![Basics
Nano equivalent =110-9
pH = -log [H+] : Sorensen formula
[H+] = 40 nEq/L (16 to 160 nEq/L) at pH-7.4](https://image.slidesharecdn.com/balanceacidobase-240207172338-317ddc56/85/balance-acido-base-pptx-22-320.jpg)
![Henderson-Hasselbalch Equation
o Correlates metabolic & respiratory regulations
-
HCO3
pH = pK + log ----------------
.03 x [PaCO2]
o Simplified
-
HCO3
pH ~ ---------
PaCO2](https://image.slidesharecdn.com/balanceacidobase-240207172338-317ddc56/85/balance-acido-base-pptx-23-320.jpg)
![Characteristicsof 縁 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
-](https://image.slidesharecdn.com/balanceacidobase-240207172338-317ddc56/85/balance-acido-base-pptx-33-320.jpg)
![Anion Gap
AG = [Na+
] - [Cl-
+HCO3
-
]
Elevated anion gap represents
metabolic acidosis
Normal value: 12 賊 4 mEq/L
Major unmeasured anions
albumin
phosphates
sulfates
organic anions](https://image.slidesharecdn.com/balanceacidobase-240207172338-317ddc56/85/balance-acido-base-pptx-36-320.jpg)
![7. Calculate the anion gap if it is
more there is Metabolic acidosis
AG = [Na+] - [Cl- +HCO3
-]](https://image.slidesharecdn.com/balanceacidobase-240207172338-317ddc56/85/balance-acido-base-pptx-48-320.jpg)
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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
- 6. ABGSyringe
- 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
- 12. Gas exchange
- 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
- 21. AcidBaseStatus
- 22. Basics Nano equivalent =110-9 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 縁 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 賊 4 mEq/L Major unmeasured anions albumin phosphates sulfates organic anions
- 37. Unmeasured cations Unmeasured anions Na+ Cl- HCO3 - Cations = Anions Anion Gap= Metabolic Acidosis
- 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 patients 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