CoMEP TEACHING ACID / BASE BALANCE – INTERPRETATION OF RESULTS Dr. Alan S. Hutchison Clinical Biochemistry South Glasgow
Getting over the fear factor: …. <ul><li>(A little) physiology </li></ul><ul><li>Simple acid-base disorders </li></ul><ul>...
<ul><li>Volatile acids </li></ul><ul><li>H +  + HCO 3 -   H 2 CO 3   H 2 O + CO 2 </li></ul><ul><li>15,000 – 25,000 mmol/d...
Disposal of non-volatile acids <ul><li>Buffering </li></ul><ul><li>Respiratory system </li></ul><ul><li>Renal regeneration...
HCO 3 -  / H 2 CO 3  buffering system  <ul><li>60% of blood buffering </li></ul><ul><li>Central role in respiratory mechan...
Disposal of non-volatile acids <ul><li>2H +  + SO 4 2-  + 2Na +  + 2 HCO 3 -   </li></ul><ul><li>2Na +  + SO 4 2-  + 2H 2 ...
Blood gas analysis <ul><li>Measured </li></ul><ul><li>[H + ] (36 – 43 nmol/L) pH  (7.44 – 7.37) </li></ul><ul><li>P CO 2  ...
Those of a nervous disposition, look away now……
Henderson-Hasselbalch Equation <ul><li>pH = pK + log [HCO 3 -  ] / [H 2 CO 3 ] </li></ul><ul><li>  = pK + log [HCO 3 -  ] ...
Simple acid / base disorders    [HCO 3 -  ]     P CO 2    Respiratory alkalosis    [HCO 3 -  ]     P CO 2    Respira...
<ul><li>METABOLIC ACIDOSIS </li></ul><ul><li>Anion – cation gap </li></ul><ul><li>= [Na + ] – ([Cl - ] + [HCO 3 -  ]) </li...
Causes of metabolic acidosis <ul><li>Anion – cation gap increased: </li></ul><ul><li>renal failure, ketoacidosis, lactic a...
METABOLIC ALKALOSIS Causes: vomiting, n/g suction, diarrhoea, villous adenoma of colon, diuretics, penicillin, Conn’s, Cus...
<ul><li>RESPIRATORY ACIDOSIS </li></ul><ul><li>Causes: Any cause of hypoventilation, e.g. CNS depression, neuromuscular di...
RESPIRATORY ALKALOSIS Causes: Any cause of hyperventilation, e.g. anxiety, CNS lesions, stimulants, fever, toxaemia, hyper...
Mixed acid / base disorders <ul><li>Respiratory acidosis / metabolic acidosis </li></ul><ul><li>Respiratory acidosis / met...
Expected degrees of compensation <ul><li>Metabolic acidosis </li></ul><ul><li>P CO 2  (kPa) = 0.2[HCO 3 -  ] + 1.05 +/- 0....
Expected degrees of compensation <ul><li>Metabolic alkalosis </li></ul><ul><li>P CO 2  (kPa) = 0.12[HCO 3 -  ] + 1.18 </li...
Expected degrees of compensation <ul><li>Respiratory acidosis </li></ul><ul><li>Acute: [HCO 3 -  ] increases by 1 mmol/L f...
Expected degrees of compensation <ul><li>Respiratory alkalosis </li></ul><ul><li>Acute: [HCO 3 -  ] falls by 2 mmol/L for ...
 
72-year-old man post cardiac arrest [HCO 3 -  ] mmol/L  (23-30) Pa CO 2  kPa  (4.6-6.0) pH [H + ] nmol/L  (36-43) 14 8.9 6...
 
72-year-old man post cardiac arrest Mixed metabolic acidosis and respiratory acidosis [HCO 3 -  ] mmol/L  (23-30) Pa CO 2 ...
62-year-old woman with congestive cardiac failure [HCO 3 -  ] mmol/L  (23-30) Pa CO 2  kPa  (4.6-6.0) pH [H + ] nmol/L  (3...
 
62-year-old woman with congestive cardiac failure Mixed metabolic alkalosis and respiratory alkalosis [HCO 3 -  ] mmol/L  ...
45-year-old woman with pulmonary thrombo-embolism [HCO 3 -  ] mmol/L  (23-30) Pa CO 2  kPa  (4.6-6.0) pH [H + ] nmol/L  (3...
 
45-year-old woman with pulmonary thrombo-embolism Mixed metabolic acidosis and respiratory alkalosis [HCO 3 -  ] mmol/L  (...
80-year-old man with cor pulmonale [HCO 3 -  ] mmol/L  (23-30) Pa CO 2  kPa  (4.6-6.0) pH [H + ] nmol/L  (36-43) 51 9.3 7....
 
80-year-old man with cor pulmonale Mixed metabolic alkalosis and respiratory acidosis [HCO 3 -  ] mmol/L  (23-30) Pa CO 2 ...
72-year-old man with l.v.f. treated with a diuretic Mixed metabolic alkalosis and respiratory alkalosis Add a lactic acido...
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Acid / Base Balance – Interpretation of Results comep oc 2010

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Acid / Base Balance – Interpretation of Results comep oc 2010

  1. 1. CoMEP TEACHING ACID / BASE BALANCE – INTERPRETATION OF RESULTS Dr. Alan S. Hutchison Clinical Biochemistry South Glasgow
  2. 2. Getting over the fear factor: …. <ul><li>(A little) physiology </li></ul><ul><li>Simple acid-base disorders </li></ul><ul><li>Mixed acid-base disorders </li></ul>
  3. 3. <ul><li>Volatile acids </li></ul><ul><li>H + + HCO 3 - H 2 CO 3 H 2 O + CO 2 </li></ul><ul><li>15,000 – 25,000 mmol/day </li></ul><ul><li>Non-volatile acids, e.g. </li></ul><ul><li>Lactic acid, ketoacids, free fatty acids, sulphuric acid, phosphoric acid </li></ul><ul><li>50 – 100 mmol/day under non-pathological conditions </li></ul>
  4. 4. Disposal of non-volatile acids <ul><li>Buffering </li></ul><ul><li>Respiratory system </li></ul><ul><li>Renal regeneration </li></ul>
  5. 5. HCO 3 - / H 2 CO 3 buffering system <ul><li>60% of blood buffering </li></ul><ul><li>Central role in respiratory mechanisms </li></ul><ul><li>Central role in renal handling of H + </li></ul>
  6. 6. Disposal of non-volatile acids <ul><li>2H + + SO 4 2- + 2Na + + 2 HCO 3 - </li></ul><ul><li>2Na + + SO 4 2- + 2H 2 O + 2CO 2 [lungs] </li></ul><ul><li>Carbon dioxide is removed via the lungs </li></ul><ul><li>Bicarbonate is regenerated in the renal tubules </li></ul>
  7. 7. Blood gas analysis <ul><li>Measured </li></ul><ul><li>[H + ] (36 – 43 nmol/L) pH (7.44 – 7.37) </li></ul><ul><li>P CO 2 (a = 4.6 – 6.0 kPa, v = 4.8 – 6.7 kPa) </li></ul><ul><li>P O 2 (a = 10.5 – 13.5 kPa, v = 4.0 – 6.7 kPa) </li></ul><ul><li>Hb (sometimes) </li></ul><ul><li>Calculated </li></ul><ul><li>actual bicarbonate (23 – 30 mmol/L), </li></ul><ul><li>standard bicarbonate, base excess, oxygen content etc. </li></ul>
  8. 8. Those of a nervous disposition, look away now……
  9. 9. Henderson-Hasselbalch Equation <ul><li>pH = pK + log [HCO 3 - ] / [H 2 CO 3 ] </li></ul><ul><li> = pK + log [HCO 3 - ] / α P CO 2 </li></ul><ul><li>( α = 0.03 for mmHg, 0.23 for kPa) </li></ul><ul><li>[H + ] = 24 x P CO 2 / [HCO 3 - ] (for mmHg) </li></ul><ul><li>[H + ] = 180 x P CO 2 / [HCO 3 - ] (for kPa) </li></ul>
  10. 10. Simple acid / base disorders  [HCO 3 - ]  P CO 2  Respiratory alkalosis  [HCO 3 - ]  P CO 2  Respiratory acidosis  P CO 2  [HCO 3 - ]  Metabolic alkalosis  P CO 2  [HCO 3 - ]  Metabolic acidosis Compensation Primary derangement [H + ] Disorder
  11. 11. <ul><li>METABOLIC ACIDOSIS </li></ul><ul><li>Anion – cation gap </li></ul><ul><li>= [Na + ] – ([Cl - ] + [HCO 3 - ]) </li></ul><ul><li>Normally 8 – 16 mmol/L, depending on methodology </li></ul>8 2.5 7.22 60 [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43)
  12. 12. Causes of metabolic acidosis <ul><li>Anion – cation gap increased: </li></ul><ul><li>renal failure, ketoacidosis, lactic acidosis, toxins e.g. salicylate, inborn errors of metabolism </li></ul><ul><li>Anion – cation gap normal: </li></ul><ul><li>renal tubular acidosis, diarrhoea, carbonic anhydrase inhibitors, ureteric diversion, mild renal failure </li></ul>
  13. 13. METABOLIC ALKALOSIS Causes: vomiting, n/g suction, diarrhoea, villous adenoma of colon, diuretics, penicillin, Conn’s, Cushing’s & Bartter’s syndromes, liquorice ingestion, re-feeding, bicarbonate infusion 35 6.3 7.49 32 [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43)
  14. 14. <ul><li>RESPIRATORY ACIDOSIS </li></ul><ul><li>Causes: Any cause of hypoventilation, e.g. CNS depression, neuromuscular disorders, thoracic cage limitation, acute or chronic OPD, ventilator malfunction, cardiac arrest </li></ul>[HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) (chronic) 39 10.0 7.35 45 (acute) 28 9.7 7.31 49
  15. 15. RESPIRATORY ALKALOSIS Causes: Any cause of hyperventilation, e.g. anxiety, CNS lesions, stimulants, fever, toxaemia, hyperthyroidism, pregnancy, hepatic disease, LVF, PTE, pneumonia [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) (chronic) 17 3.3 7.40 40 (acute) 22 3.3 7.47 34
  16. 16. Mixed acid / base disorders <ul><li>Respiratory acidosis / metabolic acidosis </li></ul><ul><li>Respiratory acidosis / metabolic alkalosis </li></ul><ul><li>Respiratory alkalosis / metabolic acidosis </li></ul><ul><li>Respiratory alkalosis / metabolic alkalosis </li></ul><ul><li>Metabolic acidosis / metabolic alkalosis </li></ul><ul><li>Metabolic acidosis / metabolic alkalosis / respiratory acidosis </li></ul><ul><li>Metabolic acidosis / metabolic alkalosis / respiratory alkalosis </li></ul>
  17. 17. Expected degrees of compensation <ul><li>Metabolic acidosis </li></ul><ul><li>P CO 2 (kPa) = 0.2[HCO 3 - ] + 1.05 +/- 0.26 </li></ul><ul><li>If bicarbonate = 10 mmol/l, expected P CO 2 = 2.79 – 3.31 kPa </li></ul><ul><li>OR </li></ul><ul><li> P CO 2 = 0.13 – 0.17 x  [HCO 3 - ] </li></ul><ul><li>If bicarbonate = 10 mmol/l, expected P CO 2 = 3.05 kPa </li></ul>
  18. 18. Expected degrees of compensation <ul><li>Metabolic alkalosis </li></ul><ul><li>P CO 2 (kPa) = 0.12[HCO 3 - ] + 1.18 </li></ul><ul><li>OR </li></ul><ul><li> P CO 2 = 0.08 kPa for each  [HCO 3 - ] in mmol/L </li></ul>
  19. 19. Expected degrees of compensation <ul><li>Respiratory acidosis </li></ul><ul><li>Acute: [HCO 3 - ] increases by 1 mmol/L for every 1.3 kPa increase in P CO 2 </li></ul><ul><li>Chronic: [HCO 3 - ] increases by 3.5 mmol/L for every 1.3 kPa increase in P CO 2 </li></ul>
  20. 20. Expected degrees of compensation <ul><li>Respiratory alkalosis </li></ul><ul><li>Acute: [HCO 3 - ] falls by 2 mmol/L for every 1.3 kPa fall in P CO 2 </li></ul><ul><li>Chronic: [HCO 3 - ] falls by 5 mmol/L for every 1.3 kPa fall in P CO 2 </li></ul>
  21. 22. 72-year-old man post cardiac arrest [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 14 8.9 6.93 118
  22. 24. 72-year-old man post cardiac arrest Mixed metabolic acidosis and respiratory acidosis [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 14 8.9 6.93 118
  23. 25. 62-year-old woman with congestive cardiac failure [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 31 3.5 7.64 21
  24. 27. 62-year-old woman with congestive cardiac failure Mixed metabolic alkalosis and respiratory alkalosis [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 31 3.5 7.64 21
  25. 28. 45-year-old woman with pulmonary thrombo-embolism [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 14 2.7 7.45 35
  26. 30. 45-year-old woman with pulmonary thrombo-embolism Mixed metabolic acidosis and respiratory alkalosis [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 14 2.7 7.45 35
  27. 31. 80-year-old man with cor pulmonale [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 51 9.3 7.48 33
  28. 33. 80-year-old man with cor pulmonale Mixed metabolic alkalosis and respiratory acidosis [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 51 9.3 7.48 33
  29. 34. 72-year-old man with l.v.f. treated with a diuretic Mixed metabolic alkalosis and respiratory alkalosis Add a lactic acidosis 12 94 140 34 4.0 7.67 21 Anion-cation gap (8-16) [Cl - ] mmol/L (97-107) [Na + ] mmol/L (135-145) [HCO 3 - ] mmol/L (23-30) Pa CO 2 kPa (4.6-6.0) pH [H + ] nmol/L (36-43) 18 94 140 28 4.0 7.58 26

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