Thursday, September 24, 2009

ABG interpretation









ARTERIAL BLOOD GAS INTERPRETATION

  1. ACIDOSIS & ALKALOSIS ABG INTERPRETATION CRISBERT I. CUALTEROS, M.D.
      • 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-
      • 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
      • 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
    • 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
    • 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
    • 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
    • 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
    •  /  <>
    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
    • 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 <>
    • 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
    • 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  < 3 =" 15">
  56. PRINCIPLES OF HCO 3 THERAPY
    • LACTIC ACIDOSIS
    • Primary effort should be improving O 2 delivery
    • Use NaCO 3 only when HCO 3 <>
    • 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 <>
    • 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
    • METABOLIC ALKALOSIS
    • Vomiting
    • Remote diuretic use
    • Post hypercapnea
    • Chronic diarrhea
    • Cystic fibrosis
    • Acute alkali administration
    • 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?
    • 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.
    • 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
    • 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
    • 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
    • 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
    • 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?
    • 1) aspiration pneumonia
    • 2) alcohol ketoacidosis
    • 3) vomiting
    CASE 5 What are the causes of his acid base disturbance?
    • 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
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