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ABG Analysis & Interpretation

This presentation discuss about acid-base-gas normal ratio and its indication in relation to varying abnormal level and how to manage it. This includes clinical analysis practice.

ABG Analysis & Interpretation

  1. 1. ABG ANALYSIS By Pamela M. Veroy RN, MAN Source: DAVID W. WOODRUFF, MSN, RN-BC, CNS, CEN. 6 "Easy"Steps“ to "ABG“ Analysis ©199762011 Ed4Nurses,“ Inc.
  2. 2. ABG Analysis • An arterial blood gas (ABG) test measures the acidity (pH) and the levels of oxygen and carbon dioxide in the blood from an artery. This test is used to check how well your lungs are able to move oxygen into the blood and remove carbon dioxide from the blood.
  3. 3. ABG • An arterial blood gas measurement provides valuable information about the blood pH and the partial pressures of arterial carbon dioxide (PaCO2) and oxygen (PaO2). • Most analysers calculate serum bicarbonate (HCO3 -) and the base excess.
  4. 4. 1. Know the Normal Values Variable Normal Range pH 7.35 - 7.45 pCO2 35-45 Bicarbonate (HCO3) 22-26
  5. 5. Is the pH in Normal Values?
  6. 6. 2. Is the PaCO2 normal?
  7. 7. 3. Match the paCO2 and/or the HCO3 with the pH • Next thing you need to determine is whether the acid base is Respiratory or Metabolic. • paCO2 = Respiratory HCO3 = Metabolic
  8. 8. Match the paCO2 and/or the HCO3 with the pH
  9. 9. Let’s do Mnemonic (Analysis)
  10. 10. Do the “Tic-Tac-Toe” Method By Gil Wayne, RN (NurseLab) Acid Normal Basic
  11. 11. The 6 Easy Steps to ABG Analysis: 1. Is the pH normal? 2. Is the CO2 normal? 3. Is the HCO3 normal? 4. Match the CO2 or the HCO3 with the pH. 5. Does the CO2 or the HCO3 got the opposite Direction of the pH? 6. Are the pO2 and the O2 saturation normal?
  12. 12. Step1:Analyze the pH • Step 1: Analyze the pH • The firt step in analyzing the ABG is to look for the pH, Normal blood pH is 7.4, plus or minus 0.05, forming the range 7.35 to 7.45 • < 7.35, it is acidic • > 7.45,it is alkalotic
  13. 13. Step 2: Analyze the CO2 • Examine the pCO2. Normal pCo2 levels are 35-45 mmHg. • <35 is alkalotic • > 45 is acidic.
  14. 14. Step 3: Analyze the HCO3 • Examine the HCO3 level. Normal HCO3 level is 22-26 mEq/L. • <22 HCO3 acidic • >26 HCO3 alkalotic
  15. 15. Anion Gap • In plasma, the sum of the cations (sodium plus potassium) is normally greater than that of the anions (chloride plus bicarbonate) by approximately 14 mmol/L. This is known as the anion gap. The normal reference range for the anion gap is in the equation and is most often due to compensation for gastrointestinal bicarbonate loss (eg, severe/prolonged diarrhoea).
  16. 16. Anion – a negatively charge atom • common anions known are Most of the times the atoms of these elements combine with hydrogen or oxygen to form anion. However there are certain exceptions to this general rule.
  17. 17. Step 4: Match the CO2 or the HCO3 with the pH • Next match either the pCO2 or the with the pH to determine the acid-base disorder. For example, if the then the acid-base disturbance is being caused by the respiratory system. • -This is called RESPIRATORY ACIDOSIS • If the the acid-base disturbance is being caused by the metabolic (or renal) system. So this case is METABOLIC ALKALOSIS
  18. 18. Step 5: Does the CO2 or HCO3 go the opposite direction of the pH? • If YES – there is compensation by that system. • EX. The pH is acidotic, the CO2 is acidotic, and the HCO3 is alkalotic. • - The CO2 matches the pH making the Primary acid-base disorder RESPIRATORY ACIDOSIS. • The HCO3 is opposite of the pH and would be evidence of compensation from the metabolic system.
  19. 19. Use HC03 to verify metabolic effect Normal HCO3- is 22-26 - Compensation may not always be complete. - Complete compensation returns the pH balance to normal. - There are times when the imbalance is too large for compensation to restore the pH to normal. - This is called partial compensation.
  20. 20. How it compensate?
  21. 21. How it compensate the pH? • Respiratory sytem balances the pH by the increase/decrease of Resp. Rate to control the CO2 level. • The renal system balances pH by producing HCO3 or by eliminating hydrogen ions (H+). • Ex. Patient is shock– will undergo anaerobic metabolism, which produces lactic acid. The production of lactic acid will bind or use up available HCO3 & will be manifested by a decreased in the HCO3 level. Therefore, the HCO3 level is an indicator of metabolic acid-base balance.
  22. 22. Compensation Compensation – is the attempt of the body to maintain homeostasis by correcting the pH. - Dissolved CO2 produced by cellular processes & exhaled by the lungs – balances the pH - HCO3 (Bicarbonate) – produced by the kidneys. - Kidney help control the pH by eliminating (H+) ions from the components of carbonic acid (H2CO3)=from Water (H2O)combined with CO2.
  23. 23. Assume metabolic cause when respiratory is ruled out.
  24. 24. Is there appropriate compensation? Is it chronic or acute? Respiratory Acidosis  Acute: for every 10 increase in pCO2 -> HCO3 increases by 1 and there is a decrease of 0.08 in pH MEMORIZE  Chronic: for every 10 increase in pCO2 -> HCO3 increases by 4 and there is a decrease of 0.03 in pH Respiratory Alkalosis Acute: for every 10 decrease in pCO2 -> HCO3 decreases by 2 and there is a increase of 0.08 in PH MEMORIZE Chronic: for every 10 decrease in pCO2 -> HCO3 decreases by 5 and there is a increase of 0.03 in PH
  25. 25. Is there appropriate compensation? Is it acute or chronic ? Metabolic Acidosis Winter’s formula: pCO2 = 1.5[HCO3] + 8 ± 2 MEMORIZE If serum pCO2 > expected pCO2 -> additional respiratory acidosis Another useful tool in estimating the PCO2 in metabolic acidosis is the recognition that the pCO2 is always approximately equal to the last 2 digits of the pH. Metabolic Alkalosis For every 10 increase in HCO3 -> pCO2 increases by 6
  26. 26. Step 6: Analyze the pO2 and the O2 saturation • Finally, evaluate the PaO2 and O2 sat If they are below normal there is evidence of hypoxemia. • Normal Values (At sea level): Range: pH 7.35-7.45 pCO2 35-45 mmHg pO2 80-100Hg O2 Saturation 95-100% HCO3- 22-26 mEq/L Base Excess + or -2
  27. 27. Step 6: Analyze the pO2 and the O2 saturation • The higher the PaO2, the more oxygen is bound to hemoglobin and the higher the saturation (until the limit of 100% saturation is reached).
  28. 28. ABG Analysis ABG Value Which step? Rationale pH 7.39 Step 1 Normal pH PaCO2 40 Step 2 Normal PaCO2
  29. 29. ABG Analysis ABG Value Which step? Rationale pH 7.2 Step 1 Low pH indicates acidosis PaCO2 50 Step 2 High PaCO2 indicates respiratory cause for acidosis Interpretation
  30. 30. ABG Analysis BG Value Which step? Rationale pH 7.49 Step 1 High pH indicates alkalosis PaCO2 30 Step 2 Low PaCO2 indicates respiratory cause for alkalosis (low respiratory acid is causing higher pH) Interpretation
  31. 31. ABG Analysis ABG Value Which step? Rationale pH 7.23 Step 1 Low pH indicates acidosis PaCO2 31 Step 3 Low PaCO2 rules out respiratory cause for acidosis, therefore metabolic cause. Low respiratory acid is compensating for lower pH. Interpret ation
  33. 33. ABG Analysis ABG Value Which step? Rationale pH 7.48 Step 1 High pHindicates alkalosis PaCO2 47 Step 3 High PaC02and High pH indicates metabolic cause of alkalosis. Respiratory acid is compensating for high pH. Interpretati on
  34. 34. Partially compensated metabolic alkalosis
  35. 35. ABG Analysis ABG Value Which step? Rationale pH 7.43 Step 1 pH is normal but higher than 7.4, therefore compensated alkalosis. PaCO2 33 Step 3 Low PaCO2caus es alkalosis Interpre tation
  36. 36. Compensated respiratory alkalosis
  37. 37. Causes of metabolic acidosis • Increased anion gap:Lactic acidosis: shock, infection, hypoxia. • Urate (renal failure). • Ketones (diabetes mellitus, alcohol). • Drugs or toxins: salicylates, metformin, ethylene glycol, methanol, cyanide.
  38. 38. Causes of metabolic acidosis • Normal anion gap (due to loss of bicarbonate or ingestion hydrogen ions): • Renal tubular acidosis.(is a disease that occurs when the kidneys fail to excrete acids into the urine, which causes a person's blood to remain too acidic.) • Diarrhoea. • Addison's disease.-a disease characterized by progressive anemia, low blood pressure, great weakness, and bronze discoloration of the skin. It is caused by inadequate secretion of hormones by the adrenal cortex. • Pancreatic fistulae. • Drugs or toxins: acetazolamide, ammonium chloride.
  39. 39. Metabolic alkalosis  Calculate the urinary chloride to differentiate saline responsive vs saline resistant  Must be off diuretics in order to interpret urine chloride Saline responsive UCL<10 Saline-resistant UCL >10 Vomiting If hypertensive: Cushings, Conn’s -is a condition associated with the development of high blood pressure and low potassium levels in the blood. -Renal failure with alkali administration NG suction If not hypertensive: severe hypokalemia, hypomagnesemia, Over-diuresis Exogenous corticosteroid administration Post-hypercapnia
  40. 40. Causes of respiratory acidosis • Acute:Depression of the central respiratory centre by cerebrovascular disease or drugs. • Inability to ventilate adequately due to neuromuscular disease - eg, myasthenia gravis, amyotrophic lateral sclerosis, Guillain- Barré syndrome, muscular dystrophy. • Airway obstruction related to asthma or exacerbation of chronic obstructive pulmonary disease (COPD).
  41. 41. Causes of respiratory acidosis • Chronic:Chronic respiratory acidosis may be secondary to many disorders - eg, COPD,obesity hypoventilation syndrome (Pickwickian syndrome), neuromuscular disorders and restrictive ventilatory defects such as interstitial fibrosis or thoracic deformities.
  42. 42. Respiratory Alkalosis • Respiratory alkalosis results from hyperventilation - eg, anxiety, stroke, meningitis, altitude, pregnancy (see the separate article on Hyperventilation).
  43. 43. Ready for Case Analysis? YES/NO?
  44. 44. Case No. 1 • Problems: • PaCO2 is low. • pH is on the high side of normal, therefore compen sated respiratory alkalosis. • Also, PaO2 is low, probably due to mucous displacing air in the alveoli affected by the pneumonia Mrs. Puffer is a 35-year-old single mother, just getting off the night shift. She reports to the ED in the early morning with shortness of breath. She has cyanosis of the lips. She has had a productive cough for 2 weeks. Her temperature is 39 degrees celsius, blood pressure 110/76, heart rate 108, respirations 32, rapid and shallow. Breath sounds are diminished in both bases, with coarse rhonchi in the upper lobes. Chest X-ray indicates bilateral pneumonia. ABG results are: pH= 7.44 PaCO2= 28 HCO3= 24 PaO2= 54
  45. 45. Continuation of Case No.1 • Solutions: • Mrs. Puffer most likely has ARDS (Acute respiratory distress syndrome) along with her pneumonia. • The alkalosis need not be treated directly. Mrs. Puffer is hyperventilating to increase oxygenation, which is incidentally . • High FiO2 (The fraction of inspired O2) can help, but if she has interstitial lung fluid, she may , or a BiPAP to raise her PaO2. Expect orders for antibiotics, and possibly steroidal anti-inflammatory agents. • Chest physiotherapy and vigorous coughing or suctioning will help the patient clear her airways of excess mucous and increase the number of functioning alveoli.
  46. 46. Continuation of case no.1 BiPAP to raise her PaO2. A non-invasive clinical mngt. • Bilevel Positive Airway Pressure, and is very similar in function and design to a CPAP machine (continuous positive airway pressure). Similar to a CPAP machine,
  47. 47. Case No 2 • Problem: • pH is high, • PaCO2 is low • respiratory alkalosis. Solution: • If he is hyperventilating from an anxiety attack, the simplest solution is to have him breathe into a paper bag. He will rebreathe some exhaled CO2.This will increase PaCO2 and trigger his normal respiratory drive to take over breathing control. • * Please note this will not work on a person with chronic CO2 retention, such as a COPD patient. These people develop a hypoxic drive, and do not respond to CO2 changes. Mr. Worried is a 52-year-old widow. He is retired and living alone. He enters the ED complaining of shortness of breath and tingling in fingers. His breathing is shallow and rapid. He denies diabetes; blood sugar is normal. There are no EKG changes. He has no significant respiratory or cardiac history. He takes several antianxiety medications. He says he has had anxiety attacks before. While being worked up for chest pain an ABG is done: ABG results are: pH= 7.48 PaCO2= 28 HCO3= 22 PaO2= 85
  48. 48. Case No. 3 • Problem: • The pH is acidotic, • PaCO2 is 25 (low) which should create alkalosis. • This is a for the metabolic acidosis. • The underlying problem is, of course, a metabolic acidosis. • Solution: • Insulin, so the body can use the sugar in the blood and stop making ketones, which are an acidic by- product of protein metabolism. • In the mean time, pH should be maintained near normal so that oxygenation is not compromised You are the critical care nurse about to receive Mr. Sweet, a 24-year-old DKA (diabetic ketoacidosis) patient from the ED. The medical diagnosis tells you to expect acidosis. In report you learn that his blood glucose on arrival was 780. He has been started on an insulin drip and has received one amp of bicarb. You will be doing finger stick blood sugars every hour. ABG results are: pH= 7.33 PaCO2= 25 HCO3=12 PaO2= 89
  49. 49. End of Report
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This presentation discuss about acid-base-gas normal ratio and its indication in relation to varying abnormal level and how to manage it. This includes clinical analysis practice.


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