Arterial Blood Gases

• What are arterial blood gases (ABGs) commonly used to monitor?

  Acute respiratory conditions, especially type 2 respiratory failure.
• What information do ABGs provide?

  They provide information about acid-base balance, blood gases, bicarbonate, lactate, haemoglobin, and electrolytes.
• What are the normal values for pH and PaO2 in arterial blood gases?

  • pH: 7.35 – 7.45
  • PaO2: 10.7 – 13.3 kPa
• What are the normal values for PaCO2 and HCO3 in arterial blood gases?

  • PaCO2: 4.7 – 6.0 kPa
  • HCO3: 22 – 26 mmol/L
• What are the normal values for base excess and lactate in arterial blood gases?

  • Base excess: -2 – +2
  • Lactate: 0.5 – 1 mmol/L
• What does a low PaO2 indicate?

  A low PaO2 indicates hypoxia.
• What is the FiO2 in room air?

  21%
• What is the purpose of Venturi masks?

  Venturi masks are used to control the FiO2.
• What indicates type 1 respiratory failure?

  Normal PaCO2 with low PaO2 indicates type 1 respiratory failure.
• What indicates type 2 respiratory failure?

  Raised PaCO2 with low PaO2 indicates type 2 respiratory failure.
• What are the pH levels indicating acidosis and alkalosis?

  • Acidosis: pH under 7.35
  • Normal: pH 7.35 – 7.45
  • Alkalosis: pH above 7.45
• How does carbon dioxide affect blood acidity?

  Carbon dioxide makes blood acidotic by breaking down into carbonic acid.
• What does low pH with raised PaCO2 indicate?

  It indicates respiratory acidosis.
• What happens to bicarbonate production during acute respiratory acidosis?

  Bicarbonate cannot be produced fast enough to compensate for rising carbon dioxide.
• What does raised bicarbonate indicate in chronic CO2 retention?

  It indicates that the kidneys have produced additional bicarbonate to balance the acidic CO2.
• What is respiratory alkalosis?

  Respiratory alkalosis occurs when a patient has a raised respiratory rate and "blows off" too much CO2.
• What are common scenarios for respiratory alkalosis?

  Common scenarios include hyperventilation syndrome and pulmonary embolism.
• What characterizes metabolic acidosis?

  Metabolic acidosis is characterized by low pH and low bicarbonate.
• What are the causes of metabolic acidosis?

  • Raised lactate (indicating tissue hypoxia)
  • Raised ketones (in diabetic ketoacidosis)
  • Increased hydrogen ions (due to renal failure)
  • Reduced bicarbonate (due to diarrhoea or renal failure)
• What characterizes metabolic alkalosis?

  Metabolic alkalosis is characterized by raised pH and raised bicarbonate.
• What causes metabolic alkalosis?

  • Loss of hydrogen ions from the gastrointestinal tract (due to vomiting)
  • Loss of hydrogen ions from the kidneys (due to increased aldosterone activity)
• What conditions can lead to increased aldosterone activity?

  • Conn’s syndrome (primary hyperaldosteronism)
  • Liver cirrhosis
  • Heart failure
  • Loop diuretics
  • Thiazide diuretics
• When was the last update of this material?

  May 2023.
• What is the benefit of testing your knowledge of arterial blood gases?

  It helps identify what you missed and strengthens your understanding and retention.
• What resources are available for learning about arterial blood gases?

  • How to Learn Medicine Course
  • Digital Flashcards
  • Anki-like Fact Trainer
  • Short Answer Questions
  • Multiple Choice Questions
  • Extended Matching Questions
  • Revision Tracking Tool
  • OSCE Practice Tool