This document discusses acid-base disorders and interpretation of arterial blood gases (ABGs). It defines acidosis and alkalosis, and describes respiratory and metabolic causes. Simple and mixed acid-base disorders are explained. Compensation by the lungs and kidneys in response to primary disorders is discussed. A stepwise approach to ABG interpretation is provided, including determining the primary disorder, checking for compensation, calculating the anion gap, and identifying specific etiologies. Characteristics of simple acid-base disturbances and combined disorders are summarized.

1. ACIDOSIS & ALKALOSIS ABG INTERPRETATION CRISBERT I. CUALTEROS, M.D.

2. Acidosis – presence of a process which tends to lower pH by virtue of gain of H+ or loss of HCO3 Alkalosis – presence of a process which tends to raise pH by virtue of loss of H+ or addition of HCO3-

3. Respiratory – processes which lead to acidosis or alkalosis through a primary alteration in ventilation and resultant excessive elimination or retention of CO2 Metabolic – processes which lead to acidosis or alkalosis through their effects on the kidneys and the consequent disruption of H+ and HCO3- control

4. Acid Base Balance pH is maintained within a narrow range to preserve normal cell function Buffers –minimize the change in pH resulting from production of acid -> provides immediate protection from acid The primary buffer system is HCO3 - HCO3- + H+  H2CO3  H2O + CO2

5. Simple acid-base disorder – a single primary process of acidosis or alkalosis Mixed acid-base disorder – presence of more than one acid base disorder simultaneously

6. Compensation – the normal response of the respiratory system or kidneys to change in pH induced by a primary acid-base disorder No overcompensation ( except occasionally primary resp. alkalosis) Kidneys slow, lungs fast Lack of compensation (or over) determines a second primary disorder The degree of appropriate compensation is predictable

7. Role of the kidney To retain and regenerate HCO3- thereby regenerating the buffer with the net effect of eliminating the acid H+ secretion HCO3- reabsorption Role of the respiratory system eliminate CO2

8. Characteristics of the simple acid-base disturbances  [HCO3-]  Pco2  Respiratory alkalosis  [HCO3-]  Pco2  Respiratory acidosis  Pco2  [HCO3-]  Metabolic alkalosis  Pco2  [HCO3-]  Metabolic acidosis Compensated response Primary Primary pH Disorder

9. Combined Alkalosis Alk Respiratory Alkalosis Acid Alkalotic Metabolic Alkalosis Alk Acidotic Alkali Metabolic Acidosis Acid Alkalotic Combined respiratory and metabolic Acidosis Acid Respiratory Acidosis Alk Acidotic Acid Interpretation HCO3 PCO 2 pH

10. STEPWISE APPROACH Determine primary disorder Check the compensatory response Calculate the anion gap Identify specific etiologies for the acid-base disorder Prescribe treatment

12. DETERMINE THE PRIMARY DISORDER

13. pH = 7.35 – 7.45 pCO2 = 35 – 45 mmHg lungs (Reference Value = 40) HCO3 = 22 – 26 mmol/L kidneys (Reference value = 24)

14. DETERMINE PRIMARY DISORDER Check the trend of the pH, HCO 3 , pCO 2 The change that produces the pH is the primary disorder pH = 7.25 HCO 3 = 12 pCO 2 = 30 ACIDOSIS ACIDOSIS ALKALOSIS METABOLIC ACIDOSIS

15. DETERMINE PRIMARY DISORDER Check the trend of the pH, HCO 3 , pCO 2 The change that produces the pH is the primary disorder pH = 7.25 HCO 3 = 28 pCO 2 = 60 ACIDOSIS ALKALOSIS ACIDOSIS RESPIRATORY ACIDOSIS

16. DETERMINE PRIMARY DISORDER Check the trend of the pH, HCO 3 , pCO 2 The change that produces the pH is the primary disorder pH = 7.55 HCO 3 = 19 pCO 2 = 20 ALKALOSIS ACIDOSIS ALKALOSIS RESPIRATORY ALKALOSIS

17. DETERMINE PRIMARY DISORDER If the trend is the same, check the percent difference The bigger % difference is the 1 0 disorder pH = 7.25 HCO 3 = 16 pCO 2 = 60 ACIDOSIS ACIDOSIS ACIDOSIS RESPIRATORY ACIDOSIS (16-24)/24 = 0.33 (60-40)/40 = 0.5

18. DETERMINE PRIMARY DISORDER If the trend is the same, check the percent difference The bigger %difference is the 1 0 disorder pH = 7.55 HCO 3 = 38 pCO 2 = 30 ALKALOSIS ALKALOSIS ALKALOSIS METABOLIC ALKALOSIS (38-24)/24 = 0.58 (30-40)/40 = 0.25

19. CHECK THE COMPENSATORY RESPONSE

20. COMPENSATORY RESPONSE HENDERSEN-HASSELBACH EQUATION 24 x pCO 2 H = ---------------- HCO 3 Metabolic or Respiratory Acidosis

21. COMPENSATORY RESPONSE HENDERSEN-HASSELBACH EQUATION 24 x pCO 2 H = ---------------- HCO 3 Metabolic or Respiratory Alkalosis

22. PREDICTION OF COMPENSATORY RESPONSES ON SIMPLE ACID BASE DISORDERS Metabolic Acidosis PaCO2 = (1.5 X HCO3) + 8 ± 2 Metabolic Alkalosis PaCO2 will increase 0.75 mmHg per 1 mmol/L increase in HCO3 (0.7 x HCO3) + 20 ± 1.5 Respiratory Acidosis Acute HCO3 will increase 1 mmol/L per 10 mmHg increase in PaCO2 ( ↓ pH by 0.08/10 mm Hg ↑ PaCO2) Chronic HCO3 will increase 4 mmol/L per 10 mmHg increase in PaCO2 ( ↓ pH by 0.03/10 mm Hg ↑ PaCO2) Respiratory Alkalosis Acute HCO3 will decrease 2 mmol/L per 10 mmHg decrease in PaCO2 Chronic HCO3 will decrease 4 mmol/L per 10 mmHg decrease in PaCO2

23. COMPENSATORY RESPONSE METABOLIC ACIDOSIS PaCO2 = (1.5 X HCO3) + 8 ± 2 HCO 3 =12 PaCO 2 =1.5 X 12 + 8 = 26 ± 2 PaCO 2 = 1.5 X 7 + 8 = 18.5 ± 2 HCO 3 =7

24. COMPENSATORY RESPONSE HCO 3 = 35 pCO 2 =11 X 0.75 = 8.25 = 8.25 + 40 = 48.25 pCO 2 = 16 x 0.75 = 12 = 12 + 40 = 52 HCO 3 = 40 METABOLIC ALKALOSIS PaCO2 will increase 0.75 mmHg per 1 mmol/L increase in HCO3

25. COMPENSATORY RESPONSE pCO 2 = 55 HCO 3 = 55-40/10= 1.5 1.5 + 24 = 25.5 HCO 3 = 80-40/10= 4 4+24 = 28 pCO 2 =80 ACUTE RESPIRATORY ACIDOSIS HCO3 will increase 1 mmol/L per 10 mmHg increase in PaCO2

26. COMPENSATORY RESPONSE pCO 3 = 55 HCO 3 = 55-40/10 x 4 = 1.5 x 4 = 6 6 + 24 = 30 CHRONIC RESPIRATORY ACIDOSIS HCO3 will increase 4 mmol/L per 10 mmHg increase in PaCO2

27. COMPENSATORY RESPONSE HCO 3 = 80-40/10 x 4 = 16 + 24 = 40 pCO 3 = 80 CHRONIC RESPIRATORY ACIDOSIS HCO3 will increase 4 mmol/L per 10 mmHg increase in PaCO2

28. COMPENSATORY RESPONSE RESPIRATORY ALKALOSIS Acute: HCO3 will decrease 2 mmol/L per 10 mmHg decrease in PaCO2 Chronic: HCO3 will decrease 4 mmol/L per 10 mmHg decrease in PaCO2

29. CALCULATE THE ANION GAP

30. ANION GAP Na – (HCO 3 + Cl) = 10-12 mmol/L Na = 135 HCO 3 = 15 Cl = 97 RBS = 100 mg% Anion Gap = 135 – (15 + 97) =135 -112 = 23

31. ANION GAP Na – (HCO 3 + Cl) = 10-12 Na = 135 HCO 3 = 15 Cl = 97 RBS = 500 mg% Corrected Na = Na + RBS mg% -100 x 1.4 100 Anion Gap = 135 + 5.6 – 112 = 28.6

32. CHECK THE DELTA / DELTA

33. DELTA - DELTA If with high AG metabolic acidosis 12 – AG  HCO 3 If normal AG metabolic acidosis 12 – Cl  HCO 3 A high AG always indicates the presence of a HAG metabolic acidosis

34. DELTA - DELTA  /  = 1  /  > 1  /  < 1 Pure Anion gap metabolic acidosis AG Metabolic Acidosis + metabolic alkalosis AG Metabolic Acidosis + non-AG metabolic acidosis

35. CASE 1 56F with vomiting and diarrhea 3 days ago despite intake of loperamide. Her last urine output was 12 hours ago. PE showed BP = 80/60, HR = 110, RR = 28. There is poor skin turgor.

36. CASE 1 serum Na = 130 pH = 7.30 K = 2.5 pCO 2 = 30 Cl = 105 HCO 3 = 15 BUN = 42 pO 2 = 90 crea = 2.0 RBS = 100 BUN / crea = 21 PRE-RENAL AZOTEMIA

37. CASE 1 serum Na = 130 pH = 7.30 ↓ K = 2.5 pCO 2 = 30 ↓ Cl = 105 HCO 3 = 15 ↓ BUN = 42 pO 2 = 90 crea = 2.0 RBS = 100  pH = acidosis,  pCO 2 =alk,  HCO 3 = acidosis Metabolic Acidosis

38. CASE 1 serum Na = 130 pH = 7.30 ↓ K = 2.5 pCO 2 = 30 ↓ Cl = 105 HCO 3 = 15 ↓ BUN = 42 pO 2 = 90 crea = 2.0 RBS = 100 Expected pCO 2 = (15 x 1.5) + 8 ± 2 = 28.5-32.5 Simple Metabolic Acidosis

39. CASE 1 serum Na = 130 pH = 7.30 K = 2.5 pCO 2 = 30 Cl = 105 HCO 3 = 15 BUN = 42 pO 2 = 90 crea = 2.0 RBS = 100 Anion Gap = Na – (HCO3+Cl) 130 – (15+105) = 10 NAG Metabolic Acidosis

40. NORMAL ANION GAP METABOLIC ACIDOSIS Diarrhea Renal Tubular Acidosis Interstitial nephritis External pancreatic or small-bowel drainage Urinary tract obstruction

41. CASE 1 serum Na = 130 pH = 7.30 K = 2.5 pCO 2 = 30 Cl = 105 HCO 3 = 15 BUN = 15 pO 2 = 90 crea = 177 RBS = 100  /  = (105-100)/(24-15) = 0.56 NAGMA + HAGMA

42. CASE 1 56F with vomiting and diarrhea 3 days ago despite intake of loperamide. Her last urine output was 12 hours ago. PE showed BP = 80/60, HR = 110, RR = 28. There is poor skin turgor. pH 7.30, HCO 3 =15, pCO 2 =30, Na=130 K=2.5 How will you correct the acid base disorder?

43. CASE 1 1) Hydrate 2) Hydrate + IV NaHCO 3 3) Hydrate + oral NaHCO 3 4) Hydrate + correct hypokalemia How will you correct the acid base disorder?

44. INDICATIONS FOR HCO 3 THERAPY pH < 7.2 and HCO 3 < 5 – 10 mmHg When there is inadequate ventilatory compensation Elderly on beta blockers in severe acidosis with compromised cardiac function Concurrent severe AG and NAGMA Severe acidosis with renal failure or intoxication

45. COMPLICATIONS OF HCO 3 THERAPY Volume overload Hypernatremia Hyperosmolarity Hypokalemia Intracellular acidosis Causes overshoot alkalosis Stimulates organic acid production  tissue O 2 delivery NaHCO 3 50 ml = 45 mEq Na NaHCO 3 gr X tab = 7 mEq Na

46. POTASSIUM CORRECTION K deficit = { (4.0 – K) X 350 } / 3 + 60 1 kalium durule = 10 mEq K 1 medium sized banana = 10 mEq K K deficit = { (4.0 – 2.5) X 350 } / 3 + 60 = 235 mEq K to replace in 1 day

47. CASE 2 30M with epilepsy has a grand mal seizure. Labs showed: pH = 7.14 ↓ Na = 140 pCO 2 = 45 K = 4 HCO 3 = 17 ↓ Cl = 98 Metabolic Acidosis

48. CASE 2 30M with epilepsy has a grand mal seizure. Labs showed: pH = 7.14 Na = 140 pCO 2 = 45 K = 4 HCO 3 = 17 Cl = 98 Expected pCO 2 = (17 X 1.5) + 8 ± 2 = 33.5-37.5 Metabolic & Respiratory Acidosis

49. CASE 2 30M with epilepsy has a grand mal seizure. Labs showed: pH = 7.14 Na = 140 pCO 2 = 45 K = 4 HCO 3 = 17 Cl = 98 Anion Gap = Na – (HCO3+Cl) 140 – (17+98) = 25 HAGMA + RAc

50. HIGH ANION GAP METABOLIC ACIDOSIS Ketoacidosis – DM, alcohol, starvation INH, methanol, lactic acid Renal failure Ethylene Glycol

51. CASE 2 30M with epilepsy has a grand mal seizure. Labs showed: pH = 7.14 Na = 140 pCO 2 = 45 K = 4 HCO 3 = 17 Cl = 98 HAGMA + MAlk + RAc  /  = (25-12)/(24-17) = 1.9

52. CASE 2 30M with epilepsy has a grand mal seizure. Labs showed: pH = 7.14 Na = 140 pCO 2 = 45 K = 4 HCO 3 = 17 Cl = 98 How will you correct the acid base disorder?

53. CASE 2 1) IV NaHCO 3 using HCO 3 deficit 2) oral NaHCO 3 at 1 mEq/kg/day 3) intubate 4) no treatment How will you correct the acid base disorder?

54. CASE 2 HCO 3 DEFICIT = (D – A) x 0.5 x kg BW How will you correct the acid base disorder? HCO 3 deficit = (18 – 17) x 0.5 x 60 = 30 Give ½ as bolus and the other ½ as drip in 24 hrs

55. CASE 2 HCO 3 DEFICIT = (D – A) x 0.5 x kg BW How will you correct the acid base disorder? HCO 3 deficit = (18 – 17) x 0.5 x 60 = 30 As HCO 3  < 5-10, the V d increases; hence use 0.7 to 0.1 dHCO 3 = 15 - 18 Maintenance 1 mEq/day Give ½ as bolus and the other ½ as drip in 24 hrs

56. PRINCIPLES OF HCO 3 THERAPY LACTIC ACIDOSIS Primary effort should be improving O 2 delivery Use NaCO 3 only when HCO 3 < 5 mmol/L In states of  CO, raising the CO will have more impact on the pH In cases of low alveolar ventilation,  ventilation to lower the tissue pCO 2

57. PRINCIPLES OF HCO 3 THERAPY KETOACIDOSIS Rate of H + production is slow; NaHCO 3 tx may just provoke severe hypokalemia Should be given if… 1) severe hyperkalemia despite insulin 2) HCO 3 < 5 mmol/L 3) worsening acidemia inspite of insulin

58. CASE 3 19F, fashion model, is surprised to find her K=2.7 mmol/L because she was normokalemic 6 months ago. She admits to being on a diet of fruit and vegetables but denies vomiting and the use of diuretics or laxatives. She is asymptomatic. BP = 90/55 with subtle signs of volume contraction.

59. CASE 3 serum Na 138 63 K 2.7 34 Cl 96 0 HCO 3 30 0 pH 7.45 5.6 pCO 2 45 Metabolic Alkalosis Plasma Urine  pH = alk,  pCO 2 =acidosis  HCO 3 = alkalosis

60. CASE 3 Expected PCO 2 = 6 x 0.75 = 4.5+40 = 44.5 CompensatedMetabolic Alkalosis serum Na 138 63 K 2.7 34 Cl 96 0 HCO 3 30 0 pH 7.45 5.6 pCO 2 45 Plasma Urine PaCO2 will increase 0.75 mmHg per 1 mmol/L increase in HCO3 from 24

61. CASE 3 Anion Gap = Na – (HCO3+Cl) 138 – (30+96) = 12 NAG Plasma Urine serum Na 138 63 K 2.7 34 Cl 96 0 HCO 3 30 0 pH 7.45 5.6 pCO 2 45

62. CASE 3 Plasma Urine serum Na 138 63 K 2.7 34 Cl 96 0 HCO 3 30 0 pH 7.45 5.6 pCO 2 45 What is the cause of the acid base disorder?

63. CASE 3 What is the cause of the acid base disorder? 1) diuretic intake 2) surreptitious vomiting 3) Bartter’s syndrome 4) Adrenal tumor 5) nonreabsorbable anion

64. CASE 3 How should her acid-base disorder be managed? 1) correct hypokalemia 2) hydrate with NSS 3) administer acidyfing agent 4) give carbonic anhydrase inhibitor

65. METABOLIC ALKALOSIS Vomiting Remote diuretic use Post hypercapnea Chronic diarrhea Cystic fibrosis Acute alkali administration

66. METABOLIC ALKALOSIS Bartter’s syndrome Severe potassium depletion Current diuretic use Hypercalcemia Hyperaldosteronism Cushing’s syndrome Gastric aspiration

67. MANAGEMENT OF METABOLIC ALKALOSIS Chloride repletion Potassium repletion Tx hypermineralocorticoidism Dialysis Carbonic anhydrase inhibitors Acidyfing agents  HCl, NH 4 Cl

68. INDICATIONS OF HCl pH > 7.55 and HCO 3 > 35 with contraindications for NaCl or KCl use Immediate correction of metabolic alkalosis in the presence of hepatic encephalopathy, cardiac arrhythmias, digitalis intoxication When initial response to NaCl, KCl, or acetalozamide is too slow or too little

69. USE OF HCl HCL requirement = (A – D) x 0.5 x kg BW 0.1 – 0.2 N HCl solution = 100 – 200 mEq Do not exceed 0.2 mEq/kg/hour of HCl HCO 3 = 70 wt = 60 kg HCl = 1,380 mEq

70. CASE 4 73M with long standing COPD (pCO 2 stable at 52-58 mmHg), cor pulmonale, and peripheral edema had been taking furosemide for 6 months. Five days ago, he had anorexia, malaise, and productive cough. He continued his medications until he developed nausea. Later he was found disoriented and somnolent

71. CASE 4 PE: BP 110/70, HR 110, RR 24, T=40 respiratory distress prolonged expiratory phase postural drop in BP drowsy, disoriented scattered rhonchi and rales BLFs distant heart sounds trace pitting edema

72. CASE 4 admission after 48 hrs  pH = acidosis  pCO 2 =acidosis,  HCO 3 = alk Respiratory Acidosis serum Na 136 139 K 3.2 3.9 Cl 78 86 HCO 3 40 38 pH 7.33 7.42 pCO 2 78 61 pO 2 43 56

74. CASE 4 serum Na 136 139 K 3.2 3.9 Cl 78 86 HCO 3 40 38 pH 7.33 7.42 pCO 2 78 61 pO 2 43 56 admission after 48 hrs Expected HCO 3 = 78-40/10 = 3.8 + 24 = 27.8 Respiratory Acidosis & M. Alkalosis

75. CASE 4 serum Na 136 139 K 3.2 3.9 Cl 78 86 HCO 3 40 38 pH 7.33 7.42 pCO 2 78 61 pO 2 43 56 How should this patient be managed? admission after 48 hrs

76. CASE 4 1) intubation and mechanical ventilation 2) low flow oxygenation by nasal prong 3) oxygen by face mask 4) sodium bicarbonate infusion with KCl How should this patient be managed?

77. RESPIRATORY ACIDOSIS CHRONIC: COPD, intracranial tumors ACUTE: pneumonia, head trauma, general anesthetics, sedatives

78. MANAGEMENT OF RESPIRATORY ACIDOSIS Correct underlying cause for hypoventilation  effective alveolar ventilation  intubate, mechanically ventilate Antagonize sedative drugs Stimulate respiration (e.g. progesterone) Correct metabolic alkalosis

79. CASE 5 42M, alcoholic, brought to the ER intoxicated. He was found at Rizal park in a pool of vomitus. PE showed unkempt and incoherent patient with a markedly contracted ECF volume. T=39 0 C with crackles on the RULF.

80. serum Na = 130 pH = 7.53 K = 2.9 pCO2 = 25 Cl = 80 HCO3 = 20 BUN = 34 pO2 = 60 crea = 1.4 alb = 38 RBS = 15 mmol/L CASE 5 PRE-RENAL BUN/Crea = 24

81. serum Na = 130 pH = 7.53 ↑ K = 2.9 pCO2 = 25 ↓ Cl = 80 HCO3 = 20 ↓ BUN = 34 pO2 = 60 crea = 1.4 alb = 38 RBS = 120 mmol/L CASE 5 Respiratory Alkalosis

82. serum Na = 130 pH = 7.53 K = 2.9 pCO2 = 25 Cl = 80 HCO3 = 20 BUN = 12 pO2 = 60 crea = 120 alb = 38 RBS = 120 mmol/L CASE 5 Compensated Respiratory Alkalosis HCO 3 = 40-25/10 x 2= 3 24 - 3 = 21 Acute respiratory alkalosis: HCO3 will decrease 2 mmol/L per 10 mmHg decrease in PaCO2

83. serum Na = 130 pH = 7.53 K = 2.9 pCO2 = 25 Cl = 80 HCO3 = 20 BUN = 12 pO2 = 60 crea = 120 alb = 38 RBS = 15 mmol/L CASE 5 HAGMA + RAlk Anion Gap = 130 – (80 + 20) = 30

84. serum Na = 130 pH = 7.53 K = 2.9 pCO2 = 25 Cl = 80 HCO3 = 20 BUN = 12 pO2 = 60 crea = 120 alb = 38 RBS = 15 mmol/L CASE 5 What are the causes of his acid base disturbance?

85. 1) aspiration pneumonia 2) alcohol ketoacidosis 3) vomiting CASE 5 What are the causes of his acid base disturbance?

86. RESPIRATORY ALKALOSIS Hyperventilation, Pregnancy, Liver failure, Methylxanthines

87. MANAGEMENT OF RESPIRATORY ALKALOSIS Correct underlying cause of hyperventilation Rebreathe carbon dioxide Mechanical control of ventilation  increase dead space  decrease back up rate  decrease tidal volume  paralyze respiratory muscles

88. QUESTIONS?

89. Thank You