ABG APPROACH

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  • 1.CONTRAINDICATION FOR ARTERIAL PUNCTURE : INFECTION AT SITE. ALLENS TEST NEGATIVE. ON ANTICOAGULANT THERAPY. SEVERE PERIPHERAL VASCULAR DISEASE. DISTAL TO SURGICAL SHUNT.

2. WHY TO ORDER AN ABG Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management Improvement in acid/base managementallows for optimal function of medications Acid/base status may alter electrolyte levelscritical to patient status/care Follow up 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. EQUATIONSHenderson Hasselbalch equation: pH = 6.1 + log [HCO3-]0.03( Pco2)Kassirer-Bleich equation: [H+] = 24 PCO2 / [HCO3-] 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. HYDROGEN ION CONC AT dif PH pH [H+] 7.7 207.5 31 7.440 7.350 7.180 7.0 100 6.8 160 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. STEP 1PH < 7.35 - ACIDOSISPH > 7.45 - ALKALOSIS 9. STEP 2 ACID BASE CHANGESAcid-Base DisorderPrimary Change Compensatory ChangeRespiratory acidosisPCO2 upHCO3 upRespiratory alkalosis PCO2 downHCO3 downMetabolic acidosisHCO3 downPCO2 downMetabolic alkalosis HCO3 upPCO2 up 10. CompensationPrimary DisorderCompensatory Mechanism Metabolic acidosis Increased ventilationMetabolic alkalosis Decreased ventilationRespiratory acidosisIncreased 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 tubuleDecreased renal excretion of H+ in thedistal tubule 11. The Boston formulae*StateRuleFormula RangeMetabolic acidosisfor acid-base derangementPCOsimply guesstimated using the Boston formulae: + 81.Compensation 1.5+8 can be 2(mmHg) = 1.5*bicarbonate 2Metabolic alkalosis0.7+20PCO 2 (mmHg) = 0.7*bicarbonate +205Acute respiratorybicarbonate (mmol/l) drops 2 mmol/l 2 for 10?alkalosis for every 10 mmHg PCO 2 dropChronic respiratory 4 for 10likewise, but 5 mmol/l?alkalosis bicarbonate (mmol/l) increases 1Acute respiratory 1 for 10mmol/l?acidosisfor every 10 mmHgChronic respiratory 4 for 10likewise, but 4 mmol/l?acidosis 12. HARRISONMETABOLIC ACIDOSIS-HCO3 1.25 PCO2METABOLIC ALKALOSIS:HCO3-0.75 PCO2 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- andPO4- Low albumin will reduce the normalgap 14. HIGH AGNORMAL AGLACTIC ACIDOSIS DIARRHOEAUREMIC ACIDOSIS FITUL AKETO ACIDOSIS RTASALISYLSTEACETOZOLAMIDEETHELENE GLYCOL MASSIVE NS INFUSIONETHANOL HYPERALIMENTATION 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. NAGMA SAG normal.( Na Cl + HCo3) When Hco3 is lost, to maintain electro neutralityCl is conserved by the kidneys and so Anion Gap isnormal. Key Point : Normal Gap acidosis denotes loss ofHco3. Also called hypercholeremic acidosis. NAGMA. 17. HIGH AGNORMAL AGLACTIC ACIDOSIS DIARRHOEAUREMIC ACIDOSIS FITUL AKETO ACIDOSIS RTASALISYLSTEACETOZOLAMIDEETHELENE GLYCOL MASSIVE NS INFUSIONETHANOL HYPERALIMENTATION 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 beenconsidered a critical value or cutoff. 19. Urine Anion Gap UAG = (UNa +UK) UCl. Normal UAG = -10 to +10. If UAG is negative,more than -20it 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. 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 risein AG, a metabolic alkalosis is concurrentlypresent with the AG metabolic acidosis.AG/ HCO3 > 1 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. RESPIRATORY ALKALOSIS Central nervous system stimulation: Fever, pain, fear,cerebrovascular accident, CNS infection, trauma,tumor. Hypoxia: High altitude, profound anemia, pulmonarydisease. 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. METABOLIC ALKALOSISCHLORIDE RESPONSIVE CHLORIDE RESISTANTURINE CL < 25 URINE CL> 25DIURETICSHYPERALDOOSTERONE STATECORTICOSTEROIDSCUSHINGGI LOSS- DIARRHOEA, VILLOUSBARTTERSADENOMAPOTTASIUM DEPLETIONVOMITINGMASSIVE BLOOD TRANSFUSIONSUCTIONRx K+ REPLACEMENTRx 0.9% NS , K+ REPLENIHMENT 24. TIPS Do not interpret any blood gas data for acid-basediagnosis without closely examining the serumelectrolytes: 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. TIPS Simplified rules predict the pH and HCO3- for agiven change in PaCO2. If the pH or HCO3- ishigher or lower than expected for the change inPaCO2, the patient probably has a metabolic acid-base disorder as well. In maximally-compensated metabolic acidosis, thenumerical value of PaCO2 should be the same (orclose to) as the last two digits of arterial pH. Thisobservation reflects the formula for expectedrespiratory compensation in metabolic acidosis: Expected PaCO2 = [1.5 x serum hco3] + (8 2) 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. JAYARAMAN AKI 28. LATHA MYASTHENIA GRAVIS 29. LATHA IN VENTILLATOR 30. SAMUNDESHWARI 31. DIABETIC KETO ACIDOSIS 32. THANK YOU