ABG and It's Interpretation, By Dr. Vivek Dev
- 1. ABG and It’s Interpretation A Comprehensive Guide to Understanding Arterial Blood Gases Dr. Vivek Dev, MBBS Medical Officer Neurosurgery Department Neuro Cardio & Multispecialty
- 2. Outlines • ABG Component • Indications to ABG Sampling • Contraindications to ABG Sampling • Equipments Required for ABG Sampling • Sites for ABG Sampling • Procedure for ABG sampling • Technical Errors During ABG Sampling • Step-by-Step ABG Interpretation
- 3. Arterial Blood Gas (ABG) • Measures the partial pressures of oxygen (PaO2) and Carbon dioxide (PaCO2), as well as the pH and bicarbonate (HCO3-) levels in arterial blood
- 4. ABG Component • pH: Indicates the acidity or alkalinity of the blood. • Normal Range: 7.35-7.45. • Significance: Determines if the blood is acidic (pH < 7.35) or alkaline (pH > 7.45), reflecting the overall acid-base status. • PaO2 (Partial Pressure of Oxygen): Measures the amount of oxygen dissolved in arterial blood. • Normal Range: 75-100 mmHg. • Significance: Assesses how well oxygen is being transferred from the lungs to the blood, indicating oxygenation status.
- 5. ABG Component • PaCO2 (Partial Pressure of Carbon Dioxide): Measures the amount of carbon dioxide dissolved in arterial blood. • Normal Range: 35-45 mmHg. • Significance: Evaluates the effectiveness of ventilation; high PaCO2 suggests hypoventilation (respiratory acidosis), while low PaCO2 indicates hyperventilation (respiratory alkalosis). • HCO3- (Bicarbonate): Reflects the metabolic component of acid- base balance. • Normal Range: 22-26 mEq/L. • Significance: Helps determine if a metabolic issue (e.g., metabolic acidosis or alkalosis) is affecting blood pH.
- 6. ABG Component • SaO2 (Oxygen Saturation): The percentage of hemoglobin saturated with oxygen. • Normal Range: 94-100%. • Significance: Indicates how effectively oxygen is being carried by hemoglobin in the blood.
- 7. Indications to ABG Sampling • Respiratory Function: • Suspected respiratory failure. • Acute or chronic lung diseases (e.g., COPD, asthma). • Monitoring ventilation in critically ill patients. • Acid-Base Disorders: • Unexplained altered mental status. • Suspected metabolic conditions (e.g., DKA, sepsis, renal failure). • Severe electrolyte imbalances. • Oxygenation: • Confirming and assessing hypoxemia. • Post-cardiopulmonary resuscitation (CPR) evaluation. • Monitoring oxygen therapy effectiveness.
- 8. Indications to ABG Sampling • Therapy Response: • Adjusting ventilator settings. • Monitoring metabolic interventions (e.g., bicarbonate therapy). • Preoperative Evaluation: • Assessing baseline respiratory function in patients with pulmonary disease. • Hemoglobinopathies: • Suspected carbon monoxide (CO) poisoning. • Suspected methemoglobinemia.
- 9. Contraindications to ABG Sampling • Local infection (evidence of erythema or swelling at the sample site) • Distorted anatomy (unable to palpate the pulse). Anatomy is often distorted by repeated previous attempts at ABG sampling. • Arterio-venous fistula at or near the sample site. • Known coagulopathy or recent thrombolysis • Peripheral vascular disease of the limb with the sample site
- 10. Equipments Required for ABG Sampling • Arterial Blood Gas Syringe: For collecting the sample. • Needle: To access the artery. • Antiseptic Solution: For skin cleaning. • Gloves: For protection and sterility. • Bandage or Gauze: To stop bleeding post-sampling. • Labeling Materials: For identifying the sample. • Ice or Cooling Container: To preserve the sample.
- 11. Sites for ABG Sampling • Radial Artery • Location: Wrist, on the thumb side. • Reason: Most commonly used due to its accessibility and relatively low risk of complications. • Brachial Artery • Location: Inner arm, near the elbow. • Reason: Used when radial artery access is difficult; higher risk of complications compared to radial.
- 12. Sites for ABG Sampling • Femoral Artery • Location: Groin area • Reason: Used in critical situations or when other sites are inaccessible; higher risk of complications and requires more skill • Dorsalis Pedis Artery • Location: Top of the foot • Reason: Alternative site when other arteries are not accessible.
- 13. Procedure for ABG sampling • ABG sampling is most commonly performed at the radial artery. • The patency of the ulnar artery must be assessed before ABG sampling from the radial artery. • This is to ensure that the arterial supply to the hand will not be compromised should injury occur to the radial artery during the ABG sampling process. • The assessment of the patency of the ulnar artery is called Allen’s test.
- 14. ALLEN’S TEST • Both the radial and ulnar arteries are occluded with the patient’s fist tightly clenched • Patient releases their clenched fist. Pressure on radial and ulnar arteries is maintained • Pressure released on ulnar artery Assess how long the palm takes to return to normal colour. Normal is less than 2 seconds Prolongation of time indicates an abnormal test. *AN ABNORMAL ALLEN’S TEST IS A CONTRAINDICATION TO RADIAL ARTERY SAMPLING*
- 15. Procedure for ABG sampling • Obtain verbal consent from the patient explaining the procedure. • Check for contraindications. • Don the appropriate personal protective equipment. • Perform Allen’s test to ensure ulnar artery patency. • Position the patient’s wrist in supination and extension with a pillow or rolled-up blanket underneath the wrist. *Set-up the tray with the necessary equipment: cleaning swab, ABG sampling syringe, gauze and tape*
- 16. Procedure for ABG sampling • Clean the patient’s skin with the cleaning swab • Palpate for the radial pulse • When the location of the pulse is identified- the operator should fix this between their index and middle fingers. • Take the ABG sampling syringe in the other hand and insert the needle distally to the index and middle fingers which are fixing the patient’s radial artery. • . Depending on the ABG sampling syringe, when the needle enters the artery, the syringe will self-fill or there will be a “flash-back” and the operator will require to aspirate using the plunger. • Withdraw 1-2 mls of sample • Remove the syringe from the radial artery and immediately apply pressure using gauze.
- 17. Procedure for ABG sampling
- 20. Precautions • Ideally use pre-heparinised ABG syringes • Syringes should be Flushed with 0.5ml of 1:1000 Heparin solution and emptied • Do not leave excessive heparin in the syringe. HEPARIN DILUTIONAL EFFECT HCO3 - pCO2
- 21. Technical Errors During ABG Sampling • Air Bubbles in the Syringe: • Issue: Can alter the results, particularly PaO2 and PaCO2. • Prevention: Ensure no air bubbles are present before sending the sample to the lab. • Improper Needle Insertion: • Issue: Can cause inadequate blood flow or damage to the artery • Prevention: Use correct angle (30-45 degrees) and technique to avoid complications. • Contamination: • Issue: Can affect the accuracy of results. • Prevention: Use sterile equipment and clean the site properly.
- 22. Technical Errors During ABG Sampling • Inadequate Mixing: • Issue: Blood may clot if not mixed properly with heparin. • Prevention: Gently mix the sample by rolling it between the hands. • Delayed Analysis: • Issue: Can lead to changes in gas levels and pH. • Prevention: Analyze the sample promptly or store on ice if there's a delay. • Incorrect Site Selection: • Issue: Can lead to complications or inaccurate results. • Prevention: Ensure correct site selection and proper technique.
- 23. ABG Interpretation • Step 1: Assess pH • pH < 7.35: Acidosis • pH > 7.45: Alkalosis • Step 2: Determine Respiratory Component (PaCO2) • PaCO2 > 45 mmHg: Respiratory Acidosis • PaCO2 < 35 mmHg: Respiratory Alkalosis • Step 3: Determine Metabolic Component (HCO3-) • HCO3- < 22 mEq/L: Metabolic Acidosis • HCO3- > 26 mEq/L: Metabolic Alkalosis
- 24. ABG Interpretation • Step 4: Determine Compensation • Assess whether the body is attempting to compensate for the primary disorder. • Full compensation: pH is normal but PaCO2 or HCO3- is abnormal. • Partial compensation: pH is abnormal with compensatory changes in PaCO2 or HCO3- • No compensation: pH is abnormal, while one of the component of PaCO2 or HCO3- are normal with no compensatory mechanism.
- 25. Disorder Primary Response Compensatory Response Metabolic Acidosis (H+ ) pH HCO3 - pCO2 Metabolic Alkalosis (H+ ) pH HCO3 - pCO2 Respiratory Acidosis (H+ ) pH pCO2 HCO3 - Respiratory Alkalosis (H+ ) pH pCO2 HCO3 -
- 26. Respiratory Disorders • Respiratory Acidosis: • Causes: Hypoventilation, COPD, respiratory muscle fatigue, sedative overdose. • ABG Findings: pH < 7.35, PaCO2 > 45 mmHg, normal or increased HCO3- if compensated. • Symptoms: Dyspnea, headache, confusion, lethargy. • Management: Improve ventilation, treat underlying cause, possible use of mechanical ventilation.
- 27. Respiratory Disorders • Respiratory Alkalosis: • Causes: Hyperventilation, anxiety, fever, pain, sepsis. • ABG Findings: pH > 7.45, PaCO2 < 35 mmHg, normal or decreased HCO3- if compensated. • Symptoms: Dizziness, tingling in extremities, chest pain, confusion. • Management: Reassurance, breathing into a paper bag, treat underlying cause.
- 28. Metabolic Disorders • Metabolic Acidosis: • Causes: Diabetic ketoacidosis, renal failure, lactic acidosis, severe diarrhea. • ABG Findings: pH < 7.35, HCO3- < 22 mEq/L, normal or decreased PaCO2 if compensated. • Symptoms: Rapid breathing (Kussmaul respirations), fatigue, nausea, confusion. • Management: Treat underlying cause, sodium bicarbonate in severe cases, hydration. HCO3 - Deficit(mEq)= 0.5 x Body weight (kg) x (24 - HCO3 - )
- 29. Metabolic Disorders • Metabolic Alkalosis: • Causes: Prolonged vomiting, excessive bicarbonate intake, diuretic use, hypokalemia. • ABG Findings: pH > 7.45, HCO3- > 26 mEq/L, normal or increased PaCO2 if compensated. • Symptoms: Muscle cramps, twitching, irritability, arrhythmias. • Management: Correct underlying cause, restore fluid and electrolyte balance.
- 30. Lactate and Lactic Acidosis • A byproduct of anaerobic metabolism. • Normal Range: 0.5-2.2 mmol/L (arterial). • Significance of Elevated Lactate Levels: • Lactic Acidosis: A form of metabolic acidosis with elevated lactate levels. • Common Causes: • Sepsis: Severe infection leading to tissue hypoxia. • Shock: Poor perfusion states causing anaerobic metabolism. • Severe Hypoxia: Insufficient oxygen delivery to tissues. • Clinical Presentation: Rapid breathing, confusion, hypotension, and potential organ failure. • Management: Address underlying cause (e.g., fluids, antibiotics for sepsis), consider oxygen therapy.
- 31. Compensation Mechanisms • Respiratory Compensation: • Mechanism: Lungs adjust ventilation to alter PaCO2 levels. • Timeframe: Minutes to hours. • Example: Metabolic acidosis with respiratory compensation results in hyperventilation to decrease PaCO2. • Renal Compensation: • Mechanism: Kidneys adjust HCO3- reabsorption and H+ excretion. • Timeframe: Hours to days. • Example: Respiratory acidosis with renal compensation results in increased HCO3- reabsorption to neutralize acidity.
- 32. Mixed Acid-Base Disorders • Occurs when two or more primary acid-base disturbances are present simultaneously. • Recognition of Mixed Disorders: • Examples: • Respiratory Acidosis with Metabolic Alkalosis: • Seen in COPD patients on diuretics. • ABG shows high PaCO2 and high HCO3-, pH may be near normal. • Respiratory Alkalosis with Metabolic Acidosis: • Seen in sepsis or salicylate poisoning. • ABG shows low PaCO2 and low HCO3-, pH may be near normal.
- 33. Abnormality pH pCO2 HCO3 - Respiratory Acidosis Uncompensated Partially Compensated Fully Compensated Respiratory Alkalosis Uncompensated Partially Compensated Fully Compensated Metabolic Acidosis Uncompensated Partially Compensated Fully Compensated Metabolic Alkalosis Uncompensated Partially Compensated Fully Compensated
- 34. ABG Samples
- 40. Thank You
Editor's Notes
- #19: Normal ABG
- #28: Components of the Formula:* - *Body Weight (kg):* Use the patient’s actual body weight. - *24 mEq/L:* This represents the normal bicarbonate level in the blood. - *HCO₃⁻ (mEq/L):* This is the bicarbonate level obtained from the patient’s ABG.- * Example Calculation:* - If a patient weighs 70 kg and their bicarbonate level from the ABG is 10 mEq/L: {Bicarbonate Deficit} = 0.5 \times 70 \times (24 - 10) = 0.5 \times 70 \times 14 = 490 \text{ mEq} \] - This means the patient is approximately 490 mEq short of bicarbonate. The general practice is to administer half of the calculated bicarbonate deficit initially, which allows for gradual correction and reduces the risk of overcorrection (which could cause metabolic alkalosis). you would administer 245 mL of the solution. - This dose is usually given over a period of 2-4 hours, not too rapidly, to allow the body to adjust.
- #35: Resoiratory Alkalosis
- #36: Normal ABG
- #37: Fully compensated Metabolic Acidosis
- #38: Respiratory Alkalosis