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ABG

Dr. Meena

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ABG

  1. 1. ARTERIAL BLOOD GAS ANALYSIS S.MEENATCHI SUNDARI, II YEAR PG. A.Y.T 1
  2. 2. DEFINITION It is a diagnostic procedure in which a blood is obtained from an artery directly by an arterial puncture or accessed by a way of indwelling arterial catheter A.Y.T 2
  3. 3. EQUIPMENT Blood gas kit OR • 1ml /2ml syringe • 23-26 gauge needle • Stopper or cap • Alcohol swab • Disposable gloves • Plastic bag & crushed ice • Lidocaine (optional) • Vial of heparin (1:1000) • Par code or label A.Y.T 3
  4. 4. Preparatory phase: • Record patient inspired oxygen concentration • Check patient temperature • Explain the procedure to the patient • Provide privacy for client • If not using hepranized syringe , hepranize the needle • Perform Allen's test • Wait at least 20 minutes before drawing blood for ABG after initiating, changing, or discontinuing oxygen therapy, or settings of mechanical ventilation, after suctioning the patient or after extubation. A.Y.T 4
  5. 5.  EXCESSIVE HEPARIN Dilutional effect on results ↓ HCO3 - & PaCO2 Only .05 ml heperin required for 1 ml blood. So syringe be emptied of heparin after flushing or only dead space volume is sufficient or dry heperin should be used
  6. 6. ALLEN’S TEST It is a test done to determine that collateral circulation is present from the ulnar artery in case thrombosis occur in the radial A.Y.T 6
  7. 7. Sites for obtaining abg • Radial artery ( most common ) • Brachial artery • Femoral artery Radial is the most preferable site used because: • It is easy to access • It is not a deep artery which facilitate palpation, stabilization and puncturing • The artery has a collateral blood circulation A.Y.T 7
  8. 8. Performance phase: • Wash hands • Put on gloves • Palpate the artery for maximum pulsation • If radial, perform Allen's test • Place a small towel roll under the patient wrist • Instruct the patient to breath normally during the test and warn him that he may feel brief cramping or throbbing pain at the puncture site • Clean with alcohol swab in circular motion • Skin and subcutaneous tissue may be infiltrated with local anesthetic agent if needed A.Y.T 8
  9. 9. • Insert needle at 45 radial , 60 brachial and 90 femoral • Withdraw the needle and apply digital pressure • Check bubbles in syringe • Place the capped syringe in the container of ice immediately • Maintain firm pressure on the puncture site for 5 minutes, if patient has coagulation abnormalities apply pressure for 10 – 15 minutes A.Y.T 9
  10. 10. AIR BUBBLES : 1. PO2 ∼150 mmHg & PCO2 ∼0 mm Hg in air bubble(R.A.) 2. Mixing with sample, lead to ↑ PaO2 & ↓ PaCO2 To avoid air bubble, sample drawn very slowly and preferabily in glass syringe Steady State: Sampling should done during steady state after change in oxygen therepy or ventilator parameter Steady state is achieved usually within 3-10 minutes
  11. 11. Follow up phase: • Send labeled, iced specimen to the lab immediately • Palpate the pulse distal to the puncture site • Assess for cold hands, numbness, tingling or discoloration • Documentation include: results of Allen's test, time the sample was drawn, temperature, puncture site, time pressure was applied and if O2 therapy is there • Make sure it’s noted on the slip whether the patient is breathing room air or oxygen. If oxygen, document the number of liters . If the patient is receiving mechanical ventilation, FIO2 should be documented A.Y.T 11
  12. 12. complication • Arteriospasm • Hematoma • Hemorrhage • Distal ischemia • Infection • Numbness A.Y.T 12
  13. 13. ABG component • PH: measures hydrogen ion concentration in the blood, it shows blood’ acidity or alkalinity • PCO2 : It is the partial pressure of CO2 that is carried by the blood for excretion by the lungs, known as respiratory parameter • PO2: It is the partial pressure of O2 that is dissolved in the blood , it reflects the body ability to pick up oxygen from the lungs • HCO3 : known as the metabolic parameter, it reflects the kidney’s ability to retain and excrete bicarbonate A .Y .T 13
  14. 14. Parameter 37 C (Change every 10 min) 4 C (Change every 10 min) ↓ pH 0.01 0.001 ↑ PCO2 1 mm Hg 0.1 mm Hg ↓ PO2 0.1 vol % 0.01 vol % Temp Effect On Change of ABG Values
  15. 15. A.Y.T15
  16. 16. Steps for ABG analysis 1. What is the pH? Acidemia or Alkalemia? 2. What is the primary disorder present? 3. Is there appropriate compensation? 4. Is the compensation acute or chronic? 5. Is there an anion gap? 6. If there is a AG check the delta gap?
  17. 17. Normal values:  PH = 7.35 – 7.45  PCO2 = 35 – 45 mmhg  PO2 = 80 – 100 mmhg  HCO3 = 22 – 28 meq/L A.Y.T17
  18. 18. Calculation of pH 203.0 log10.6 3 PaCO HCO pH × += − [ ] − + ×= 3 2 24 HCO PaCO H Henderson- Hesselbach equation
  19. 19. Step 1  Look at the pH: is the blood acidemic or alkalemic? pH normal value 7.35-7.45 ACIDIC:below 7.35 ALKALOSIS:above 7.45
  20. 20. Step 2: What is the primary disorder? What disorder is present? pH pCO2 HCO3 Respiratory Acidosis pH low high high Metabolic Acidosis pH low low low Respiratory Alkalosis pH high low low Metabolic Alkalosis pH high high high ROME
  21. 21. Step 4: Calculation of compensation Mean "whole body" response equations for simple acid-base disturbances. Note: The formula calculates the change in the compensatory parameter. Disorder pH Primary change Compensatory Response Equation Metabolic Acidosis ↓ ↓ [HCO3 - ] ↓ PCO2 ΔPCO2 ≈ 1.2 × ΔHCO3 Metabolic Alkalosis ↑ ↑ [HCO3 - ] ↑ PCO2 ΔPCO2 ≈ 0.7 × ΔHCO3 Respiratory Acidosis ↓ ↑ PCO2 ↑ [HCO3 - ] Acute: ΔHCO3 - ≈ 0.1 × ΔPCO2 Chronic: ΔHCO3 - ≈ 0.3 × ΔPCO2 Respiratory Alkalosis ↑ ↓ PCO2 ↓ [HCO3 - ] Acute: ΔHCO3 - ≈ 0.2 × ΔPCO2 Chronic: ΔHCO3 - ≈ 0.5 × ΔPCO2
  22. 22. 1.2 0.7 0.1 0.3 0.2 0.5 Compensation Formula Simplified Acute Chronic Metabolic Respiratory Acidosis Alkalosis Acidosis Alkalosis
  23. 23. Step 3-4: Is there appropriate compensation? Is it chronic or acute?  Respiratory Acidosis  Acute (Uncompensated): for every 10 increase in pCO2 -> HCO3 increases by 1 and there is a decrease of 0.08 in pH  Chronic (Compensated): for every 10 increase in pCO2 -> HCO3 increases by 4 and there is a decrease of 0.03 in pH  Respiratory Alkalosis  Acute (Uncompensated): for every 10 decrease in pCO2 -> HCO3 decreases by 2 and there is a increase of 0.08 in PH  Chronic (Compensated): for every 10 decrease in pCO2 -> HCO3 decreases by 5 and there is a increase of 0.03 in PH  Partial Compensated: Change in pH will be between 0.03 to 0.08 for every 10 mmHg change in PCO2
  24. 24. Step 3-4: Is there appropriate compensation?  Metabolic Acidosis  Winter’s formula: Expected pCO2 = 1.5[HCO3] + 8 ± 2 OR ∆ pCO2 = 1.2 (∆ HCO3)  If serum pCO2 > expected pCO2 -> additional respiratory acidosis and vice versa  Metabolic Alkalosis  Expected PCO2 = 0.7 × HCO3 + (21 ± 2) OR ∆ pCO2 = 0.7 (∆ HCO3)  If serum pCO2 < expected pCO2 - additional respiratory alkalosis and vice versa
  25. 25. Step 5: Calculate the anion gap  AG used to assess acid-base status esp in D/D of metabolic acidosis  ∆ AG & ∆ HCO3 - used to assess mixed acid-base disorders AG based on principle of electroneutrality:  Total Serum Cations = Total Serum Anions  Na + (K + Ca + Mg) = HCO3 + Cl + (PO4 + SO4 + Protein + Organic Acids)  Na + UC = HCO3 + Cl + UA  Na – (HCO3 + Cl) = UA – UC  Na – (HCO3 + Cl) = AG  Normal =12 ± 2
  26. 26. Contd…  AG corrected = AG + 2.5[4 – albumin]  If there is an anion Gap then calculate the Delta/delta gap (step 6) to determine additional hidden nongap metabolic acidosis or metabolic alkalosis  If there is no anion gap then start analyzing for non-anion gap acidosis
  27. 27. Step 6: Calculate Delta Gap  Delta gap = (actual AG – 12) + HCO3  Adjusted HCO3 should be 24 (+_ 6) {18-30}  If delta gap > 30 -> additional metabolic alkalosis  If delta gap < 18 -> additional non-gap metabolic acidosis  If delta gap 18 – 30 -> no additional metabolic disorders
  28. 28. Step 5: Calculate the “gaps” Anion gap = Na+ − [Cl− + HCO3 − ] Δ AG = Anion gap − 12 Δ HCO3 = 24 − HCO3 Δ AG = Δ HCO3 − , then Pure high AG Met. Acidosis Δ AG > Δ HCO3 − , then High AG Met Acidosis + Met. Alkalosis Δ AG < Δ HCO3 − , then High AG Met Acidosis + HCMA
  29. 29. Nongap metabolic acidosis  For non-gap metabolic acidosis, calculate the urine anion gap  URINARY AG Total Urine Cations = Total Urine Anions Na + K + (NH4 and other UC) = Cl + UA (Na + K) + UC = Cl + UA (Na + K) – Cl = UA – UC (Na + K) – Cl = AG  Distinguish GI from renal causes of loss of HCO3 by estimating Urinary NH4+ .  Hence a -ve UAG (av -20 meq/L) seen in GI, while +ve value (av +23 meq/L) seen in renal problem. UAG = UNA + UK – UCL
  30. 30. Metobolic acidosis: Anion gap acidosis
  31. 31. Causes of nongap metabolic acidosis - DURHAM Diarrhea, ileostomy, colostomy, enteric fistulas Ureteral diversions or pancreatic fistulas RTA type I or IV, early renal failure Hyperailmentation, hydrochloric acid administration Acetazolamide, Addison’s Miscellaneous – post-hypocapnia, toulene, sevelamer, cholestyramine ingestion
  32. 32. Dictums in ABG AnalysisDictums in ABG Analysis 1. Primary change & Compensatory change always occur in the same direction. 2. pH and Primary parameter change in the same direction suggests a metabolic problem. pH and Primary parameter change in the opposite direction suggests a respiratory problem. 3. Renal and pulmonary compensatory mechanisms return pH toward but rarely to normal. Corollary: A normal pH in the presence of changes in PCO2 or HCO3 suggets a mixed acid-base disorder.
  33. 33. Steps for ABG analysis 1. What is the pH? Acidemia or Alkalemia? 2. What is the primary disorder present? 3. Is there appropriate compensation? 4. Is the compensation acute or chronic? 5. Is there an anion gap? 6. If there is a AG check the delta gap?

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