Makindo Medical Notes.com

Related Subjects: |Respiratory Failure |Non invasive ventilation (NIV) |Intubation and Mechanical Ventilation |Critical illness neuromuscular weakness |Multiple Organ Dysfunction Syndrome |Haemodialysis |Dobutamine

About

• 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".

Benefits

• 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

Risks

• 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

Different types

• Negative pressure ventilation: Iron lungs and normal breathing air is sucked in
• Positive pressure: Air is blown in which is usual method by ventilator

Clinical

• Breathless, agitated, cyanosed, Tired, fatiguing, drowsy
• Using accessory muscles, Hypotension, Elevated JVP

Possible Indications

• 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

Objective Criteria

• Respiratory rate > 35/min
• Tidal volume < 5ml/kg
• Vital capacity < 15 ml/kg
• PaO₂ < 8 Kpa despite 60% Oxygen
• PaCO₂ > 8PKa

Procedure

• Requires in conscious patients anaesthesia and muscle relaxation
• It may cause hypotension

Complications

• 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

• Volume-controlled
  • 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 (barotrauma)
• Pressure-controlled
  • 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 ventilation (PSV) Provides positive pressure to augment patient’s spontaneous breaths; useful for weaning
  • Positive end-expiratory pressure (PEEP) 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 gases
  • Extracorporeal membrane oxygenation (ECMO) Oxygenation and CO₂ clearance achieved using an external vascular bypass with oxygenator. Used in severe ARDS

More Information

• 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 failure.
• 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 ventilation.
• 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

References

• Mechanical Ventilation Made Easy: Ventilator Basics (2022)