Respiratory Data & Imaging

• Arterial blood gas (ABG) analysis

  A common test carried out on critically ill patients to provide key information about acid state, respiratory function, metabolic function, and oxygen level
• Purpose of ABG analysis

  • Provides information about:
  • Acid state
  • Respiratory function
  • Metabolic function
  • Oxygen level
  • Other information: lactate, electrolytes, SaO2, co-oximetry
• ABG interpretation procedure


  Measure concentrations of gases by partial pressures

  2. Acid is the concentration of hydrogen ions ([H+])

  3. An increase in PaCO2 leads to acidosis

  4. pH is a negative logarithm of the [H+]

  • An increase in [H+] causes a FALL in pH
  • Small changes in pH mean BIG changes in [H+]

  5. Acidaemia or alkalaemia refers to the blood pH change

  6. Acidosis or alkalosis refers to the process bringing about the pH changes

  7. In the acute situation the body does not fully compensate

  8. Marker of the respiratory system is PaCO2

  9. Marker of the metabolic system is HCO3- or SBE
• Standard Base Excess (SBE)

  A measure of metabolic acid-base status
• Learning objectives


  At the end of this session, further practice and on completion of the recommended reading, you will be able to:

  • Identify core anatomical features on a plain CXR
  • Demonstrate a systematic method for CXR interpretation
  • List common medical radiological abnormalities
  • Diagnose common medical conditions by their CXR appearance
• The body has two acid disposal systems: respiratory system and metabolic system
• Acid production and removal


  Cells produce CO2 and acid as waste products of normal metabolism

  Respiratory system removes acid by converting H2CO3 to H2O and CO2

  Metabolic system removes acid by increasing HCO3- concentration
• Increase in PaCO2


  Leads to acidosis
• Increase in [H+]


  Causes a fall in pH
• Small changes in pH mean big changes in [H+]
• Acidaemia


  Blood pH change towards acidity
• Alkalaemia


  Blood pH change towards alkalinity
• Chest Radiology: An Introduction


  • Medical Knowledge, Skills & Behaviours for Patient Care I (UM4001)
  • Michael Ticchio, MSc PA-C
  • Senior Lecturer, Physician Associate Programmes
• Acidosis


  Process bringing about a pH change towards acidity
• Alkalosis


  Process bringing about a pH change towards alkalinity
• In the acute situation, the body does not fully compensate for acid-base disturbances
• Compensation is in the same direction as the primary problem
• Times up


  1. What technical issues can you see?

  2. What pathological problems can you see?
• Reasons for a normal pH

  • Respiratory acidosis with metabolic compensation

  Respiratory alkalosis with metabolic compensation

  Metabolic acidosis with respiratory compensation
• The anion gap can help clarify the cause of metabolic acidosis
• Normal anion gap is 4-12 mmol/L, high anion gap is above 12 mmol/L
• Increased anion gap indicates unmeasured anions, normal anion gap indicates measured anions
• Interpreting PaO2 requires considering the FiO2
• Radiological anatomy


  • Chest radiology introduction
  • 3D body onto a 2D image
• PaO2 should be higher than the FiO2, as oxygen is taken up in the lungs
• PaO2 less than 10 kPa indicates impaired oxygen uptake
• Mediastinum


  Orientation of the heart
• Heart & valves


  CXR: Location of heart valves
• Lungs & Fissures


  • CXR: Horizontal fissure
  • Why are lungs split into lobes?
• Oblique (major) fissure


  T4 to the 6th rib near the MCL
• Horizontal (minor) fissure


  4th rib costal cartilage to the oblique fissure in the midaxillary line
• Chest Radiology


  A Continuation
• Right Upper Lobe


  • CXR: Lateral view
  • RUL
• Medical Knowledge, Skills & Behaviours for Patient Care I (UM4001)

  Course title
• Michael Ticchio, MSc PA-C


  Senior Lecturer, Physician Associate Programmes
• Right Middle Lobe


  • CXR: Lateral view
  • RML
• Learning objectives


  • Demonstrate a systematic method for CXR interpretation
  • Diagnose common medical conditions by their CXR appearance
  • Recall advantages and disadvantages of CT imaging
  • List indications for chest CT
  • Identify anatomical features on a chest CT
  • Identify common medical conditions on chest CT
• Right Lower Lobe


  • CXR: Lateral view
  • RLL
• CXR: Systematic interpretation


  1. 10 second stare

  2. A: Adequacy; alignment; apparatus

  3. B: Bones & joints

  4. C: Central structures

  5. S: Soft tissue

  6. Lateral (lungs) & peripheral

  7. 4 Pit fall areas
• Where is the abnormality?

  CXR: Lateral view