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# ABG APPROACH

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### ABG APPROACH

1. 1. CONTRAINDICATION FOR ARTERIAL PUNCTURE : INFECTION AT SITE. ALLEN’S TEST NEGATIVE. ON ANTICOAGULANT THERAPY. SEVERE PERIPHERAL VASCULAR DISEASE. DISTAL TO SURGICAL SHUNT.
2. 2. WHY TO ORDER AN ABG Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management Improvement in acid/base management allows for optimal function of medications Acid/base status may alter electrolyte levels critical to patient status/care Follow up
3. 3. NORMAL VALUES Ph- 7.35-7.45 Po2- 95mmhg- 100mmhg PCO2- 36mmhg -44mmhg HCO3- 22 – 26mEq/L AG – 8-12 OG- -10 - +10
4. 4. EQUATIONSHenderson Hasselbalch equation: pH = 6.1 + log [HCO3-] 0.03( Pco2)Kassirer-Bleich equation: [H+] = 24 × PCO2 / [HCO3-]
5. 5. DERIVATION OF HH EQUATION (H+) ∞(acid) / (base) (H+) =Ka(HA)/ (A-) pH=pKa + log (A-)/ (HA) pH= pKa + log (HCO3) / 0.03 ( CO2)
6. 6. HYDROGEN ION CONC AT dif PH pH [H+] 7.7 20 7.5 31 7.4 40 7.3 50 7.1 80 7.0 100 6.8 160
7. 7. APPROACH TO ABG Acidosis or alkalosis. Respiratory or metabolic. If respiratory – Acute or chronic. If metabolic acidosis – High AG or normal AG Is the compensation adequate Rule out mixed disorders
8. 8. STEP 1PH < 7.35 - ACIDOSISPH > 7.45 - ALKALOSIS
9. 9. STEP 2 ACID BASE CHANGESAcid-Base Disorder Primary Change Compensatory ChangeRespiratory acidosis PCO2 up HCO3 upRespiratory alkalosis PCO2 down HCO3 downMetabolic acidosis HCO3 down PCO2 downMetabolic alkalosis HCO3 up PCO2 up
10. 10. CompensationPrimary Disorder Compensatory Mechanism Metabolic acidosis Increased ventilationMetabolic alkalosis Decreased ventilationRespiratory acidosis Increased renal reabsorption of HCO3- in the proximal tubule Increased renal excretion of H in the distal tubuleRespiratory alkalosis Decreased renal reabsorption of HCO3- in the proximal tubule Decreased renal excretion of H+ in the distal tubule
11. 11. The Boston formulae*State Rule Formula RangeMetabolic acidosisfor acid-base derangementPCOsimply guesstimated using the Boston formulae: + 8 1.Compensation 1.5+8 can be 2 (mmHg) = 1.5*bicarbonate 2Metabolic alkalosis 0.7+20 PCO 2 (mmHg) = 0.7*bicarbonate +20 5Acute respiratory bicarbonate (mmol/l) drops 2 mmol/l 2 for 10 ?alkalosis for every 10 mmHg PCO 2 dropChronic respiratory 4 for 10 likewise, but 5 mmol/l ?alkalosis bicarbonate (mmol/l) increases 1Acute respiratory 1 for 10 mmol/l ?acidosis for every 10 mmHgChronic respiratory 4 for 10 likewise, but 4 mmol/l ?acidosis
12. 12. HARRISONMETABOLIC ACIDOSIS- HCO3 – 1.25 PCO2METABOLIC ALKALOSIS: HCO3- 0.75 PCO2
13. 13. STEP 4 ANION GAP The principle of electroneutrality (Na+ + K+) – (Cl- + HCO3- ) Usually 12-16 mEq/l Difference is due to the unmeasured – ve charge on the proteins, and SO4- and PO4- Low albumin will reduce the ‘normal’ gap
14. 14. HIGH AG NORMAL AG•LACTIC ACIDOSIS •DIARRHOEA•UREMIC ACIDOSIS •FITUL A•KETO ACIDOSIS •RTA•SALISYLSTE •ACETOZOLAMIDE•ETHELENE GLYCOL •MASSIVE NS INFUSION•ETHANOL •HYPERALIMENTATION
15. 15. HAGMA SAG increased. (Na – Cl + HCo3) The added Acid is buffered by Hco3, Hco3 Falls and Anion Gap is increased.Key Point : Increased Anion Gap means an acid has been added to the blood. HAGMA.
16. 16. NAGMA SAG normal.( Na – Cl + HCo3) When Hco3 is lost, to maintain electro neutrality Cl is conserved by the kidney’s and so Anion Gap is normal. Key Point : Normal Gap acidosis denotes loss of Hco3. Also called hypercholeremic acidosis. NAGMA.
17. 17. HIGH AG NORMAL AG•LACTIC ACIDOSIS •DIARRHOEA•UREMIC ACIDOSIS •FITUL A•KETO ACIDOSIS •RTA•SALISYLSTE •ACETOZOLAMIDE•ETHELENE GLYCOL •MASSIVE NS INFUSION•ETHANOL •HYPERALIMENTATION
18. 18. OSMOLAL GAP osmolal gap = MO - CO MO = Measured Osmolality CO = Calculated Osmolality. 2 x Na + GLU/18 + UN/2.8 Normal OG = -10 to +10 An OG value greater than + 14 has traditionally been considered a critical value or cutoff.
19. 19. Urine Anion Gap UAG = (UNa +UK) – UCl. Normal UAG = -10 to +10. If UAG is negative,more than -20 it is due GI loss. If the UAG is positive, more than +10 then it is due to renal loss of Hco3. UAG is an indirect measure of NH3 secretion in the Distal Tubule.
20. 20. STEP 6 If the decrease in bicarbonate is more than the rise in the AG, concurrent with the AG metabolic acidosis there is also a second type of metabolic acidosis present, a non-AG metabolic acidosis. AG/ HCO3 < 1 If the decrease in bicarbonate is less than the rise in AG, a metabolic alkalosis is concurrently present with the AG metabolic acidosis. AG/ HCO3 > 1
21. 21. RESPIRATORY ACIDOSIS Upper airway obstruction Lower airway obstruction Cardiogenic or non-cardiogenic pulmonary edema Pneumonia Pulmonary emboli Fat emboli Central nervous system depression Neuromascular impairment Ventilatory restriction
22. 22. RESPIRATORY ALKALOSIS Central nervous system stimulation: Fever, pain, fear, cerebrovascular accident, CNS infection, trauma, tumor. Hypoxia: High altitude, profound anemia, pulmonary disease. Stimulation of chest receptors: Pulmonary edema, pulmonary emboli, pneumonia, pneumothorax, pleural effusion. Drugs or hormones : Salicylates, medroxyprogesterone, catecholamines. Miscellaneous: Sepsis, pregnancy, liver disease, hyperthyroidism.
23. 23. METABOLIC ALKALOSISCHLORIDE RESPONSIVE CHLORIDE RESISTANTURINE CL < 25 URINE CL> 25•DIURETICS •HYPERALDOOSTERONE STATE•CORTICOSTEROIDS •CUSHING•GI LOSS- DIARRHOEA, VILLOUS •BARTTERSADENOMA •POTTASIUM DEPLETION•VOMITING •MASSIVE BLOOD TRANSFUSION•SUCTION •Rx – K+ REPLACEMENT•Rx – 0.9% NS , K+ REPLENIHMENT
24. 24. TIPS Do not interpret any blood gas data for acid-base diagnosis without closely examining the serum electrolytes: Na+, K+, Cl-, Single acid-base disorders do not lead to normal blood pH. Although pH can end up in the normal range (7.35 - 7.45) with a single mild acid-base disorder, a truly normal pH with distinctly abnormal HCO3- and PaCO2 invariably suggests two or more primary disorders. and CO2.
25. 25. TIPS Simplified rules predict the pH and HCO3- for a given change in PaCO2. If the pH or HCO3- is higher or lower than expected for the change in PaCO2, the patient probably has a metabolic acid- base disorder as well. In maximally-compensated metabolic acidosis, the numerical value of PaCO2 should be the same (or close to) as the last two digits of arterial pH. This observation reflects the formula for expected respiratory compensation in metabolic acidosis: Expected PaCO2 = [1.5 x serum hco3] + (8 ± 2)
26. 26. correction Ph< 7.1 HCO3 < 10 BICARB DEFICIT  VOD=Body wt( 0.4 + 2.4 / 5 )  Correction = Vod ( bicarb defict) 400 mEq increases Hco3 by 12 mEq
27. 27.  JAYARAMAN  AKI
28. 28.  LATHA  MYASTHENIA GRAVIS
29. 29.  LATHA  IN VENTILLATOR
30. 30.  SAMUNDESHWARI
31. 31.  DIABETIC KETO ACIDOSIS
32. 32. THANK YOU