Invasive ventilation

Invasive ventilation is a form of mechanical ventilation which requires endotracheal intubation or, if ventilation is required long-term, a tracheostomy. It is more effective than NIV, but it’s more invasive and can therefore increase the risk for ventilator associated pneumonia (VAP). It is difficult to wean people off invasive ventilation and back on spontaneous ventilation. It may take weeks.

Intubation and invasive ventilation is usually the last resort of respiratory therapy. It's only used if regular oxygen therapy or non-invasive ventilation is insufficient, although they don't necessarily have to be tried before proceeding to invasive ventilation. The only way to properly protect an airway is by intubation.

Indications

• Same as for non-invasive ventilation, if NIV is insufficient or if the patient is critically ill
• General anaesthesia
• Decreased level of consciousness (generally GCS < 8)
  • Opioid intoxication
  • Stroke
  • Head injury
• Severe hypoxaemia
  • Acute respiratory distress syndrome
  • Cervical spinal injury
• Airway obstruction
  • Foreign body
  • Epiglottitis
  • Angioedema

Modes

The ventilator can either be in pressure control mode or volume control mode. In volume control mode, the operator sets a tidal volume for the patient, and the machine selects the pressure required to achieve that tidal volume. Pressure control mode is the opposite. There are advantages and disadvantages of each mode.

A ventilator can also provide positive end-expiratory pressure (PEEP), where it keeps a positive pressure in the airways after the expiration to prevent alveolar collapse (atelectasis) during expiration. A small amount (3 – 5 cmH2O) of PEEP is used in most ventilated patients. This has other advantages as well but also some disadvantages:

• Advantages
  • Prevents atelectasis
  • Increases functional residual capacity (FRC)
  • Increases gas exchange area
  • Increases compliance
  • Decreases preload
  • Decreases afterload
  • Decreases V/Q mismatch
  • Decreases work of breathing
• Disadvantages
  • Decreased CO2 elimination
  • May decrease cardiac output in right heart failure or hypovolaemia
  • Increases ICP
  • Increases intrathoracic pressure -> may cause PTX

Complications

Ventilator-induced lung injury (VILI) refers to injury of the lung due to the ventilator. It’s usually avoidable when using appropriate and proper settings and parameters. This can occur in the form of barotrauma (excessive pressure causes rupture of alveoli), volutrauma (excessive volume causes overdistension of alveoli), biotrauma (release of inflammatory mediators), and atelectrauma (repeated opening and closing of alveoli).