Table 2

The three determinants of ventilation and common pathophysiological conditions associated with failure to wean

Central drive

  • Sedation, analgesia or anaesthesia

  • Coma

  • Raised intracranial pressure

  • Hypercapnia

Respiratory muscle strength

  • Hypophosphataemia

  • Disuse atrophy

  • Sepsis

  • Polyneuropathy/myopathy

Load applied to the muscles

  • Hyperinflation

  • Left ventricular failure

  • Bronchospasm

  • Lung fibrosis