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Basic Blood Gas Interpretation

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  1. Basic Blood Gas Interpretation 205b

  2. Values Measured • PaO2 – amount of oxygen in the arterial blood • SaO2 – percent saturation of the hemoglobin as measured by a CO-oximeter

  3. Values Measured • SpO2– percent saturation of the hemoglobin as measured by a pulse oximeter • Hb – amount of hemoglobin present

  4. Values Measured • Hct (Hematocrit) – percent of the blood that is composed of cells • pH – concentration of hydrogen ions (H+) in the arterial blood

  5. Values Measured • PaCO2– amount of carbon dioxide in the arterial blood • HCO3ˉ – amount of bicarbonate in the arterial blood

  6. Values Measured • B.E. (base excess/base deficit) – the total of all buffering systems in the arterial blood • CO – amount of carbon monoxide present in the arterial blood

  7. Determination of Oxygenation Normal Values SaO2 93% – 97% 88-92% COPD/lung disease Hb Males: 13.5 – 16.5 g/dl Females: 12 – 15 g/dl Hct Males: 42 – 54% Females: 38 – 47% • PaO2 • 80 – 100 mmHg • Mild hypoxemia • 60 – 79 mmHg • Moderate hypoxemia • 40 – 59 mmHg • Severe hypoxemia • < 40 mmHg

  8. Determination of Oxygenation • Normal Values • CaO2 • Males: 17.1 – 21.7 ml/dl • Females: 14.9 – 19.7 ml/dl • COHb • <3%

  9. Method of Determining Oxygenation • Evaluate the PaO2 • 80 – 100 mmHg: normal oxygenation • > 100 mmHg: hyperoxygenation • 60 – 79 mmHg: mild hypoxemia

  10. Method of Determining Oxygenation • Evaluate the PaO2 • 40 – 59 mmHg: moderate hypoxemia • < 40 mmHg: severe hypoxemia

  11. Method of Determining Oxygenation • Evaluate the SaO2 • > 93%: normal oxygenation • < 93%: may be hypoxemic; examine the hemoglobin

  12. Method of Determining Oxygenation • Evaluate the Hb • 12 – 16 g/dl: normal • < 12 g/dl: anemic • > 16 g/dl: polycythemic

  13. Method of Determining Oxygenation • Evaluate the CaO2 • 17 – 20 ml/dl: normal • 15 – 17 ml/dl: mild hypoxia • 12 – 14.9 ml/dl: moderate hypoxia • < 12 ml/dl: severe hypoxia

  14. Method of Determining Oxygenation • Other factors in oxygenation • Abnormal forms of hemoglobin: • Detectable by CO-oximeter, not pulse oximeter

  15. Estimate PaO2 • Predicated PaO2 based on age= Estimated value of what there PaO2 might be • PaO2= 110 – half the person’s age • example: 20 year old. 110 – 10= PaO2 100 • (PaO2 of 60 will equal approximately 90% saturation based on the oxyhemoglobin curve)

  16. Determination of Acid Base Balance • pH is equal to the –log of the hydrogen ion • pH = – Log [H+]

  17. Determination of Acid Base Balance • Henderson-Hasselbalch equation • pH = pK + Log HCO3 H2CO3 • pH = pK + Log HCO3 (Renal) Paco2 x0.03 (Lungs)

  18. Determination of Acid Base Balance • pH measures the blood’s acidity or alkalinity • Must always be determined first when assessing acid- base balance

  19. Determination of Acid Base Balance • PaCO2 is our stimulus to breathe • A high PaCO2 indicates that not enough carbon dioxide is being exhaled • A low PaCO2 indicates that too much carbon dioxide is being eliminated

  20. Determination of Acid Base Balance • Evaluate base excess or bicarbonate (metabolic parameter) • Is it acidic or alkaline • 22- 26 mEq/L is normal • > 26 Indicates metabolic alkalosis • < 22 Indicates metabolic acidosis

  21. Determination of Acid Base Balance • Bicarbonate is the base or buffer that “neutralizes” hydrogen ions (HCO3) • Bicarbonate is made in the red blood cells, liver, and kidney

  22. Determination of Acid Base Balance • When bicarbonate levels are elevated, an excess of alkalinity exists in the metabolic systems • When bicarbonate levels are low, an excess of acidity exists in the metabolic systems

  23. Determination of Acid Base Balance • If the pH is not normal, identify whether it is acidic or alkaline

  24. Determination of Acid Base Balance • Identify whether the PaCO2or bicarbonate disturbance (acidosis or alkalosis) matches The pH change (acidosis or alkalosis) • This is the “cause” of the problem and represents where treatment should be directed. (e.g. if pH is acidic, PaCO2is alkaline and bicarbonate is acidic, the problem is a metabolic acidosis)

  25. Determination of Acid Base Balance • If the pH is not 7.40 but within the normal range (7.35 - 7.45), the disturbance is fully compensated • If both the respiratory and metabolic parameters match the pH, the problem is a combined disturbance

  26. Determination of Acid Base Balance • A change in the opposite direction (acidosis or alkalosis) by the parameter (PaCO2 or bicarbonate) that does not match the pH is an attempt to restore the pH (referred to as partial compensation)

  27. Evaluation of Compensation

  28. Arterial Punctures • Indications1 • Need to evaluate ventilation, acid-base balance, and oxygenation of blood • Assess the patient’s response to therapy • Monitor and assess the severity and progression of a disease process 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  29. Arterial Punctures • Contraindications1 • Negative Allen test • Presence of a surgical shunt proximal to the sample site http://www.youtube.com/watch?v=HRcVVGBb9fg 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  30. Dialysis shunt

  31. Arterial Punctures • Contraindications1 • Presence of a lesion at the sample site • Coagulopathy or medium to high dose anticoagulation therapy (relative contraindication) 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  32. Hematoma

  33. Arterial Punctures • Hazards and complications1 • Arteriospasm • Air or clotted blood emboli • Hematoma 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  34. Arterial Punctures • Hazards and complications1 • Hemorrhage • Pain • Arterial occlusion 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  35. Arterial Punctures • Hazards and complications1 • Trauma to the vessel • Vasovagal response • Patient or sample contamination • Anaphylaxis (if local anesthetic used, Xylocain) 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  36. Arterial Punctures • Assessment of need for arterial sample1 • Initiation, change, or discontinuation of therapy (oxygen or ventilatory support) • History and physical indicators 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  37. Arterial Punctures • Assessment of need for arterial sample1 • Presence of other abnormal diagnostic tests or findings • Baseline study for pulmonary rehabilitation program 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  38. Arterial Punctures • Frequency of monitoring1 • Dependent upon clinical status of the patient and presence of indications • If frequent monitoring required, use alternating sites or indwelling arterial catheter 1 Excerpt from the AARC Clinical Practice Guideline for Sampling for Arterial Blood Gas Analysis

  39. Arterial Punctures • Allen Test • Performed to determine presence of adequate collateral circulation in the hand • Cannot be used with uncooperative or unconscious patients

  40. Arterial Punctures • Allen Test • Procedure • Have patient clench hand into a tight fist • Apply pressure to occlude flow through the radial and ulnar arteries • Open hand; observe to ensure that the palm and fingers are blanched

  41. Arterial Punctures • Allen Test • Procedure • Remove pressure from the ulnar artery • Observe time necessary for flushing of hand • Test is negative for collateral circulation if flushing does not occur within 20 seconds; an alternative site is chosen

  42. The Modified Allen Test The modified Allen test. A, The hand is clenched into a tight fist and pressure is applied to the radial and ulnar arteries. B, The hand is opened (but not fully extended); the palm and fingers are blanched. C, Removal of pressure on the ulnar artery should result in flushing of the entire hand.

  43. Procedure For Obtaining an Arterial Sample (Radius) • Confirm the order in the patient’s chart • Note any contraindications and notify physician if any exist

  44. Procedure For Obtaining an Arterial Sample (Radius) • Ensure that patient is in a steady state (no changes in oxygen status for at least twenty minutes) • Obtain and assemble necessary equipment

  45. Procedure For Obtaining an Arterial Sample (Radius) • Wash hands, don protective equipment, explain the procedure to the patient • Position the patient correctly

  46. Procedure For Obtaining an Arterial Sample (Radius) • Perform an Allen test and confirm collateral circulation • Cleanse the site with 70% isopropyl alcohol or other antiseptic

  47. Procedure For Obtaining an Arterial Sample (Radius) • Inject local anesthetic, if hospital protocol • Heparinize the syringe, if not already heparinized

  48. Procedure For Obtaining an Arterial Sample (Radius) • Palpate and secure the artery • Insert the needle, bevel up, at a 45° angle through the skin until blood pulsates into the syringe

  49. Procedure For Obtaining an Arterial Sample (Radius) • Withdraw the needle when sufficient sample is obtained • Apply firm pressure to the puncture site using a gauze pad

  50. Procedure For Obtaining an Arterial Sample (Radius) • Maintain pressure for a minimum of five minutes, longer if patient is on anticoagulant therapy • Expel any air bubbles from the syringe