Blood Gas Analysis

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Blood Gas Analysis

  1. 1. Blood Gas analysis<br />DR. MANSOOR AQILASSOCIATE PROFESSOR,KING SAUD UNIVERSITY HOSPITALSRIYADH.<br />
  2. 2. Clinical case<br />
  3. 3. Maintained within narrow limits<br />pH 7.36 to 7.44<br /> pH = Alkalemia (Alkalosis) <br /> pH = Acidemia (Acidosis)<br />BLOOD pH<br />
  4. 4. NORMAL<br />7.4<br />ACIDOSIS<br />ALKALOSIS<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  5. 5. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  6. 6. BLOOD pH<br />
  7. 7. The challenge<br />7.4<br /> ACIDOSIS<br />7.8<br />7.0<br />Volatile ACID (CO2) & <br />Fixed acids<br />Defense of normal alkalinity<br />
  8. 8. Types of Acids<br />Volatile acids<br />Easily move from liquid to gas state within the body<br />Lung can remove<br />H2CO3 + renal enzyme  H2O + CO2 (both of which are exhaled)<br />Carbon dioxide is therefore considered an acid<br />
  9. 9. Types of Acids<br /><ul><li>Nonvolatile acids(Fixed acids)</li></ul>Cannot be changed to gas state within the body<br />Examples<br />Keto acids<br />Lactic acids<br />
  10. 10. The challenge<br />Sources of acids:<br />Volatile acid<br />CO2 + H2O  H2CO3  H+ + HCO3<br />Fixed acids<br />Organic and inorganic source<br />Lactic acid, ketones, Sulfuric and phosphoric acid <br />Kidney plays an important role handling fixed acids.<br />
  11. 11. HYDROGEN ION SOURCES<br /><ul><li>CO2 15000 mmol/day</li></ul>CO2 + H2O H2CO3 H+ + HCO3-<br /><ul><li>Noncarbonic acids 70 mmol/day</li></li></ul><li>DEFENCE AGAINST pH CHANGE<br />Acute (minutes to hours)<br />Ventilation<br />Buffering<br />
  12. 12. DEFENCE AGAINST pH CHANGE<br />Acute (minutes to hours)<br />Long term<br />Renal excretion<br />Hepatic metabolism<br />
  13. 13. Chemical Buffers<br />The body uses pH buffers in the blood to guard against sudden changes in acidity<br />A pH buffer works chemically to minimize changes in the pH of a solution<br />H+<br />OH-<br />H+<br />Buffer<br />OH-<br />OH-<br />H+<br />
  14. 14.
  15. 15. BUFFERS<br />Intracellular Buffers<br />Proteins<br />Haemoglobin<br />Phosphate<br />Extracellular Buffers<br />Proteins<br />Bicarbonate<br />
  16. 16.
  17. 17. Biological systems and Buffering:<br />The power of a buffer depends on:<br />Concentration of the buffer.<br />Whether the pK is close to the pH of the system.<br />
  18. 18. Bicarbonate buffer systems:<br />CO2 + H2O  H2CO3  H+ + HCO3-<br />Maintains a ratio of 20 parts bicarbonate to 1 part carbonic acid<br />
  19. 19. Bicarbonate Buffer System<br />If strong acid is added:<br />HCl + NaHCO3 = H2CO3 + NaCl<br />Hydrogen ions released combine with the bicarbonate ions and form carbonic acid (a weak acid)<br />The pH of the solution decreases only slightly<br />
  20. 20. BICARBONATE BUFFER SYSTEM<br />H+<br />H2CO3H+ + HCO3-<br />Hydrogen ions generated by metabolism or by ingestion react with bicarbonate base to form more carbonic acid<br />H2CO3<br />HCO3-<br />20<br />
  21. 21. BICARBONATE BUFFER SYSTEM<br />H+<br />Equilibrium shifts toward the formation of acid<br />Hydrogen ions that are lost (vomiting) causes carbonic acid to dissociate yielding replacement H+ and bicarbonate<br />H2CO3<br />HCO3-<br />
  22. 22. Bicarbonate Buffer System<br />If strong base is added:<br />NaOH + H2CO3 = NaHCO3 + H2O<br />It reacts with the carbonic acid to form sodium bicarbonate (a weak base)<br />The pH of the solution rises only slightly<br />This system is the only important ECF buffer<br />
  23. 23. Bicarbonate buffer systems:<br />CO2 + H2O  H2CO3  H+ + HCO3-<br />pK = 6.1 [HCO3-] = 24 mmol/L<br />
  24. 24. Bicarbonate buffer systems:<br />
  25. 25. Phosphate buffer systems<br />Phosphate buffer H2PO4- / HPO4<br />pK = 6.8 and has a low concentration.<br />Role as intracellular and urinary buffer.<br />
  26. 26. Phosphate buffer systems<br />H2PO4- / HPO4-2<br />
  27. 27. Protein buffers:<br />A. Amino acid residues of proteins take up H+<br />(pK=7.0) are most important <br />NH2 NH3-<br />B. Hemoglobin is important due to high concentrationand its increased buffering capacity when deoxygenated.<br />
  28. 28. Relative Buffering power:<br />
  29. 29. Relative Buffering power:<br />
  30. 30. Compensation<br />
  31. 31. Renal buffering mechanisms <br />Renal - kidney excretes H+ and replenishes [HCO3-] .<br />But, this is a slow process taking hours to days.<br />
  32. 32. Renal buffering mechanisms <br />
  33. 33. Renal buffering mechanisms <br />
  34. 34. METABOLIC DISORDERS<br />
  35. 35. RESPIRATORY ACIDOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  36. 36. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  37. 37. RESPIRATORY ACIDOSIS<br />H2O + CO2  H2CO3  H+ + HCO3- <br />Cause - hypoventilation<br />Retention of CO2 <br />Drives equation rightward<br />Increases both [H+] and [HCO3-]<br />
  38. 38. RESPIRATORY ALKALOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  39. 39. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  40. 40. RESPIRATORY ALKALOSIS<br />H2O + CO2  H2CO3  H+ + HCO3- <br />2. Respiratory Alkalosis <br />cause - hyperventilation<br />Blows off CO2 <br />Drives equation leftward decreasing both [H+] and [HCO3-]<br />
  41. 41. METABOLIC ACIDOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  42. 42. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  43. 43. Metabolic Acidosis<br />Deficit in HCO3- and decreased pH<br />Causes:<br /> Increased production of nonvolatile acids.<br /> Decreased H+ secretion in the kidney<br /> Increased HCO3- loss in kidney<br /> Increased Cl- reabsorption by the kidney.<br />
  44. 44. Metabolic Acidosis<br />Body response is increased ventilation to blow off excess CO2<br />
  45. 45. METABOLIC ALKALOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  46. 46. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  47. 47. Metabolic Alkalosis<br />Primarily due to Increased HCO3- , increased pH <br />Causes<br /><ul><li>Administration of excess HCO3-
  48. 48. Increased secretion of H+ by kidney and gut
  49. 49. Sudden volume contraction which leads to increased Na+retention.This leads to water and HCO3- to follow the Na+</li></li></ul><li>PARTIALLY COMPENSATED RESPIRATORY ACIDOSIS<br />7.4<br />7.0<br />7.8<br />ACID<br />(CO2)<br /><ul><li>BASE
  50. 50. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  51. 51. PARTIALLY COMPENSATED RESPIRATORY ALKALOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  52. 52. (HCO3)</li></ul>METABOLIC COMPONENT<br />RESPIRATORY COMPONENT<br />
  53. 53. 7.4<br />7.0<br />7.8<br />ACID<br />(CO2)<br /><ul><li>BASE
  54. 54. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />PARTIALLY COMPENSATED METABOLIC ACIDOSIS<br />
  55. 55. PARTIALLY COMPENSATED METABOLIC ALKALOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  56. 56. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  57. 57. MIXED ACIDOSIS<br />7.4<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  58. 58. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  59. 59. COMPENSATED STATE<br />7.4<br />ACIDOSIS<br />ALKALOSIS<br />7.8<br />7.0<br />ACID<br />(CO2)<br /><ul><li>BASE
  60. 60. (HCO3)</li></ul>RESPIRATORY COMPONENT<br />METABOLIC COMPONENT<br />
  61. 61. Acute ventilatory failure (acute respiratory acidosis)<br />N<br />
  62. 62. Chronic ventilatory failure<br />(compensated respiratory acidosis)<br />Normal <br />
  63. 63. Acute alveolar hyperventilation(acute respiratory alkalosis)<br />Normal <br />
  64. 64. Chronic alveolar hyperventilation(compensated respiratory alkalosis)<br />Normal <br />
  65. 65. Acute metabolic acidosis<br />Normal <br />
  66. 66. Chronic metabolic acidosis<br />Normal <br />
  67. 67. Acute Metabolic Alkalosis<br />Normal <br />
  68. 68. Chronic metabolic alkalosis <br />Normal <br />Normal <br />
  69. 69. Anion Gap<br />AG = [Na + ] - [Cl ‾ + HCO3‾ ]<br />• AG represents unaccounted for anions (R ‾ )<br />• Normal anion gap = 10<br />
  70. 70. Anion Gap<br />Cations are Na + & K +<br />Major Anions are Cl ‾ & HCO3 ‾<br />
  71. 71. Anion gap<br />Unmeasured Anions<br />vs<br />Unmeasured Cations<br />Proteins, mostly albumin 15 mEq/L <br />Calcium 5 mEq/L <br />Organic acids 5 mEq/L <br />Potassium 4.5 mEq/L <br />Phosphates 2 mEq/L <br />Magnesium 1.5 mEq/L <br />Sulfates 1 mEq/L <br />Totals: 23 mEq/L <br />11 mEq/L <br />
  72. 72. Rules For Analyzing The ABG’s<br />• Look at the anion gap.<br />
  73. 73. Differential diagnosis of metabolic acidosis<br />Elevated anion gap<br />Uremia<br />Ketoacidosis<br />Lactic acidosis<br />Methanol toxicity<br />Ethylene glycol toxicity<br />Salicylate<br />Paraldehyde <br />Normal anion gap<br />Renal tubular acidosis<br />Dirrhoea<br />Carbonic anhydrase inhibition<br />Ureteral diversion<br />Early renal failure<br />Hydronephrosis<br />HCL administration<br />Saline administration<br />
  74. 74. Diagnosis of acid base disturbance<br />
  75. 75. Determining the predicted “Respiratory pH”<br />Acute 10 mmHg increase in PCO2 results in pH decrease of approximately 0.05 units<br />Acute 10 mmHg decrease in PCO2 results in pH increase of approximately 0.10 units<br />
  76. 76. Determining the predicted “Respiratory pH”<br />First determine the difference between the measured PaCO2 and 40 mmHg and move the decimal point two places left.<br />60 - 40 = 20 X 1/2 0.10<br />40 – 30 = 10 0.10<br />
  77. 77. Determining the predicted “Respiratory pH”<br />If the PaCO2 is greater than 40 subtract half of the difference from 7.40<br />? If this Pt has pH = 7.2 <br />? If this Pt has pH = 7.33<br />60 - 40 = 20 X ½ =10 = 0.10<br />pH = 7.40 – 0.10 = 7.30<br />
  78. 78. Determining the predicted “Respiratory pH”<br />If the PaCO2 is less than 40 add the difference to 7.40<br />40 - 30 = 10 0.10<br />pH = 7.40 + 0.10 = 7.50<br />
  79. 79. Determining the predicted “Respiratory pH”<br />pH 7.04<br />PCO2 76<br />76 - 40 = 36 X ½ = 18 0.18<br />7.40 - 0.18 = 7.22<br />
  80. 80. Determining the predicted “Respiratory pH”<br />pH 7.21<br />PCO2 90<br />90 - 40 = 50 X ½ = 25 0.25<br />7.40 – 0.25 = 7.15<br />
  81. 81. Determining the predicted “Respiratory pH”<br />pH 7.47<br />PCO2 18<br />40 – 18 = 22 0.22<br />7.40 + 0.22 = 7.62<br />
  82. 82. Determining the Metabolic component<br />RULE<br />10 mmol/L variance from the normal buffer base represents a pH change of approximately 0.15 units.<br />
  83. 83. pH 7.21<br />PCO2 90<br />90 - 40 = 50 X ½ = 0.25<br />7.40 – 0.25 = 7.15<br />Determining the Metabolic component<br /> 7.21 -7.15 = 0.06 X 2/3 = 0.04 = 4 mmol/L base excess<br />
  84. 84. pH 7.04<br />PCO2 76<br />76 - 40 = 36 X ½ = 0.18<br />7.40 - 0.18 =7.22<br />Determining the Metabolic component<br /> 7.22 -7.04 = 0.18 X 2/3 =12 mmol/L base deficit<br />
  85. 85. Determining the Metabolic component<br />pH 7.47<br />PCO2 18<br />40 – 18 = 22 = 0.22<br />7.40 + 0.22 = 7.62<br />Determining the Metabolic component<br /> 7.62-7.47 = 0.15 X 2/3 =10 mmol/L base deficit<br />
  86. 86. Diagnosis of acid base disturbance<br />Examine arterial pH: Is acidemia or alkalemia present? <br /> Examine PaCO2: Is the change in PaCO2 consistent with a respiratory component? <br />If the change in PaCO2 does not explain the change in arterial pH, does the change in [HCO3–] indicate a metabolic component? <br />Make a tentative diagnosis (see Table). <br />
  87. 87. Diagnosis of acid base disturbance<br />Compare the change in [HCO3–] with the change in PaCO2. Does a compensatory response exist (Table)? <br />If the compensatory response is more or less than expected, by definition a mixed acid–base disorder exists. <br />Calculate the plasma anion gap in the case of metabolic acidosis. <br />Measure urinary chloride concentration in the case of metabolic alkalosis.<br />
  88. 88.
  89. 89. Clinical case<br />
  90. 90. Clinical case<br />
  91. 91. Clinical case<br />
  92. 92. Clinical case<br />
  93. 93. Clinical case<br />
  94. 94. Thank U<br />
  95. 95. Base Excess/ Deficit<br />The degree of deviation from normal total body buffer base can be calculated independent of compensatory PCO2 changes<br />The amount of acid of base that must be added to return the blood pH to 7.4 and PCO2 to 40 at full O2 saturation and 370 C<br />

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