03 Blood Gasesby Mh Feb05


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03 Blood Gasesby Mh Feb05

  2. 2. <ul><li>A 16-year old girl being treated for DKA. </li></ul><ul><li>NA 138, K 4.8, Cl 112, HCO 3 14 </li></ul><ul><li>pH 7.28, Lactate 3, Urine ketones -ve </li></ul><ul><li>What type of acidosis? </li></ul><ul><li>Give 3 conditions in which it found? </li></ul>
  3. 3. <ul><li>A 14-year old boy investigated for short stature. </li></ul><ul><li>NA 140, K 2.8, Cl 114, HCO 3 14 </li></ul><ul><li>What type of acidosis? </li></ul><ul><li>Give 1 possible condition? </li></ul>
  4. 4. <ul><li>A 6-year old girl is found unconscious with temp 38.2Cboy investigated for short stature. </li></ul><ul><li>CSF 4 lymphocytes, Protein 0.5, Glucose 3.3 </li></ul><ul><li>U 9 </li></ul><ul><li>HCO 3 11 </li></ul><ul><li>Name 4 tests you would do? </li></ul><ul><li>Give a possible diagnosis? </li></ul>
  5. 5. ANION GAP <ul><li>(NA+K)-( HCO 3 +Cl) </li></ul><ul><li>10-18mol/l </li></ul><ul><li>Negatives and Positives must balance </li></ul><ul><li>Tells us if HCl retention (normal gap) or another acid (increased gap) </li></ul>
  6. 6. ANION GAP <ul><li>Normal gap: </li></ul><ul><ul><ul><ul><li>increased GI HCO 3 loss </li></ul></ul></ul></ul><ul><ul><ul><ul><li>increased renal HCO 3 loss </li></ul></ul></ul></ul><ul><ul><ul><ul><li>decreased renal H + loss </li></ul></ul></ul></ul><ul><ul><ul><ul><li>increased HCl production </li></ul></ul></ul></ul><ul><li>Another acid (increased gap): </li></ul><ul><ul><ul><ul><li>Lactate - L-lacate Type A and B and D-Lactate </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Ketones </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Exogenous </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Renal failure </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Accumulation of organic acids </li></ul></ul></ul></ul>
  7. 7. Base Excess <ul><li>The year after introducing Standard Bicarbonate, Astrup and Siggard -Andersen in 1958 introduced Base Excess as a better method of measuring the metabolic component. In essence the method calculated the quantity of Acid or Alkali required to return the plasma in-vitro to a normal pH under standard conditions. </li></ul>
  8. 8. Base Excess <ul><li>The Base Excess: is defined as the amount of acid (in mmol) required to restore 1 litre of blood to its normal pH, at a PCO2 of 5.3kPa (40mmHg) </li></ul><ul><li>During the calculation any change in pH due to the PCO2 of the sample is eliminated, therefore, the base excess reflects only the metabolic component of any disturbance of acid base balance </li></ul><ul><li>If there is a metabolic alkalosis then acid would have to be added to return the blood pH to normal, therefore, the base excess will be positive </li></ul><ul><li>If there is a metabolic acidosis, acid would need to be subtracted to return blood pH to normal, therefore, the base excess is negative. </li></ul>
  9. 9. Base Excess <ul><li>If base deficit/ base excess is consistent with abnormality in pH then the primary abnormality is metabolic </li></ul><ul><li>If both PaCO 2 and base excess/deficit are altered in a way that is consistent with the abnormality in pH then a mixed picture is present </li></ul>
  10. 10. Flenley acid-base nomogram
  11. 11. Standard Bicarbonate <ul><li>The Standard Bicarbonate: this is similar to the base excess. It is defined as the calculated bicarbonate concentration of the sample corrected to a PCO2 of 5.3kPa (40mmHg). Again abnormal values for the standard bicarbonate are only due the metabolic component of an acid base disturbance. A raised standard bicarbonate concentration indicates a metabolic alkalosis whilst a low value indicates a metabolic acidosis. </li></ul>
  12. 12. Interpretation Guidelines <ul><li>Step 1: Look at pH - this is the starting point. </li></ul><ul><li>If within normal range, a normal or compensated state exists. </li></ul><ul><li>If outside normal limits, assess whether acidosis or alkalosis is present. </li></ul><ul><li>The body never overcompensates. Whichever state exists on the pH scale is the primary abnormality. </li></ul>
  13. 13. Interpretation Guidelines <ul><li>Step 2: Assess hypoxemic state. </li></ul><ul><li>If PaO 2 is <60 mmHg, hypoxic state exists. </li></ul><ul><li>If PaO 2 is between 80 -100 mmHg, a normal condition exists. </li></ul><ul><li>If PaO 2 is >100 mmHg, a hyperoxic state exists. </li></ul>
  14. 14. Interpretation Guidelines <ul><li>Step 3: Assess ventilatory status. </li></ul><ul><li>If PaCO 2 is <35 mmHg, it is termed &quot;alkalosis&quot; (alveolar hyperventilation or hypocarbia). </li></ul><ul><li>If PaCO 2 is between 35-45 mmHg, it is within normal limits. </li></ul><ul><li>If PaCO 2 is >45 mmHg, it is termed &quot;acidosis&quot; (ventilatory failure or hypercarbia). </li></ul><ul><li>If possible, determine whether this is an acute or chronic state (see the compensation explanation). </li></ul>
  15. 15. Interpretation Guidelines <ul><li>Step 4: Assess metabolic component. </li></ul><ul><li>1. If bicarbonate (HCO 3 -) is <22 mEq/l, it is termed &quot;acidosis&quot;. </li></ul><ul><li>2. If bicarbonate is between 22-28 mEq/l, it is within normal limits. </li></ul><ul><li>3. If bicarbonate is >28 mEq/l, it is termed &quot;alkalosis&quot;. </li></ul><ul><li>4. If possible, determine whether this is an acute or chronic state (see the compensation explanation). </li></ul>
  16. 16. Eight Primary Blood Gas Classifications <ul><li>Classification pH PaCO2 HCO3- </li></ul><ul><li>Acute ventilatory failure v ^ N </li></ul><ul><li>(acute respiratory acidosis) </li></ul><ul><li>Chronic ventilatory failure v N ^ ^ </li></ul><ul><li>(compensated respiratory acidosis) </li></ul><ul><li>Acute alveolar hyperventilation ^ v N (acute respiratory alkalosis) </li></ul><ul><li>Chronic alveolar hyperventilation ^ N v v </li></ul><ul><li>(compensated respiratory alkalosis) </li></ul><ul><li>Acute metabolic acidosis v N v </li></ul><ul><li>Chronic metabolic acidosis v N v v </li></ul><ul><li>Acute metabolic alkalosis ^ N ^ </li></ul><ul><li>Chronic metabolic alkalosis ^ N ^ ^ </li></ul><ul><li>Hint: in compensated states, the PaCO 2 and HCO 3 - have matching arrows (directions). </li></ul>
  17. 17. Man with liver failure and D&V <ul><li>Na 134, k3.6, HCO 3 10, Cl 112, PaCO2 2.2, pH7.38 </li></ul><ul><li>Categorise these abnormailities </li></ul>
  18. 18. 63 year man with progressive weakness <ul><li>Hb72, Urea 48.8, Normocytic anaemia </li></ul><ul><li>Na 140, K 5.6, HCO 3 24, Cl 96, PaCO2 5.2, pH7.4 </li></ul><ul><li>What is acid-base disturbance? </li></ul><ul><li>What is the cause? </li></ul>
  19. 19. 23 year old unconscious woman <ul><li>pH 6.96, PaO2 17.4, PaCO2 1.1, Urea 12.6, Glucose 2.1, there is a reducing sugar in the urine </li></ul><ul><li>What is the diagnosis? </li></ul>