Non-Invasive Ventilation (NIV) delivers pressurized air through a mask or nasal interface, avoiding the need for an invasive tube in the windpipe. The two most common forms of this support are Continuous Positive Airway Pressure (CPAP) and Non-Invasive Positive Pressure Ventilation (NIPPV), which is often referred to by the brand name BiPAP. While both devices apply positive pressure to assist breathing, their underlying mechanisms and intended physiological goals are fundamentally different. CPAP provides a single pressure, whereas NIPPV provides dual pressures.
Understanding the Mechanisms of Pressure Delivery
Continuous Positive Airway Pressure (CPAP) operates by delivering a single, fixed pressure level that remains constant throughout the entire respiratory cycle, covering both inhalation and exhalation. This consistent pressure acts like an air splint, effectively holding the upper airway open and preventing its collapse, which is its primary function. The steady pressure also extends down into the lungs, helping to “recruit” or open up collapsed air sacs, known as alveoli, thereby improving oxygen exchange. CPAP does not actively assist the patient in taking a breath; the user must initiate and complete every breath against the fixed pressure.
Non-Invasive Positive Pressure Ventilation (NIPPV), conversely, employs two distinct pressure settings, which allows it to provide actual ventilatory assistance. The device delivers a higher pressure, called Inspiratory Positive Airway Pressure (IPAP), when the patient inhales. It then drops to a lower pressure, Expiratory Positive Airway Pressure (EPAP), during exhalation. The physiological work of breathing is reduced because the difference between the IPAP and the EPAP provides pressure support, which actively increases the volume of air moved with each breath. This dual-pressure mechanism is capable of generating a larger tidal volume, which makes it particularly effective for removing excess carbon dioxide (CO2) from the bloodstream.
Primary Clinical Applications
The difference in pressure mechanics dictates which device is selected for a patient’s specific medical condition. CPAP is the treatment of choice for conditions where the primary problem is an anatomical obstruction or airway collapse, most notably Obstructive Sleep Apnea (OSA), where continuous pressure splints the floppy tissues of the pharynx open. CPAP is also utilized in acute settings for patients with cardiogenic pulmonary edema, where the positive pressure helps push fluid back out of the alveoli and into the circulation, while opening the lung tissue for better oxygenation.
NIPPV is reserved for conditions characterized by ventilatory failure or when the work of breathing is too high. This often includes acute exacerbations of Chronic Obstructive Pulmonary Disease (COPD), where the patient’s respiratory muscles are fatigued and struggling to exhale trapped air. By providing a boost of inspiratory pressure (IPAP) and allowing a lower expiratory pressure (EPAP), NIPPV unloads the respiratory muscles and facilitates the expulsion of CO2. NIPPV is also used for acute respiratory failure and for patients with neuromuscular disorders whose muscles are too weak to take a deep enough breath on their own.
Patient Experience and Adherence
The user experience with CPAP and NIPPV is significantly influenced by the pressure profile, affecting comfort and long-term adherence. For patients who require high pressure settings, NIPPV can often feel more comfortable than CPAP because the pressure drops during the exhalation phase. Attempting to exhale against a high, continuous CPAP pressure can feel difficult and unnatural, leading some patients to struggle with acceptance of the therapy. The lower EPAP setting on an NIPPV device makes the process of breathing out much easier, improving the overall tolerability of the support.
Common side effects, such as mask irritation, dry mouth, and aerophagia, can occur with both types of support, but they may be exacerbated by higher pressures. For some individuals, the difference in pressure between IPAP and EPAP, or the machine’s attempt to synchronize with their breathing, can feel awkward or mistimed, which is a compliance challenge unique to NIPPV. While CPAP is prescribed as a long-term, nightly therapy for chronic conditions like OSA, NIPPV is frequently initiated in a hospital setting for acute respiratory distress.