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

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

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

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

Standard Bicarbonate: Plasma HCO3 after equilibration to a PaCO2 of 40 mm Hg : Reflects non-respiratory acid base change : No quantification of the extent of the buffer base abnormality No click Base Excess: D base to normalise HCO3 (to 24) with PaCO2 at 40 mm Hg (Sigaard-Andersen) : Reflects metabolic part of acid base D : No info. over that derived from pH, pCO2 and HCO3 : Misinterpreted in chronic or mixed disorders

Oxygenation Indices: O2 Content of blood: (Don’t forget hemoglobin) No click Oxygenation Indices: O2 Content of blood: Hb. x O2 Sat + Dissolved O2 (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 )

Normal arterio/venous difference No click 0 10 20 30 40 50 60 70 80 90 100 PaO2 100 80 Rt. Shift Oxygen delivered to tissues with normally placed curve 60 Delivered oxygen with Rt. Shift curve 40 Normal 20 Shift of the curve ……changes saturation for a given PaO2

Alveolar-arterial Difference Inspired O2 = 21 % piO2 = (760-45) x . 21 = 150 mmHg palvO2 = piO2 – pCO2 / RQ = 150 – 40 / 0.8 = 150 – 50 = 100 mm Hg O2 CO2 PaO2 = 90 mmHg palvO2 – partO2 = 10 mmHg One click and wait

Alveolar- arterial Difference No click Alveolar- arterial Difference Oxygenation Failure WIDE GAP piO2 = 150 pCO2 = 40 palvO2= 150 – 40/.8 =150-50 =100 PaO2 = 45 D = 100 - 45 = 55 Ventilation Failure NORMAL GAP piO2 = 150 pCO2 = 80 palvO2= 150-80/.8 =150-100 = 50 PaO2 = 45 D = 50 - 45 = 5 O2 CO2 PAO2 (partial pres. of O2. in the alveolus.) = 150 - ( PaCO2 / .8 ) 760 – 45 = 715 : 21 % of 715 = 150

Expected PaO2 = No click FiO2 × 5 = PaO2 Normal situation 20 × 5 = 100

The essentials The Blood Gas Report: normals… pH 7.40 + 0.05 No click The essentials The Blood Gas Report: normals… pH 7.40 + 0.05 PaCO2 40 + 5 mm Hg PaO2 80 - 100 mm Hg HCO3 24 + 4 mmol/L O2 Sat >95 Always mention and see FIO2 HCO3

The No click 5 Steps for Successful Blood Gas Analysis

Step 1 Step 2 CO2 will change pH in opposite direction Look at the pH Is the patient acidemic pH < 7.35 or alkalemic pH > 7.45 Step 2 Who is responsible for this change in pH ( culprit )? CO2 will change pH in opposite direction Bicarb. will change pH in same direction Acidemia: With HCO3 < 20 mmol/L = metabolic With PCO2 >45 mm hg = respiratory Alkalemia: With HCO3 >28 mmol/L = metabolic With PCO2 <35 mm Hg = respiratory

No click Step 3 If there is a primary respiratory disturbance, is it acute ? 10 mm Change PaCO2 .08 change in pH ( Acute ) .03 change in pH ( Chronic ) =

Step 4 If the disturbance is metabolic is the respiratory compensation appropriate? For metabolic acidosis: Expected PaCO2 = (1.5 x [HCO3]) + 8 ) + 2 or simply… expected PaCO2 = last two digits of pH For metabolic alkalosis: Expected PaCO2 = 6 mm for 10 mEq. rise in Bicarb. Suspect if ............. actual PaCO2 is more than expected : additional …respiratory acidosis actual PaCO2 is less than expected : additional …respiratory alkalosis No click

No click Step 4 cont. If there is metabolic acidosis, is there a wide anion gap ? Na - (Cl-+ HCO3-) = 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

5 No click th step Clinical correlation

Same direction HCO3 pH META. Same direction PaCO2 RESP. pH No click HCO3 pH META. Same direction PaCO2 RESP. pH Opposite direction

No click Remember the format pH PaCO2 PaO2

METABOLIC ACIDOSIS HYPER VENTILATION Low Alkali Three clicks pH PaCO2 BICARB CHANGES pH in same direction Compensation Bicarbonate Low Alkali Primary lesion Primary lesion METABOLIC ACIDOSIS

METABOLIC ALKALOSIS HYPO VENTILATION Three clicks pH PaCO2 BICARB CHANGES pH in same direction Compensation Bicarbonate High Alkali Primary lesion METABOLIC ALKALOSIS

Respiratory acidosis Three clicks Wait for red circle pH CO 2 CHANGES pH in opposite direction BICARB compensation PaCO 2 High CO2 Primary lesion Respiratory acidosis

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

Respiratory alkalosis Three clicks Wait for red circle pH PaCO 2 CHANGES pH in opposite direction BICARB compensation PaCO 2 Primary lesion Low PaCO2 Primary lesion Respiratory alkalosis

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

No click pH PaCO2 of 10 Acute change .08 Chronic change .03

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

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

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

Acute respiratory alkalosis One click for answer Case 1 16 year old female with sudden onset of dyspnea. No Cough or Chest Pain Vitals normal but RR 56, anxious. Blood Gas Report Measured 37.0o C pH 7.523 PaCO2 30.1 mm Hg PaO2 105.3 mm Hg Calculated Data HCO3 act 22 mmol / L O2 Sat 98.3 % PO2 (A - a) 8 mm Hg D PO2 (a / A) 0.93 Entered Data FiO2 21.0 % Acute respiratory alkalosis And why acute ?

Case 2 6 year old male with progressive respiratory distress Muscular dystrophy . Five clicks pH <7.35 :acidemia Blood Gas Report Measured 37.0o C pH 7.301 PaCO2 76.2 mm Hg PaO2 45.5 mm Hg Calculated Data HCO3 act 35.1 mmol / L O2 Sat 78 % PO2 (A - a) 9.5 mm Hg D PO2 (a / A) 0.83 Entered Data FiO2 21 % Res. Acidemia : High PaCO2 and low pH D CO2 =76-40=36 Expected D pH for ( Acute ) = .08 for 10 Expected ( Acute ) pH = 7.40 - 0.29=7.11 Chronic resp. acidosis Hypoxemia Normal A-a gradient Chronic respiratory acidosis With hypoxia due to hypoventilation Hypoventilation

Acute respiratory change Last two digits pH 80 – PaCO2 No click PaCO2 pH 70 7.10 60 7.20 50 7.30 40 7.40 30 7.50 20 7.60 Acute respiratory change

8-year-old male asthmatic with resp. distress Six clicks 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. Blood Gas Report Measured 37.0o C pH 7. 24 PaCO2 49.1 mm Hg PaO2 66.3 mm Hg Calculated Data HCO3 act 18.0 mmol / L O2 Sat 92 % PO2 (A - a) mm Hg D PO2 (a / A) Entered Data FiO2 30 % 153-66= 87 pH <7.35 ; acidemia PaCO2 >45; respiratory acidemia D CO2 = 49 - 40 = 9 Expected D pH ( Acute ) = 9/10 x 0.08 = 0.072 Expected pH ( Acute ) = 7.40 - 0.072 = 7.328 Acute resp. acidosis Hypoxia 30 × 5 = 150 WITH INCREASE IN CO2 BICARB MUST RISE ? Bicarbonate is low……… Metabolic acidosis + respiratory acidosis piO2 = 715x.3=214.5 / palvO2 = 214-49/.8=153 Wide A / a gradient

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

Case 5 : 10 year old child with encephalitis Four clicks Blood Gas Report Measured 37.0o C pH 7.46 PaCO2 28.1 mm Hg PaO2 55.3 mm Hg Calculated Data HCO3 act 19.2 mmol / L O2 Sat % PO2 (A - a) mm Hg D PO2 (a / A) Entered Data FiO2 24.0 % pH almost within normal range Mild alkalosis PaCO2 is low , respiratory low by around 10 ( Acute ) by .08 (Chronic ) by .03 Bicarb looks low ? Is it expected ? BICARBINATURIA

Case 6…………. One click pH 7.39 PCO2 l5mmHg HCO3 8mmol/L PaO2 90 mmHg 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. For metabolic acidosis: FULL COMPENSATION Expected PaCO2 = (1.5 x [HCO3]) + 8 ) + 2 (Winter’s equation) PCO 2 ……SHOULD BE 20

Adolescent boy with appendicitis , posted for surgery , he is a known Case 7………. Adolescent boy with appendicitis , posted for surgery , he is a known case of SLE. His pre-op ABG shows : Room air pH 7.39 pCO2 l5mmHg paO2 90 mmHg HCO3 8mmol/L No click 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 ?

No click Patient was hypo volumic , received Normal Saline bolus... Corrected acidosis He was operated ….but post-op became drowsy His ABG…….. FiO2….30% pH 7.38 PaCO2 38 PaO2 60 1) Why hypoxemia ? 2) Were the lungs bad to begin with ? ( Pre OP PaO2 90 mmHg ) 3) Micro atelectesis during surgery ? Anesthetist goofed up the case 4) Pure and simple hypoventilation …..Sedation ?

Oxygenation status good …..? One click 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 PaCO2 l5mmHg PaO2 90 mmHg HCO3 8mmol/L Oxygenation status good …..? Pre OP .....A/a gradient palvO2 = PiO2 – PaCO2 / RQ = 150 – 15 / 0.8 = 150 – 18 = 132 mm Hg 132 – 90= 42 WIDE A / a gradient

Apparently the lungs looked good with PaO2 of 90……. No click Apparently the lungs looked good with PaO2 of 90……. But have a good look at the ABG again With wash out of CO 2 ………. The expected PaO2 should have been more than 90 . This coupled with correction of acidosis ( normalizing PaCO2 ) Lowered the PaO2 …post operatively. Conclusion …….. Lungs were not normal to begin with ( SLE )……..

Learning point Correlate PaO2 with FiO2 No click Learning point Correlate PaO2 with FiO2 But please also correlate with PaCO2

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

pH Bicarb. CO2 THANKS