Arterial Blood Gases Talk

6,108 views

Published on

Published in: Health & Medicine
1 Comment
7 Likes
Statistics
Notes
  • Dear Dr. Tuan. While I am impressed with your collection of presentations, I would really have preferred to be asked before MY WORK is published on the internet in this way.

    I would be grateful if you would remove this presentation from this site without delay.
    Thank you.
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
No Downloads
Views
Total views
6,108
On SlideShare
0
From Embeds
0
Number of Embeds
60
Actions
Shares
0
Downloads
445
Comments
1
Likes
7
Embeds 0
No embeds

No notes for slide

Arterial Blood Gases Talk

  1. 1. Arterial Blood Gases Dr. Michael J. Baffsky
  2. 2. How to take an ABG <ul><li>Clean procedure (gloves, alco wipe) </li></ul><ul><li>Have gauze for application of pressure post arterial puncture </li></ul><ul><ul><li>4 mins of pressure is ideal </li></ul></ul><ul><ul><li>Especially in patients who are anticoagulated </li></ul></ul><ul><li>23G needle easier , but use what you prefer </li></ul><ul><li>ROTATION and INVERSION of the tube for 20 seconds to dissolve and mix the heparin </li></ul><ul><li>Ice only necessary if there will be a delay from sampling to testing. </li></ul>
  3. 3. Why use ice anyway?
  4. 4. What values do you get? <ul><li>pH - measures acidity/alkalinity </li></ul><ul><li>pCO2 (partial pressure of CO2) </li></ul><ul><ul><li>measures respiratory component </li></ul></ul><ul><li>[HCO3-] – (bicarbonate concentration) </li></ul><ul><ul><li>measures metabolic component </li></ul></ul><ul><ul><li>derived value (H-H equation) </li></ul></ul><ul><li>pO2 (partial pressure of O2) </li></ul><ul><li>BE (base excess) </li></ul><ul><li>O2 saturation </li></ul><ul><li>Sometimes AG (anion gap) </li></ul><ul><li>Sometimes electrolytes and glucose </li></ul>
  5. 5. Normal Ranges <ul><li>pH </li></ul><ul><ul><li>7.35 to 7.45 </li></ul></ul><ul><li>pCO2 </li></ul><ul><ul><li>36 to 44 </li></ul></ul><ul><li>pO2 </li></ul><ul><ul><li>vary with oxygen therapy </li></ul></ul><ul><ul><li>on room air will be < 100 </li></ul></ul><ul><li>HCO3 </li></ul><ul><ul><li>22 to 26 </li></ul></ul><ul><li>Anion Gap </li></ul><ul><ul><li>8 to 16 mmol/L </li></ul></ul><ul><li>Base excess (deficit) </li></ul><ul><ul><li>-3 to +3 mmol/L </li></ul></ul>
  6. 6. Questions to ask? <ul><li>Is the patient acidotic or alkalotic? </li></ul><ul><li>Is the primary cause respiratory or metabolic? </li></ul><ul><li>Is there compensation? </li></ul><ul><li>Is the patient hypoxic? </li></ul><ul><ul><li>(oxygen status, A-a) </li></ul></ul><ul><li>What is going on? </li></ul>
  7. 7. Questions to ask? <ul><li>Is the patient acidotic or alkalotic? </li></ul><ul><li>Is the primary cause respiratory or metabolic? </li></ul><ul><li>Is there compensation? </li></ul><ul><li>Is the patient hypoxic? </li></ul><ul><ul><li>(oxygen status, A-a) </li></ul></ul><ul><li>What is going on? </li></ul>
  8. 8. Is the patient acidotic or alkalotic? <ul><li>If pH < 7.35, the patient is acidotic </li></ul><ul><li>If pH > 7.45, the patient is alkalotic </li></ul><ul><li>This is IRRELEVANT of the cause </li></ul><ul><li>NB: pH drops by 0.017 per ˚ C increase </li></ul><ul><ul><ul><ul><li>(not significant in most clinical situations) </li></ul></ul></ul></ul>
  9. 9. Questions to ask? <ul><li>Is the patient acidotic or alkalotic? </li></ul><ul><li>Is the primary cause respiratory or metabolic? </li></ul><ul><li>Is there compensation? </li></ul><ul><li>Is the patient hypoxic? </li></ul><ul><ul><li>(oxygen status, A-a) </li></ul></ul><ul><li>What is going on? </li></ul>
  10. 10. Metabolic Respiratory Respiratory   Metabolic Low PaCO2 High PaCO2 Low PaCO2   High PaCO2 Acidosis   Alkalosis Low pH   High pH
  11. 11. Recall, there may be a MIXED pattern!!
  12. 12. Questions to ask? <ul><li>Is the patient acidotic or alkalotic? </li></ul><ul><li>Is the primary cause respiratory or metabolic? </li></ul><ul><li>Is there compensation? </li></ul><ul><li>Is the patient hypoxic? </li></ul><ul><ul><li>(oxygen status, A-a) </li></ul></ul><ul><li>What is going on? </li></ul>
  13. 13. Compensation <ul><li>There is no ‘overcompensation’ </li></ul>
  14. 14. Compensation <ul><li>Approximate responses to a primary acid-base problem </li></ul><ul><li>Metabolic acidosis </li></ul><ul><li>pCO2 will fall approx 1.2 times the HCO3- fall </li></ul><ul><li>Metabolic alkalosis </li></ul><ul><li>pCO2 will rise approx 0.7 times the HCO3- rise </li></ul><ul><li>Respiratory acidosis </li></ul><ul><li>Acute: HCO3- will rise approx 0.1 times the pCO2 rise </li></ul><ul><li>Chronic: HCO3- will rise approx 0.35 times the pCO2 rise </li></ul><ul><li>Respiratory alkalosis </li></ul><ul><li>Acute: HCO3- will fall approx 0.2 times the pCO2 fall </li></ul><ul><li>Chronic: HCO3- will fall approx 0.5 times the pCO2 fall </li></ul><ul><li>Also, a 10mmHg change in pCO2 from 40mmHg should cause a change in pH of 0.08 </li></ul>
  15. 15. Compensation (example) <ul><li>Set of gases: </li></ul><ul><ul><li>pH 7.25 pCO2 70mmHg [HCO3-] 31 mmol/L </li></ul></ul><ul><ul><li>Assume the patient has known chronic respiratory insufficiency </li></ul></ul><ul><li>Expected rise in [HCO3-] is about 0.35 times the pCO2 rise </li></ul><ul><ul><li>pCO2 rise is 30 (70-40) </li></ul></ul><ul><ul><li>Expect the [HCO3-] rise to be about 10.5 </li></ul></ul><ul><ul><li>So, [HCO3-] should be about 36 (upper norm, 26, + 10) </li></ul></ul><ul><li>In this example, it is LOWER than expected, and while the primary problem is respiratory acidosis, there must be metabolic acidosis occurring as well. </li></ul>
  16. 16. Question <ul><li>pH 7.25 pCO2 70mmHg [HCO3-] 31 mmol/L </li></ul><ul><li>How would you interpret these if the patient was young, and did NOT have chronic lung disease? </li></ul><ul><li>Expected [HCO3-] rise would be 30 times 0.1 = 3 </li></ul><ul><li>So, the [HCO3-] would be 29 (26+3) </li></ul><ul><li>In this case, you can say the patient probably has a respiratory acidosis with metabolic alkalosis, as you would not expect the [HCO3-] to be that high in compensation only. </li></ul>
  17. 17. Is there another quicker way to do this?
  18. 18. The Base Excess <ul><li>The BE (or base deficit) is defined as the amount of acid (or base) required to be added to whole blood to achieve a pH of 7.4 at 37 ˚C and paCO2 of 40mmHg. </li></ul><ul><li>If the base is in excess </li></ul><ul><ul><li>may be due to decrease in metabolic acids </li></ul></ul><ul><ul><li>may be due to increase in buffers (e.g. HCO3-) </li></ul></ul><ul><li>If the base is in deficit </li></ul><ul><ul><li>may be due to excess metabolic acids </li></ul></ul>
  19. 19. The Anion Gap <ul><li>[Na+ + K+] – [Cl- + HCO3-] </li></ul><ul><li>Measuring of a sample includes most cations, but NOT all anions. </li></ul><ul><ul><li>e.g. proteins, sulphates, phosphates, some acids </li></ul></ul><ul><li>Electroneutrality dictates these must be equal. </li></ul><ul><li>Normal gap 8-16 mmol/L </li></ul>
  20. 20. Interpretation of the anion gap <ul><li>The anion gap increases due to an increase in unmeasured anions due to a metabolic acidosis </li></ul><ul><ul><li>Ketoacidosis, lactic acidosis, uraemia, salicylate/methanol/ethylene glycol poisoning </li></ul></ul><ul><li>If the AG is NORMAL with a metabolic acidosis and increased Cl-, think of:- </li></ul><ul><ul><li>Diarrhoea, pancreatic fistula, renal tubular acidosis. </li></ul></ul><ul><ul><li>Treatment with either HCl, HN4Cl or acetazolamide. </li></ul></ul><ul><li>A decreased gap may be due to low protein states </li></ul>
  21. 21. Causes of acute respiratory acidosis <ul><ul><li>Respiratory pathophysiology </li></ul></ul><ul><ul><ul><li>respiratory arrest </li></ul></ul></ul><ul><ul><ul><li>airway obstruction </li></ul></ul></ul><ul><ul><ul><li>severe pneumonia </li></ul></ul></ul><ul><ul><ul><li>chest trauma </li></ul></ul></ul><ul><ul><ul><li>pneumothorax </li></ul></ul></ul><ul><ul><li>Acute drug intoxication </li></ul></ul><ul><ul><ul><li>especially narcotics, sedatives </li></ul></ul></ul><ul><ul><li>Residual neuromuscular blockade </li></ul></ul><ul><ul><li>Head trauma </li></ul></ul>
  22. 22. Causes of chronic respiratory acidosis <ul><ul><li>Chronic lung disease (esp CAL) </li></ul></ul><ul><ul><li>Neuromuscular disease </li></ul></ul><ul><ul><li>Extreme obesity (with OSA) </li></ul></ul><ul><ul><li>Chest wall deformity </li></ul></ul>
  23. 23. Causes of Respiratory Alkalosis <ul><ul><li>Pain </li></ul></ul><ul><ul><li>Anxiety </li></ul></ul><ul><ul><li>Hyperventilation </li></ul></ul><ul><ul><li>Hypoxemia </li></ul></ul><ul><ul><li>Restrictive lung disease </li></ul></ul><ul><ul><li>Severe congestive heart failure </li></ul></ul><ul><ul><li>Pulmonary emboli </li></ul></ul><ul><ul><li>Drugs </li></ul></ul><ul><ul><li>Sepsis </li></ul></ul><ul><ul><li>Fever </li></ul></ul><ul><ul><li>Thyrotoxicosis </li></ul></ul><ul><ul><li>Pregnancy </li></ul></ul><ul><ul><li>Overaggressive mechanical ventilation </li></ul></ul><ul><ul><li>Hepatic failure </li></ul></ul>
  24. 24. Causes of metabolic acidosis with raised anion gap <ul><li>Ketoacidosis </li></ul><ul><ul><li>diabetic, alcoholic, starvation </li></ul></ul><ul><li>Lactic acidosis </li></ul><ul><ul><li>hypoxia, shock, sepsis, seizures </li></ul></ul><ul><li>Toxin ingestion </li></ul><ul><ul><li>methanol, ethylene glycol, ethanol, isopropyl alcohol, paraldehyde, toluene </li></ul></ul><ul><li>Renal failure </li></ul><ul><ul><li>uraemia </li></ul></ul>
  25. 25. Causes of metabolic acidosis with normal anion gap <ul><ul><li>Renal tubular acidosis </li></ul></ul><ul><ul><li>Post respiratory alkalosis </li></ul></ul><ul><ul><li>Hypoaldosteronism </li></ul></ul><ul><ul><li>Potassium sparing diuretics </li></ul></ul><ul><ul><li>Pancreatic loss of bicarbonate </li></ul></ul><ul><ul><li>Acid administration (HCl, NH4Cl) </li></ul></ul><ul><ul><li>Cholestyramine </li></ul></ul><ul><ul><li>Diarrhoea </li></ul></ul><ul><ul><li>Carbonic anhydrase inhibitors </li></ul></ul>
  26. 26. Causes of Metabolic Alkalosis <ul><li>Diuretics </li></ul><ul><li>NG suction </li></ul><ul><li>Vomiting </li></ul><ul><li>Post hypercapnic </li></ul><ul><li>Cushing’s syndrome </li></ul><ul><li>Excessive alkali intake </li></ul>
  27. 27. Mixed Acid-Base Disturbances <ul><li>Metabolic acidosis and respiratory acidosis </li></ul><ul><ul><li>e.g. aspirin and sedative overdose </li></ul></ul><ul><li>Metabolic acidosis and respiratory alkalosis </li></ul><ul><ul><li>e.g. sepsis </li></ul></ul><ul><li>Metabolic acidosis and alkalosis </li></ul><ul><ul><li>e.g. vomiting with DKA </li></ul></ul><ul><li>Metabolic alkalosis and respiratory acidosis </li></ul><ul><ul><li>e.g. CAL and vomiting or diuretic use </li></ul></ul><ul><li>Metabolic alkalosis and respiratory alkalosis </li></ul><ul><ul><li>e.g. pregnancy and vomiting </li></ul></ul>
  28. 28. Questions to ask? <ul><li>Is the patient acidotic or alkalotic? </li></ul><ul><li>Is the primary cause respiratory or metabolic? </li></ul><ul><li>Is there compensation? </li></ul><ul><li>Is the patient hypoxic? </li></ul><ul><ul><li>(oxygen status, A-a) </li></ul></ul><ul><li>What is going on? </li></ul>
  29. 29. Oxygen status <ul><li>Hypoxaemia </li></ul><ul><ul><li>decreased oxygen content of blood </li></ul></ul><ul><ul><li>pO2 less than 60 mmHg and saturation is less than 90% </li></ul></ul><ul><li>Hypoxia </li></ul><ul><ul><li>Levels of pO2 sufficiently low to have an adverse effect on tissue function </li></ul></ul>
  30. 30. Types of Hypoxia <ul><li>Hypoxic hypoxia </li></ul><ul><ul><li>due to low blood pO2 </li></ul></ul><ul><ul><ul><li>e.g. due to lung disease processes </li></ul></ul></ul><ul><li>Anaemic hypoxia </li></ul><ul><ul><li>inadequate O2 delivery to tissues </li></ul></ul><ul><ul><ul><li>e.g. in anaemia or CO poisoning </li></ul></ul></ul><ul><li>Circulatory hypoxia </li></ul><ul><ul><li>inadequate blood flow to tissues </li></ul></ul><ul><ul><ul><li>e.g. shock </li></ul></ul></ul><ul><li>Histotoxic hypoxia </li></ul><ul><ul><li>inability of tissue to use the oxygen </li></ul></ul><ul><ul><ul><li>classically, in cyanide poisoning </li></ul></ul></ul>
  31. 31. Causes of Hypoxemia <ul><li>Inadequate inspiratory pO2 </li></ul><ul><li>Hypoventilation </li></ul><ul><li>Right to left shunt </li></ul><ul><li>V/Q mismatch </li></ul><ul><li>Problems at the gas exchange surface </li></ul>
  32. 32. The A-a gradient <ul><li>Difference between alveolar and arterial pO2 </li></ul><ul><ul><li>used as an index for shunting and V/Q mismatch (also diffusion problems) </li></ul></ul><ul><ul><li>normally about 5 mmHg (up to 15, in older patients, esp. lying down) </li></ul></ul><ul><li>pAO2 - paO2 </li></ul><ul><li>pA02 obtained from the Alveolar Gas Eq. </li></ul><ul><ul><li>pAO2 = pIO2 – (paCO2 / R) </li></ul></ul>
  33. 33. A-a gradient <ul><li>Normal A-a </li></ul><ul><ul><li>Hypoxaemia due to: </li></ul></ul><ul><ul><ul><li>Hypoventilation </li></ul></ul></ul><ul><ul><ul><li>Decreased FiO2 </li></ul></ul></ul><ul><li>Increased A-a </li></ul><ul><ul><li>Hypoxaemia due to: </li></ul></ul><ul><ul><ul><li>VQ mismatch (e.g. PE (increases dead space)) </li></ul></ul></ul><ul><ul><ul><li>Shunting (increasing FIO2 NOT help!) </li></ul></ul></ul><ul><ul><ul><li>Diffusion problems </li></ul></ul></ul>
  34. 34. ANY QUESTIONS?
  35. 35. THE END Thank You

×