What are the types of non-invasive ventilation (NIV), including Continuous Positive Airway Pressure (CPAP), Bi-level Positive Airway Pressure (BiPAP), and Adaptive Servo-Ventilation (ASV)?

Types of Non-Invasive Ventilation

Non-invasive ventilation encompasses several distinct modalities including CPAP, BiPAP/BiLevel, pressure support ventilation, assist/control modes, and adaptive servo-ventilation, each with specific physiological mechanisms and clinical applications. 1

Primary NIV Modalities

Continuous Positive Airway Pressure (CPAP)

• CPAP delivers a single constant positive pressure throughout the entire respiratory cycle, maintaining the same pressure during both inspiration and expiration 1, 2
• Works by recruiting collapsed alveoli, unloading inspiratory muscles, and offsetting intrinsic PEEP in COPD patients 2
• Primarily corrects hypoxemia rather than providing ventilatory support 1, 2
• Most effective for cardiogenic pulmonary edema, chest wall trauma with hypoxemia, and diffuse pneumonia 2
• Typical pressure setting is 10 cmH₂O 3

Bilevel Positive Airway Pressure (BiPAP/BiLevel)

• BiPAP provides two distinct pressure levels: higher inspiratory positive airway pressure (IPAP) during inspiration and lower expiratory positive airway pressure (EPAP) during expiration 1, 2
• More effective than CPAP for hypercapnic respiratory failure and patients who cannot tolerate high CPAP pressures 2
• Combines pressure support with CPAP principles, providing ventilatory assistance during inspiration 2
• Standard initial settings: EPAP 5 cmH₂O with inspiratory pressure between 12-25 cmH₂O 3
• Preferred for acute COPD exacerbations with respiratory acidosis, patients developing hypercapnia during CPAP, and ventilator weaning 2

Critical caveat: Rebreathing can occur with BiPAP if exhaust ports become occluded, and normal EPAP levels may not completely eliminate rebreathing, especially with increased respiratory frequency 2

Advanced NIV Modes

Assisted Spontaneous Breathing (Pressure Support Ventilation)

• The patient's respiratory effort triggers the ventilator both on and off, with the patient determining respiratory frequency and timing of each breath 1, 4
• Often termed pressure support (PS) because it involves setting pressure rather than volume 1
• Major limitation: If the patient fails to make respiratory effort, no respiratory assistance will occur 1

Assist/Control Ventilation (ACV)

• Delivers a preset number of mandatory breaths per minute in the absence of patient effort while allowing patient-triggered breaths 1, 4
• All breaths (mandatory and triggered) deliver identical preset parameters 4
• Patient-triggered breaths delay the next machine-determined breath, creating synchronization (SIMV) 1
• Also called spontaneous/timed (S/T) or IE mode on NIV machines 1
• Prevents central apneas during sleep, making it preferable to pressure support for patients at risk of hypoventilation 5

Controlled Mechanical Ventilation (CMV)

• Provides full ventilatory support with no patient effort required, delivering preset breaths at fixed intervals regardless of patient respiratory drive 1, 4
• Pressure control variant: Resulting tidal volume varies based on airway resistance, airflow limitation, and lung/chest wall compliance 1, 4
• Volume control variant: Tidal volume is fixed and the ventilator generates whatever pressure is necessary to deliver this volume 1, 4

Adaptive Servo-Ventilation (ASV)

• Positive airway pressure therapy in which air pressure target is adjusted according to the patient's breathing patterns 1
• More effective than standard NPPV in treating central sleep apnea, mixed apneas, and complex sleep apnea, with significantly lower apnea/hypopnea index 6
• Developed to treat central and complex sleep apnea syndromes 7

Critical warning: In patients with NYHA class II-IV heart failure with reduced ejection fraction and central sleep apnea, adaptive servo-ventilation causes harm and should not be used 1

Practical Implementation Considerations

Equipment and Terminology

• BiPAP ventilators are simpler to use, cheaper, and more flexible than other ventilator types, and have been used in the majority of randomized controlled trials of NIV 2
• Terminology for ventilation modes varies significantly between ventilator manufacturers, potentially causing confusion in clinical practice 1, 4
• In the UK and many centers, volume ventilators are rarely employed for non-invasive ventilation outside specialist centers 4

Contraindications (Apply to All NIV Modalities)

• Recent facial or upper airway surgery 2
• Facial abnormalities or fixed upper airway obstruction 2
• Vomiting patients 2
• Impaired consciousness 1
• Severe hypoxemia 1
• Copious respiratory secretions 1