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CCA SERIES: ABG Interpretation ISOC MedEd 24/10/24BY DANIEL CHOUDHARYWhat does an ABG tell us? • pH [7.35-7.45] • PaCO [4.7-6.0kPa] 2 • PaO [11-13kPa] 2 • HCO - [22-26 mEq/L] 3 • Base Excess [-2 to +2 mmol/L] • Lactate [<2.2mmol/L] (if raised think SEPSIS) • +more, but let us focus on theseWhy do an ABG? • To work out if a patient is in respiratory failure • Suspected metabolic disturbances • To work out acid-base abnormalities • Don’t like the patient • Assess Oxygen therapy • To get a quick lactate value When might we need this?Background PhysiologyRespiratory Failures Type 1 Type2 HYPOXEMIC (Low oxygen) HYPERCAPNIC (High CO ) 2 NORMOCAPNIC (Normal/low CO ) Can also be Hypoxemic 2 Heavily associated with acute conditions VENTILATION FAILURE Failure of lungs to provide adequate oxygenFailure of lungs to clear CO 2 With this in mind can we think of potential examples of each respiratory failure?Respiratory Failures • Type 1 PE Pneumothorax Severe Asthma (Early) Pulmonary Oedema • Type 2 COPD Opioid Overdose Chest wall deformities Obesity relatedAcid-Base Control (simplified) • The body maintains Acid base balance in two key-ways • The respiratory system controls CO bala2ce, the higher the CO2 in the blood the more acidic (lower) pH Slower breathing retains more CO 2 Faster expels more CO 2 • The Kidneys regulate HCO - levels by choosing how much is reabsorbed, more HCO - 3 3 the higher the pH This means the kidneys can compensate for a low pH by buffering it with more HCO -3IF ALL ELSE FAILS • MORE CO 2ESS pH • MORE HCO -, MORE pH 3Metabolic disorders • ACIDOSIS Usually classified by anion gap, all positive ions minus all negative ions HCO3- can be balanced with Cl- High anion gap Anything that leads to acid accumulation, increased ingestion/production or reduced clearance Normal anion gap Anything that causes increased clearance of HCO3-, balanced by Cl-• High Anion GapMetabolic Disorders continued • Metabolic alkalosis Anything that loses acid, or gains bicarb Causes include Vomiting Cushing’s syndrome Diuretics Bicarbonate intake Licorice intakeCauses of Acid-base disturbances • Respiratory Causes • Anxiety, Pneumothorax, COPD, PE, Life threatening Asthma, Opioid overuse • Metabolic Causes • Diarrhea, Addison's disease, DKA, Vomiting, Aspirin overdose, Licorice • Try sort these causes into alkalosis’ and acidosis’Causes of Acid-base disturbances • Respiratory Causes • Anxiety, Pneumothorax, COPD, PE, Life threatening Asthma, Opioid overuse • Metabolic Causes • Diarrhea, Addison's disease, DKA, Vomiting, Aspirin overdose, Licorice, • ACIDOSIS/ALKALOSISCauses of Acid-base disturbances • Respiratory Causes • Anxiety, Pneumothorax, COPD, PE, Life threatening Asthma, Opioid overuse • Metabolic Causes • Diarrhea, Addison's disease, DKA, Vomiting, Aspirin overdose, Licorice, • ACIDOSIS/ALKALOSISWalk throughA step-by-step approach • Firstly check the pH, this will tell you if we are dealing with an Acid/Alkalosis, if normal could still have an acid/base abnormality but with full compensation • Normal range [7.35-7.45] • 1. pH 7.32 2.pH 7.49 Which is an acidosis and which is an alkalosis?A step-by-step approach • Firstly check the pH, this will tell you if we are dealing with an Acid/Alkalosis, if normal could still have an acid/base abnormality but with full compensation • Normal range [7.35-7.45] • 1. pH 7.32 2.pH 7.49 Which is an acidosis and which is an alkalosis?Step 2 • Secondly, check the CO2 levels. This can help give context to the pH results, as we mentioned earlier changing CO2 levels directly affect pH • If it makes sense, it’s a respiratory alka/acidosis. If it doesn’t seem to make sense, it is probably a compensation from a metabolic acid/alka. • Normal range [4.7-6.0kPa] • 1. 3.9 kPa 2. 7.4 kPa Which of these results would you expect in a pH 7.32 patient? Which of these results would indicate partial compensation in a 7.32 patient?Step 2 • Secondly, check the CO2 levels. This can help give context to the pH results, as we mentioned earlier changing CO2 levels directly affect pH • If it makes sense, it’s a respiratory alka/acidosis. If it doesn’t seem to make sense, it is probably a compensation from a metabolic acid/alka. • Normal range [4.7-6.0kPa] • 1. 3.9 kPa 2. 7.4 kPa Which of these results would you expect in a pH 7.32 patient? 2 Which of these results would indicate partial compensation in a 7.32 patient? 1Step 3 • Secondly, check the HCO3- levels. This can help give context to the pH results, as we mentioned earlier changing HCO3- levels directly affect pH • If it makes sense, it’s a metabolic alka/acidosis. If it doesn’t seem to make sense, it is probably a compensation. • Normal range [22-26mmol/l] • 1. 20mmol/l 2. 28mmol/l Which of these results would you expect in a pH 7.49 patient?Step 3 • Secondly, check the HCO3- levels. This can help give context to the pH results, as we mentioned earlier changing HCO3- levels directly affect pH • If it makes sense, it’s a metabolic alka/acidosis. If it doesn’t seem to make sense, it is probably a compensation. • Normal range [22-26mmol/l] • 1. 20mmol/l 2. 28mmol/l Which of these results would you expect in a pH 7.49 patient? 2.Base Excess • Base excess is given in ABGs, it is a measure of all bases and represents how much base is needed to return to the amount of acid or base that needs to be added to a blood sample to return it to a normal pH of 7.4 Not that useful as you can work out everything without itStep 4 • At this stage you should be able to diagnose the acid base abnormality Respiratory Acidosis: High PaCO₂ with low pH. Respiratory Alkalosis: Low PaCO₂ with high pH Metabolic Acidosis: Low HCO₃⁻ with low pH Metabolic Alkalosis: High HCO₃⁻ with high pH. If there is no compensation, think acute What would compensation look like in each of these? Step 4 STILL • At this stage you should be able to diagnose the acid base abnormality Respiratory Acidosis with partial M comp: High PaCO₂, High HCO3- with low pH. Respiratory Alkalosis with partial M comp: Low PaCO₂, Low HCO3- with high pH Metabolic Acidosis with partial R comp.: Low HCO₃⁻, Low CO2 with low pH Metabolic Alkalosis with partial R comp: High HCO₃⁻, High CO2 with high pH. (NVL) You might see this in the context of COPD as ‘acute on chronic’ as normally they should be pH balanced so something is acutely worsening their chronic diseaseStep 4 STILL STILL • Mixed is when you have both at the same time Mixed Acidosis: High PaCO₂, Low HCO3- with low pH. Mixed Alkalosis: Low PaCO₂, High HCO3- with high pHStep 5 • Now we want to check for any Respiratory failures, very simple • If oxygen is low and CO n2rmal/low, Type 1 • If CO raised, type 2 2 But remember, patient might be on supplementary oxygen which might mask results.Putting it all together Check Determine Check for Check pH Check CO 2 HCO - Acid-Base Resp. failure 3 abnormalityPractice timeRun through practice • pH: 7.50 (normal range: 7.35-7.45) High=Alkalotic • PaCO₂: 6.4 kPa (normal range: 4.7 – 6.0 kPa) High, but we expect low • PaO₂: 11.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 29 mmol/L High, consistentange 22-26 mmol/L) with metabolic • Base Excess (BE): +7 (normal range -2 to +2) Metabolic Alkalosis Partial respiratory compensationRun through practice • pH: 7.30 (normal range: 7.35-7.45) Low=Acidotic • PaCO₂: 7.2 kPa High, consistent with7 – 6.0 kPa) acidosis • PaO₂: 8.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 32 mmol/L (normal range 22-26 mmol/L) High, consistent with metabolic • Base Excess (BE): +5 compensational range -2 to +2) Describe the findings? What condition might cause this ABG? What O 2aturation would you titrate to in COPD?Run through practice • pH: 7.30 (normal range: 7.35-7.45) Low=Acidotic • PaCO₂: 7.2 kPa High, consistent with7 – 6.0 kPa) acidosis • PaO₂: 8.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 32 mmol/L (normal range 22-26 mmol/L) High, consistent with metabolic • Base Excess (BE): +5 compensational range -2 to +2) Describe the findings? Respiratory acidosis with partial m com What condition might cause this ABG? COPD, Chest wall deformity, MND What O 2aturation would you titrate to in COPD? 88-92Question 1 • pH: 7.37 (normal range: 7.35-7.45) Normal, towards acid • PaCO₂: 3.2 kPa (normal range: 4.7 – 6.0 kPa) Low, should be normal • PaO₂: 14.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 14 mmol/L Low, consistentrange 22-26 mmol/L) with metabolic • Base Excess (BE): -8 Acidosisnormal range -2 to +2) Describe the findings? What respiratory rate would you expect from this patient? These results in a diabetic patient would make you worried for? What breathing pattern would you expect in a diabetic patient? Question 1 • pH: 7.37 (normal range: 7.35-7.45) Normal, towards acid • PaCO₂: 3.2 kPa Low, should be normal– 6.0 kPa) • PaO₂: 14.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 14 mmol/L (normal range 22-26 mmol/L) Low, consistent with metabolic • Base Excess (BE): -8 Acidosisnormal range -2 to +2) Describe the findings? Fully compensated m acidosis What respiratory rate would you expect from this patient? Increased, These results in a diabetic patient would make you worried for? DKA What breathing pattern would you expect in a diabetic patient? KaussmalQuestion 2 • A 24-year-old woman presents to the emergency department with shortness of breath, chest tightness, and tingling in her hands and face • pH: 7.53 (normal range: 7.35-7.45) • PaCO₂: 3.5 kPa (normal range: 4.7 – 6.0 kPa) • PaO₂: 13.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 22 mmol/L (normal range 22-26 mmol/L) • Base Excess (BE): 0 (normal range -2 to +2) Describe the findings? Potential diagnosis? Why is bicarbonate normal?Question 2 • A 24-year-old woman presents to the emergency department with shortness of breath, chest tightness, and tingling in her hands and face. • pH: 7.53 (normal range: 7.35-7.45) • PaCO₂: 3.5 kPa (normal range: 4.7 – 6.0 kPa) • PaO₂: 13.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 22 mmol/L (normal range 22-26 mmol/L) • Base Excess (BE): 0 (normal range -2 to +2) Describe the findings? Acute Respiratory Alkalosis Potential diagnosis? Anxiety attack Why is bicarbonate normal? As it’s acute, not enough time to compensateQuestion 3 • pH: 7.17 (nLowal range: 7.35-7.45) • PaCO₂: 9.2 kPa High, acidotice: 4.7 – 6.0 kPa) • PaO₂: 7.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 14 mmol/L (normal range 22-26 mmol/L) Low, acid tic • Base Excess (BE): -5 (normal range -2 to +2) Describe the findings?Question 3 • pH: 7.17 (normal range: 7.35-7.45) Low • PaCO₂: 9.2 kPa (normal range: 4.7 – 6.0 kPa) High, acidotic • PaO₂: 7.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 14 mmol/L Low, acid ticl range 22-26 mmol/L) • Base Excess (BE): -5 (normal range -2 to +2) Describe the findings? Mixed acidosis• A 25-year-old woman with a history of asthma presents to the emergency department with worsening shortness of breath, chest tightness, and wheezing after exposure to a known allergen. Despite using her inhaler, her symptoms have not improved. On examination, she is tachypnoeic, using accessory muscles to breathe, and has widespread wheezing on auscultation • pH: 7.53 (normal range: 7.35-7.45) • PaCO₂: 4.5 kPa (normal range: 4.7 – 6.0 kPa) • PaO₂: 7.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 23 mmol/L (normal range 22-26 mmol/L) • Base Excess (BE): 0 (normal range -2 to +2) Describe the abnormality? What is the acronym used in acute asthma and what steps next? • A 25-year-old woman with a history of asthma presents to the emergency department with worsening shortness of breath, chest tightness, and wheezing after exposure to a known allergen. Despite using her inhaler, her symptoms have not improved. On examination, she is tachypnoeic, using accessory muscles to breathe, and has widespread wheezing on auscultation • pH: 7.53 (normal range: 7.35-7.45) • PaCO₂: 4.5 kPa (normal range: 4.7 – 6.0 kPa) • PaO₂: 7.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 23 mmol/L (normal range 22-26 mmol/L) • Base Excess (BE): 0 (normal range -2 to +2) Describe the abnormality? Respiratory alkalosis Type 1 resp failure What is the acronym used in acute asthma and what steps next? OSHIMTE• The same patient, is handed over to the night shift team a few hours later. Her respiratory rate has slowed, she is no longer seems struggling to breathe, and her wheezing has become quieter. An ABG is performed on supplemental oxygen. • pH: 7.23 (normal range: 7.35-7.45) • PaCO₂: 6.5 kPa (normal range: 4.7 – 6.0 kPa) • PaO₂: 12.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 26 mmol/L (normal range 22-26 mmol/L) • Base Excess (BE): +2 (normal range -2 to +2) Describe the abnormality? Why are we very worried right now? What are signs the patient is going into respiratory arrest?• The same patient, is handed over to the night shift team a few hours later. Her respiratory rate has slowed, she is no longer seems struggling to breathe, and her wheezing has become quieter. An ABG is performed on supplemental oxygen. • pH: 7.23 (normal range: 7.35-7.45) • PaCO₂: 6.5 kPa (normal range: 4.7 – 6.0 kPa) • PaO₂: 9.2 kPa (normal, range: 10.5 – 13.5 kPa) • HCO₃⁻: 26 mmol/L (normal range 22-26 mmol/L) • Base Excess (BE): +2 (normal range -2 to +2) Describe the abnormality? Resp acidosis, type 2 failure Why are we very worried right now? Patient is becoming exhausted What are signs the patient is going into respiratory arrest? Silent chest, Paradoxical breathing, bradycardia, confusionMore questions • A 45-year-old woman presents with persistent vomiting over the past week due to severe gastritis. She reports feeling weak and dizzy. • What is the expected acid base abnormality? • What would you expect the patients breathing to be like? • What metabolite are we worried about in chronic vomiting?More questions • A 45-year-old woman presents with persistent vomiting over the past week due to severe gastritis. She reports feeling weak and dizzy. • What is the expected acid base abnormality? Metabolic Alkalosis • What would you expect the patients breathing to be like? Slow breathing • What metabolite are we worried about in chronic vomiting? Worried about HYPOkalaemiaMore questions • A 75-year-old woman is brought to the emergency department with fever, confusion, and low blood pressure. She has a high white cell count, a likely source of infection and a raised lactate. • What is the expected acid base abnormality? • What is the expected anion gap? • What is the sepsis 6?More questions • A 75-year-old woman is brought to the emergency department with fever, confusion, and low blood pressure. She has a high white cell count, a likely source of infection and a raised lactate. • What is the expected acid base abnormality? Metabolic Acidosis • What is the expected anion gap? Raised anion gap • What is the sepsis 6? Give oxygen, abx, fluids, Take lactate, urine output, blood culturesTHE ENDThanks for coming!