Critical Care Refresher Course: Acute Respiratory Failure

Mechanical Ventilation Physiology (Antonelli)

Revision of basic physiology – mechanical vs normal breathing

Purpose of mechanical ventilation

  • maintain or improve ventilation and tissue oxygenation
  • decrease work of breathing

Effects of mechanical ventilation on respiratory system

  • Increase V/Q
  • Decrease elastic workload
  • Decrease resistive workload
  • Decrease workload to overcome iPEEP

 

References

Review of respiratory mechanics in mechanical and spontaneous ventilation

Mechanical ventilation: past lessons and the near future

Clinical review: Update on neurally adjusted ventilatory assist – report of a round-table conference

 

COPD and mechanical ventilation (Mancebo)

COPD

  • expiratory airflow limitations
  • loss of elastic recoil
  • dynamic airway compression when lung deflate
  • dynamic hyperinflation

Look carefully at the flow/pressure ventilatory loops in order to optimise mechanical support

Strategy

  • Bronchodilators
  • Reduce ventilatory requirements
  • Modify ventilatory settings
  • Use ETT with large diameter
  • Use equipment with low expitatory resistance
  • If difficult to wean, look at CV performance and LV dysfunction

 

References

Mechanical ventilation in COPD

Physiological comparison of three spontaneous breathing trials in difficult-to-wean patients.

 

ARDS and Mechanical Ventilation (Saha)

Achieve adequate gas exchange without iatrogenic damage – volutrauma, barotrauma, atelectatrauma

No evidence that smaller tidal volumes (TV = 3ml/kg) is better currently. Awaiting SUPERNOVA Trial

Weak evidence for recruitment manoeuvres

If you are going to PRONE ventilate, you need at least 16 hours

Fluid balance – negative better

 

References

Xtravent study – lower tidal volumes

Recruitment manoeuvres

Neuromuscular blockers in ARDS

PRONE ventilation and ARDS

OSCAR HFOV Trial

OSCILLATE Trial