html5-img
1 / 50

ARTERIAL BLOOD GAS

ARTERIAL BLOOD GAS. Section of Pediatric Pulmonology UPCM-Philippine General Hospital. Clinical Application of Blood Gases 5 th Edition. Shapiro, et. Al. ABG measures respiratory function. 1. Oxygenation status. 2. Acid-base balance. Points to Remember.

kassidy-tierney
Télécharger la présentation

ARTERIAL BLOOD GAS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ARTERIAL BLOOD GAS Section of Pediatric Pulmonology UPCM-Philippine General Hospital

  2. Clinical Application of Blood Gases 5th Edition Shapiro, et. Al.

  3. ABG measures respiratoryfunction 1. Oxygenation status 2. Acid-base balance

  4. Points to Remember • Body always tries to maintain normal pH • CO2 – respiratory • HCO3 – metabolic • Lungs compensate rapidly • Kidneys compensate slowly • There is no overcompensation except • in chronic ventilatory failure • Consider the underlying disease

  5. Normal ABG Values • pH 7.35-7.45 • 7.3-7.5 clinically acceptable • PO280-100 • 60-80 for newborn, preterm • < 1 mm Hg for every year > age 60 • PCO2 35-45 • 30-50 clinically acceptable

  6. Oxygenation Status At room air, sea level: PaO2 80-100 normal or acceptable PaO2 < 80 mild hypoxemia PaO2 < 60 moderate hypoxemia PaO2 < 40 severe hypoxemia On oxygen support: PaO2 80-100 corrected hypoxemia PaO2 > N overcorrected hypoxemia PaO2 < N uncorrected hypoxemia

  7. Nomenclature for pH & PaCO2 Outside of normal range pH > 7.45 Alkalemia pH < 7.35 Acidemia PaCO2 > 45 mmHg Respiratory Acidosis (hypercapnia) PaCO2 < 35 mmHg Respiratory Alkalosis (hypocapnia)

  8. FiO2 vs PaO2 The minimally acceptable PaO2 increases by approximately 50 mmHg for every 10% increment of inspired oxygen concentration.

  9. PAO2 = [ FiO2 (PB – PH20) ] – PaCO2 0.8 FiO2 vs PaO2 PaO2 = FiO2 x 5

  10. PAO2 = [ FiO2 (PB – PH20) ] – PaCO2 0.8 What is the expected PAO2if you are breathing normally at room air? = [ .21(760 – 47) ] – 40 / 0.8 = 150 – 50 = 100 PaO2 = FiO2 x 5 = .21 x 5 = 105

  11. PAO2 vs PaO2 In normal individuals the PAO2 is more or less equal to the PaO2 with a normal shunt of about 5 %

  12. P(A-a)O2 = PAO2 - PaO2 FiO2 vs PaO2 Normal: < 30 mm Hg at room air < 50 mm Hg at FiO2 1.0 > 450 mmHg is indicative of severe respiratory failure

  13. PaCO2 – pH RELATIONSHIP • For every 10 mm Hg increase in the PaCO2, the • pH will decrease by 0.05 unit. • For every 10 mm Hg decrease in the PaCO2, the • pH will increase by 0.10 unit.

  14. Respiratory pH (pHR) PaCO2 pHR 80 7.2 60 7.3 40 7.4 30 7.5 20 7.6

  15. For every  in pCO2 of 10 , pH  by 0.05 Respiratory pH (pHR) PaCO2 pHR 80 7.2 60 7.3 40 7.4

  16. Computing for pHR • Normal pCO2 = 40 and normal pH = 7.4 If actual pCO2 > 40: pHR = (40 – Actual pCO2) x 0.05 + 7.4 10

  17. PaCO2 pHR For every in pCO2 of 10 , pH  by 0.1 40 7.4 30 7.5 20 7.6 Respiratory pH (pHR)

  18. pHR = (40 – Actual pCO2) x 0.1 + 7.4 10 Computing for pHR • Normal pCO2 = 40 and normal pH = 7.4 If actual pCO2 > 40: pHR = (40 – Actual pCO2) x 0.05 + 7.4 10 If actual pCO2 < 40:

  19. If actual pCO2 > 40: pHR = (40 – Actual pCO2) x 0.05 + 7.4 10 pHR = (40 – 45) x 0.05 + 7.4 10 What is the expected pH when the pCO2 is 45? = 7.375

  20. If actual pCO2 < 40: pHR = (40 – Actual pCO2) x 0.1 + 7.4 10 pHR = (40 – 35) x 0.1 + 7.4 10 What is the expected pH when the pCO2 is 35? = 7.45

  21. pHR vs pH If pHR compared to actual pH is: < 0.03  purely respiratory > 0.03  compensated

  22. pHR vs pH If actual pH > pHR partially compensated If actual pH < pHR mixed If actual pH = pHR purely respiratory

  23. PaCO2 – Plasma BICARBONATE RELATIONSHIP • An acute PaCO2 increase of 10 mmHg will • increase the plasma bicarbonate by 1 mmol/L • An acute PaCO2 decrease of 10 mmHg will • decrease the plasma bicarbonate by 2 mmol/L The difference between the calculated respiratory plasma bicarbonate value and the actual plasma bicarbonate value provides a rapid and easy assessment of the metabolic component.

  24. Approximate PaCO2-pH Relationship PaCO2 pH HCO3 (mmHg) (mmol/L) 80 7.20 28 60 7.30 26 40 7.40 24 30 7.50 22 20 7.60 20

  25. Minute Ventilation vs PaCO2 MV PaCO2 Range N 40 35-45 2N 30 25-35 4N 20 15-25 The existence of a significant minute MV to PaCO2 disparity should alert the clinician to the possibility that a deadspace-producing pathologic condition may be present.

  26. FiO2-PaO2 RELATIONSHIP Inspired Oxygen to PaO2 Relationship in Normal lungs. FiO2 Inspired O2(%) PaO2 0.30 30 >150 0.40 40 >200 0.50 50 >250 0.80 80 >400 1.00 100 >500

  27. DETERMINING BASE EXCESS/DEFICIT Under normal circumstances, a 10 mmol/L variance from the normal buffer base represents a pH change of approximately 0.15 unit. If we move the pH decimal point two places to the right, we have a 10 to 15 relationship, which can be expressed as a 2/3 realtionship.

  28. BE or BD = (actual pH – pHR) x 2 3 The difference between the measured pH & the predicted respiratory pH is the metabolic pH change. x 100

  29. BE or BD = (actual pH – pHR) x 200 3 Base excess or deficit 0.15 pH change  10 mEq/L buffer change BE: actual pH > pHR BD: actual pH < pHR Normal BE or BD:  2

  30. INTERPRETIVE APPROACH Step 1. Assessment of the PCO2 and pH. a. Classify the CO2 tension. b. Consider the pH and determine classification. c. Consider the base excess/deficit or bicarbonate levels and determine classification. Step 2. Assessment of Arterial Oxygenation a. PaO2 b. SaO2

  31. acidosis acidosis alkalosis alkalosis acidosis alkalosis acidosis acidosis alkalosis alkalosis pH < 7.35 pH 7.35 – 7.4 pH 7.4 – 7.45 pH > 7.45 pCO2 < 35 pCO2 35-45 normal normal pCO2 > 45

  32. part comp comp comp metabolic metabolic respiratory respiratory acidosis acidosis alkalosis alkalosis metabolic metabolic acidosis alkalosis comp comp part comp respiratory respiratory metabolic metabolic acidosis acidosis alkalosis alkalosis pH < 7.35 pH 7.35 – 7.4 pH 7.4 – 7.45 pH > 7.45 pCO2 < 35 pCO2 35-45 normal normal pCO2 > 45

  33. Physiologic Mechanisms of Hypoxemia • Alveolar hypoventilation • Ventilation-perfusion mismatch • Right-to-left shunt • Diffusion limitation • Decreased ambient oxygen tension

  34. CO2  variable N- CVS N Clinical response A- neuro- muscular P A- CVS P Response to O2 good good poor good CXR N- central W- alveolar W- lung N- CVS minimal W Physiologic Mechanisms of Hypoxemia Alveolar hypo-ventilation V/Q mismatch R to L shunt Diffusion limitation W –white N - normal P - poor A - absent

  35. Metabolic acidosis • Renal failure (RTA) • Ketoacidosis (DKA, starvation) • Lactic acidosis

  36. Anion Gap = Na – (Cl + HCO3) Normal: < 15 mEq/L

  37. Anion Gap Increased Normal Loss of buffer Renal HCO3 loss Renal tubular acidosis Acetazolamide Renal dysplasia GI HCO3 loss Diarrhea Cholestyramine Small bowel drainage Dilutional acidosis Hyperalimentation acidosis • Organic acid accumulation • Acute renal failure • Inborn error of metabolism • Lactic acidosis • Late metabolic acidosis • Toxins

  38. Metabolic alkalosis • Hypokalemia • Hypochloremia • Vomiting • Massive steroid administration • NaHCO3 administration

  39. Respiratory acidosis • 1. Hypoventilation • Inadequate respiratory effort • CNS problems • Neuromuscular disease • Mechanical ventilator settings • Upper airway not patent • Decreased lung tissue • Decreased lung compliance

  40. Respiratory acidosis • 2. Abnormal ventilation-perfusion ratio • a. Obstruction of small airways • b. Atelectasis • c. Pneumonia • d. Pulmonary edema • 3. Increased extrapulmonary shunt • Pulmonary vasoconstriction • RDS, severe infection • Pulmonary hypoplasia • Cyanotic heart disease

  41. Respiratory alkalosis • With hypoxemia • a. Acute pulmonary disease • pneumonia and atelectasis, RDS, acute asthma • Acute myocardial disease • MI, pulmonary edema, heart failure, CP bypass • 2. Without hypoxemia • Anxiety, neurosis, psychosis • Pain • CNS disease • Anemia • Carbon monoxide poisoning

  42. Disorders Expected compensation Metabolic pCO2 = 1.5 x HCO3 + 8 +/- 2 Acidosis Metabolic pCO2 increase by 7 mmHg for each Alkalosis 10 mEq/L increase in HCO3

  43. Disorder Expected compensation • Respiratory acidosis • Acute HCO3 increase by 1 for each 10mmHg increase in pCO2 Chronic HCO3 increase by 3.5 for each 10mmHg increase in pCO2 Respiratory Alkalosis Acute HCO3 decrease by 2 for each 10mmHg decrease in pCO2 Chronic HCO3 decrease by 4 for each 10mmHg decrease in pCO2

  44. Exercises Compute for the pHR and interpret the ABG values

  45. pHR = (40 - 32) x 0.1 + 7.4 = 7.48 BE/BD = (7.45 – 7.48) x 200 = -2 10 3 respiratory alkalosis 1. pH 7.45 pO2 65 pCO2 32 FiO2 .21 HCO3 compensated with mild hypoxemia

  46. pHR = (40 - 30) x 0.1 + 7.4 = 7.5 BE/BD = (7.3 – 7.5) x 200 = -13 10 3 metabolic acidosis 2. pH 7.3 pO2 120 pCO2 30 FiO2 .30 HCO3 partially compensated with overcorrected hypoxemia

  47. pHR = (40 - 55) x 0.05 + 7.4 = 7.325 BE/BD = (7.25 – 7.325) x 200 = - 5 10 3 acidosis 3. pH 7.25 pO2 90 pCO2 55 FiO2 .40 N HCO3 uncompensated respiratory with corrected hypoxemia

  48. N N pHR = (40 - 35) x 0.1 + 7.4 = 7.45 BE/BD = (7.42 – 7.45) x 200 = -2 10 3 normal acid-base balance 4. pH 7.42 pO2 200 pCO2 35 FiO2 .35 HCO3 N with overcorrected hypoxemia

  49. Calculating FiO2 requirement using the ABG FiO2 = (desired PaO2) + PaCO2 PaO2 RQ PAO2 Pb – PH20

  50. Thank you for listening

More Related