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Arterial Blood Gasses

Arterial Blood Gasses. At the end of this self study the participant will: 1. Correctly identify the following: Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis See BJH Policy: Arterial Blood Gas Sampling

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Arterial Blood Gasses

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  1. Arterial Blood Gasses At the end of this self study the participant will: 1. Correctly identify the following: Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis See BJH Policy: Arterial Blood Gas Sampling Physician alert levels per BJC Laboratory: (http://www.testcatalog.org/nrr/catalogs/bjc/catalog/)

  2. pH • Normal pH: 7.35 to 7.45 • For normal metabolism to occur pH must be maintained in the normal range: • When the pH is below 7.35, blood is acidic. • When the pH is above 7.45, blood is alkalotic. • Physician alert values for blood pH are below 7.2 OR above 7.6 • Values outside of that range may interfere with cellular functioning, and if uncorrected, will lead to death.

  3. PaCO2 - partial pressure of CO2 • Definition: the amount of carbon dioxide gas dissolved in the blood • Normal PaCO2 : 35-45 mmHg (torr) • Physician alert value at BJH is 75 mmHg or greater • Carbon Dioxide is acidic • as PaCO2, pH levels , (acidic) • as PaCO2 , pH levels , (alkaline) • Blood carries CO2 to the lungs, where excess CO2 combines with H2O to form carbonic acid (H2CO3). • The level of H2CO3 in blood determines blood pH • H2CO3 triggers the lungs to adjust the rate and depth of ventilation to stabilize CO2 .

  4. HCO3 (Bicarb) (Base) • Normal HCO3 : 22-26 mEq/L • Kidneys excrete or retain bicarbonate (HCO3) according to pH level. • HCO3 , pH levels : alkaline • HCO3 , pH levels : acidic • Kidneys may take from hours to days to correct an imbalance. • Remember: the lungs and kidneys work together. • Goal: maintain blood pH by balancing 1 part acid to 20 parts base.

  5. PaO2 partial pressure of O2 • Normal PaO2 - 80-105 mmHg • Physician alert value 40 or less • PaO2 (Partial Pressure of Oxygen) amount of oxygen dissolved in the blood. (The other 97% of oxygen is attached to the hemoglobin) • It primarily measures the effectiveness of the lungs in pulling oxygen into the blood stream from the atmosphere. • Critical Threshold <60 mmHg

  6. PaO2 • Elevated PaO2 levels are associated with: • Increased oxygen levels in the inhaled air • Polycythemia • Decreased PaO2 levels are associated with: • Decreased oxygen levels in the inhaled air • Anemia • Heart decompensation • Chronic obstructive pulmonary disease • Restrictive pulmonary disease • Hypoventilation

  7. SaO2: Arterial Oxygen Saturation • Definition: % of hemoglobin combined with O2 • Normal SaO2 on room air is in excess of 95%. • deep or rapid breathing can to 98-99%. • Oxygen-enriched air (40% - 100%), can push SaO2 to 100%. • Oxygen Saturation will fall if  O2 available: • increased altitudes. • Airway obstruction (e.g. asthmatic attack) • Alveolar lung disease. • Oxygen Saturation will rise if: • Deep or rapid breathing occurs •  oxygen levels (supplemental O2)

  8. Summary of ABG Acid/Base

  9. Indications for ABG • Inadequate Ventilation? • Not awake or breathing too fast, (concern about respiratory muscle fatigue) • Are there concerns about oxygenation that can’t be addressed with pulse ox? • Carbon Monoxide (carboxyhemoglobinemia) • Methemoglobinemia (e.g., benzocaine intoxication) • Are there concerns about acid-base balance? • Sepsis, DKA, Poly-drug overdose • Chronic CO2 retention • Miscellaneous • After intubation • Monitor vent settings • Pre-op baseline

  10. Potential Electrolyte Changes pH < 7.35 H+ Cell • Goal: serum electoneutrality • Acidemia: pH below 7.35 • H+ ions enter cells to correct low plasma pH • K+ ions leave cells • Result: possible hyperkalemia • Alkalosis: pH above 7.45 •  HCO3 will lower H+ • K+ ions enter cell • Result: possible hypokalemia K+ pH > 7.45 Cell K+

  11. ABG Interpretation • First, pH • Normal, 7.35-7.45 • If normal, quit here • Second pH • pH < 7.35 Acidosis • pH >7.45 Alkalosis • Third, Cause • If CO2 is abnormal, respiratory cause • If HCO3 is abnormal, metabolic cause

  12. Respiratory Alkalosis • pH >7.45 • pCO2 <35 • Always due to “blowing off” carbon dioxide • hypoxemia • psychogenic • compensation for metabolic acidosis • stimulation of CNS • inappropriate mechanical ventilation

  13. Respiratory Alkalosis Physical Assessment • Dizziness • Tingling • Lightheadedness • Numbness • Hypocalcemia • Hypokalemia (K+ enters cell for electroneutrality) • Hyperventilation

  14. Respiratory Alkalosis Treatment • Treat cause • based on pH • emergent treatment not indicated until pH >7.55 • Decrease ventilation • change vent settings, sedation, pain control • Supportive measures • Emotional support, relieve stress

  15. Respiratory Acidosis • pH <7.35 • PCO2 >45 • Always due to inadequate excretion of carbon dioxide. • Root of problem is Inadequate Alveolar Ventilation • pH term is acidosis • PCO2 term is hypercarbia

  16. Respiratory Acidosis Physical Assessment • Hypoventilation/Dyspnea • Mental status changes • Lethargy • Headache • Cough/Wheezing • Acute Respiratory Acidosis Indicates Sudden Failure To Breathe and Requires Immediate Investigation

  17. Causes of Respiratory Acidosis • Increased dead space • pulmonary emboli • chronic bronchitis/ emphysema • Increased CO2 production • elevated temperature • high carbohydrate diet • Depressed respiratory drive • CNS depression • CNS depressants • head injury • respiratory diseases • Respiratory muscle fatigue / dysfunction • ARDS • neuromuscular diseases • chest trauma

  18. Respiratory Acidosis Treatment • Treat cause • based on pH • Bronchodilators if warranted by underlying condition • Supportive Measures • Airway • Artificial Ventilation • Consider Bag/Valve • Consider intubation (laryngeal mask airway (LMA) shown) • Oxygen Supplementation

  19. Metabolic Alkalosis • pH >7.45 • HCO3 >26 • Too much alkalinity • excess bicarb administration • antacid overuse • alkaline drugs • Lactated Ringers administration • Metabolic acid loss • vomiting • NG suctioning • diuretics • steroids

  20. Metabolic Alkalosis Physical Presentation Chvostek’s sign • Hypoventilation • Electrolyte Disturbances • Cardiac Dysrythmias • Alkalosis ionizes calcium, so may exhibit S&S hypocalcemia • tetany, Chvostek/Trousseau’s signs, seizures Trousseau’s sign

  21. Metabolic Alkalosis Treatment • Lungs can provide limited compensation • Treat underlying cause • Correct electrolytes • Diamox (carbonic anhydrase inhibitor) • Inhibition reduces reabsorption of NaHCO3 • Ammonium chloride • metabolized into urea and HCL

  22. pH <7.35 HCO3 <22 Increased HCO3 loss Diarrhea (GI preps) GI fistula Increased H+ production lactic acidosis ketoacidosis renal failure External influences Salicylate intoxication Ethanol, methanol or isopropyl alcohol intoxication Metabolic Acidosis

  23. Metabolic Acidosis Physical Assessment • Hyperventilation • Kussmaul respiratory pattern • Headache • Mental Status Changes • Hyperkalemia • acidosis draws K+ out of the cells • Hypercalcemia • Increased parathyroid hormone causes hypercalcemia and increased bicarb excretion

  24. Metabolic Acidosis Treatment • Treat underlying condition • based on pH – if pH <7.2 may need IV bicarbonate until cause is controlled • Lactic acidosis, ketoacidosis • If kidney disease is cause, may require hemodialysis • Acute metabolic acidosis may indicate tissue hypoxia • requires further assessment • consider oxygen therapy

  25. ABG Practice • pH 7.55 • PaCO2 28 • HCO3 24 • PaO2 84 • Interpretation? • Normal • Respiratory Acidosis • Respiratory Alkalosis • Metabolic Acidosis • Metabolic Alkalosis Answer: Respiratory Alkalosis pH is above 7.45, PaCO2 is below 35

  26. ABG Practice • Normal • Respiratory Acidosis • Respiratory Alkalosis • Metabolic Acidosis • Metabolic Alkalosis • pH 7.28 • PaCO2 54 • HCO3 24 • PaO2 59 • Interpretation? Answer: Respiratory Acidosis pH is below 7.35, PaCO2 is above 45

  27. ABG Practice • pH 7.42 • PaCO2 38 • HCO3 24 • PaO2 89 • Interpretation? • Normal • Respiratory Acidosis • Respiratory Alkalosis • Metabolic Acidosis • Metabolic Alkalosis Answer: Normal ABG

  28. ABG Practice • pH 7.31 • PaCO2 38 • HCO3 19 • PaO2 89 • Interpretation? • Normal • Respiratory Acidosis • Respiratory Alkalosis • Metabolic Acidosis • Metabolic Alkalosis Answer: Metabolic Acidosis pH is below 7.35, HCO3 is below 22

  29. ABG Practice • pH 7.50 • PaCO2 42 • HCO3 31 • PaO2 82 • Interpretation? • Normal • Respiratory Acidosis • Respiratory Alkalosis • Metabolic Acidosis • Metabolic Alkalosis Answer: Metabolic Alkalosis pH is above 7.45, HCO3 is above 26

  30. Next module:ABG - Compensation pH 7.35-7.45 CO2 HCO3

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