Makindo Medical Notes

Patients need to be conscious and have sufficient respiratory drive to benefit from NIV. Those who are drowsy and who have poor respiratory drive may need Intubation and ventilation.

Introduction

• Normal physiology involves using external intercostal muscles and descent of the diaphragm to create a negative intrathoracic and airways pressure relative to atmospheric pressure, allowing air to flow into the alveoli.
• Non-invasive ventilation (NIV) involves using a tight-fitting face mask or hood with a ventilator to provide positive pressure, pushing air into the lungs.
• Positive airway pressure can be delivered continuously (CPAP) or adjusted with the respiratory cycle (BiPAP).
• NIV can avoid complications of intubation and invasive ventilation, improve outcomes (e.g., reduce mortality rates, shorten hospital stay), and decrease costs. It is mainly used for patients with Type II respiratory failure.

Types of NIV

• Continuous Positive Airway Pressure (CPAP): Provides continuous positive pressure throughout the respiratory cycle. Commonly used in Type I respiratory failure (e.g., pulmonary oedema). It keeps airways open, improves oxygenation, and reduces work of breathing. Suitable for patients with conditions like cardiogenic pulmonary oedema or sleep apnoea.
• Bi-level Positive Airway Pressure (BiPAP): Provides two different pressure levels: a higher pressure during inspiration (IPAP) and a lower pressure during expiration (EPAP). It is mainly used for Type II respiratory failure with acidosis (e.g., COPD exacerbations). BiPAP aids both oxygenation and CO₂ clearance.

Advantages of NIV over Invasive Ventilation

• Reduced risk of ventilator-associated pneumonia.
• Shorter duration of hospital stay.
• Lower healthcare costs.
• Reduced need for sedation compared to intubation.
• Beneficial for patients with COPD exacerbations and hypercapnic respiratory failure.

Application of NIV

• Used for both Type I and Type II respiratory failure, such as in COPD exacerbations, pulmonary oedema, or post-operative respiratory support.
• A tight-fitting mask is required, and patients must be able to tolerate the sensation of breathing against resistance.
• NIV reduces the work of breathing, aids alveolar recruitment, and improves gas exchange.
• Helps avoid invasive intubation in suitable cases and can be delivered at home or in a hospital setting.

Indications for NIV

• pH < 7.35 with relative hypercarbia (Type II RF).
• Cardiogenic pulmonary oedema (Type I RF) without evidence of shock.
• Support for immunosuppressed patients with acute respiratory failure.
• Assisting weaning from mechanical ventilation, particularly in COPD patients.
• Post-operative respiratory failure or after lung resection surgery.
• Palliative care for symptom relief (e.g., breathlessness).

Contraindications

• Life-threatening hypoxaemia (< 60 mmHg on 100% FiO₂) requiring intubation.
• Impaired consciousness (e.g., GCS < 9).
• Inability to protect the airway or excessive secretions.
• Facial trauma or burns preventing mask fitting.
• Untreated pneumothorax.

Settings for NIV

• BiPAP: Initial IPAP of 10 cmH₂O and EPAP of 4-5 cmH₂O, with adjustments based on patient response.
• CPAP: Initial settings at 5 cmH₂O, increasing to 10 cmH₂O if needed.
• Aim for the lowest pressure that achieves SaO₂ > 90% or PaO₂ > 60 mmHg without clinical deterioration.
• If no improvement within four hours, consider intubation and invasive ventilation.

Side Effects of NIV

• Increased intrathoracic pressure may reduce venous return and cardiac output, potentially causing a drop in blood pressure.
• Positive pressure can cause gastric distension, leading to discomfort and increased risk of aspiration.
• Skin breakdown and pressure sores due to tight-fitting masks.

Home NIV

• May be considered for chronic, stable respiratory failure due to conditions like:
  • Severe spinal deformity.
  • Neuromuscular disorders (e.g., muscular dystrophy).
  • Cystic fibrosis or motor neurone disease.
  • Central alveolar hypoventilation syndrome.
• Typically used overnight or for prolonged periods to support breathing and improve quality of life.

Indications for Intubation and Ventilation

• Respiratory arrest or significant respiratory distress unresponsive to NIV.
• Severe hypoxaemia (PaO₂ < 8 kPa) despite high FiO₂ and NIV.
• Persistent hypercapnia or acidosis despite NIV.
• GCS < 9 or inability to protect the airway.
• Failure of NIV to stabilize the patient within four hours.

References

• Non-Invasive Ventilation: Indications and Outcomes
• ATS Clinical Practice Guidelines on NIV