• Reabsorbing of bicarbonate (HCO3) takes place in
  the renal tubule cells.
• Overall result in reabsorbtion of NA, HCO3 and
  loss in filtrate of CO2 H2O, Na, K, Cl,
  dihydrogen, phosphate and ammonium sulfate.
• Proximal and distal tubules role
• Na and HCO3 travel from the filtrate in the lumen
  then into the tubule cell- Na is exchanged for H
  ion.

64

• H ion combines with the HCO3 and carbonic acid
  dissociates into H2O and CO2.
• CO2 diffuses into the tubule cells combining with
  hydroxyl forming bicarbonate.
• Reabsorbtion of bicarbonate occurs in the blood
  system.

65
Sodium ion exchange for hydrogen ion

• Occurs in the kidneys
• Hydrogen reacts with a molecule of disodium
  hydrogen phosphate (Na2HPO4) forming dihydrogen
  phosphates in the filtrate.
• Na is reabsorbed by combining with hydrogen ion
  and ammonia to form ammonium ion to form ammonium
  sulfate.

66
Factors that effect reabsorbtion of H2CO3

• Blood/plasma bicarbonate level-increase above
  26-30 mmol/L bicarbonate is excreted
• Blood/Plasma decrease below 26-30 mmol/L body
  needs to retain bicarbonate
• Na and H ion exchange fails accumulation of
  sulfates, phosphate and chloride.
• Increase of ketones

67
Buffering system and Henderson-Hasselbalch eq.

• With the pH equation we can check the production,
  retention and excretion of acids and bases using
  the equation
• Check the blood pH-which is regulated by the
  lungs and kidneys

68

• The equation uses constants to correct for body
  difference
• 6.1 for pK of bicarbonate (HCO3)- equilibrium
  between carbonic acid and CO2 in plasma (1800)
• 0.03 is used because _at_ 37ºC solubility factor 1
  constant for PO2 and the factor to convert
  millimoles per liter of H2CO3 is 0.0307 mmol/L
• 1.3 is used because add the log of 20 (1.3) to pK
  of bicarbonate to yield normal pH.

69
Acid-Base Disorders

• Acidosis (decrease pH) vs. Alkalosis (increased
  pH)
• Due from metabolic (kidney) or respiratory
  (lungs).
• Pulmonary
• Inadequate elimination and excess production of
  CO2 in the body.
• Body compensates by respiration rate and kidney.

70
Acidosis

• 2 Types
• Metabolic Acidosis
• Decrease pH, increase H (lt201 ratio)
• Bicarbonate decreased (lt24 mmol/L)
• Reduce excretion of acids
• Caused by acid producing substance or process
• Renal compensation increase H ion by increasing
  PO4 and NH4 excretion and retain HCO3
• Respiratory compensation Hyperventilation,
  decrease CO2 in circulation.

71

• 2. Respiratory Acidosis caused by
  hypoventilation (decrease the elimination of CO2
  in the lungs, it builds up in the blood)
• In plasma see increase in CO2 decrease in pH,
  increase in H and HCO3
• Respiratory compensation_ hyperventilation
• Renal compensation- increase H excretion in the
  form of NH, increase reabsorbtion of Na and
  HCO3- slow process
• Diseases emphysema, drugs , congestive heart
  failure, bronchopneumonia.

72
Alkalosis

• 2 types
• Metabolic alkalosis pH increased, H decreased,
  CO2 increased, HCO3 increased.
• Renal compensation- excrete HCO3 and retain H
  ions.
• Respiratory compensation Hypoventilation with
  CO2 retention

73

• Respiratory alkalosis increased pH, decreased H,
  decreased CO2, decreased HCO3.
• Renal compensation decrease renal excretion of H
  ions, HCO3 excreted.
• Respiratory increase CO2 by hyperventilation

74
Blood Gas

• Determining blood pH to diagnose acidosis vs.
  alkalosis and to determine the origin
  (respiratory or metabolic)
• Evaluated by determining O2 and CO2 exchange by
  measuring partial pressure of O2 along with pH.
• Specimen collected is arterial blood

75
Tissue oxygenation occurs

• Atmospheric O2 available
• Gas exchange is sufficient
• Hemoglobulin is loaded with O2
• Transport and release mechanism of O2 is properly
  working.

76

• O2 is diffused into the lung- how much depends
  on
• Quality of O2
• Quantity of O2
• Rate of cellular CO2 production
• Rate of respiration
• Lung capacity

77

• Oxygen saturation
• Ration of oxygen that is bound to the Hgb. Vs
  Total Hgb.
• Determined by
• Arteriole puncture
• Venous puncture
• Mix
• Utilizing an Oximeter
• Formula Hgb X 1.39ml/g binding capacity.

78
Hemoglobulin and Oxygen dissociation

• O2 dissociates to Adult hemoglobulin A readily.
• Hgb holds on the O2 until O2 tension is reduced
  to 60 mmHG- then O2 released rapidly.
• Partial pressure of O _at_ the saturation of Hgb is
  represent by p50 or 50 saturation.

79

• If the partial pressure decreases there is and
  increase in O2Hgb- Shift to the (R) increase in
  CO2
• If the partial pressure increases there is an
  decrease in O2Hgb- Shift to the (L) decrease in
  CO2.
• Factors effecting the affinity of Hgb for O2
• Temperature
• Increase or decrease in CO2

80

• 2,3 Diphosphoglucerate (2,3 DPG)
• Phosphate combines in the RBC, binds to ßchain of
  Hgb-causes a shift to the (R), and O2 unloads.
• Assay
• Measured by saturation of O2 (SO2) in tissue.
• Measured spectrophotometrically using Oximeter
  (Hgb, O2Hgb, COHgb, and Met Hgb,)

81

• Errors any error that normally occurs with the
  use of a Spectrophotometer.
• Saturation O2 determines the ability of the lungs
  to carry O2 by measuring how much O2 is found in
  the RBC, how saturated it is. The most accurate
  results are obtained when
• Ventilation is stabilized
• Reframe from smoking at least 4hrs.
• Collect anaerobically
• Mix properly with anticoagulant
• Analyze immediately

82
Blood Gas Analysis

• Use electrode method for sensing and measuring
• PO2 measured by amperometric method
• PCO2 potentiometric
• pH potentiometric
• Other analytes measured by the equation HCO3,
  total CO2, Base excess, SO2

83

• PO2 Measurement
• Measures the amount of current flow in a circuit
  and is related to the amount of O2 being reduced
  at the cathode.
• Gas permeable membrane covering the electrode
  tip- this allows O2 to diffuse into the
  electrolyte solution. Electrons drawn from the
  anode to cathode to reduce O2- 4electrons drawn
  for every mole of O2 present in the solution (41
  ratio).

84

• Errors Protein build-up, debris, tip damaged or
  bubbled, change in temperature.
• Sample handling Do not expose to room air and an
  increase in WBC can increase metabolic activity
  and decrease PO2.

85
2nd Method for measurement of PO2

• Continuous measurement with transcutaneous
  electrode placed directly on the skin- based on
  O2 diffusion through the capillaries in the skin.

86
pH and PCO2 measurement

• pH utilizes a glass membrane sensitive to
  hydrogen ions- placed around an internal Ag-AgCl
  electrode.
• Measures the potential developed at the glass
  memebrane as a result of the hydrogen ions from
  an unknown solution. It is proportional to the
  difference in the hydrogen ions between the
  sample and buffer solution in the electrode.
• Reference electrode calomel (Hg-HgCl) or half
  cell (Ag-AgCl)
• Errors temperature change, KCl bridge, protein
  build-up

87

• PCO2 is measured using a modified pH electrode
• Glass membrane semi-permeable
• Bicarbonate buffer
• As CO2 diffuse across the membrane to bicarbonate
  buffer- it forms carbonic acid, which dissociates
  to bicarbonate and hydrogen ions the change in
  activity of the hydrogen ions is measured by the
  pH electrode as is related to the pCO2.

88

• Instrumentation
• Calibration
• Temperature control
• Utilize phosphate buffer
• Monitor barometric pressure.

89
Calculation

• Utilize the pH equation
• pH pK log HCO3
• H2CO3
• Or
• pH 6.1 log HCO3
• H2CO3

90
Carbonic Acid

• Use solubility coefficient of CO2 in plasma _at_
  37ºC 0.0307
• Formula CO2 a X pCO2
• 0.03 X pCO2

91
Total CO2

• Bicarbonate plus dissolved CO2 X H2CO2 CO2
• Formula tCO2 HCO3 (0.0307 x pCO2)

92
Base Excess

• Metabolic component of patients acid-base
  disorder calculated from pH, pCO2, Hgb.
• Amount of titrateble acid or base required to
  return the plasma pH to 7.4 _at_ pCO2 of 40mm/Hg _at_
  37ºC.
• () BE excess bicarbonate or deficit of
  noncarbonic acid- metabolic alkalosis

93

• (-) BE deficit bicarbonate, excess non-carbonic
  acid-metabolic acidosis.
• Test must be monitored closely and assume test
  performed _at_ 37ºC.
• Quality Assurance
• Choose correct site for test
• Use Heparin
• Glass syringe
• Anaerobically
• Mixed properly
• Free of air bubbles