Question 10

College answer

Not available.

Discussion

The average reader doing these papers to prepare for the CICM Second Part Exam will probably want to see a model answer representing something the average trainee could write in under 10 minutes, rather than an elaborate explanation of how and why prone ventilation works. That elaborate explanation is available on the prone ventilation page, and in the physiology-oriented CICM First Part Exam page dealing with the effects of positioning on the mechanics of breathing. 

• Rationale
  • Improved V/Q matching
  • More homogeneous ventilation because of reduced difference between the dorsal and ventral pleural pressure
  • Less lung deformation, thus improved compliance
  • Increased FRC
  • Improved drainage of secretions
  • Improved response to recruitment manoeuvres 
  • Improved chest wall mechanics in obesity
• Advantages
  • Decreased oxygen requirements, therefore less oxygen toxicity
  • Low cost and low risk (especially in the awake patient)
  • Supported by more evidence than alternative rescue therapies (eg. inhaled pulmonary vasodilators)
  • Widely available, in contrast to other rescue strategies (eg. ECMO)
• Disadvantages
  • Contraindicated in spinal/pelvic instability, open abdomen, ventral burns or wounds, abdominal compartment syndrome
  • Needs to be done early in the course
  • Oxygenation benefits are often reversed by de-proning
  • For awake patients:
    • Uncomfortable
    • Impedes communication
    • Often cannot be tolerated for periods which would have a therapeutic effect (eg. 12-16 hours)
  • For intubated patients:
    • Difficulty of positioning and increased nursing workload
    • Decreased airway and central line site safety
    • Pressure areas, facial oedema
    • Raised intraabdominal and intracranial pressure
    • Haemodynamic instability is exacerbated
• PROSEVA trial:
  • ​​​​​​​Important findings:
    • Significant improvement in 28-day and 90-day mortality: 16% in prone vs. 32.8% in supine group
    • No increase in adverse events in prone group
  • Strengths:
    • Standardised ventilation and weaning strategy
    • Appropriate power calculation
    • Intention to treat analysis
  • Weaknesses:
    • 2015 patients not screened for inclusion, raising suspicion of selection bias
    • Some differences in baseline characteristics (eg. SOFA score)
    • All centres were very experienced in prone ventilation (reduces generalizability)