What is ventilation?
Ventilation is the process of exchanging air between the lungs and the ambient air. Gas exchange occurs at the alveoli, where oxygen (O₂) and carbon dioxide (CO₂) are transferred across cell membranes.
What is mechanical ventilation?
Mechanical ventilation is ventilation delivered by a machine/ventilator. Invasive ventilation is provided via an Endotracheal Tube (ETT), which can be oral, nasal, or through a tracheostomy.
What is respiratory failure?
Respiratory failure is the inability to maintain adequate gas exchange, characterized by abnormal arterial blood gas (ABG) levels.
What are the types of respiratory failure?
- Type I: Hypoxia (PaO₂ <8 kPa) with normal or low CO₂, caused by V/Q mismatch.
- Type II: Hypoxia (PaO₂ <8 kPa) and hypercapnia (PaCO₂ >6 kPa), caused by ventilatory failure.
What is Type II Respiratory Failure?
- Acute: ↑PaCO₂, ↓pH, ↔HCO₃
- Chronic: ↑PaCO₂, ↔pH, ↑HCO₃
- Acute on Chronic: ↑PaCO₂, ↓pH, ↑HCO₃
What causes respiratory failure?
- Disease affecting ventilatory control or respiratory muscles (brain injury, neuromuscular disorders).
- Increased respiratory load exceeding muscle capacity (e.g., COPD, reduced lung compliance).
What are the indications for mechanical ventilation?
- invasive: Organ failure, airway protection, sedation, trauma, post-surgery, pH <7.35 & PaCO₂ >6 kPa.
- Non-Invasive (NIV): To avoid intubation, weaning from ventilation, long-term support, pH <7.35 but >7.1 & PaCO₂ >6 kPa.
What are the aims of invasive mechanical ventilation?
- Reduce work of breathing (support mode)
- Take over ventilation completely (controlled mode)
- Maintain PaO₂, reduce PaCO₂, normalize pH
- Allow medical management time for recovery
How does mechanical ventilation work?
- Volume/pressure modes: Adjust tidal volume for effective ventilation.
- PEEP: Keeps airways open for gas exchange and CO₂ clearance.
- Pressure control: Increases pressure to improve CO₂ washout
What is tidal volume augmentation?
- Set based on ideal body weight (6–8 mL/kg IBW).
- Adjust pressure levels in pressure-controlled modes to reach target volume.
What are comfort parameters in ventilation?
- Respiratory rate (RR): Set rate for assisted/control mode.
- Ti ratio: Inspiration time (1:2, 1:3, etc.).
- Flow/Ramp: Gradual increase to peak inspiration.
What are mixed ventilation modes?
- PRVC: Pressure-regulated volume control
- SIMV: Synchronized Intermittent Mandatory Ventilation
- Bi-level ventilation: Controlled, assisted, or support mode.
What is Non-Invasive Ventilation (NIV)?
Ventilation provided via a mask, nasal pillow, or mouthpiece, delivering positive pressure during inhalation/exhalation.
What are the types of NIV?
- CPAP (Continuous Positive Airway Pressure): Splints open airway during breathing, used in OSA and cardiac failure.
- BiPAP (Bi-level Positive Airway Pressure): Flow-triggered with backup rate, useful in Type II respiratory failure.
What are the key parameters in NIV?
- IPAP: Inspiratory Positive Airway Pressure
- EPAP: Expiratory Positive Airway Pressure
- Pressure Support: Difference between IPAP and EPAP
- Tidal Volume (TV): Volume of air delivered per breath
- Respiratory Rate (RR): Number of breaths per minute
What are the indications for NIV?
- Acute: Respiratory acidosis (pH <7.35 but >7.1, PaCO₂ >6 kPa), avoiding intubation, weaning from ventilation.
- Chronic: Compensated respiratory failure, nocturnal hypoventilation, spirometry abnormalities, sleep-disordered breathing (SDB), transplant bridging.
What are the contraindications for NIV?
- Absolute: Pneumothorax, severe hypotension, severe lung disease, cardiac arrhythmias, neurological instability, recent surgery, facial trauma.
- Relative: Anxiety, excess secretions, need for continuous ventilatory assistance.
What are the complications of NIV?
- Skin breakdown (especially over the nose)
- Secretion retention
- Gastric distension
- Air leaks and discomfort
- Claustrophobia
- Sleep fragmentation
What are the interface options for NIV?
- Nasal masks
- Full-face masks
- Nasal pillows
- Mouthpieces
- Tracheostomy
