Non-Invasive Ventilation (NIV) offers respiratory support without requiring a tube inserted into the trachea. Bilevel Positive Airway Pressure, commonly known as BiPAP, is a widely used form of NIV. This machine provides pressurized air through a mask, keeping the patient’s airways open and assisting the lungs. The system delivers two distinct pressures, and understanding Pressure Support is essential for grasping how this technology aids breathing.
Understanding the Dual Pressure Settings of BiPAP
BiPAP delivers two separate pressures corresponding to the two phases of the breathing cycle. The Inspiratory Positive Airway Pressure (IPAP) is the higher pressure setting applied during inhalation. IPAP acts as a mechanical boost, making it easier for the lungs to draw in air and increasing the volume delivered with each breath.
The Expiratory Positive Airway Pressure (EPAP) is the lower pressure maintained during exhalation. EPAP serves to keep the small airways and alveoli open at the end of the breath. By preventing these structures from collapsing, EPAP promotes better oxygen transfer into the bloodstream, improving oxygenation. These two pressures support the entire respiratory cycle, but the difference between them provides the actual ventilatory assistance.
Defining Pressure Support and Its Calculation
Pressure Support (PS) is not a separate setting on the BiPAP machine but is the measurement of the difference between the two primary pressures. It is calculated using the formula: PS = IPAP – EPAP. This pressure differential represents the extra pressure the BiPAP device delivers solely during the inspiratory phase.
The goal of this added pressure is to augment the patient’s spontaneous breath, effectively giving the inhalation a “push.” Pressure support is directly proportional to the patient’s tidal volume, which is the amount of air moved into or out of the lungs with each breath. A higher pressure support level results in a larger tidal volume, assuming the patient’s lung mechanics remain stable.
Clinicians manage pressure support by adjusting the IPAP and EPAP settings, rather than setting the PS value directly. For example, IPAP 12 and EPAP 5 results in a pressure support of 7 cm H₂O. If the clinician needs to increase tidal volume, they typically increase the IPAP setting while holding the EPAP constant. The level of pressure support determines the volume of air delivered and the degree of ventilatory assistance provided.
How Pressure Support Reduces the Work of Breathing
Pressure support provides mechanical assistance designed to alleviate strain on the body’s respiratory muscles, including the diaphragm and intercostal muscles. During respiratory distress, these muscles work harder and faster to move air, leading to fatigue and inefficient breathing. By delivering a positive pressure boost during inhalation, the BiPAP machine takes over a portion of the patient’s effort to draw air into the lungs.
Preventing Fatigue and Improving Gas Exchange
This reduction in the work of breathing allows the respiratory muscles to rest and recover, preventing the exhaustion that can lead to respiratory failure. Pressure support directly increases the tidal volume, which is necessary to effectively move air in and out of the lungs. The improved tidal volume facilitates better gas exchange by ensuring that carbon dioxide (CO₂) is cleared from the bloodstream efficiently. Because the pressure boost aids ventilation, it indirectly helps improve oxygenation by making room for fresh air within the lungs.
When Pressure Support is Used Clinically
Pressure support is a fundamental component of BiPAP therapy used to manage conditions involving inadequate ventilation or respiratory muscle fatigue. This support is frequently employed for patients experiencing an acute exacerbation of Chronic Obstructive Pulmonary Disease (COPD). COPD exacerbations often lead to a buildup of carbon dioxide in the blood (hypercapnia), and the pressure boost helps these patients expel trapped air and clear the excess CO₂.
Pressure support is also a standard intervention for individuals with chronic hypoventilation syndromes, such as Obesity Hypoventilation Syndrome. In these cases, the body’s natural drive to breathe is diminished, especially during sleep. Providing nocturnal ventilatory support ensures consistent gas exchange overnight. Furthermore, using pressure support is often a strategy to prevent the need for invasive mechanical ventilation in moderate respiratory failure, allowing recovery without the risks associated with intubation.