Non-Invasive Ventilation

NIV provides inspiratory muscle rest for patients who are subject to ventilatory failure due to excessive WOB. It delivers a predetermined volume or pressure either automatically or, more frequently, in response to patient effort. Either positive or negative pressure can be delivered.

• Positive
• Delivered via mask or mouthpiece
• IPPB, CPAP, BiPAP
• Delivered using the natural airway but with external pressure
• Iron lung, jackets, cuirass

NIV carries reduced risk of infection (Guerin, 1997), is more comfortable, easier for speech and swallowing and is more convenient (Bach, 1994). However NIV does not protect the airway and provides no direct access to the trachea.

For acutely ill patients, NIV unloads the respiratory muscles, reduces breathlessness and corrects respiratory acidosis.

It can benefit:

• Exacerbations of COPD or CF with increased PaCO2 and reduced pH
• Acute asthma to reduce effort of maintaining dynamic hyperinflation
• Acute restrictive disorders eg pneumonia or ARDs
• Severe pulmonary oedema - NIV could prevent intubation
• Weaning from mechanical ventilation

The aims of non-invasive ventilation (NIV) are to:

·   Improve gas exchange

·   Reduce WoB

·   Restore balance of the ventilator pump

·   Improve functional ability

·   Reduce fear and anxiety
·   Reduce need for intubation

Indications

• Moderate --> severe dyspnoea
• Use of accessory muscles (SCM and scalenes)
• Respiratory failure that is not responding to oxygen therapy
• Weaning from mechanical ventilation

Contraindications

• Respiratory arrest
• CV instability
• Changes in mental status
• High aspiration risk
• Viscous or copious secretions
• Reduced consciousness (unprotected airways)
• Pneumothroax possibly due to barotrauma
• Recent facial or gastroesophageal surgery
• Fixed nasopharangeal abnormalities
• Burns
• Extreme obesity

Patients with acute respiratory failure have shown increased breathing patterns (Girault, 1997), increased survival rates (Keenan, 1997) and a 70% success rate in correcting gas exchange and avoiding intubation (Meduri, 1996).

Home NIV should be considered if there is daytime hypercapnia and symptoms of nocturnal hypoventilation. These are:

• Mornign headache
• Daytime sleepiness
• Breathlessness
• Anorexia

Home NIV shows an 87% positive response (Goldstein, 1995) with sustained improvement in gas exchange and reduced hospitalisation (Leger, 1994). Nocturnal ventilation is used when possible as it compensates for the loss of accessory muscles.

Complications of positive pressure ventilation include:

• Pressure sores - use forehead spacers
• Mask leaks - different sizes, types and bubble masks
• Gastric distension - occurs with volume controlled machines or patients with low chest wall compliance - adopt left lying position and use lowest effective pressures
• Nasal dryness - nasal drops
• Mouth dryness - reduce leaks
• Skin irritation - clean mask daily

Continuous Positive Airway Pressure

Used for type I respiratory failure (hypoxaemia; PaO2 < 8kPa) in reversible, acute respiratory problems such as asthma, pneumonia, pulmonary embolism and pulmonary oedema. 

It maintains a constant, positive pressure throughout the respiratory cycle; thereby keeping the alveoli and bronchioles open; reversing atelectasis and increasing gas exchange.

It is used in spontaneous breathing patients to reduce WOB and increase lung compliance.

Bi-level Positive Airway Pressure

Acute or chronic type II respiratory failure (hypoxaemia and hypercapnia; PaCO2 > 6.7kPa) in pathologies such as COPD, CF, bronchiectasis, sleep apnoea and neuromuscular disease.

It provides respiratory support to offload and rest the respiratory muscles, therefore reducing WOB.

There are two levels of positive pressure (BiPAP)

·   IPAP inspiratory positive airway pressure

·   Augments tidal volume

·   Facilitates CO₂ washout

·   Reduces WoB

·   EPAP expiratory positive airway pressure

·   Splints airways open

·   Recrutis alveoli

·   Prevents atelectasis

·   Improves alveolar ventilation

·   Improves oxygenation

These are initiated by the patient but aid respiration. Physiotherapist presets EPAP and IPAP:

• IPAP > EPAP
• BiPAP aligns to the patients breathing pattern
• If the patient does not initiate a breath, BiPAP will do so

Intermittent Positive Pressure Breathing

This is pressure-supported inspiration that is triggered by the patient, sustained by positive pressure and followed by passive expiration therefore easing WOB.

Indications

• Atelectasis (partial or complete collapse)
• Sputum retention due to
• Drowsniness
• Weakness
• Fatigue

Contraindications

• Unwilling
• Restless
• In pain

The patient needs to be relaxed as muscle splinting will prevent the patient from accepting the positive pressure, and make the experience uncomfortable rather than unusual.