Abg workshop ppt
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Abg workshop ppt
- 1. ARTERIAL BLOOD GAS ANALYSIS 1 DR.SWARNALINGAM THANGAVELU M.B.B.S.,M.D ASSOCIATE PROFESSOR, DEPARTMENT OF ANAESTHESIOLOGY
- 2. EVERYTHING SHOULD BE MADE SIMPLE, BUT NOT SIMPLER - ALBERT EINSTEIN 2
- 3. OBJECTIVES 3 Background of acid base disturbances Terminology used in acid base disturbances Arterial blood sampling procedure Interpretation of Arterial blood gas report
- 4. BACKGROUND
- 5. INDICATIONS 5 To assess the adequacy of ventilation and oxygenation Establish the diagnosis and severity of respiratory failure To guide therapy for oxygen administration To assess the changes in acid-base homeostasis and guide treatment To manage patients in ICUs To monitor patients during cardiopulmonary surgery Determine prognosis in critically ill patients
- 6. IMPORTANT CONSIDERATIONS DURING ARTERIAL BLOOD SAMPLING 6 Before withdrawing a sample, kindly ensure that the patient is in a steady state of oxygenation It takes about 3 minutes for patients with healthy lungs and 20 minutes in COPD lungs to reach a steady state after any alteration of ventilator parameters or the FiO2 has been done General rule- atleast 30 minutes should be allowed for the patient to achieve a steady state before any sample is withdrawn for ABG
- 7. Allen’s test for checking collateral blood flow to hand Excess heparin- causes a drop in PaCO2 Air bubble in the sample or leaving the sample exposed open to air should be prevented Avoid delay in running the sample (If not placed in ice box)- PaO2 decreases very fast
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- 20. NORMAL ABG REPORT 20 PaO2 (mmHg) PaCO2 (mmHg) pH HCO3 mEq/L Base deficit/ Excess mEq/L SaO2 (%) Arterial 80-100 35-45 7.36-7.44 22-28 ±2 >95% Venous 37-42 42-50 7.34-7.42 - ±2 75%
- 21. HOW TO KNOW WHETHER THE SAMPLE IS ARTERIAL, VENOUS OR MIXED? 21 Arterial Venous Ask the person Blood pulsates into the syringe Syringe plunger may rise on its own Does not PO2 and O2 saturation PO2 value of >40mmHg or O2 saturation >75% -most likely not a venous sample Very low Peripheral venous PO2 is always <40mmHg, O2 Saturation <75% pH Abnormal or normal, Not diagnostic Abnormal or normal, Not diagnostic PCO2 Abnormal or normal, Not diagnostic Abnormal or normal, Not diagnostic Multiple attempts Lower PO2 due to its venous mixture - Venous admixture Lower PO2. The values depend upon venous admixture
- 22. 22 Sometimes there is no way to know whether the blood sample is arterial or venous?
- 23. PARAMETERS IN A BLOOD GAS REPORT • FiO2 [ Fractional concentration of O2 in inspired air ] • PaO2 [ Partial pressure of O2 in arterial blood ] • PaCO2 [ Partial pressure of CO2 in arterial blood ] • pH [ Measure of hydrogen ion concentration of a solution ] • SaO2 [ Oxygen saturation of Hemoglobin in arterial blood ] 23
- 24. HCO3 A (Actual) Parameter for non-respiratory component of acid-base balance HCO3 S (Standard) Reported after standardizing at PCO2 of 40mmHg, Temperature 37˚C, SO2 100% Base Excess HCO3 amount above or below normal content (0) of buffer base, (+) or (-) Depends upon entered Hb value, measured pH and PCO2 values A-a DO2 Difference between PO2 Alveolar and PO2 arterial 24
- 25. TERMINOLOGY • Acidemia : Blood pH <7.35 • Acidosis: A primary physiological process that occuring alone, tends to cause acidemia • Alkalemia: Blood pH >7.45 • Alkalosis: A primary physiological process that occuring alone, tends to cause alkalemia 25
- 27. Manifest as initial changes in PaCO2 or HCO3 If PaCO2 changes first, disorder is respiratory If HCO3 changes first, disorder is metabolic 27
- 28. 28 Respiratory acidosis (PaCO2 rises first) Respiratory alkalosis (PaCO2 falls first) Metabolic acidosis ( HCO3 falls first) Metabolic alkalosis ( HCO3 rises first)
- 29. COMPENSATION enal compenstation for respiratory imbalances is slow and incomplete 29 Secondary changes in HCO3 or PaCO2 occuring in response to the primary event to normalize pH when the acid-base imbalance exists over a period of time The compensation is done by the organ system which is not primarily affected. Respiratory compensation for metabolic problems is usually rapid and almost complete Renal compensation for respiratory imbalances is slow and incomplete
- 30. 30 Primary disorder First Change Effect Compensation Respiratory acidosis PaCO2 rises pH decreases Secondary retention of HCO3 by kidneys (Slow & incomplete) Respiratory alkalosis PaCO2 falls pH increases Secondary increased excretion of HCO3 by kidneys Metabolic acidosis HCO3 falls pH decreases Secondary hyperventilation by lungs to lower PaCO2 ( Rapid & almost complete) Metabolic alkalosis HCO3 rises pH increases Secondary hypoventilation by lungs to raise PaCO2
- 31. READING THE REPORT STEP-BY-STEP APPROACH 31
- 32. STEP 1 32 Check if the required parameters have been correctly fed in ABG machine
- 33. P at Patient’s temperature, hemoglobin, FiO2 and barometric pressure ient’s temperature, hemoglobin, FiO2 and barometric pressure T The results in ABG report are bound to change ( incorrect and misleading) if the above values are not correctly filled he results in ABG report are bound to change ( incorrect and misleading) if the above values are not correctly filled 33
- 34. STEP 2 34 Detect the adequacy of oxygenation
- 35. Look at PaO2, SaO2 values and the FiO2 which the patient is receiving PaO2 = 109-0.43 × age Relate PaO2 values with FiO2 which the patient is receiving Value of PaO2 can be predicted by multiplying inspired % of O2 with 5 in otherwise healthy lungs or with 3 in patients of COPD 35
- 36. CLASSIFY HYPOXEMIA Uncorrected hypoxemia Patient is receiving O2 but PaO2 is < 60mmHg Corrected hypoxemia PaO2 has risen to >60mmHg but is < 100mmHg Excessively corrected hypoxemia PaO2 rises to > 100mmHg but is surely less than predicted value
- 37. TOTAL OXYGEN CONTENT • Gives the true assessment of adequacy of oxygenation and hypoxemia in all clinical situations • Especially in conditions where PaO2 or SaO2 found to inaccurate Anemia MetHb CO poisoning • Normal value: 16-22ml/dl CaO2= Hb (gm%) × 1.34 × SaO2+0.003× PaO2 (mmHg)
- 38. STEP 3 38 Classify pH as normal, acidemia or alkalemia
- 39. 39 pH Inference 7.35-7.45 Normal pH No metabolic disorder Compensated disorder < 7.35 Acidemia Uncompensated disorder > 7.35 Alkalemia Uncompensated disorder
- 40. STEP 4 40 Analyze whether the disorder is respiratory or metabolic
- 41. 41 Respiratory Metabolic Analyse pH and PCO2 in relation to normal values Moving in opposite direction- disorder is respiratory Moving in same direction- disorder is not respiratory ( ? Metabolic) Analyse pH and HCO3 in relation to normal values Moving in same direction- disorder is metabolic Moves in opposite direction- primary disorder is not metabolic (? Respiratory)
- 42. ACRONYM- ROME RO • Respiratory Opposite ME • Metabolic Equal
- 43. STEP 5 43 Evaluate compensation and correlate pH, PaCO2 and HCO3
- 44. Lungs and kidneys are primary buffer response systems If pH is found to be outside the normal range- no compensation or partial pH in normal range- full compensation or no acid base balance If the primary disturbance is respiratory, then there will be increase or decrease in HCO3 to compensate for the alterations in the PaCO2 and vice versa 44
- 45. STEP 6 45 Calculate the actual compensation seen in the report and match it with the expected
- 46. 46 Disorder Event Compensation Respiratory acidosis Acute 10mmHg rise in PaCO2 Chronic 10mmHg rise in PaCO2 1mEq/L rise in HCO3 levels 4mEq/L rise in HCO3 levels Respiratory alkalosis Acute 10mmHg fall in PaCO2 Chronic 10mmHg fall in PaCO2 2mEq/L fall in HCO3 levels 4mEq/L fall in HCO3 levels Metabolic acidosis 1mEq/L decrease in HCO3 1.25mmHg decrease in PaCO2 Metabolic alkalosis 1mEq/L increase in HCO3 0.75mmHg increase in PaCO2
- 47. STEP 7 47 Find out whether the disorder is mixed
- 48. TWO METHODS Check the relative movement of pH in relation to both PaCO2 and HCO3. If both the pairs are moving and in correct direction, it is a mixed disorder Analyse compensation by assuming the primary disorder as respiratory or metabolic. If the analysis shows no compensation, it is a mixed disorder 48
- 49. STEP 8 Unmask hidden disorders 49
- 50. Serum electrolyte reports ( Na, K, Cl and HCO3) to unmask hidden disorders Three parameters need to be determined 1. Anion gap (AG) 2. Bicarbonate gap (BG) 3. Venous CO2 and its change from normal 50
- 51. ANION GAP It is the difference of all the routinely measured cations & anions in the blood AG = ( Na + K)- (Cl + HCO3). Usually K is omitted due to small numerical value Normal value: 12 ± 4 mEq/L ∆ AG= Measured AG- 12 ( Normal expected AG) Elevated AG above 16 implies anion gap metabolic acidosis is present
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- 55. SUMMARY 55 pH is depressed Acidosis If CO2 is elevated, there is a respiratory component to the acidosis (But it could also include a metabolic component) If CO2 is not elevated, the only possible explanation is the presence of a metabolic acidosis ( Bicarbonate must be reduced) If the CO2 is elevated and the bicarbonate is decreased, it is a combined respiratory and metabolic acidosis
- 56. pH is elevated 56 Alkalosis If CO2 is depressed, there is a respiratory component to the alkalosis (But it could also include a metabolic component) If CO2 is not depressed, the only possible explanation is the presence of a metabolic alkalosis ( Bicarbonate must be elevated) If the CO2 is depressed and the bicarbonate is elevated, it is a combined respiratory and metabolic alkalosis
- 57. L LISTEN not to contradict or confute nor to believe and take for granted but to WEIGH AND CONSIDER THANK YOU 57
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- 62. 62 pH 7.6 PCO2 20mmHg PO2 95 mmHg HCO3 18 mEq/L Respiratory alkalosis
- 63. 63 pH 7.2 PCO2 80 mmHg PO2 70 mmHg HCO3 30 mEq/L ?
- 64. 64 pH 7.2 PCO2 80 mmHg PO2 80 mmHg HCO3 30 mEq/L Respiratory acidosis
- 68. 68 pH 6.98 PCO2 62mmHg PO2 80mmHg HCO3 14 mEq/L Combined respiratory and metabolic acidosis
- 69. 69 pH 7.3 PCO2 30mmHg PO2 68 mmHg HCO3 14 mEq/L ?
- 70. 70 pH 7.3 PCO2 30mmHg PO2 68 mmHg HCO3 14 mEq/L Partially compensated metabolic acidosis with hypoxemia