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balance acido base.pptx

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This document provides an overview of arterial blood gas (ABG) analysis including the procedure, interpretation of results, and applications. It discusses how ABG can be used to assess respiratory failure, monitor patients on ventilators, and evaluate acid-base imbalances. The key steps in ABG interpretation involve analyzing gas exchange by looking at pO2, A-a gradient, and pCO2/FiO2 ratio, and acid-base status by examining pH, pCO2, HCO3, and the Henderson-Hasselbalch equation. Mixed disorders are identified when compensation is inadequate or pCO2 and HCO3 move in opposite directions. The anion gap is also calculated to detect metabolic acidosis

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Arterial Blood Gas analysis Dr Abdullah PG 2 (Medicine) AMU Aligarh
Overview ABG Sampling Interpretation of ABG  Gas Exchange  Acid Base status
Applications of ABG o To document respiratory failure and assess its severity o To monitor patients on ventilators and assist in weaning o To assess acid base imbalance in critical illness o To assess response to therapeutic interventions and mechanical ventilation o To assess pre-op patients
ABG – Procedure and Precautions Where to place -- the options Radial Dorsalis Pedis Femoral Brachial
Technical Errors Excessive Heparin  Ideally : Pre-heparinised ABG syringes  Syringe FLUSHED with 0.5ml 1:1000 Heparin & emptied  DO NOT LEAVE EXCESSIVE HEPARIN IN THE SYRINGE HEPARIN DILUTIONAL EFFECT HCO3 - pCO2
ABGSyringe
Technical Errors  Risk of alteration of results  with: 1) size of syringe/needle 2) vol of sample  Syringes must have > 50% blood  Use only 3ml or less syringe  25% lower values if 1 ml sample taken in 10 ml syringe (0.25 ml heparin in needle)
Technical Errors Air Bubbles  pO2 150 mm Hg & pCO2 0 mm Hg 🠶Contact with AIR BUBBLES  pO2 &  pCO2  Seal syringe immediately after sampling - Body Temperature  Affects values of pCO2 and HCO3 only  ABG Analyser controlled for Normal Body temperatures
Technical Errors WBC Counts  0.01 ml O2 consumed/dL/min  Marked increase in high TLC/plt counts :  pO2  Chilling / immediate analysis ABG Syringe must be transported earliest via COLD CHAIN Change/10 min Uniced 370C Iced 40C pH 0.01 0.001 pCO2 1 mm Hg 0.1 mm Hg pO2 0.1% 0.01%
ABGEquipment 3 electrode system that measures three fundamental variables - pO2, pCO2 and pH All others parameters such as HCO3 - computed by software using standard formulae
Interpretation of ABG  Gas exchange  Acid Base Status
Gas exchange
AssessmentOf Gasexchange PaO2 vs SpO2 Alveolar-arterial O2 gradient PaO2/FiO2 ratio PaCO2
Determinants of PaO2 PaO2 is dependant upon Age, FiO2, Patm As Age the expected PaO2 • PaO2 = 109 - 0.4 (Age) As FiO2 the expected PaO2 • Alveolar Gas Equation: • PAO2= (PB- PH20) x FiO2- pCO2/R
Hypoxemia o Normal PaO2 : 95 – 100 mm Hg o Mild Hypoxemia : PaO2 60 – 80 mm Hg o Moderate Hypoxemia : PaO2 40 – 60 mm Hg – tachycardia, hypertension, cool extremities o Severe Hypoxemia : PaO2 < 40 mm Hg – severe arrhythmias, brain injury, death
Alveolar-arterial O2 gradient o P(A-a)O2 is the alveolar-arterial difference in partial pressure of oxygen o PAO2 = 150 – PaCO2/RQ o Normal range : 5 - 25 mm Hg (increases with age) o Increase P(A-a)O2 : lung parenchymal disease
PaO2 / FiO2 ratio Inspired Air FiO2 = 21% PiO2 = 150 mmHg PalvO2 = 100 mmHg PaO2 = 90 mmHg O2 CO2
Berlincriteria for ARDSseverity PaO2 / FiO2 ratio Inference 200 - 300 mm Hg Mild ARDS 100 - 200 mm Hg Moderate ARDS < 100 mm Hg Severe ARDS ARDS is characterized by an acute onset within 1 week, bilateral radiographic pulmonary infiltrates, respiratory failure not fully explained by heart failure or volume overload, and a PaO2/FiO2 ratio < 300 mm Hg
Hypercapnia o PaCO2 is directly proportional to CO2 production and inversely proportional to alveolar ventilation o Normal PaCO2 is 35 – 45 mm Hg
balance acido base.pptx
AcidBaseStatus
Basics •Nano equivalent =1×10-9 pH = -log [H+] : Sorensen formula •[H+] = 40 nEq/L (16 to 160 nEq/L) at pH-7.4
Henderson-Hasselbalch Equation o Correlates metabolic & respiratory regulations - HCO3 pH = pK + log ---------------- .03 x [PaCO2] o Simplified - HCO3 pH ~ --------- PaCO2
balance acido base.pptx
Bicarbonate Buffer System CO2 + H2O carbonic anhydrase H2CO3 H+ + HCO3 - Acidosis : Acid = H+ - H+ + HCO3 H2CO3 CO2 + H2O Alkalosis : Alkali + Weak Acid = H2CO3 CO2 + H20 - HCO3 + H+ H2CO3 + Alkali
Respiratory Regulation H+ PaCO2 H+ PaCO2 ALVEOLAR VENTILATION ALVEOLAR VENTILATION
Renal Regulation Kidneys control the acid-base balance by excreting either a basic or an acidic urine - - • Excretion of HCO3 • Regeneration of HCO3 with excretion of H+
Excretion of excess H+ & generation of new - HCO3 : The Ammonia Buffer System • In chronic acidosis, the dominant mechanism + of acid eliminated excretion of NH4 GLUTAMINE HCO3 - NH3 REABSORBED NH3 + H+ NH4 + EXCRETED
Response… Bicarbonate Buffer System • Acts in few seconds Respiratory Regulation • Starts within minutes good response by 2hrs, complete by 12-24 hrs Renal Regulation • Starts after few hrs, complete by 5-7 days
Abnormal Values pH < 7.35 • Acidosis (metabolic and/or respiratory) pH > 7.45 • Alkalosis (metabolic and/or respiratory) paCO2 > 45 mm Hg • Respiratory acidosis (alveolar hypoventilation) paCO2 < 35 mm Hg • Respiratory alkalosis (alveolar hyperventilation) HCO3 - < 22 meq/L • Metabolic acidosis HCO3 - > 26 meq/L • Metabolic alkalosis
Simple Acid-BaseDisorders Simple acid-base disorder – a single primary process of acidosis or alkalosis with or without compensation
Compensation… - The body always tries to normalize the pH so…  pCO2 and HCO3 rise & fall together in simple disorders  Compensation never overcorrects the pH  Lack of compensation in an appropriate time defines a 2nd disorder  Require normally functioning lungs and kidneys
Characteristicsof  acid-basedisorders DISORDER PRIMARY RESPONSE COMPENSATORY RESPONSE Metabolic acidosis  [H+]  PH  HCO3 -  pCO2 Metabolic alkalosis  [H+]  PH  HCO3 -  pCO2 Respiratory y acidosis  [H+]  PH  pCO2  HCO3 - Respiratory y alkalosis  [H+]  PH  pCO2  HCO3 -
Disorder Compensatory response Respiratoryacidosis Acute ↑ HCO3 – 1 mEq/L per 10 mm Hg ↑ pCO2 Chronic ↑ HCO3 – 3.5 mEq/L per 10 mm Hg ↑ pCO2 Respiratoryalkalosis Acute ↓ HCO3 – 2 mEq/L per 10 mm Hg ↓ pCO2 Chronic ↓ HCO3 – 5 mEq/L per 10 mm Hg ↓ pCO2 Metabolic acidosis ↓ pCO2 1.3 mm Hg per 1 mEq/L ↓ HCO3 – (Limit of CO2 is 10 mm Hg) Metabolic alkalosis ↑ pCO2 0.7 mm Hg per 1 mEq/L ↑ HCO3 – (Limit of CO2 is 55 mm Hg)
Mixed Acid-baseDisorders Presence of more than one acid base - disorder simultaneously Clues to a mixed disorder: o Normal pH with abnormal HCO3 or pCO2 - o pCO2 and HCO3 move in opposite directions o pH changes in an opposite direction for a known primary disorder
Anion Gap AG = [Na+ ] - [Cl- +HCO3 - ] • Elevated anion gap represents metabolic acidosis • Normal value: 12 ± 4 mEq/L • Major unmeasured anions – albumin – phosphates – sulfates – organic anions
Unmeasured cations Unmeasured anions Na+ Cl- HCO3 - Cations = Anions Anion Gap= Metabolic Acidosis
Increased Anion Gap o Diabetic Ketoacidosis o Chronic Kidney Disease o Lactic Acidosis o Alcoholic Ketoacidosis o Aspirin Poisoning o Methanol Poisoning o Ethylene Glycol Poisoning o Starvation Normal Anion Gap o Diarrhea o Renal Tubular Acidosis o Addisons Disease o Carbonic Anhydrase Inhibitors
Delta Gap o The difference between patient’s AG & normal AG o The coexistence of 2 metabolic acid-base disorders may be apparent Delta gap = Anion gap – 12 - Delta Gap + HCO3 = 22-26 mEq/l  If >26, consider additional metabolic alkalosis  If <22, consider additional non AG metabolic acidosis
STEP-BY-STEP ANALYSIS OF ACID-BASE STATUS
1. Look at the pO2 (<80 mm Hg) and O2 saturation(<90%) for hypoxemia
2. Look at the pH  < 7.35 : ACIDOSIS  > 7.45 : ALKALOSIS  7.35 – 7.45 : normal/mixed disorder
3. Look at pCO2  > 45 mm Hg : Increased (Acidic)  < 35 mm Hg : Decreased (Alkalotic)
3 4. Look at the HCO -  > 26 mEq/L : Increased (Alkalotic)  < 22 mEq/L : Decreased (Acidic)
5. Determine the acid-base disorder, - match either the pCO2 or the HCO3 with the pH
6. Compensation… are the CO2 or HCO3 - of opposite type ?
Is the compensation adequate?? METABOLIC DISORDER PCO2expected • PCO2measured ≠ PCO2expected MIXED DISORDER RESPIRATORY DISORDER pHexpected • pHm ≠ pHe range MIXED DISORDER
7. Calculate the anion gap if it is more there is Metabolic acidosis AG = [Na+] - [Cl- +HCO3 -]
8. Does the anion gap explain the - change in HCO3 ? Calculate Delta gap (rule out co-existence of 2 acid-base disorders)
9. Examine the patient to determine whether the clinical signs are compatible with the acid-base analysis…
balance acido base.pptx
Treat the patient not the ABG!!! Thankyou…

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balance acido base.pptx

  • 1. Arterial Blood Gas analysis Dr Abdullah PG 2 (Medicine) AMU Aligarh
  • 2. Overview ABG Sampling Interpretation of ABG  Gas Exchange  Acid Base status
  • 3. Applications of ABG o To document respiratory failure and assess its severity o To monitor patients on ventilators and assist in weaning o To assess acid base imbalance in critical illness o To assess response to therapeutic interventions and mechanical ventilation o To assess pre-op patients
  • 4. ABG – Procedure and Precautions Where to place -- the options Radial Dorsalis Pedis Femoral Brachial
  • 5. Technical Errors Excessive Heparin  Ideally : Pre-heparinised ABG syringes  Syringe FLUSHED with 0.5ml 1:1000 Heparin & emptied  DO NOT LEAVE EXCESSIVE HEPARIN IN THE SYRINGE HEPARIN DILUTIONAL EFFECT HCO3 - pCO2
  • 7. Technical Errors  Risk of alteration of results  with: 1) size of syringe/needle 2) vol of sample  Syringes must have > 50% blood  Use only 3ml or less syringe  25% lower values if 1 ml sample taken in 10 ml syringe (0.25 ml heparin in needle)
  • 8. Technical Errors Air Bubbles  pO2 150 mm Hg & pCO2 0 mm Hg 🠶Contact with AIR BUBBLES  pO2 &  pCO2  Seal syringe immediately after sampling - Body Temperature  Affects values of pCO2 and HCO3 only  ABG Analyser controlled for Normal Body temperatures
  • 9. Technical Errors WBC Counts  0.01 ml O2 consumed/dL/min  Marked increase in high TLC/plt counts :  pO2  Chilling / immediate analysis ABG Syringe must be transported earliest via COLD CHAIN Change/10 min Uniced 370C Iced 40C pH 0.01 0.001 pCO2 1 mm Hg 0.1 mm Hg pO2 0.1% 0.01%
  • 10. ABGEquipment 3 electrode system that measures three fundamental variables - pO2, pCO2 and pH All others parameters such as HCO3 - computed by software using standard formulae
  • 11. Interpretation of ABG  Gas exchange  Acid Base Status
  • 13. AssessmentOf Gasexchange PaO2 vs SpO2 Alveolar-arterial O2 gradient PaO2/FiO2 ratio PaCO2
  • 14. Determinants of PaO2 PaO2 is dependant upon Age, FiO2, Patm As Age the expected PaO2 • PaO2 = 109 - 0.4 (Age) As FiO2 the expected PaO2 • Alveolar Gas Equation: • PAO2= (PB- PH20) x FiO2- pCO2/R
  • 15. Hypoxemia o Normal PaO2 : 95 – 100 mm Hg o Mild Hypoxemia : PaO2 60 – 80 mm Hg o Moderate Hypoxemia : PaO2 40 – 60 mm Hg – tachycardia, hypertension, cool extremities o Severe Hypoxemia : PaO2 < 40 mm Hg – severe arrhythmias, brain injury, death
  • 16. Alveolar-arterial O2 gradient o P(A-a)O2 is the alveolar-arterial difference in partial pressure of oxygen o PAO2 = 150 – PaCO2/RQ o Normal range : 5 - 25 mm Hg (increases with age) o Increase P(A-a)O2 : lung parenchymal disease
  • 17. PaO2 / FiO2 ratio Inspired Air FiO2 = 21% PiO2 = 150 mmHg PalvO2 = 100 mmHg PaO2 = 90 mmHg O2 CO2
  • 18. Berlincriteria for ARDSseverity PaO2 / FiO2 ratio Inference 200 - 300 mm Hg Mild ARDS 100 - 200 mm Hg Moderate ARDS < 100 mm Hg Severe ARDS ARDS is characterized by an acute onset within 1 week, bilateral radiographic pulmonary infiltrates, respiratory failure not fully explained by heart failure or volume overload, and a PaO2/FiO2 ratio < 300 mm Hg
  • 19. Hypercapnia o PaCO2 is directly proportional to CO2 production and inversely proportional to alveolar ventilation o Normal PaCO2 is 35 – 45 mm Hg
  • 22. Basics •Nano equivalent =1×10-9 pH = -log [H+] : Sorensen formula •[H+] = 40 nEq/L (16 to 160 nEq/L) at pH-7.4
  • 23. Henderson-Hasselbalch Equation o Correlates metabolic & respiratory regulations - HCO3 pH = pK + log ---------------- .03 x [PaCO2] o Simplified - HCO3 pH ~ --------- PaCO2
  • 25. Bicarbonate Buffer System CO2 + H2O carbonic anhydrase H2CO3 H+ + HCO3 - Acidosis : Acid = H+ - H+ + HCO3 H2CO3 CO2 + H2O Alkalosis : Alkali + Weak Acid = H2CO3 CO2 + H20 - HCO3 + H+ H2CO3 + Alkali
  • 26. Respiratory Regulation H+ PaCO2 H+ PaCO2 ALVEOLAR VENTILATION ALVEOLAR VENTILATION
  • 27. Renal Regulation Kidneys control the acid-base balance by excreting either a basic or an acidic urine - - • Excretion of HCO3 • Regeneration of HCO3 with excretion of H+
  • 28. Excretion of excess H+ & generation of new - HCO3 : The Ammonia Buffer System • In chronic acidosis, the dominant mechanism + of acid eliminated excretion of NH4 GLUTAMINE HCO3 - NH3 REABSORBED NH3 + H+ NH4 + EXCRETED
  • 29. Response… Bicarbonate Buffer System • Acts in few seconds Respiratory Regulation • Starts within minutes good response by 2hrs, complete by 12-24 hrs Renal Regulation • Starts after few hrs, complete by 5-7 days
  • 30. Abnormal Values pH < 7.35 • Acidosis (metabolic and/or respiratory) pH > 7.45 • Alkalosis (metabolic and/or respiratory) paCO2 > 45 mm Hg • Respiratory acidosis (alveolar hypoventilation) paCO2 < 35 mm Hg • Respiratory alkalosis (alveolar hyperventilation) HCO3 - < 22 meq/L • Metabolic acidosis HCO3 - > 26 meq/L • Metabolic alkalosis
  • 31. Simple Acid-BaseDisorders Simple acid-base disorder – a single primary process of acidosis or alkalosis with or without compensation
  • 32. Compensation… - The body always tries to normalize the pH so…  pCO2 and HCO3 rise & fall together in simple disorders  Compensation never overcorrects the pH  Lack of compensation in an appropriate time defines a 2nd disorder  Require normally functioning lungs and kidneys
  • 33. Characteristicsof  acid-basedisorders DISORDER PRIMARY RESPONSE COMPENSATORY RESPONSE Metabolic acidosis  [H+]  PH  HCO3 -  pCO2 Metabolic alkalosis  [H+]  PH  HCO3 -  pCO2 Respiratory y acidosis  [H+]  PH  pCO2  HCO3 - Respiratory y alkalosis  [H+]  PH  pCO2  HCO3 -
  • 34. Disorder Compensatory response Respiratoryacidosis Acute ↑ HCO3 – 1 mEq/L per 10 mm Hg ↑ pCO2 Chronic ↑ HCO3 – 3.5 mEq/L per 10 mm Hg ↑ pCO2 Respiratoryalkalosis Acute ↓ HCO3 – 2 mEq/L per 10 mm Hg ↓ pCO2 Chronic ↓ HCO3 – 5 mEq/L per 10 mm Hg ↓ pCO2 Metabolic acidosis ↓ pCO2 1.3 mm Hg per 1 mEq/L ↓ HCO3 – (Limit of CO2 is 10 mm Hg) Metabolic alkalosis ↑ pCO2 0.7 mm Hg per 1 mEq/L ↑ HCO3 – (Limit of CO2 is 55 mm Hg)
  • 35. Mixed Acid-baseDisorders Presence of more than one acid base - disorder simultaneously Clues to a mixed disorder: o Normal pH with abnormal HCO3 or pCO2 - o pCO2 and HCO3 move in opposite directions o pH changes in an opposite direction for a known primary disorder
  • 36. Anion Gap AG = [Na+ ] - [Cl- +HCO3 - ] • Elevated anion gap represents metabolic acidosis • Normal value: 12 ± 4 mEq/L • Major unmeasured anions – albumin – phosphates – sulfates – organic anions
  • 38. Increased Anion Gap o Diabetic Ketoacidosis o Chronic Kidney Disease o Lactic Acidosis o Alcoholic Ketoacidosis o Aspirin Poisoning o Methanol Poisoning o Ethylene Glycol Poisoning o Starvation Normal Anion Gap o Diarrhea o Renal Tubular Acidosis o Addisons Disease o Carbonic Anhydrase Inhibitors
  • 39. Delta Gap o The difference between patient’s AG & normal AG o The coexistence of 2 metabolic acid-base disorders may be apparent Delta gap = Anion gap – 12 - Delta Gap + HCO3 = 22-26 mEq/l  If >26, consider additional metabolic alkalosis  If <22, consider additional non AG metabolic acidosis
  • 41. 1. Look at the pO2 (<80 mm Hg) and O2 saturation(<90%) for hypoxemia
  • 42. 2. Look at the pH  < 7.35 : ACIDOSIS  > 7.45 : ALKALOSIS  7.35 – 7.45 : normal/mixed disorder
  • 43. 3. Look at pCO2  > 45 mm Hg : Increased (Acidic)  < 35 mm Hg : Decreased (Alkalotic)
  • 44. 3 4. Look at the HCO -  > 26 mEq/L : Increased (Alkalotic)  < 22 mEq/L : Decreased (Acidic)
  • 45. 5. Determine the acid-base disorder, - match either the pCO2 or the HCO3 with the pH
  • 46. 6. Compensation… are the CO2 or HCO3 - of opposite type ?
  • 47. Is the compensation adequate?? METABOLIC DISORDER PCO2expected • PCO2measured ≠ PCO2expected MIXED DISORDER RESPIRATORY DISORDER pHexpected • pHm ≠ pHe range MIXED DISORDER
  • 48. 7. Calculate the anion gap if it is more there is Metabolic acidosis AG = [Na+] - [Cl- +HCO3 -]
  • 49. 8. Does the anion gap explain the - change in HCO3 ? Calculate Delta gap (rule out co-existence of 2 acid-base disorders)
  • 50. 9. Examine the patient to determine whether the clinical signs are compatible with the acid-base analysis…
  • 52. Treat the patient not the ABG!!! Thankyou…