Presentation is loading. Please wait.

Presentation is loading. Please wait.

1 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 4 Arterial Blood Gas Assessments Arterial Blood Gas.

Similar presentations


Presentation on theme: "1 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 4 Arterial Blood Gas Assessments Arterial Blood Gas."— Presentation transcript:

1 1 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 4 Arterial Blood Gas Assessments Arterial Blood Gas Assessments

2 2 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 4-1. Normal Blood Gas Values

3 3 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Box 4-1. Acid-Base Disturbance Classifications

4 4 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. This Chapter Provides the Following Review  The PCO 2 /HCO 3 /pH relationship—an essential cornerstone of ABG interpretations  The six most common acid-base abnormalities seen in the clinical setting  The metabolic acid-base abnormalities  The hazards of oxygen therapy in the patient with chronic ventilatory failure with hypoxemia

5 5 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-1. Nomogram of the PCO 2 /HCO 3 /pH relationship. -

6 6 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-2. Acute ventilatory failure is confirmed when the reported PCO 2, pH, and HCO 3 values all intersect within the red-colored respiratory acidosis bar. For example, when the PCO 2 is 60 mm Hg at a time when the pH is 7.28 and the HCO 3 is 26 mEq/L, acute ventilatory failure is confirmed. -

7 7 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-3. Acute alveolar hyperventilation is confirmed when the reported PCO 2, pH, and HCO 3 values all intersect within the red-colored respiratory alkalosis bar. For example, when the reported PCO 2 is 25 mm Hg at a time when the pH is 7.55 and the HCO 3 is 21 mEq/L, acute alveolar hyperventilation is confirmed.

8 8 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. A Quick Clinical Calculation for Acute PaCO 2 Changes in pH and HCO 3

9 9 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Increases in PaCO 2 (e.g., Acute Hypoventilation)

10 10 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Using the Normal ABG Values as a Baseline—pH 7.40, PaCO 2 40, and HCO 3 24:  For every 10 mm Hg the PaCO 2 increases, the pH will decrease about 0.06 units and the HCO 3 will increase about 1 mEq/L.  Or, for every 20 mm Hg the PaCO 2 increases, the pH will decrease about 0.12 units and the HCO 3 will increase about 2 mEq/L.

11 11 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Using the Normal ABG Values as a Baseline— pH 7.40, PaCO 2 40, and HCO 3 24 (Cont’d)  Thus if the patient’s PaCO 2 suddenly were to increase to, say, 60 mm Hg, the expected pH change would be about 7.28 and the HCO 3 would be about 26 mEq/L.

12 12 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Using the Normal ABG Values as a Baseline— pH 7.40, PaCO 2 40, and HCO 3 24 (Cont’d)  It should be noted, however, that if the patient’s PaO 2 is severely low, lactic acid may also be present.  This results in a combined metabolic and respiratory acidosis.  In such cases the patient’s expected pH and HCO 3 values would both be lower than expected for a particular PaCO 2 level.

13 13 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Decreases in PaCO 2 (e.g., Acute Hyperventilation)

14 14 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Using the Normal ABG Values as a Baseline— pH 7.40, PaCO 2 40, and HCO 3 24  For every 5 mm Hg the PaCO 2 decreases, the pH will increase about 0.06 units and the HCO 3 will decrease about 1 mEq/L.  Or, for every 10 mm Hg the PaCO 2 decreases, the pH will increase about 0.12 units and the HCO 3 will decrease about 2 mEq/L.

15 15 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Using the Normal ABG Values as a Baseline— pH 7.40, PaCO 2 40, and HCO 3 24 (Cont’d)  Thus if the patient’s PaCO 2 suddenly were to decrease to, say, 30 mm Hg, the expected pH change would be about 7.52 and the HCO 3 would be about 22 mEq/L.

16 16 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  Again, it should be noted, however, that if the patient’s PaO 2 is severely low, lactic acid may also be present.  In such cases the patient’s expected pH and HCO 3 values would both be lower than expected for a particular PaCO 2 level. Using the Normal ABG Values as a Baseline— pH 7.40, PaCO 2 40, and HCO 3 24 (Cont’d)

17 17 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 4-2. General Rule of Thumb for the Paco 2 / HCO −3 /pH Relationship

18 18 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. The Six Most Common Acid-Base Abnormalities Seen in the Clinical Setting  Acute alveolar hyperventilation  Acute ventilatory failure  Chronic ventilatory failure with hypoxemia  Acute alveolar hyperventilation superimposed on chronic ventilatory failure  Acute ventilatory failure superimposed on chronic ventilatory failure

19 19 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Alveolar Hyperventilation with Hypoxemia (Acute Respiratory Alkalosis)  pH: increased7.55  Pa CO 2 : decreased29 mm Hg  HCO 3 : decreased22 mEq/L  PaO 2 : decreased61 mm Hg* ABG ChangesExample *When pulmonary pathology is present

20 20 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. The most common cause of acute alveolar hyperventilation is: Hypoxemia

21 21 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-4. Relationship of venous admixture to the stimulation of peripheral chemoreceptors in response to alveolar consolidation.

22 22 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-5. The PaO 2 and PaCO 2 trends during acute alveolar hyperventilation.

23 23 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Box 4-2. Pathophysiologic Mechanisms That Lead to a Reduction in the Paco 2

24 24 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Ventilatory Failure with Hypoxemia (Acute Respiratory Acidosis)  pH: decreased7.21  Pa CO 2 : increased79 mm Hg  HCO 3 : increased (slightly)28 mEq/L  Pa O 2 : decreased57 mm Hg ABG ChangesExample

25 25 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Chronic Ventilatory Failure with Hypoxemia (Compensated Respiratory Acidosis) pH: normal7.38 PaCO 2 : increased66 mm Hg HCO 3 : increased (significantly)35 mEq/L PaO 2 : decreased63 mm Hg ABG ChangesExample

26 26 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Box 4-3. Respiratory Diseases Associated with Chronic Ventilatory Failure during the Advanced Stages

27 27 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-6. The PaO 2 and PaCO 2 trends during acute or chronic ventilatory failure.

28 28 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Ventilatory Changes Superimposed on Chronic Ventilatory Failurez  Acute alveolar hyperventilation superimposed on chronic ventilatory failure  Acute ventilatory failure superimposed on chronic ventilatory failure

29 29 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Alveolar Hyperventilation Superimposed on Chronic Ventilatory Failure (Acute Hyperventilation on Compensated Respiratory Acidosis) pH: increased7.53 PaCO 2 : increased51 mm Hg HCO 3 : increased37 mEq/L PaO 2 : decreased46 mm Hg ABG ChangesExample

30 30 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 4-3. Examples of Acute Changes in Chronic Ventilatory Failure

31 31 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Acute Ventilatory Failure Superimposed on Chronic Ventilatory Failure (Acute Hypoventilation on Compensated Respiratory Acidosis) pH: decreased7.21 PaCO 2 : increased110 mm Hg HCO 3 : increased43 mEq/L PaO 2 : decreased34 mm Hg ABG ChangesExample

32 32 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Table 4-3. Examples of Acute Changes in Chronic Ventilatory Failure

33 33 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Lactic Acidosis Metabolic Acidosis  Because acute hypoxemia is commonly associated with respiratory disorders, acute metabolic acidosis (caused by lactic acid) often further compromises respiratory acid- base status.

34 34 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Lactic Acidosis Metabolic Acidosis (Cont’d) pH: decreased 7.21 PaCO 2 : normal or decreased 35 mm Hg HCO 3 : decreased 19 mEq/L PaO 2 : decreased 34 mm Hg ABG Changes Example

35 35 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-1. Nomogram of the PCO 2 /HCO 3 /pH relationship.

36 36 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Metabolic Acid-Base Abnormalities

37 37 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Metabolic Acidosis pH: decreased7.26 PaCO 2 : normal37 mm Hg HCO 3 : decreased18 mEq/L PaO 2 : normal94 mm Hg (or decreased if lactic(or 52 mm Hg if acidosis is present) lactic acidosis is present) ABG ChangesExample

38 38 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc..  The anion gap is used to determine if a patient’s metabolic acidosis is caused by either: 1. the accumulation of fixed acids (e.g., lactic acids, keto acids, or salicylate intoxication), or 2. an excessive loss of HCO 3 Anion Gap

39 39 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  The law of electroneutrality states that the total number of plasma positively charged ions (cations) must equal the total number of plasma negatively charged ions (anions) in the body fluids.  To calculate the anion gap, the most commonly measured cations are sodium (Na + ) ions. Anion Gap (Cont’d)

40 40 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  The most commonly measured anions are chloride (Cl − ) ions and bicarbonate (HCO 3 ) ions.  The normal plasma concentrations of these cations and anions are as follows: Na + : 140 mEq/L Cl − : 105 mEq/L HCO 3 : 24 mEq/L Anion Gap (Cont’d)

41 41 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  Mathematically, the anion gap is the calculated difference between the Na + ions and the sum of the HCO 3 and Cl − ions: Anion gap = [Na + ] − ([Cl − ] + [HCO 3 ]) Anion gap = [Na + ] − ([Cl − ] + [HCO 3 ]) = 140 − = 140 − = 140 − 129 = 140 − 129 = 11 mEq/L = 11 mEq/L Anion Gap (Cont’d)

42 42 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  The normal range for the anion gap is 9 to 14 mEq/L.  An anion gap greater than 14 mEq/L represents metabolic acidosis. Anion Gap (Cont’d)

43 43 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  An elevated anion gap is frequently caused by the accumulation of fixed acids—for example: Lactic acids Lactic acids Keto acids Keto acids Salicylate intoxication Salicylate intoxication Anion Gap (Cont’d)

44 44 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  This is because the H + ions that are generated by the fixed acids chemically react with—and are buffered by—the plasma HCO 3  This action causes 1. The HCO 3 concentration to decrease and 2. The anion gap to increase Anion Gap (Cont’d)

45 45 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  Clinically, when the patient exhibits both metabolic acidosis and an increased anion gap, the respiratory care practitioner must investigate further to determine the source of the fixed acids.  This needs to be done in order to appropriately treat the patient. Anion Gap (Cont’d)

46 46 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  For example, metabolic acidosis caused by: 1. Lactic acids justifies the need for oxygen therapy—to reverse the accumulation of the lactic acids, or 2. Ketone acids justifies the need for insulin—to reverse the accumulation of the ketone acids. Anion Gap (Cont’d)

47 47 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  It is interesting that metabolic acidosis caused by an excessive loss of HCO 3 does not cause the anion gap to increase.  For example, in renal disease or severe diarrhea Anion Gap (Cont’d)

48 48 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  This is because as the HCO 3 concentration decreases, the Cl − concentration usually increases to maintain electroneutrality.  In short, for each HCO 3 ion that is lost, a Cl − anion takes its place  Law of electroneutrality Anion Gap (Cont’d)

49 49 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  This action maintains a normal anion gap.  Metabolic acidosis caused by a decreased HCO 3 level is commonly called hyperchloremic metabolic acidosis. Anion Gap (Cont’d)

50 50 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  When metabolic acidosis is accompanied by an increased anion gap, the most likely cause of the acidosis is fixed acids.  Lactic acids  Keto acids  Salicylate intoxication Summary

51 51 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.  Or, when metabolic acidosis is seen with a normal anion gap, the most likely cause of the acidosis is an excessive loss of HCO 3  For example, caused by renal disease or severe diarrhea Summary (Cont’d)

52 52 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Metabolic Alkalosis pH: increased7.56 PaCO 2 : normal44 mm Hg HCO 3 : decreased27 mEq/L PaO 2 : normal94 mm Hg ABG ChangesExample

53 53 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Figure 4-1. Nomogram of the PCO 2 /HCO 3 /pH relationship.

54 54 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Box 4-4. Common Causes of Metabolic Acid-Base Abnormalities

55 55 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. The Hazards of Oxygen Therapy in Patients with Chronic Ventilatory Failure with Hypoxemia  High oxygen concentrations may suppress the patient’s so-called hypoxic drive to breathe.


Download ppt "1 Mosby items and derived items © 2011, 2006 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 4 Arterial Blood Gas Assessments Arterial Blood Gas."

Similar presentations


Ads by Google