This document provides an overview of arterial blood gas analysis and interpretation. It discusses the key components of an ABG report including pH, PaCO2, PaO2, HCO3 and oxygen saturation. It outlines a 4 step method for ABG interpretation including identifying the primary disturbance, determining if it is respiratory or metabolic, and assessing for compensation. Several case examples are provided to demonstrate application of this analytical approach.

1. Arterial Blood Gas Analysis …..1 Dr Satish Deopujari Pediatrician Hon. Prof. ( Pediatrics) JNMC Chairman National Intensive care chapter Indian academy of pediatrics [email_address] Visit us at…. http://rdsoxy.org No click

2. The Goal : To provide Bedside approach to ABG analysis No click

3. H ION CONC. N.MOLS / L. pH 20 7.70 30 7.52 40 7.40 50 7.30 60 7.22 H ION OH ION 0 14 pH stand for "power of hydrogen" H + = 80 - last two digits of pH Don’t click wait …..till Last message …….. “H = 80-last two digits of pH”

4. Bicarbonate: No click Henderson - Hasselbach equation: pH = pK + Log HCO3 Dissolved CO2

5. Standard Bicarbonate: Plasma HCO 3 after equilibration to a PaCO 2 of 40 mm Hg : Reflects non-respiratory acid base change : No quantification of the extent of the buffer base abnormality Base Excess:  base to normalise HCO 3 (to 24) with PaCO 2 at 40 mm Hg (Sigaard-Andersen) : Reflects metabolic part of acid base  : No info. over that derived from pH, pCO 2 and HCO 3 : Misinterpreted in chronic or mixed disorders No click

6. Oxygenation Indices: O 2 Content of blood: Hb. x O 2 Sat + Dissolved O 2 (Don’t forget hemoglobin) Oxygen Saturation: reported as ABG report ( Derived from oxygen dis. curve not a measured value ) Alveolar / arterial gradient: ( Useful … to classify respiratory failure ) No click

7. 0 10 20 30 40 50 60 70 80 90 100 PaO 2 20 40 60 80 100 Rt. Shift Normal arterio/venous difference Shift of the curve ……changes saturation for a given PaO 2 Normal No click Oxygen delivered to tissues with normally placed curve Delivered oxygen with Rt. Shift curve

8. Alveolar-arterial Difference Inspired O 2 = 21 % p i O 2 = (760-45) x . 21 = 150 mmHg O 2 CO 2 p alv O 2 = p i O 2 – pCO 2 / RQ = 150 – 40 / 0.8 = 150 – 50 = 100 mm Hg PaO 2 = 90 mmHg p alv O 2 – p art O 2 = 10 mmHg One click and wait

9. Alveolar- arterial Difference O 2 CO 2 Oxygenation Failure WIDE GAP p i O 2 = 150 pCO 2 = 40 p alv O 2 = 150 – 40/.8 =150-50 =100 PaO 2 = 45  = 100 - 45 = 55 Ventilation Failure NORMAL GAP p i O 2 = 150 pCO 2 = 80 p alv O 2 = 150-80/.8 =150-100 = 50 PaO 2 = 45  = 50 - 45 = 5 PAO 2 (partial pres. of O 2 . in the alveolus.) = 150 - ( PaCO 2 / .8 ) 760 – 45 = 715 : 21 % of 715 = 150 No click

10. 20 × 5 = 100 Expected PaO 2 = FiO 2 × 5 = PaO 2 Normal situation No click

11. The Blood Gas Report: normals… pH 7.40 + 0.05 PaCO 2 40 + 5 mm Hg PaO 2 80 - 100 mm Hg HCO 3 24 + 4 mmol/L O2 Sat >95 Always mention and see FIO2 The essentials HCO3 No click

12. 5 The Steps for Successful Blood Gas Analysis No click

13. Step 2 Who is responsible for this change in pH ( culprit )? CO 2 will change pH in opposite direction Bicarb. will change pH in same direction Acidemia: With HCO 3 < 20 mmol/L = metabolic With PCO 2 >45 mm hg = respiratory Alkalemia: With HCO 3 >28 mmol/L = metabolic With PCO 2 <35 mm Hg = respiratory Step 1 Look at the pH Is the patient acidemic pH < 7.35 or alkalemic pH > 7.45

14. Step 3 If there is a primary respiratory disturbance, is it acute ? .08 change in pH ( Acute ) .03 change in pH ( Chronic ) 10 mm Change PaCO 2 = No click

15. Step 4 If the disturbance is metabolic is the respiratory compensation appropriate? For metabolic acidosis: Expected PaCO 2 = (1.5 x [HCO 3 ]) + 8 ) + 2 or simply… expected PaCO 2 = last two digits of pH For metabolic alkalosis: Expected PaCO 2 = 6 mm for 10 mEq. rise in Bicarb. Suspect if ............. actual PaCO 2 is more than expected : additional … respiratory acidosis actual PaCO 2 is less than expected : additional … respiratory alkalosis No click

16. Step 4 cont. If there is metabolic acidosis, is there a wide anion gap ? Na - (Cl - + HCO 3 - ) = Anion Gap usually <12 If >12, Anion Gap Acidosis : M ethanol U remia D iabetic Ketoacidosis P araldehyde I nfection (lactic acid) E thylene Glycol S alicylate Common pediatric causes Lactic acidosis 2) Metabolic disorders 3) Renal failure No click

17. th step Clinical correlation 5 No click

18. HCO3 META. pH PaCO 2 pH RESP. Same direction Opposite direction Same direction No click

19. Remember the format pH PaCO 2 PaO 2 No click

20. Primary lesion Primary lesion Compensation pH Bicarbonate PaCO 2 METABOLIC ACIDOSIS HYPER VENTILATION BICARB CHANGES pH in same direction Low Alkali Three clicks

21. Primary lesion Compensation pH Bicarbonate PaCO 2 METABOLIC ALKALOSIS HYPO VENTILATION BICARB CHANGES pH in same direction High Alkali Three clicks

22. Primary lesion compensation pH PaCO 2 BICARB Respiratory acidosis CO 2 CHANGES pH in opposite direction High CO 2 Three clicks Wait for red circle

23. pH CO2+H20=H2CO3 = H + HCO3 + HCO3 HCO3 RESP. ACIDOSIS ALKALOSIS META. PCO2 HIGH H HIGH HCO3 + four clicks ACUTE RISE : PCO2 10 : pH .08 CHRONIC RISE : PCO2 10 : pH .03

24. Primary lesion Primary lesion compensation pH PaCO 2 BICARB Respiratory alkalosis PaCO 2 CHANGES pH in opposite direction Low PaCO 2 Three clicks Wait for red circle

25. CO2 + H20 = H2CO3 = H + HCO3 + pH SERUM HCO3 LOW H IONS …LOW HCO3 RESP. ALK. ACID. META. CO2 + Bicarbonate Six clicks

26. PaCO 2 of 10 pH Acute change .08 Chronic change .03 No click

27. INTERPRETATION OF A.B.G. FOUR STEP METHOD OF DEOSAT LOOK FOR pH WHO IS THE CULPRIT ? IF RESPIRATORY ACUTE / CHRONIC ? IF METABOLIC / COMP. / ANION GAP CLINICAL CORRELATION No click

28. compensation considered complete when the pH returns to normal range Clinical blood gases by Malley No click

29. COMPENSION LIMITS METABLIC ACIDOSIS PaCO2 = Up to 10 ? METABOLIC ALKALOSIS PaCO2 = Maximum 6O RESPIRATORY ACIDOSIS BICARB = Maximum 40 RESPIRATORY ALKALOSIS BICARB = Up to 10 No click

30. Blood Gas Report Measured 37.0 o C pH 7.523 PaCO 2 30.1 mm Hg PaO 2 105.3 mm Hg Calculated Data HCO 3 act 22 mmol / L O 2 Sat 98.3 % PO 2 (A - a) 8 mm Hg  PO 2 (a / A) 0.93 Entered Data FiO 2 21.0 % Case 1 16 year old female with sudden onset of dyspnea. No Cough or Chest Pain Vitals normal but RR 56, anxious. One click for answer Acute respiratory alkalosis And why acute ?

31. Case 2 6 year old male with progressive respiratory distress Muscular dystrophy . Blood Gas Report Measured 37.0 o C pH 7.301 PaCO 2 76.2 mm Hg PaO 2 45.5 mm Hg Calculated Data HCO 3 act 35.1 mmol / L O 2 Sat 78 % PO 2 (A - a) 9.5 mm Hg  PO 2 (a / A) 0.83 Entered Data FiO 2 21 %  CO 2 =76-40=36 Expected  pH for ( Acute ) = .08 for 10 Expected ( Acute ) pH = 7.40 - 0.29=7.11 Chronic resp. acidosis Hypoventilation Chronic respiratory acidosis With hypoxia due to hypoventilation Five clicks pH <7.35 :acidemia Res. Acidemia : High PaCO 2 and low pH Hypoxemia Normal A-a gradient

32. 7.60 20 7.50 30 7.40 40 7.30 50 7.20 60 7.10 70 pH PaCO 2 Acute respiratory change No click Last two digits pH 80 – PaCO 2

33. Case 3 8-year-old male asthmatic; 3 days of cough, dyspnea and orthopnea not responding to usual bronchodilators. O/E: Respiratory distress; suprasternal and intercostal retraction; tired looking; on 4 L NC. p i O 2 = 715x.3=214.5 / p alv O 2 = 214-49/.8=153 Wide A / a gradient  CO 2 = 49 - 40 = 9 Expected  pH ( Acute ) = 9/10 x 0.08 = 0.072 Expected pH ( Acute ) = 7.40 - 0.072 = 7.328 Acute resp. acidosis 8-year-old male asthmatic with resp. distress Six clicks Blood Gas Report Measured 37.0 o C pH 7. 24 PaCO 2 49.1 mm Hg PaO 2 66.3 mm Hg Calculated Data HCO 3 act 18.0 mmol / L O2 Sat 92 % PO 2 (A - a) mm Hg  PO 2 (a / A) Entered Data FiO 2 30 % 153-66= 87 pH <7.35 ; acidemia PaCO 2 >45; respiratory acidemia Hypoxia WITH INCREASE IN CO2 BICARB MUST RISE ? Bicarbonate is low……… Metabolic acidosis + respiratory acidosis 30 × 5 = 150

34. Case 4 8 year old diabetic with respi. distress fatigue and loss of appetite. Blood Gas Report Measured 37.0 o C pH 7.23 PaCO2 23 mm Hg PaO2 110.5 mm Hg Calculated Data HCO 3 act 14 mmol / L O2 Sat % PO2 (A - a) mm Hg  PO2 (a / A) Entered Data FiO2 21.0 % If Na = 130, Cl = 90 Anion Gap = 130 - (90 + 14) = 130 – 104 = 26 Three clicks pH <7.35 ; acidemia HCO3 <22; metabolic acidemia Last two digits of pH Correspond with co2

35. Blood Gas Report Measured 37.0 o C pH 7.46 PaCO2 28.1 mm Hg PaO2 55.3 mm Hg Calculated Data HCO 3 act 19.2 mmol / L O2 Sat % PO2 (A - a) mm Hg  PO2 (a / A) Entered Data FiO2 24.0 % Case 5 : 10 year old child with encephalitis BICARBINATURIA Four clicks pH almost within normal range Mild alkalosis PaCO 2 is low , respiratory low by around 10 ( Acute ) by .08 (Chronic ) by .03 Bicarb looks low ? Is it expected ?

36. These findings are most consistent with…. a) Metabolic acidosis with compensatory Hypocapnia. b) Primary metabolic acidosis with respiratory alkalosis. c) Acute respiratory alkalosis fully compensated. d) Chronic respiratory alkalosis fully compensated. pH 7.39 PCO 2 l5mmHg HCO 3 8mmol/L PaO 2 90 mmHg For metabolic acidosis: FULL COMPENSATION Expected PaCO 2 = (1.5 x [HCO3]) + 8 ) + 2 (Winter’s equation) PCO 2 ……SHOULD BE 20 Case 6…………. One click

37. Adolescent boy with appendicitis , posted for surgery , he is a known case of SLE. His pre-op ABG shows : Room air pH 7.39 pCO 2 l5mmHg paO 2 90 mmHg HCO 3 8mmol/L These findings are most consistent with…. a) Metabolic acidosis with compensatory Hypocapnia. b) Primary metabolic acidosis with respiratory alkalosis. c) Acute respiratory alkalosis fully compensated. d) Chronic respiratory alkalosis fully compensated. What is the probable cause for the above findings ? Are they OK as far as oxygenation is concerned ? Case 7………. No click

38. Patient was hypo volumic , received Normal Saline bolus... Corrected acidosis He was operated ….but post-op became drowsy His ABG…….. FiO 2 ….30% pH 7.38 PaCO 2 38 PaO 2 60 1) Why hypoxemia ? 2) Were the lungs bad to begin with ? ( Pre OP PaO 2 90 mmHg ) 3) Micro atelectesis during surgery ? Anesthetist goofed up the case 4) Pure and simple hypoventilation …..Sedation ? No click

39. Why hypoxemia ? Lungs were bad to begin with ? Micro atelectesis during surgery Pure and simple hypoventilation ? sedation PRE OP ….ABG on room air pH 7.39 PaCO 2 l5mmHg PaO 2 90 mmHg HCO 3 8mmol/L Pre OP .....A/a gradient p alv O 2 = P i O 2 – PaCO 2 / RQ = 150 – 15 / 0.8 = 150 – 18 = 132 mm Hg 132 – 90= 42 WIDE A / a gradient Oxygenation status good …..? One click

40. Apparently the lungs looked good with PaO 2 of 90……. But have a good look at the ABG again With wash out of CO 2 ………. The expected PaO 2 should have been more than 90 . This coupled with correction of acidosis ( normalizing PaCO 2 ) Lowered the PaO 2 …post operatively. Conclusion …….. Lungs were not normal to begin with ( SLE )…….. No click

41. Correlate PaO 2 with FiO 2 But please also correlate with PaCO 2 Learning point No click

42. Respiratory Alkalosis Is it acute ? Case 8,,,,,,,,,,,,,,,,,, pH 7.583 PCO2 19.8 HCO3 18.7 What is the Diagnosis Click for answer

43. THANKS Bicarb. pH CO2