02 Blood Gas

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  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
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  • 5/18/01 ABG Interpretation MUDPILES Methanol Uremia DKA Paraldehyde Isopropyl alcohol Lactic acidosis Ethylene glycol, ethanol Salicylates
  • 5/18/01 ABG Interpretation Fall in HCO 3 matched by equal rise in Cl, with no overall change in anion gap  hyperchloremic metabolic acidosis Sulfamylon mafenide acetate used for burns inhibits carbonic anhydrase Cholestyramine - Questran cholesterol lowering agent - chloride form of anion exchange resin produces hyperchloremic acidosis
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
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  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 5/18/01 ABG Interpretation
  • 02 Blood Gas

    1. 1. Marc D. Berg, MD – DeVos Children’s Hospital Rita R. Ongjoco, DO – Sinai Hospital of Baltimore 12/30/02 ABG Interpretation
    2. 2. ABG Interpretation <ul><li>First, does the patient have an acidosis or an alkalosis </li></ul><ul><li>Second, what is the primary problem – metabolic or respiratory </li></ul><ul><li>Third, is there any compensation by the patient – respiratory compensation is immediate while renal compensation takes time </li></ul>12/30/02 ABG Interpretation
    3. 3. ABG Interpretation <ul><li>It would be extremely unusual for either the respiratory or renal system to overcompensate </li></ul><ul><li>The pH determines the primary problem </li></ul><ul><li>After determining the primary and compensatory acid/base balance, evaluate the effectiveness of oxygenation </li></ul>12/30/02 ABG Interpretation
    4. 4. Normal Values <ul><li>pH 7.35 to 7.45 </li></ul><ul><li>paCO 2 36 to 44 mm Hg </li></ul><ul><li>HCO 3 22 to 26 meq/L </li></ul>12/30/02 ABG Interpretation
    5. 5. Abnormal Values <ul><li>pH < 7.35 </li></ul><ul><ul><li>Acidosis (metabolic and/or respiratory) </li></ul></ul><ul><li>pH > 7.45 </li></ul><ul><ul><li>Alkalosis (metabolic and/or respiratory) </li></ul></ul><ul><li>paCO 2 > 44 mmHg </li></ul><ul><ul><li>Respiratory acidosis (alveolar hypoventilation) </li></ul></ul><ul><li>paCO 2 < 36 mmHg </li></ul><ul><ul><li>Respiratory alkalosis (alveolar hyperventilation) </li></ul></ul><ul><li>HCO 3 < 22 meq/L </li></ul><ul><ul><li>Metabolic acidosis </li></ul></ul><ul><li>HCO 3 > 26 meq/L </li></ul><ul><ul><li>Metabolic alkalosis </li></ul></ul>12/30/02 ABG Interpretation
    6. 6. Putting It Together - Respiratory <ul><li>So </li></ul><ul><li>paCO 2 > 44 with a pH < 7.35 represents a respiratory acidosis </li></ul><ul><li>paCO 2 < 36 with a pH > 7.45 represents a respiratory alkalosis </li></ul><ul><li>For a primary respiratory problem, pH and paCO 2 move in the opposite direction </li></ul><ul><ul><li>For each deviation in paCO 2 of 10 mm Hg in either direction, 0. 08 pH units change in the opposite direction </li></ul></ul>12/30/02 ABG Interpretation
    7. 7. Putting It Together - Metabolic <ul><li>And </li></ul><ul><li>HCO 3 < 22 with a pH < 7.35 represents a metabolic acidosis </li></ul><ul><li>HCO 3 > 26 with a pH > 7.45 represents a metabolic alkalosis </li></ul><ul><li>For a primary metabolic problem, pH and HCO 3 are in the same direction, and paCO 2 is also in the same direction </li></ul>12/30/02 ABG Interpretation
    8. 8. Compensation <ul><li>The body’s attempt to return the acid/base status to normal (i.e. pH closer to 7.4) </li></ul><ul><li>Primary Problem Compensation </li></ul><ul><li>respiratory acidosis metabolic alkalosis </li></ul><ul><li>respiratory alkalosis metabolic acidosis </li></ul><ul><li>metabolic acidosis respiratory alkalosis </li></ul><ul><li>metabolic alkalosis respiratory acidosis </li></ul>12/30/02 ABG Interpretation
    9. 9. Expected Compensation <ul><li>Respiratory acidosis </li></ul><ul><li>Acute – </li></ul><ul><ul><li>the pH decreases 0.08 units for every 10 mm Hg increase in paCO 2 ; </li></ul></ul><ul><ul><li>HCO 3  0.1-1 mEq/liter per  10 mm Hg paCO 2 </li></ul></ul><ul><li>Chronic – </li></ul><ul><ul><li>the pH decreases 0.03 units for every 10 mm Hg increase in paCO 2 ; </li></ul></ul><ul><ul><li>HCO 3  1.1-3.5 mEq/liter per  10 mm Hg paCO 2 </li></ul></ul>12/30/02 ABG Interpretation
    10. 10. Expected Compensation <ul><li>Respiratory alkalosis </li></ul><ul><li>Acute – </li></ul><ul><ul><li>the pH increases 0.08 units for every 10 mm Hg decrease in paCO 2 ; </li></ul></ul><ul><ul><li>HCO 3  0-2 mEq/liter per  10 mm Hg paCO 2 </li></ul></ul><ul><li>Chronic – </li></ul><ul><ul><li>the pH increases 0.17 units for every 10 mm Hg decrease in paCO 2 ; </li></ul></ul><ul><ul><li>HCO 3  2.1-5 mEq/liter per  10 mm Hg paCO 2 </li></ul></ul>12/30/02 ABG Interpretation
    11. 11. Expected Compensation <ul><li>Metabolic acidosis </li></ul><ul><li>paCO 2 = 1.5(HCO 3 ) + 8 (  2) </li></ul><ul><li>paCO 2  1-1.5 per  1 mEq/liter HCO 3 </li></ul><ul><li>Metabolic alkalosis </li></ul><ul><li>paCO 2 = 0.7(HCO 3 ) + 20 (  1.5) </li></ul><ul><li>paCO 2  0.5-1.0 per  1 mEq/liter HCO 3 </li></ul>12/30/02 ABG Interpretation
    12. 12. Classification of primary acid-base disturbances and compensation <ul><li>Acceptable ventilatory and metabolic acid-base status </li></ul><ul><li>Respiratory acidosis (alveolar hypoventilation) - acute, chronic </li></ul><ul><li>Respiratory alkalosis (alveolar hyperventilation) - acute, chronic </li></ul><ul><li>Metabolic acidosis – uncompensated, compensated </li></ul><ul><li>Metabolic alkalosis – uncompensated, partially compensated </li></ul>12/30/02 ABG Interpretation
    13. 13. Acute Respiratory Acidosis <ul><li>paCO 2 is elevated and pH is acidotic </li></ul><ul><li>The decrease in pH is accounted for entirely by the increase in paCO 2 </li></ul><ul><li>Bicarbonate and base excess will be in the normal range because the kidneys have not had adequate time to establish effective compensatory mechanisms </li></ul>12/30/02 ABG Interpretation
    14. 14. Acute Respiratory Acidosis <ul><li>Causes </li></ul><ul><ul><li>Respiratory pathophysiology - airway obstruction, severe pneumonia, chest trauma/pneumothorax </li></ul></ul><ul><ul><li>Acute drug intoxication (narcotics, sedatives) </li></ul></ul><ul><ul><li>Residual neuromuscular blockade </li></ul></ul><ul><ul><li>CNS disease (head trauma) </li></ul></ul>12/30/02 ABG Interpretation
    15. 15. Chronic Respiratory Acidosis <ul><li>paCO 2 is elevated with a pH in the acceptable range </li></ul><ul><li>Renal mechanisms increase the excretion of H + within 24 hours and may correct the resulting acidosis caused by chronic retention of CO 2 to a certain extent </li></ul>12/30/02 ABG Interpretation
    16. 16. Chronic Respiratory Acidosis <ul><li>Causes </li></ul><ul><ul><li>Chronic lung disease (BPD, COPD) </li></ul></ul><ul><ul><li>Neuromuscular disease </li></ul></ul><ul><ul><li>Extreme obesity </li></ul></ul><ul><ul><li>Chest wall deformity </li></ul></ul>12/30/02 ABG Interpretation
    17. 17. Acute Respiratory Alkalosis <ul><li>paCO 2 is low and the pH is alkalotic </li></ul><ul><li>The increase in pH is accounted for entirely by the decrease in paCO 2 </li></ul><ul><li>Bicarbonate and base excess will be in the normal range because the kidneys have not had sufficient time to establish effective compensatory mechanisms </li></ul>12/30/02 ABG Interpretation
    18. 18. Respiratory Alkalosis <ul><li>Causes </li></ul><ul><ul><li>Pain </li></ul></ul><ul><ul><li>Anxiety </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>12/30/02 ABG Interpretation
    19. 19. Uncompensated Metabolic Acidosis <ul><li>Normal paCO 2 , low HCO 3 , and a pH less than 7.30 </li></ul><ul><li>Occurs as a result of increased production of acids and/or failure to eliminate these acids </li></ul><ul><li>Respiratory system is not compensating by increasing alveolar ventilation (hyperventilation) </li></ul>12/30/02 ABG Interpretation
    20. 20. Compensated Metabolic Acidosis <ul><li>paCO 2 less than 30, low HCO 3 , with a pH of 7.3-7.4 </li></ul><ul><li>Patients with chronic metabolic acidosis are unable to hyperventilate sufficiently to lower paCO 2 for complete compensation to 7.4 </li></ul>12/30/02 ABG Interpretation
    21. 21. Metabolic Acidosis Elevated Anion Gap <ul><li>Causes </li></ul><ul><ul><li>Ketoacidosis - diabetic, alcoholic, starvation </li></ul></ul><ul><ul><li>Lactic acidosis - hypoxia, shock, sepsis, seizures </li></ul></ul><ul><ul><li>Toxic ingestion – salicylates, methanol, ethylene glycol, ethanol, isopropyl alcohol, paraldehyde, toluene </li></ul></ul><ul><ul><li>Renal failure - uremia </li></ul></ul>12/30/02 ABG Interpretation
    22. 22. Metabolic Acidosis Normal Anion Gap <ul><li>Causes </li></ul><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>Diarrhea </li></ul></ul><ul><ul><li>Carbonic anhydrase inhibitors </li></ul></ul><ul><ul><li>Acid administration (HCl, NH 4 Cl, arginine HCl) </li></ul></ul><ul><ul><li>Sulfamylon </li></ul></ul><ul><ul><li>Cholestyramine </li></ul></ul><ul><ul><li>Ureteral diversions </li></ul></ul>12/30/02 ABG Interpretation
    23. 23. Effectiveness of Oxygenation <ul><li>Further evaluation of the arterial blood gas requires assessment of the effectiveness of oxygenation of the blood </li></ul><ul><li>Hypoxemia – decreased oxygen content of blood - paO 2 less than 60 mm Hg and the saturation is less than 90% </li></ul><ul><li>Hypoxia – inadequate amount of oxygen available to or used by tissues for metabolic needs </li></ul>12/30/02 ABG Interpretation
    24. 24. Mechanisms of Hypoxemia <ul><li>Inadequate inspiratory partial pressure of oxygen </li></ul><ul><li>Hypoventilation </li></ul><ul><li>Right to left shunt </li></ul><ul><li>Ventilation-perfusion mismatch </li></ul><ul><li>Incomplete diffusion equilibrium </li></ul>12/30/02 ABG Interpretation
    25. 25. Assessment of Gas Exchange <ul><li>Alveolar-arterial O 2 tension difference </li></ul><ul><ul><li>A-a gradient </li></ul></ul><ul><ul><li>PAO 2 -PaO 2 </li></ul></ul><ul><ul><li>PAO 2 = FIO 2 (PB - PH 2 O) - PaCO 2 /RQ* </li></ul></ul><ul><li>arterial-Alveolar O 2 tension ratio </li></ul><ul><ul><li>PaO 2 /PAO 2 </li></ul></ul><ul><li>arterial-inspired O 2 ratio </li></ul><ul><ul><li>PaO 2 /FIO 2 </li></ul></ul><ul><ul><li>P/F ratio </li></ul></ul><ul><li>*RQ=respiratory quotient= 0.8 </li></ul>12/30/02 ABG Interpretation
    26. 26. Assessment of Gas Exchange <ul><li>ABG A-a grad </li></ul><ul><li>PaO 2 PaCO 2 RA 100% </li></ul><ul><li>Low FIO 2   N* N </li></ul><ul><li>Alveolar hypoventilation   N N </li></ul><ul><li>Altered gas exchange </li></ul><ul><li>Regional V/Q mismatch   /N/   N/  </li></ul><ul><li>Intrapulmonary R to L shunt  N/    </li></ul><ul><li>Impaired diffusion  N/   N </li></ul><ul><li>Anatomical R to L shunt </li></ul><ul><li>(intrapulmonary or intracardiac)  N/    </li></ul><ul><li>* N=normal </li></ul>12/30/02 ABG Interpretation
    27. 27. Summary <ul><li>First, does the patient have an acidosis or an alkalosis </li></ul><ul><ul><li>Look at the pH </li></ul></ul><ul><li>Second, what is the primary problem – metabolic or respiratory </li></ul><ul><ul><li>Look at the pCO 2 </li></ul></ul><ul><ul><li>If the pCO 2 change is in the opposite direction of the pH change, the primary problem is respiratory </li></ul></ul>12/30/02 ABG Interpretation
    28. 28. Summary <ul><li>Third, is there any compensation by the patient - do the calculations </li></ul><ul><ul><li>For a primary respiratory problem, is the pH change completely accounted for by the change in pCO 2 </li></ul></ul><ul><ul><ul><li>if yes, then there is no metabolic compensation </li></ul></ul></ul><ul><ul><ul><li>if not, then there is either partial compensation or concomitant metabolic problem </li></ul></ul></ul>12/30/02 ABG Interpretation
    29. 29. Summary <ul><ul><li>For a metabolic problem, calculate the expected pCO 2 </li></ul></ul><ul><ul><ul><li>if equal to calculated, then there is appropriate respiratory compensation </li></ul></ul></ul><ul><ul><ul><li>if higher than calculated, there is concomitant respiratory acidosis </li></ul></ul></ul><ul><ul><ul><li>if lower than calculated, there is concomitant respiratory alkalosis </li></ul></ul></ul>12/30/02 ABG Interpretation
    30. 30. Summary <ul><li>Next, don’t forget to look at the effectiveness of oxygenation, (and look at the patient) </li></ul><ul><ul><li>your patient may have a significantly increased work of breathing in order to maintain a “normal” blood gas </li></ul></ul><ul><ul><li>metabolic acidosis with a concomitant respiratory acidosis is concerning </li></ul></ul>12/30/02 ABG Interpretation
    31. 31. Case 1 <ul><li>Little Billy got into some of dad’s barbiturates. He suffers a significant depression of mental status and respiration. You see him in the ER 3 hours after ingestion with a respiratory rate of 4. A blood gas is obtained (after doing the ABC’s, of course). It shows pH = 7.16, pCO 2 = 70, HCO 3 = 22 </li></ul>12/30/02 ABG Interpretation
    32. 32. Case 1 <ul><li>What is the acid/base abnormality? </li></ul><ul><li>Uncompensated metabolic acidosis </li></ul><ul><li>Compensated respiratory acidosis </li></ul><ul><li>Uncompensated respiratory acidosis </li></ul><ul><li>Compensated metabolic alkalosis </li></ul>12/30/02 ABG Interpretation
    33. 33. Case 1 <ul><li>Uncompensated respiratory acidosis </li></ul><ul><li>There has not been time for metabolic compensation to occur. As the barbiturate toxicity took hold, this child slowed his respirations significantly, pCO 2 built up in the blood, and an acidosis ensued. </li></ul>12/30/02 ABG Interpretation
    34. 34. Case 2 <ul><li>Little Suzie has had vomiting and diarrhea for 3 days. In her mom’s words, “She can’t keep anything down and she’s runnin’ out.” She has had 1 wet diaper in the last 24 hours. She appears lethargic and cool to touch with a prolonged capillary refill time. After addressing her ABC’s, her blood gas reveals: pH=7.34, pCO 2 =26, HCO 3 =12 </li></ul>12/30/02 ABG Interpretation
    35. 35. Case 2 <ul><li>What is the acid/base abnormality? </li></ul><ul><li>Uncompensated metabolic acidosis </li></ul><ul><li>Compensated respiratory alkalosis </li></ul><ul><li>Uncompensated respiratory acidosis </li></ul><ul><li>Compensated metabolic acidosis </li></ul>12/30/02 ABG Interpretation
    36. 36. Case 2 <ul><li>Compensated metabolic acidosis </li></ul><ul><li>The prolong history of fluid loss through diarrhea has caused a metabolic acidosis. The mechanisms probably are twofold. First there is lactic acid production from the hypovolemia and tissue hypoperfusion. Second, there may be significant bicarbonate losses in the stool. The body has compensated by “blowing off” the CO 2 with increased respirations. </li></ul>12/30/02 ABG Interpretation
    37. 37. Case 3 <ul><li>You are evaluating a 15 year old female in the ER who was brought in by EMS from school because of abdominal pain and vomiting. Review of system is negative except for a 10 lb. weight loss over the past 2 months and polyuria for the past 2 weeks. She has no other medical problems and denies any sexual activity or drug use. On exam, she is alert and oriented, afebrile, HR 115, RR 26 and regular, BP 114/75, pulse ox 95% on RA. </li></ul>12/30/02 ABG Interpretation
    38. 38. Case 3 <ul><li>Exam is unremarkable except for mild abdominal tenderness on palpation in the midepigastric region and capillary refill time of 3 seconds. The nurse has already seen the patient and has sent off “routine” blood work. She hands you the result of the blood gas. pH = 7.21 pCO 2 = 24 pO 2 = 45 HCO 3 = 10 BE = -10 saturation = 72% </li></ul>12/30/02 ABG Interpretation
    39. 39. Case 3 <ul><li>What is the blood gas interpretation? </li></ul><ul><li>Uncompensated respiratory acidosis with severe hypoxia </li></ul><ul><li>Uncompensated metabolic alkalosis </li></ul><ul><li>Combined metabolic acidosis and respiratory acidosis with severe hypoxia </li></ul><ul><li>Metabolic acidosis with respiratory compensation </li></ul>12/30/02 ABG Interpretation
    40. 40. Case 3 <ul><li>Metabolic acidosis with respiratory compensation </li></ul><ul><li>This is a patient with new onset diabetes mellitus in ketoacidosis. Her pulse oximetry saturation and clinical examination do not reveal any respiratory problems except for tachypnea which is her compensatory mechanism for the metabolic acidosis. The nurse obtained the blood gas sample from the venous stick when she sent off the other labs. </li></ul>12/30/02 ABG Interpretation
    41. 41. References <ul><li>The ICU Book – Paul L. Marino, 1991, Algorithms for acid-base interpretations, p415-426 </li></ul><ul><li>Textbook of Pediatric Intensive Care 3 rd Edition – edited by Mark C. Rogers, 1996, Respiratory Monitoring: Interpretation of clinical blood gas values, p355-361 </li></ul><ul><li>Pediatric Critical Care – Bradley Fuhrman and Jerry Zimmerman, 1992, Acid-Base Balance and Disorders, p689-696 </li></ul><ul><li>Critical Care Physiology – Robert Bartlett, 1996, Acid-Base physiology p165-173. </li></ul>12/30/02 ABG Interpretation

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