ABG analysis presentation by Dr. Aman jain

..

1. Arterial Blood Gas Interpretation P resentor - Dr. Aman Jain Moderator - Dr. Shambhavi No of slides - 4 2

2. What is the preanalytical phase? It is the phase which includes all activities that occur prior to the sample’s insertion into the analytical instrument. Sub phase of the preanalytical process in blood gas testing includes: Ordering, Identification, Collection, Transportation, Separation/preparation It has been recognized for years that the phase of testing most prone to errors is the preanalytical phase. Pre-preanalytical Error includes : Inappropriate test ordered, order entry error, patient/specimen misidentification, sample contamination (from indwelling catheter), sample collection mishap ( hemolysis , clotting, insufficient volume), inappropriate collection container, improper storage/handling/transport.

3. ABG – Procedure and Precautions Site- (Ideally) Radial Artery Brachial Artery Femoral Artery Ideally - Pre-heparinised ABG syringes - Syringe should be FLUSHED with 0.5ml of 1:1000 Heparin solution and emptied. DO NOT LEAVE EXCESSIVE HEPARIN IN THE SYRINGE HE P A R IN DIL U TIO N AL EFFECT HCO 3 PC O 2 Only small 0.5ml Heparin for flushing and discard it Syringes must have > 50% blood. Use only 2ml or less syringe .

4. Interpretation of ABG OXYGENATION ACID BASE

5. Determination of PaO 2 2 PaO is dependant upon Age, FiO , P 2 a t m As Age the expected PaO 2 PaO 2 = 109 - 0.4 (Age) As FiO 2 the expected PaO 2 Alveolar Gas Equation: P A O 2 = (P B -P h2o ) x FiO 2 - pCO 2 /R O X Y G E N A T I O N A 2 B P O = partial pressure of oxygen in alveolar gas, P = barometric pressure (760mmHg), P h2o = water vapor pressure (47 mm Hg), FiO 2 = fraction of inspired oxygen, PCO 2 = partial pressure of CO 2 in the ABG, R = respiratory quotient (0.8)

6. Assessment of ACID BASE Balance  Definitions and Terminology ACIDOSIS – presence of a process which tends to pH by virtue of gain of H + - or loss of HCO 3 ALKALOSIS – presence of a process which tends 3 to pH by virtue of loss of H + or gain of HCO - If these changes, change pH, suffix ‘emia’ is added ACIDEMIA – reduction in arterial pH (pH<7.35) ALKALEMIA – increase in arterial pH (pH>7.45)

7. Simple Acid Base Disorder/ Primary Acid Base disorder – a single primary process of acidosis or alkalosis due to an initial change in PCO 2 and HCO 3 . Compensation - The normal response of the respiratory system or kidneys to change in pH induced by a primary acid-base disorder The Compensatory responses to a primary Acid Base disturbance are never enough to correct the change in pH , they only act to reduce the severity. Mixed Acid Base Disorder – Presence of more than one acid base disorder simultaneously .

8. STEP WISE APPROACH to Interpretation Of ABG r eports Six steps logical approach originally proposed by Narins and Emmett (1980) and modified by Morganroth in 1991

9. Normal Values ANALYTE Normal Value Units pH 7.35 - 7.45 PCO2 35 - 45 mm Hg PO2 72 – 104 mm Hg` [HCO3] 22 – 30 meq/L SaO2 95-100 % Anion Gap 12 + 4 meq/L ∆HCO3 +2 to -2 meq/L

10. STEP STEP 1 STEP 2 Is this ABG Authentic? ACIDEMIA or ALKALEMIA? RES P IR A T O R Y or M E T ABOLIC? STEP 3 Is COMPENSATION adequate? STEP 4 If METABOLIC ACIDOSIS – ANION GAP? STEP 5 If High gap Metabolic Acidosis– GAP GAP ?

11. Is this ABG authentic ?  pH = - log [H + ] Henderson-Hasselbalch equation pH = 6.1 + log HCO 3 - 0.03 x PCO 2 The [HCO3-] mentioned on the ABG is actually calculated using this equation from measured values of PCO 2 nd pH [ H+] neq/l = 24 X (PCO 2 / HCO 3 ) pH = -log [ H + ] p H ex p e c t e d = p H m e a sured = ABG is authentic

12.  Reference table for pH v/s [H + ] [ H+] neq/l = 24 X (PCO 2 / HCO 3 ) H + ion pH 100 7.00 79 7.10 63 7.20 50 7.30 45 7.35 40 7.40 35 7.45 32 7.50 25 7.60

13. Look at pH <7.35 - acidemia >7.45 – alkalemia RULE – An acid base abnormality is present even if either the pH or PCO2 are Normal. ACIDEMIA OR ALKALEMIA? STEP 1

14. IS PRIMARY DISTURBANCE RESPIRATORY OR METABOLIC? pH PCO 2 or pH PCO 2 METABOLIC pH PC O 2 or p H PC O 2 R E S P IR A T O R Y RULE- If either the pH or PCO 2 is Normal, there is a mixed metabolic and respiratory acid base disorder. RESPIRATORY or METABOLIC? STEP 2

15. STEP 3 - COMPENSATION

16. ADEQUATE COMPENSATION? IS THE COMPENSATORY RESPONSE ADEQUATE OR NOT ? METABOLIC DISORDER PCO 2 measured ≠ PCO 2 expected PCO 2expected MIXED DISORDER RESPIRATORY DISORDER pH expected acute-chronic pH m ≠ pH e range MIXED DISORDER

17. STEP STEP 1 STEP 2 Is this ABG Authentic? ACIDEMIA or ALKALEMIA? RES P IR A T O R Y or M E T ABOLIC? STEP 3 STEP 4 If Respiratory – ACUTE or CHRONIC? Is COMPENSATION adequate? STEP 4 If METABOLIC ACIDOSIS – ANION GAP? STEP 6 If High gap Metabolic Acidosis– GAP GAP?

18. Electrochemical Balance in Blood 80% 70% 60% 50% 40% 30% 20% 10% 0% 100% 90% C A T I O NS ANIONS Sulfate Ph o sp h ate Mg- OA K - Proteins Ca-HCO3 Na- Cl UA UC Na Cl HC O 3

19. Anion Gap AG based on principle of electroneutrality: Total Serum Cations = Total Serum Anions M cations + U cations = M anions + U anions Na + (K + Ca + Mg) = HCO 3 + Cl + (PO4 + SO4 + Protein + Or Na + UC But in Blood there is a = HCO 3 + Cl + UA relative abundance of Anions, ganic Acids) hence Anions > Cations Na – (HCO 3 + Cl) = UA – UC Na – (HCO 3 + Cl) = Anion Gap

20. METABOLIC ACIDOSIS- ANION GAP? STEP 4 IN METABOLIC ACIDOSIS WHAT IS THE ANION GAP? ANION GAP(AG) = Na – (HCO 3 + Cl) Normal Value = 12 + 4 ( 8 - 16 Meq/l) Adjusted Anion Gap = Observed AG +2.5(4.5- S.Albumin) 50% in S. Albumin 75% in Anion Gap !!! High Anion Gap Metabolic Acidosis Metabolic Acidosis Normal Anion Gap Acidosis

21. High Anion Gap Metabolic Acidosis M U D P I E METHANOL UREMIA - ARF/CRF DIABETIC KETOACIDOSIS & other KETOSIS PARALDEHYDE, PROPYLENE GLYCOL ISONIAZIDE, IRON L LACTIC ACIDOSIS ETHANOL, ETHYLENE GLYCOL S SA L ICY L A T E

22. CO EXISTANT METABOLIC DISORDER – “ Gap Gap ” ? STEP 5 C/O HGAG METABOLIC ACIDOSIS,ANOTHER DISORDER? ∆ Anion Gap = Measured AG – Normal AG Measured AG – 12 ∆ HCO 3 = Normal HCO 3 – Measured HCO 3 24 – Measured HCO 3 Ideally, ∆Anion Gap = ∆HCO 3 For each 1 meq/L increase in AG, HCO3 will fall by 1 meq/L ∆AG/ HCO 3 - = 1  Pure High AG Met Acidosis AG/ HCO 3 - > 1  Assoc Metabolic Alkalosis AG/ HCO 3 - < 1  Assoc N AG Met Acidosis

23. Clinical CASE SCENARIOS

24. CASE-1 pH- 7.28 ,PaCO2-24, HCO3- 12 , Na-128, K-3.8, Step 1: Acidemia Step 2: Metabolic Step 3: Appropriate compensation- 26 PCO2= 1.5 (HCO3)+8(winters formula) Step 4: Calculate AG= Na – (Cl+ HCO3) 128- (98+ 12) = 18 Elevated Anion Gap If S alb= 2.0 c AG = 18 + 2.5(4-2) = 23

25. CASE-2 pH- 7.17 , PaCO2- 65 ,HCO3- 22 Na-136, Cl-98, Sr. Alb-1.6 Step 1: Acidemia Step 2: Respirtory Step 3: Evaluate compensation – no, its decreased- metabolic acidosis Step 4: Calculate AG= Na – (Cl+ HCO3) 136- (98+ 22) = 16 If S alb= 1.6 Step 5: c AG = 16 + 2.5(4-1.6) = 22 (elevated gap Met Acidosis Step 6: Calculate Delta ratio : 22- 12/ 24- 22= 10/ 2= 5 DELTA RATIO > 2, IRRESPECTIVE OF ETIOLOGY- OF INCREASED AG, IT POINTS TO METABOLIC ALKALOSIS 48 yr, alcoholic , found unconscious ,soiled with vomitus, last seen at party 6 hrs back

26. 17 year old w/severe kyphoscoliosis , admitted for pneumonia pH 7. 42 paCO 2 29 paO 2 72 HCO 3 17 Na 140 K 4.0 Cl 109 Step 1: Check pH: Normal (towards alkalosis) Step 2: Check paCO 2 : Alkalotic (respiratory alkalosis) Step 3: Compensation: (11mmHg CO 2 ~ 5 meq HCO 3 ) Step 4: Calculate Anion Gap AG=140 –(109+17)=14 Step 5: Delta gap= 14-12/24-17= 2/ 5= 0.4 Signifies underlying normal anion gap metabolic acidosis

27. 60 year male, smoker, COPD with respiratory distress pH 7.26 paCO 2 60 paO 2 55 HCO 3 26 Na 140 K 4.0 Cl 104 Step 1: Check pH: Acidotic Step 2: Check paCO 2 : High (Respiratory) Step 3: Compensation (2 HCO 3 for 20 mmHg CO2) Step 4: AG=140-(104+26)= 10 Respiratory Acidosis

28. 45 yr old male, k/c/o COPD since 10 yrs pH 7.34 paCO 2 60 paO 2 55 HCO 3 32 Na 140 K 4.0 Cl 100 Step 1: Check pH: Acidemia Step 2: Check paCO 2 : Raised (respiratory ) Step 3: Evaluate compensation : Compensation (8 HCO 3 for 20 mmHg CO2) - adequate AG=140 –(100+30)=10 Respiratory Acidosis (Chronic) compensated

29. 75 yr woman, fever & profuse diarrhoea x 2ds, T 38.5°C, HR 130/min, BP 78/30 mmHg pH 7.29 paCO 2 30 paO 2 80 HCO 3 14 Na 128 K 3.2 Cl 94 Step 1: Check pH: Acidotic Step 2: Check paCO 2 : decreased ( Primary Metabolic) Step 3: Check compensation Expected CO 2 =1.5xHCO 3 +8=21+8=29 (appropriate) Step 4: AG=128 –(94+14)=20, Delta Anion Gap=20-12=8 Step 5: Delta Ratio=▲AG/ ▲HCO 3 =8/10=0.8 High Anion Gap Metabolic Acidosis, Additional NAG Metabolic Acidosis

30. 40 years,male , CRF, on maintenance haemodialys , Missed his last appointment . pH 7.25 paCO 2 27 paO 2 99 HCO 3 14 Na 140 K 4.0 Cl 96 S Albumin 2.5 gm% Step 1: Check pH: Acidotic Step 2: Check paCO 2 : Decreased ( Primary metabolic) Step 3: Evaluate compensation Expected CO 2 =1.5xHCO3+8= 21+8=27 (appropriate) Step 4: AG=140 –(96+12)=32, Adjusted AG=36 Step 5: Calculate Delta Ratio=▲AG/ ▲HCO3 Delta Anion Gap=36-12=24 ; Delta ratio=24/10= 2.4 High Anion Gap Metabolic Acidosis, Additional Metabolic Alkalosis

31. 55-year-old male admitted with a recurring bowel Obstruction & intractable vomiting for the last several hours pH 7.50 paCO 2 48 paO 2 90 HCO 3 38 Na 135 K 3.6 Cl 85 Step 1: Check pH: Alkalotic Step 2: Check paCO 2 : increased ( Primary Metabolic) Step 3: Evaluate compensation: 40= 0.7* (HCO3- 24) = 50 Appropriate so no additional resp disorder Step 4: AG=135 –(85+38)=12, Delta Anion Gap=12-12= 0 Metabolic Alkalosis

32. 47 year old post op, presenting with fever ,hypotension and vomiting pH 7.15 paCO 2 40 paO 2 55 HCO 3 15 Na 140 K 4.0 Cl 92 Step 1: Check pH: Acidotic Step 2: Check paCO 2 Normal, Check HCO 3- : Acidotic (Metabolic Acidosis) Step 3: Evaluate compensation Expected CO 2 =1.5xHCO 3 +8=30.8, so additional respiratory acidosis Step 4: AG=140 –(92+15)=33, Delta Anion Gap=33-12= 21 Step 5: Delta Ratio=▲AG/ ▲HCO 3 =21/9= 2.3 High AG Metabolic Acidosis with respiratory acidosis Additional metabolic alkalosis (Triple metabolic disorder)

33. 12 year old diabetic presents with Kussmaul breathing pH 7.05 paCO 2 15 paO 2 68 HCO 3 5 Na 140 K 4.0 Cl 98 Step 1: Check pH: Acidotic Step 2: Check paCO 2 : Decreased (Metabolic Acidosis) Step 3: Evaluate compensation: Expected CO 2 =1.5xHCO 3 +8=15, so no additional respiratory disorder Step 4: AG=140 –(98+12)=30, Delta Anion Gap=30-12= 18 Step 5 : Delta Ratio=▲AG/ ▲HCO3=18/19=1 High AG Metabolic Acidosis,

34. Pt of severe pneumonia with pulmonary oedema pH 7.30 paCO 2 38 HCO 3 18 Na 140 K 4 Cl 102 Step 1: Check pH: Acidotic Step 2: Check paCO 2 : N : Check HCO 3- : Acidotic Step 3: Evaluate compenstaion Metabolic Acidosis Expected CO 2 =1.5x(HCO3)+8 =35 (slight resp acidosis) Step 4: AG=140 –(102+18)=20, Delta Anion Gap=20-12= 8 Step 5: Delta Ratio=▲AG/ ▲HCO3=8/6=1.2 High AG Metabolic Acidosis

35. 48yr male, A lcoholic, found unconscious, after a party pH 7.17 paCO 2 65 HCO 3 22 Na 136 K 3.4 Cl 98 S Alb=1.6 gm% Step 1: Check pH: Acidotic Step 2: Check paCO 2 : Acidotic (Respiratory Acidosis) Step 3: Evaluate Compensation Resp acidosis: Compensation ?? NO AG=136-(98+22)=16, Adjusted AG=22, Delta Anion Gap=22-12=10 Delta Ratio=▲AG/ ▲HCO3=10/2=5 High Anion Gap Metabolic acidosis with Metabolic Alkalosis Expected CO 2 =1.5x(HCO3)+8 =42 Respiratory Acidosis High AG Metab acidosis , with M Alkalosis

36. Mixed disorders with normal pH

37. 55 yr male, alcoholic, disoriented, c/o recurrent vomiting, H ematemesis pH 7.45 paCO 2 34 HCO 3 23 Na 135 K 4.0 Cl 85 Step 1: Check pH: Normal Step 2: Check paCO 2 : slightly alkalotic Step 3: evaluate compensation ---- Bicarb……almost normal ABG Normal ??? Expected CO 2 =1.5x(HCO3)+8 =42 Step 4: AG=135-(85+23)=27, Delta Anion Gap=27-12=15 Step 5: Delta Ratio=▲AG/ ▲HCO3=15/1=15 High Anion Gap Metabolic acidosis with Metabolic Alkalosis High AG Metab acidosis with M Alkalosis with Respiratory Alkalosis

38. 61yr, morbidly obese, COPD, CHF pH 7.41 paCO 2 55 paO2 75 HCO 3 34 Na 140 K 4.0 Cl 95 Step 1: Check pH: Normal Step 2: Check paCO 2 : Acidotic ?? Step 3: Evaluate compensation ?? COPD, chronic Compensation : chronic Respiratory acidosis…6 in this case HCO3= 34 compensation not appropriate …Metabolic Alkalosis Step 4: AG=140-(95+34)=11, Delta Anion Gap=11-12=-1 Metabolic alkalosis with Primary resp acidosis (chronic)

39. 32 yr pregnant, 4 day s of non stop vomiting, afeb rile ,HR 145/ min, BP 78/62 pH 7.41 paCO 2 42 HCO 3 26 Na 146 K 3.2 Cl 92 Step 1: Check pH: Normal Step 2: Check paCO 2 : Normal, Check HCO 3- : Normal Step 3: Evaluate Compensation ABG Normal ???? Step 4: AG=146-(92+26)=28, Delta Anion Gap=28-12=16 Step 5: Delta Ratio=▲AG/ ▲HCO 3 =16/-2=-8 (negative delta ratio with N pH)

40. References Harrison’s Principles of Internal Medicine, 17 th edition, Chap 48 – Acidosis and Alkalosis Paul L.Marino – The ICU Book, 3 rd Edition Guyton and Hall – Textbook of Medical Physiology, 11 th edition Davenport – The ABC of Acid Base Chemistry, 6 th edition Cohen and Kassirer – Acid Base Hansen JE, Clinics in Chest medicine10(2), 1989, 227-37 Lippincott’s-Fluid Balance, NM Metheny World Wide Web