|Non invasive ventilation (NIV)
|Intubation and Mechanical Ventilation
|Critical illness neuromuscular weakness
|Multiple Organ Dysfunction Syndrome
- The work of breathing is taken over by a machine.
- Historically the major advance was in response to the Polio epidemic.
- Medical students manually operated "iron lungs".
- Decreases work of breathing: decreases the amount of energy and work required for each breath.
- Maintains oxygenation: can deliver an FiO2 of up to 100% to help with oxygenation. Can deliver positive end-expiratory pressure (PEEP), which is helpful in patients with refractory hypoxemia.
- Helps remove carbon dioxide: Increased respiratory rate or tidal volume.
- Provides stability: allows time for treatment
- Barotrauma: alveolar overdistention caused by increased levels of pressure.
- Ventilator-associated pneumonia (VAP): develops 48 hours or more after a patient has been intubated and placed on the ventilator.
- Auto-PEEP: A complication of mechanical ventilation that occurs when a positive pressure remains in the alveoli at the end-exhalation phase of the breathing cycle.
- Oxygen toxicity: cell damage when exposed to high levels of oxygen for an extended period of time.
- Ventilator-induced lung injury (VILI): injury that occurs while a patient is receiving mechanical ventilatory support.
- Reduced cardiac filling and output due to increased intrathoracic pressures
The benefits of mechanical ventilation often far outweigh the risks, which is why it is such a common intervention in the field of respiratory care. However, there are some complications that can occur
- Negative pressure ventilation: Iron lungs and normal breathing air is sucked in
- Positive pressure: Air is blown in which is usual method by ventilator
- Breathless, agitated, cyanosed, Tired, fatiguing, drowsy
- Using accessory muscles, Hypotension, Elevated JVP
- Protection of airway
- Respiratory arrest or rate < 8/min
- Not tolerating mask/CPAP/NIV
- PaO2 < 8 kPa (< 60 mmHg); SpO2 < 90%) despite CPAP with
FiO2 > 0.6
- Allow removal of secretions
- Vital capacity < 1.2 L in neuromuscular disease
- Worsening hypercapnia or respiratory acidosis
- Post operative ventilation until patient stable and patient can be woken up
- Severe sepsis - to minimise work breathing
- Head injury management - to lower PaCO2 to reduce intracranial pressure
- Reduce cardiac work in cardiogenic shock
- Worsening hypercapnia or respiratory acidosis
- Removing the work of breathing in exhausted patients
- Respiratory rate > 35/min
- Tidal volume < 5ml/kg
- Vital capacity < 15 ml/kg
- PaO2 < 8 Kpa despite 60% Oxygen
- PaCO2 > 8PKa
- Requires in conscious patients anaesthesia and muscle relaxation
- It may cause hypotension
- Cardiovascular compromise - most sedative drugs are negatively inotropic.
- Positive intrathoracic pressures which can reduce cardiac output.
- Over time there may be atrophy of respiratory muscles
- Pneumothorax especially with peak airway pressures > 40 cm H20.
- Ventilatory related lung injury
- Tracheostomy at about 14 days. Can lead to local damage from endotracheal tube
Types of Ventilation
- Synchronised intermittent mandatory ventilation (SIMV)
Pre-set rate and VT of mandatory breaths. Allows
spontaneous breaths (may be pressure-supported)
between mandatory breaths. Risk of excess
- Pressure-controlled ventilation (PCV): Pre-set rate and inspiratory pressure; used in acute respiratory failure to avoid high airway pressure
- Bi-level positive airway
pressure (BiPAP): Two levels of positive airway pressure (higher level
in inspiration); in fully ventilated patients
- Pressure support
Provides positive pressure to augment patient’s
spontaneous breaths; useful for weaning
- Positive end-expiratory
Applied during expiration; improves oxygenation by
recruiting atelectatic or oedematous lung; may
reduce cardiac output
- Advanced modes
- High-frequency oscillatory
ventilation (HFOV): High-frequency oscillating gas flow used to
facilitate gas exchange. Titrated against blood
- Extracorporeal membrane
Oxygenation and CO2 clearance achieved using an
external vascular bypass with oxygenator. Used in
- Ventilator mode and settings for tidal volume,
respiratory rate, positive end-expiratory pressure (PEEP) and inspiratory
to expiratory ratio is dependent on the cause of the respiratory
- Weaning from respiratory support: The majority of patients
require mechanical ventilatory support for only a few days and do
not need a process of weaning. Patients who have
required long-term ventilatory support for severe lung disease, e.g.
ARDS, may initially be unable to sustain even a modest degree of
respiratory work due to reduced lung compliance and muscle weakness;
hence they require a programme of gradual weaning from
- Tracheostomy: This is usually performed electively when endotracheal
intubation is likely to be prolonged (> 14 days). Tracheostomies
help patient comfort, aid weaning from ventilation, and allow access
for tracheal toilet and intermittent respiratory support