Understanding Non-Invasive Ventilation (NIV)

A guide for medical students and junior doctors

Illustration of a patient with non-invasive ventilation in the intensive care unit. Drawn by Sophie Elschner, https://sophssketchpad.wordpress.com/

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Introduction

Non-Invasive Ventilation (NIV) is a mode of mechanical ventilation that does not require invasive endotracheal intubation. Widely utilised in conditions like Chronic Obstructive Pulmonary Disease (COPD) exacerbations and acute cardiogenic pulmonary oedema, a good grasp of NIV is crucial for every budding physician. In this article, we’ll break down the basic principles of NIV and demystify its settings for a clear understanding.

Basic Principles

NIV works by delivering pressurised air (or oxygen-enriched air) through a mask. This pressurised air aids in improving alveolar ventilation, decreasing the work of breathing and increasing oxygenation.

Two primary modalities of NIV are:

1. Continuous Positive Airway Pressure (CPAP)

2. Bilevel Positive Airway Pressure (BiPAP or BPAP)

CPAP

Continuous Positive Airway Pressure (CPAP) delivers a single continuous level of pressure throughout the breathing cycle. It's often used in conditions like obstructive sleep apnea and acute cardiogenic pulmonary edema.

BiPAP

Bilevel Positive Airway Pressure offers two levels of pressure:

• Inspiratory Positive Airway Pressure (IPAP): This is the higher pressure level during inspiration, which assists with tidal volume and reduces the effort to breathe.

• Expiratory Positive Airway Pressure (EPAP): This is the lower pressure during expiration, which helps to keep the airways open.

Key Settings in NIV

1. IPAP and EPAP: As mentioned, BiPAP has both IPAP and EPAP settings. The difference between the two pressures affects tidal volume, and adjusting these can aid in CO2 removal. Typical starting settings might be an IPAP of 10-12 cm H2O and an EPAP of 4-6 cm H2O.

2. Oxygen (O2) percentage: Adjusted to achieve desired oxygen saturation levels. Depending on the machine, you might set a specific FiO2 or use supplemental O2 to achieve the desired saturation.

3. Ramp/ Rise time: Determines how quickly the machine reaches the set IPAP. A shorter rise time can be more comfortable for patients who are anxious or feel "out of sync" with the machine.

4. Rate (Back-Up Rate): This setting dictates the minimum breaths per minute the machine will deliver if the patient's spontaneous breathing falls below this rate.

5. Humidification: A heated humidifier can make NIV more comfortable by preventing dryness and irritation.

6. Trigger Sensitivity: Determines how much effort is required by the patient to trigger the machine to deliver a breath.

Indications for NIV

While the settings are crucial, it's equally important to recognise when NIV might be beneficial. Some common indications include:

• Acute exacerbations of COPD

• Acute cardiogenic pulmonary oedema

• Obstructive Sleep Apnea (OSA)

• Post-extubation in high-risk patients

Contraindications and Cautions

Remember, not every patient with respiratory distress should receive NIV. Contraindications include:

• Facial trauma or surgery

• Vomiting or a high risk of aspiration

• Hemodynamic instability without a clear reversible cause

• Inability to protect the airway

• Non-cooperation or agitation

• Pneumothorax

Conclusion

Non-invasive ventilation is a potent tool in managing various respiratory conditions. As with any intervention, understanding its principles, settings, indications, and contraindications is essential. NIV can often prevent the need for invasive ventilation, reduce complications, and improve patient outcomes.

NOW TEST YOURSELF

Which of the following scenarios is NOT an appropriate indication for the initiation of Non-Invasive Ventilation (NIV)?

A) Acute exacerbation of COPD B) Acute cardiogenic pulmonary edema C) A patient with significant facial trauma D) Acute respiratory failure in an immunocompromised patient E) Pre-intubation oxygenation in patients with acute respiratory distress syndrome (ARDS)

Expand to see answer and explanation

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