Tutorial ABG Interpretation Student PDF

Interpretation of Blood Gas Analysis Ms. Sammi CHAU Senior lecturer  Intended Learning Outcome At the end of the class, students should be able to: Understand the principles of arterial blood gas and the major components of arterial blood gas Explain the concept of bal...

Interpretation of Blood Gas Analysis Ms. Sammi CHAU Senior lecturer  Intended Learning Outcome At the end of the class, students should be able to: Understand the principles of arterial blood gas and the major components of arterial blood gas Explain the concept of balance of the acid-base disturbances Interpret arterial blood gases and generate differential diagnosis of respiratory and metabolic acid-base disturbances  Respiratory Failure Respiratory failure is an acute condition and medical emergency in which respiratory system fails in one or both of gas exchange functions: Carbon Oxygenation dioxide elimination  Causes of Respiratory Failure Abnormality of the chest wall Chest wound, Severe chest deformity Abnormality of lung tissue Acute respiratory distress syndrome (ARDS), Pneumonia, Pulmonary oedema, Pulmonary fibrosis Airflow obstruction COPD, Asthma, Bronchiectasis Muscle weakness Neuromuscular diseases, Spinal cord injury Others Pulmonary embolism, Intoxification (drug or alcohol), Obesity/sleep apnoea  Symptoms of Respiratory Failure Shortness of breath (dyspnoea) Rapid breathing (tachypnoea) Cyanosis (Discoloration: bluish, gray or whitish) in lips, fingers and toes Excessive sweating Confusion or agitation/restlessness Fatigue or drowsiness Headache Blurred vision  Types of Respiratory Failure Type 1 Respiratory Failure Type 2 Respiratory Failure Hypoxemic respiratory failure Hypercapnic respiratory failure Is associated with damage to the lung Occurs when alveolar ventilation is tissue which prevents adequate insufficient to remove carbon dioxide oxygenation of the blood The PaO2 in blood is normal or low The PaO2 in blood is low (45mmHg) (≤ 35mmHg) How to make differential diagnosis? ABG tells you!  What is arterial blood gas (ABG)? ABG provides an accurate measure of oxygen uptake and carbon dioxide removal by the respiratory system Sample is usually drawn from radial artery or central line Steady-state gas exchange Patient is resting quietly Constant inspired oxygen level (FiO2) Diagnostic tool to assess: 1. Oxygenation status (oxygen) 2. Ventilation status (carbon dioxide) 3. Acid-base balance Blood Gas Data pH BE PaO2 ABG HCO3- PaCO2  Blood Gas Data pH Power of hydrogen, H+ ion concentration Normal Values Level of acidity or alkalinity in blood pH 7.35 – 7.45 PaO2 (oxygenation) Partial pressure of oxygen in the blood (mmHg or kPa) PaO2 75 – 100 mmHg or PaCO2 (ventilation) 10.5 – 13.5 kPa Partial pressure of carbon dioxide in the blood (mmHg or kPa) PaCO2 35 – 45 mmHg or 4.7 – 6.0 kPa HCO3- HCO3- 22 – 26 mmol/L Bicarbonate ion level in the blood (mmol/L) Base excess (BE) BE -2 to +2 mEq/L Unit of acid required to normalize blood pH (mEq/L) SaO2 saturation SaO2 95 – 100% Percentage of oxyhemoglobin in the blood Blood Gas Data pH BE PaO2 ABG HCO3- PaCO2  Acid Base Balance What is acid base balance important? Expressed in pH An acid is a hydrogen ion donor A base is a hydrogen ion receiver Normal cellular and enzymatic activities Normal metabolism results in the production of acids Acids produced by metabolism have to be excreted or buffered Respiratory system and renal system Normal value of pH: 7.35 – 7.45 + ↑ 𝐻 = ↓ 𝑝𝐻 Blood Gas Data pH BE PaO2 ABG HCO3- PaCO2  Monitoring of Oxygenation Status Inspired gas In-line oxygen analyser (FiO2) O2 level in blood Pulse oximetry (SpO2) Partial pressure of oxygen (PaO2) from blood gas analysis Transcutaneous PO2 (TcPO2) in pediatrics Expired gas End expiratory oxygen analyser (FEO2)  Partial Pressure of Oxygen (PaO2) Normal value of PaO2: 75 – 100 mmHg or 10.5 – 13.5 kPa Partial pressure of oxygen reflects blood oxygenation In arterial blood: PaO2 In venous blood: PvO2 Alveolar gas oxygen tension: PAO2 PaO2 < 75 mmHg or < 10.5 kPa PaO2 > 100 mmHg or > 13.5 kPa Hypoxemia Hyperoxemia Blood Gas Data pH BE PaO2 ABG HCO3- PaCO2  Monitoring of Expired CO2 CO2 level in blood Transcutaneous CO2 monitoring (tcpCO2) Partial pressure of carbon dioxide (PaCO2) from blood gas analysis Expired gas End-tidal carbon dioxide from capnography (ETCO2)  Partial Pressure of Carbon Dioxide (PaCO2) Normal value of PaCO2: 35 – 45 mmHg or 4.7 – 6.0 kPa Reflect the state of alveolar ventilation Hypocapnia Hypercapnia ↓PaCO2 = or ↑ PaCO2 = or Hyperventilation Hypoventilation Hypercapnia Hypocapnia Respiratory depression causes Overbreathing that is associated with retention of CO2 reduction in CO2 Hypoventilation Hyperventilation Respiratory acidosis Respiratory alkalosis Signs and symptoms Signs and symptoms Shallow and slow breathing Rapid breathing or SOB confusion/ or disorientation Dizziness or lightheadedness Lethargy or fatigue Weakness Headache Confusion Dizziness Numbness and tingling in the fingers or Nausea around the mouth Muscle spasms in hands and feet Chest pain, palpitation Blood Gas Data pH BE PaO2 ABG HCO3- PaCO2  Bicarbonate - (HCO3 ) Bicarbonate HCO3-, a form of carbon dioxide − + 𝐻2𝑂 + 𝐶𝑂2 ↔ 𝐻2𝐶𝑂3 ↔ 𝐻𝐶𝑂3 +𝐻 A byproduct of body metabolism (from tissue) Can be exhaled via lungs and regulated by kidneys It is a base in nature Regulate the pH of the blood or acid balance Work with other electrolytes Sodium, potassium and chloride Metabolic panel (anion gap analysis) Normal value of HCO3-: 22 – 26 mmol/L Blood Gas Data pH BE PaO2 ABG HCO3- PaCO2  Base Excess (BE) The metabolic component of the acid-base balance is reflected in the base excess It is calculated value derived from the blood pH and PaCO2 Represents the amount of acid required to normalize 1L of blood to its normal pH at a PaCO2 of 40mmHg In metabolic alkalosis, the BE increases (more positive) In metabolic acidosis, the BE decreases (more negative) Normal value of BE: -2 to +2 mEq/L Acid-Base Balance & Buffer Systems  ABG: Acid-Base Balance Respiratory ↑ acidosis ↓ alkalosis PaCO2 Metabolic pH Metabolic ↑ (+) alkalosis BE HCO3- ↑ alkalosis ↓ (-) acidosis ↓ acidosis  Systemic Effect of pH pH < 7.35 pH > 7.45 Acidosis Alkalosis Right shift in oxyhaemoglobin Left shift in oxyhaemoglobin dissociation curve dissociation curve In severe acidosis, catecholamine Increased response to catecholamine responsiveness decreases and may cause cardiac collapse Alkalosis causes vasodilatation in Lower threshold for ventricular venous system (decreased vascular fibrillation resistance and tone) In the venous system, direct effect of Reduced cerebral blood flow from acidosis is vasoconstriction cerebral vasoconstriction Shifting of blood from peripheral system to pulmonary vascular bed (pulmonary oedema) Adopted from Osmosis from Elsevier  Causes of Acid-Base Disturbance Respiratory Metabolic Due to a change in CO2 level Due to a change in blood bicarbonate levels Respiratory acidosis Metabolic acidosis Hypoventilation (↑ CO2) Excessive production of acid (DKA, lactic acidosis) Respiratory alkalosis Ingestion of acids (Methanol, ethanol, ethylene glycol) Hyperventilation (↓ CO2) Inability to clear acids (renal failure) Loss of bicarbonate (diarrhoea, renal tubular acidosis) Metabolic alkalosis Persistent vomiting Hyperaldosteronaemia Diuretic use Massive transfusion  Acid-Base Balance & Homeostasis + 𝑤𝑎𝑡𝑒𝑟 + 𝑐𝑎𝑟𝑏𝑜𝑛 𝑑𝑖𝑜𝑥𝑖𝑑𝑒 ↔ 𝑐𝑎𝑟𝑏𝑜𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 ↔ 𝑏𝑖𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒 + 𝐻 − + 𝐻2𝑂 + 𝐶𝑂2 ↔ 𝐻2𝐶𝑂3 ↔ 𝐻𝐶𝑂3 + 𝐻 In the face of acid-base disturbance, the metabolic or respiratory system to maintain the homeostasis and normalize the pH  Acid-Base Regulations 1. Buffers Weak acids and weak bases Bicarbonate, Phosphate, Protein Work chemically to minimize changes in pH Regulation takes seconds to minutes to begin 2. Respiratory system By release of carbon dioxide to regulate pH Through controlling ventilation (the rate and the depth of breathing) Compensation minutes to initiate 3. Renal system Excrete excess acids or bases Compensation may need several days to take effect  Buffer System The Henderson-Hasselbalch Equation − [ 𝐻𝐶𝑂3 ] 𝑝𝐻 = 𝑝𝐾𝐴 + 𝑙𝑜𝑔 [𝐶𝑂2] − + 𝐻2𝑂 + 𝐶𝑂2 ↔ 𝐻2𝐶𝑂3 ↔ 𝐻𝐶𝑂3 +𝐻 In every ↑ 10mmHg in CO2 will lead to ↑ in 1mmol HCO3-  Acid-Base Balance & Homeostasis 2 1 ↑CO2 production causes H+ is added (more acidic) breathing faster results in ↓pH − + 𝐻2𝑂 + 𝐶𝑂2 ↔ 𝐻2𝐶𝑂3 ↔ 𝐻𝐶𝑂3 + 𝐻 3 4 Hyperventilation ↓CO2 leads to ↓ production of H+, washes out CO2 (↓CO2) then pH ↑ normalizes  Balance of Acid-Base Disturbance Respiratory Metabolic Respiratory acidosis Metabolic acidosis Increased pCO2 and decreased pH HCO3- in deficit and decreased pH with a base deficit and HCO3- Compensatory mechanism Compensatory mechanism Kidney will retain HCO3- Lungs will blow off CO2 To increase the pH To raise the pH Respiratory alkalosis Metabolic alkalosis Decreased pCO2 and increased pH HCO3- in excess and increased pH with base excess Compensatory mechanism Compensatory mechanism Lungs will retain CO2 Kidney will excrete HCO3- Kidneys conserve H+ ions and To lower the pH eliminate HCO3- in urine (alkaline)  Compensation Uncompensated pH: not within normal range Causative system is not within normal range Compensatory system within normal range Partially compensated − [ 𝑯𝑪𝑶𝟑 ] pH: not within normal range 𝒑𝑯 = 𝒑𝑲𝑨 + 𝒍𝒐𝒈 [𝑪𝑶𝟐] Causative system is not within normal range Compensatory system is not within normal range Compensated or fully compensated pH: within normal range Causative system is not within normal range Compensatory system is not within normal range Interpretation of ABG  Step-wise Approach to ABG Interpretation 1. pH – Is the pH normal? Acidic or alkalotic? 2. PaCO2 – Is PaCO2 normal? High or low? 3. HCO3- – Is HCO3- normal? High or low? 4. Determine the primary cause of acid-base disturbance 5. Determine the presence of compensation 6. PaO2 and O2 saturation – Is oxygenation normal? High or low?  Step-wise Approach to ABG Interpretation number (120) 1. pH – Is the pH normal? critical 6.8 Ep 8.0 Low pH 7.35 – 7.45 High pH Acidosis Normal pH Alkalosis  Step-wise Approach to ABG Interpretation 2. PaCO2 – Is PaCO2 normal? High or low? 35 – 45 mmHg High PaCO2 Low PaCO2 4.7 – 6.0 kPa Acidosis Normal Alkalosis PaCO2 ↑ PaCO2 = ↓ pH ↓PaCO2 = ↑pH Adopted from www.freepik.com  Step-wise Approach to ABG Interpretation 3. HCO3- – Is HCO3- normal? High or low? Low HCO3- 22 – 26 mmol/L High HCO3- Acidosis Normal Alkalosis HCO3- ↓HCO3- = ↓pH ↑HCO3- = ↑pH Adopted from www.freepik.com  Step-wise Approach to ABG Interpretation 4. Determine the acid-base disturbance is respiratory or metabolic. Match PaCO2 or HCO3- with pH If pH is acidotic (7.45), the HCO3- is alkalotic, the acid-base disturbance is caused by metabolic system. It is called metabolic alkalosis.  Step-wise Approach to ABG Interpretation I 4. Determine the disturbance is respiratory or metabolic. pH Acidosis Alkalosis ↑ PaCO2 ↓ HCO3- ↓ PaCO2 ↑ HCO3- Respiratory Metabolic Respiratory Metabolic Acidosis Acidosis Alkalosis Alkalosis  Step-wise Approach to ABG Interpretation 5. Determine the presence of compensation Does PaCO2 or HCO3- goes in the opposite direction of the pH If pH is acidotic, PaCO2 is acidotic, and HCO3- is alkalotic PaCO2 matches with pH, both acidotic, making the primary acid-base disorder respiratory acidosis HCO3- is alkalotic and goes in opposite direction of pH, suggestive of evidence of compensation from metabolic system  Step-wise Approach to ABG Interpretation 6. PaO2 and O2 saturation – Is oxygenation normal? High or low? Evaluate the oxygenation PaO2 75 – 100 mmHg Low oxygenation 10.5 – 13.5 kPa High oxygenation SaO2 95 – 100% If PaO2 and O2 saturation is below normal, this indicates hypoxemia. If PaO2 and O2 saturation is above normal, this suggests hyperoxemia.  Implications for Physiotherapy Possible modification of ventilation affecting the acid-base status of the body Able to determine the degree of compensation for a patient’s respiratory acidosis Understand why is it necessary to keep a patient’s pH within the normal range  Case Discussion Acknowledgement: Oxford Medical Education https://oxfordmedicaleducation.com/abgs/abg-examples/  Case 1 You are called to see a 54 year old lady on the ward. She is three days post-cholecystectomy and has been complaining of shortness of control breath. Her ABG is as follows: Breathing - pH: 7.49 (7.35-7.45) Al pO2: 7.5 (10–14) ↓ - meassess patient pCO2: 3.9 (4.5–6.0) Al HCO3: 22 (22-26) N BE: -1 (-2 to +2) N fallure Type Respiratory Other values within normal range 1 What would be the ABG interpretation? Respiratory Alkolosic (x compensated)  Case 2 A 64 year old gentleman with a history of COPD presents with worsening shortness of breath and increased sputum production. pH: 7.21 (7.35-7.45) Acidic sputum/dyspred - pO2: 7.2 (10–14) ↓ pCO2: 8.5 (4.5–6.0) Acidic Breathing my - HCO3: 29 (22-26) ↑ (AI) retable x pulmonary - BE: +4 (-2 to +2) Other values within normal range What would be the ABG interpretation? Type I respiratory faliure with respiratory Acidosis (partially compensated  Case 3 A 75 year old gentleman living in the community is being assessed for home oxygen. His ABG is as follows: pH: 7.36 (7.35-7.45) Normal pO2: 8.0 (10–14) ↓ pCO2: 7.6 (4.5–6.0) Acidic High HCO3: 31 (22-26) Al High BE: +5 (-2 to +2) Other values within normal range What would be the ABG interpretation?