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Arterial Blood Gas Practice Questions – Answers 1. 7.27/58/60 on 5L, HCO3- 26, anion gap is 10, albumin is 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2 = Acid (CO2>40) HCO3- = Base (HCO3- >24) Step 3: Primary disturbance = Respiratory Acidosis Step 4: If respiratory disturbance is it acute or chronic? ACUTE i. CO2 has increased by 18 ii. If chronic the pH will decrease 0.05 (0.003 x 18 = 0.054) pH would be 7.35 iii. If acute the pH will decrease 0.14 (0.008 x 18 = 0.144) pH would be 7.26. Step 5: No anion gap metabolic acidosis is present; and no adjustment needs to be made for albumin. Step 6b (1) (a): There is an acute respiratory acidosis, is there a metabolic problem too? i. ΔHCO 3 - = 1 mEq/L↑/10mmHg↑pCO 2 1. The HCO 3 - will go up 1mEq/L for every 10mmHg the pCO 2 goes up above 40 ii. The pCO2 is up by 18 so it is expected that the HCO3- will go up by 1.8. Expected HCO3- is 25.8, compared to the actual HCO3- of 26, so there is no additional metabolic disturbance. ACUTE RESPIRATORY ACIDOSIS (secondary to pneumonia) 2. 7.54/24/99 on room air, HCO3- 20, anion gap is 10, albumin is 4.0. Step 2: pH = Alkalemia (pH > 7.4) CO2 = Base (CO2<40) HCO3- = Acid (HCO3- <24) Step 3: Primary disturbance = Respiratory Alkalosis Step 4: If respiratory disturbance is it acute or chronic? ACUTE i. CO2 has decreased by 16. ii. If chronic the pH will increase 0.05 (0.003 x 16 = 0.048) pH would be 7.45 iii. If acute the pH will increase 0.13 (0.008 x 16 = 0.128) pH would be 7.53 Step 5: No anion gap metabolic acidosis is present; and no adjustment needs to be made for albumin. Step 6b (2)(a): There is an acute respiratory alkalosis, is there a metabolic problem too? i. ΔHCO 3 - = 2 mEq/L↓/10mmHg↓pCO 2 1. HCO 3 - will go down 2 mEq/L for every 10mmHg the pCO 2 goes down below 40 ii. The pCO2 is down by 16 so it is expected that the HCO3- will go down by 3.2. Expected HCO3- is 20.8, compared to the actual HCO3- of 20, so there is no additional metabolic disturbance. ACUTE RESPIRATORY ALKALOSIS (secondary to hyperventilation from anxiety) 3. 7.58/55/80 on room air, HCO3- 46, anion gap is 10, albumin is 4.0. Step 2: pH= Alkalemia (pH > 7.4) CO2 = Acid (CO2>40) HCO3-= Base (HCO3- >24) Step 3: Primary disturbance = Metabolic Alkalosis 1 Arterial Blood Gas Practice Questions – Answers Step 4: Not applicable Step 5: No anion gap is present; and no adjustment needs to be made for albumin. Metabolic Alkalosis Step 6a(2): There is a metabolic alkalosis, is there a respiratory problem also? i. ∆ pCO2=0.7 x ∆ HCO31. The CO2 will increase for every 0.7 the HCO3- increases. ii. The HCO3- is up by 22. CO2 will increase by 0.7x22 = 15.4. Expected CO2 is 55.4, compared to the actual CO2 of 55, therefore there is no additional respiratory disturbance. METABOLIC ALKALOSIS (secondary to vomiting) 4. 7.46/20/80 on room air, HCO3- 16, anion gap = 10, albumin = 4.0 Step 2: pH = Alkalemia (pH > 7.4) CO2 = Base (CO2<40) HCO3-= Acid (HCO3- <24) Step 3: Primary disturbance = Respiratory Alkalosis Step 4: If respiratory disturbance is it acute or chronic? Chronic i. CO2 has decreased by 20. ii. If chronic the pH will increase 0.06 (0.003 x 20 = 0.06) pH would be 7.46. iii. If acute the pH will increase 0.16 (0.008 x 20 = 0.16) pH would be 7.56. Step 5: No anion gap is present; and no adjustment needs to be made for albumin. Step 6b (2)(b): There is a chronic respiratory alkalosis, is there a metabolic problem also? i. Chronic: ΔHCO 3 - = 4 mEq/L↓/10mmHg↓pCO 2 1. HCO 3 - will go down 4 mEq/L for every 10mmHg the pCO 2 goes below 40. ii. The pCO2 is down by 20 so it is expected that the HCO3- will go down by 8. Expected HCO3- is 16, therefore there is no additional metabolic disorder. CHRONIC RESPIRATORY ALKALOSIS (secondary to chronic liver disease - cirrhosis) 5. 7.28/27/90 on room air, HCO3- 13, anion gap = 10, albumin = 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2 = Base (CO2<40) HCO3-= Acid (HCO3- <24) Step 3: Primary disturbance = Metabolic Acidosis Step 4: Not Applicable Step 5: No anion gap is present; and no adjustment needs to be made for albumin. Non-Anion Gap Metabolic Acidosis Step 6a1: There is a metabolic acidosis, is there a respiratory disturbance as well? i. ∆ pCO2=1.2 x ∆ HCO31. the CO2will decrease for every 1.2 the HCO3- decreases 2 Arterial Blood Gas Practice Questions – Answers ii. The HCO3- decreased by 11 so the CO2 should go down by 13.2. The expected CO2 is 26.8. The actual CO2 is 27 so there is no additional respiratory disturbance. Non-Anion Gap Metabolic Acidosis (secondary to diarrhea) 6. 7.35/52/50 on room air, HCO3- 27, anion gap = 10, albumin = 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2= (CO2>40) HCO3-= Base (HCO3- >24) Step 3: Primary disturbance = Respiratory Acidosis Step 4: If respiratory disturbance is it acute or chronic? Chronic i. CO2 has increased by 12 ii. If chronic the pH will decrease 0.04 (0.003 x 12 = 0.036) pH would be 7.36 iii. If acute the pH will decrease 0.10 (0.008 x 12 = 0.096) pH would be 7.3 Step 5: No anion gap metabolic acidosis is present; and no adjustment needs to be made for albumin. Step 6b (1) (b): There is a chronic respiratory acidosis, is there a metabolic problem too? i. ΔHCO 3 - = 3 mEq/L↑/10mmHg↑pCO 2 1. The HCO 3 - will go up 3mEq/L for every 10mmHg the pCO 2 goes up above 40 ii. The pCO2 is up by 12 3 x 1.2 = 3.6. So it is expected that the HCO3- will go up by 3.6. Expected HCO3- is 27.6, compared to the actual HCO3- of 27, so there is no additional metabolic disturbance. Chronic Respiratory Acidosis (secondary to pulmonary fibrosis) 7. 7.43/30/95 on room air, HCO3- 20, anion gap = 10, albumin = 4.0 Step 2: pH = Alkalemia (pH > 7.4) CO2= Base (CO2<40) HCO3-= Acid (HCO3- <24) Step 3: Primary Disturbance = Respiratory Alkalosis Step 4: If respiratory disturbance is it acute or chronic? Chronic i. CO2 has decreased by 10. ii. If chronic the pH will increase 0.03 (0.003 x 10 = 0.03) pH would be 7.43. iii. If acute the pH will increase 0.08 (0.008 x 10 = 0.08) pH would be 7.48. Step 5: No anion gap is present; and no adjustment needs to be made for albumin. Step 6b (2)(b): There is a respiratory alkalosis, is there a metabolic problem also? i. Chronic: ΔHCO 3 - = 4 mEq/L↓/10mmHg↓pCO 2 1. HCO 3 - will go down 4 mEq/L for every 10mmHg the pCO 2 goes below 40. 3 Arterial Blood Gas Practice Questions – Answers ii. The pCO2 is down by 10 so it is expected that the HCO3- will go down by 4. Expected HCO3- is 20 for a chronic process. Since the actual HCO 3 - is 20 there is no additional metabolic disturbance. Chronic Respiratory Alkalosis (secondary to pregnancy) 8. 7.48/49/75 on room air, HCO3- 37, anion gap = 10, albumin = 4.0 Step 2: pH= Alkalemia (pH > 7.4) CO2= Acid (CO2>40) HCO3-= Base (HCO3- >24) Step 3: Primary disturbance = Metabolic Alkalosis Step 4: Not applicable Step 5: No anion gap is present; and no adjustment needs to be made for albumin. Metabolic Alkalosis Step 6a(2): There is a metabolic alkalosis, is there a respiratory problem also? i. ∆ pCO2=0.7 x ∆ HCO31. The CO2 will increase for every 0.7 the HCO3- increases. ii. The HCO3- is up by 13. CO2 will increase by 0.7x13 = 9.1. Expected CO2 is 49, compared to the actual CO2 of 49, therefore there is no additional respiratory disturbance. METABOLIC ALKALOSIS (secondary to diuretic use - furosemide) 9. 7.21/64/70 on room air, HCO3- 26, anion gap = 10, albumin = 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2= Acid (CO2>40) HCO3-= Base (HCO3- >24) Step 3: Primary disturbance = Respiratory Acidosis Step 4: If respiratory disturbance is it acute or chronic? Acute i. CO2 has increased by 24 ii. If chronic the pH will decrease 0.072 (0.003 x 24 = 0.072) pH would be 7.33 iii. If acute the pH will decrease 0.19 (0.008 x 24 = 0.19) pH would be 7.21 Step 5: No anion gap metabolic acidosis is present; and no adjustment needs to be made for albumin. Step 6b (1) (a): There is an acute respiratory acidosis, is there a metabolic problem too? i. ΔHCO 3 - = 1 mEq/L↑/10mmHg↑pCO 2 1. The HCO 3 - will go up 1mEq/L for every 10mmHg the pCO 2 goes up above 40 ii. The pCO2 is up by 24 so it is expected that the HCO3- will go up by 2.4. Expected HCO3- is 26.4, compared to the actual HCO3- of 26, so there is no additional metabolic disturbance. ACUTE RESPIRATORY ACIDOSIS (secondary to obstruction – stridor from anaphylaxis secondary to a latex allergy) 4 Arterial Blood Gas Practice Questions – Answers 10. 7.19/35/60 on 7L, HCO3- 9, anion gap = 18, albumin = 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2= Base (CO2<40) HCO3- = Acid (HCO3- <24) Step 3: Primary disturbance: Metabolic Acidosis Step 4: Not applicable Step 5: Anion Gap = 18 + Anion Gap (alb normal so no correction necessary) i. Excess Gap = 18-10 = 8 ii. Potential HCO3- = 8 + 9 = 17 which is <22 Non-AG Met Acidosis Step 6a(1): There is a metabolic acidosis, is there a respiratory problem too? i. ∆ pCO2=1.2 x ∆ HCO31. The CO2will decrease for every 1.2 the HCO3- decreases. ii. CO2 will decrease by 1.2 (∆HCO3-) 1.2 (24-9) 18. 40 – 18= 22 Actual CO2 is higher than expected Respiratory Acidosis ANION GAP METABOLIC ACIDOSIS (secondary to diabetic ketoacidosis) NON-ANION GAP METABOLIC ACIDOSIS (secondary to chronic kidney disease or type IV Renal Tubular Acidosis (RTA 4)secondary to diabetic nephropathy),\ This problem is very complicated. Since the diabetic ketoacidosis is the presenting problem, it is therefore the primary disturbance. Presumably the CKD or RTA is a chronic issue that has been present for some time and is therefore, secondary RESPIRATORY ACIDOSIS (secondary to a strep pneumoniae pneumonia – which probably triggered the DKA) 11. 7.54/80/65 on 2L, HCO3- 54, anion gap = 12, albumin = 4.0 Step 2: pH = Alkalemia (pH > 7.4) CO2= Acid (CO2>40) HCO3- = Base (HCO3- >24) Step 3: Primary disturbance: Metabolic Alkalosis Step 4: Not applicable Step 5: Anion Gap = 12 (alb normal so no correction necessary) Step 6a(2): There is a metabolic alkalosis, is there a respiratory problem too? i. ∆ pCO2=0.7 x ∆ HCO31. The CO2 will increase for every 0.7 the HCO3- increases. ii. CO2 will increase by 0.7 (∆HCO3-) 0.7 (54-24) 21 40 + 21 = 61 Actual CO2 is higher than expected Respiratory Acidosis METABOLIC ALKALOSIS (secondary to contraction alkalosis from the furosemide) RESPIRATORY ACIDOSIS (secondary to COPD) 12. 7.6/30/83 on room air, HCO3- 28, anion gap = 12, albumin = 4.0 Step 2: pH = Alkalemia (pH > 7.4) 5 Arterial Blood Gas Practice Questions – Answers CO2= Base (CO2<40) HCO3- = Base (HCO3- >24) Step 3: Primary Disturbance: Metabolic Alkalosis (this is the primary disturbance based on the history of new onset vomiting). Step 4: Not applicable Step 5: Anion Gap = 12 (alb normal so no correction necessary) Step 6: 6a(2): There is a metabolic alkalosis, is there a respiratory problem too? i. ∆ pCO2=0.7 x ∆ HCO31. The CO2 will increase for every 0.7 the HCO3- increases. ii. CO2 will increase by 0.7 (∆HCO3-) 0.7 (28-24) 2.8 40 + 2.8 = 42.8 Actual CO2 is lower than expected Respiratory Alkalosis METABOLIC ALKALOSIS (secondary to vomiting) RESPIRATORY ALKALOSIS (secondary to pregnancy) 13. 7.25/46/78 on 2L, HCO3- 20, anion gap = 10, albumin = 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2= Acid (CO2>40) HCO3- = Acid (HCO3- <24) Step 3: Primary disturbance: Respiratory Acidosis (this is the primary disturbance based on the history of new dyspnea). Step 4: If respiratory disturbance is it acute or chronic? ACUTE (This makes sense given the history of sudden onset of shortness of breath. Since the pH is lower than expected and the HCO3- is low, there is clearly a secondary metabolic acidosis. See below for clarification.) i. CO2 has increased by 6 ii. If chronic the pH will decrease 0.02 (0.003 x 6 = 0.018) pH would be 7.38 iii. If acute the pH will decrease 0.05 (0.008 x 6 = 0.048) pH would be 7.35. Step 5: Anion Gap = 10 (alb normal so no correction necessary) Step 6b (1) (a): There is an acute respiratory acidosis, is there a metabolic problem too? i. ∆ HCO3- = 1 mEq/L↑/10mmHg↑pCO 2 1. The HCO 3 - will go up 1mEq/L for every 10mmHg the pCO 2 goes up above 40 ii. The pCO2 is up by 6 so it is expected that the HCO3- will go up by 0.6. Expected HCO3- is 24.6, compared to the actual HCO3- of 20. Since the HCO3- is lower than expected Non-Anion Gap Metabolic Acidosis (which we suspected). RESPIRATORY ACIDOSIS (secondary to pulmonary edema) NON-ANION GAP METABOLIC ACIDOSIS (secondary to chronic kidney disease) 14. 7.15/22/75 on room air, HCO3- 9, anion gap = 10, albumin = 2.0 Step 2: pH = Acidemia (pH < 7.4) CO2= Base (CO2<40) HCO3- = Acid (HCO3- <24) 6 Arterial Blood Gas Practice Questions – Answers Step Step Step 3: Primary disturbance: Metabolic Acidosis 4: If respiratory disturbance is it acute or chronic? N/A 5: Anion Gap = 15.5 Anion Gap Metabolic Acidosis i. The anion gap decreases 2.5 for every drop in albumin by 1.0. 4.0 – 2.0 = 2. 2 x 2.5 = 5. Therefore add 5 to the measured anion gap. 10 + 5 = 15. ii. Excess gap = 15 – 10 = 5 iii. Potential HCO3- = 5 + 9 = 14. 14 < 22 NAG Metabolic Acidosis Step 6a(1): There is a metabolic acidosis, is there a respiratory problem too? i. ∆ pCO2=1.2 x ∆ HCO31. The CO2will decrease for every 1.2 the HCO3- decreases. ii. Expected pCO2 = 1.2 x ∆ HCO3- 1.2 (24 -9) 1.2 (15) 18. The expected pCO2 is 22 mmHg. The actual pCO2 is 22, which is expected, so there is no concomitant disorder. ANION GAP METABOLIC ACIDOSIS (secondary to lactic acidosis from ischemic bowel) NON-ANION GAP METABOLIC ACIDOSIS (secondary to a Type IV Renal Tubular Acidosis from her Diabetes Mellitus) 15. 7.38/23/84 on room air, HCO3- 16, anion gap = 18, albumin = 4.0 Step 2: pH = Acidemia (pH < 7.4) CO2= Base (CO2<40) HCO3- = Acid (HCO3- <24) Step 3: Primary disturbance: Metabolic Acidosis Step 4: If respiratory disturbance is it acute or chronic? N/A Step 5: Anion Gap = 18 + Anion Gap (alb normal so no correction necessary) i. Excess Gap = 18-10 = 8 ii. Potential HCO3- = 8 (excess gap) + 16 (serum HCO3-) = 24 No concurrent metabolic disturbance. Step 6a(1): There is a metabolic acidosis, is there a respiratory problem too? i. ∆ pCO2=1.2 x ∆ HCO31. The CO2will decrease for every 1.2 the HCO3- decreases. ii. CO2 will decrease by 1.2 (∆HCO3-) 1.2 (24-16) 9.6. 40 – 9.6= 30.4 Actual CO2 is 23, which is less than expected, so there is also a respiratory alkalosis. ANION GAP METABOLIC ACIDOSIS (secondary aspirin) RESPIRATORY ALKALOSIS (secondary to aspirin) 7