Average Volume-Assured Pressure Support (AVAPS) is a specialized mode of non-invasive ventilation (NIV) used to manage respiratory failure. This advanced technology integrates features from both pressure-controlled and volume-controlled systems. Unlike standard bilevel positive airway pressure (BiPAP) devices, which deliver a fixed pressure setting, AVAPS automatically adapts to a patient’s changing ventilatory needs. This provides a more consistent level of respiratory support.
How AVAPS Ensures Consistent Air Delivery
The fundamental principle of AVAPS is to guarantee the delivery of a specific volume of air, known as the target tidal volume (Vte), with every breath. This is achieved by having the machine automatically adjust the inspiratory positive airway pressure (IPAP) within a pre-set range. Unlike traditional pressure support modes, which deliver a fixed pressure regardless of the resulting air volume, AVAPS uses a feedback loop.
The clinician first sets the desired tidal volume, typically between 6 to 8 milliliters per kilogram. The machine also requires minimum and maximum pressure settings, defining the safe limits for operation. The expiratory positive airway pressure (EPAP) is generally set as a fixed value, which helps keep the airways open and facilitates oxygenation.
The device continuously monitors the air volume the patient exhales after each breath. If the measured exhaled tidal volume falls below the target volume, the system recognizes that the current inspiratory pressure is insufficient. The machine gradually increases the IPAP for subsequent breaths, operating within the set maximum pressure limit. Conversely, if the exhaled volume exceeds the target, the device decreases the IPAP toward the minimum pressure limit.
This automatic pressure adjustment typically occurs smoothly over several minutes, ensuring the patient does not experience sudden, uncomfortable pressure spikes. The gradual change prevents patient-ventilator asynchrony and allows the lungs to consistently achieve the target air exchange, even when the patient’s breathing effort fluctuates. This mechanism combines the comfort of pressure support with the reliability of volume-guaranteed ventilation, ensuring adequate minute ventilation and stable carbon dioxide clearance.
Respiratory Conditions Treated with AVAPS
AVAPS is often selected over standard BiPAP when a consistent tidal volume is necessary due to fluctuating respiratory mechanics or effort. Conditions causing chronic hypoventilation, which leads to the accumulation of carbon dioxide in the blood (hypercapnia), are the primary indications for this mode. The device’s ability to maintain a target volume ensures effective gas exchange, especially during sleep when respiratory drive naturally decreases.
Chronic Obstructive Pulmonary Disease (COPD) patients who experience hypercapnia are a major group who benefit from AVAPS. In these individuals, breathing mechanics can change significantly, particularly during an exacerbation, making a fixed-pressure device less effective. AVAPS provides a steady improvement in blood gas parameters compared to standard bilevel ventilation by guaranteeing the necessary air volume to clear excess carbon dioxide.
Obesity Hypoventilation Syndrome (OHS) is another condition where AVAPS demonstrates effectiveness. The excess weight associated with OHS increases the mechanical load on the chest wall, requiring greater pressure to move air into the lungs. As the patient changes position or enters different sleep stages, the required pressure shifts. AVAPS automatically compensates to maintain the pre-set tidal volume, which is important for correcting the daytime hypercapnia common in OHS patients.
AVAPS is also beneficial for patients with restrictive lung diseases or neuromuscular disorders, such as amyotrophic lateral sclerosis (ALS), where respiratory muscle strength is inconsistent. Since the patient’s effort can vary greatly from breath to breath, the automatic pressure adjustment ensures the lungs receive the necessary volume to prevent respiratory fatigue. This volume-assured approach makes it a preferred option for managing chronic respiratory insufficiency.
Using AVAPS: Practical Considerations for Patients
Patients starting AVAPS therapy often need time to adapt to the sensation of the automatically adjusting pressure. They may feel a subtle shift in the inspiratory pressure as the machine works to maintain the targeted air volume, especially during periods of changing sleep depth or body position. Understanding that this gentle adjustment is the device working as intended can improve patient compliance and reduce anxiety.
Adherence to the prescribed settings is important for AVAPS therapy, as the machine relies on the minimum and maximum pressure limits set by the clinician. Patients should use the device for the full number of hours recommended to ensure consistent correction of blood gas levels. Any discomfort, such as mask leaks or skin irritation, should be reported to the healthcare provider, as these issues can reduce the machine’s effectiveness and disrupt sleep.
Device maintenance involves routine cleaning of the mask, tubing, and humidifier chamber to ensure optimal performance. While the machine’s internal algorithm handles the complex pressure adjustments, the device stores data on usage hours, mask leak rates, and the pressure range utilized. Clinicians monitor this data remotely or during follow-up visits to ensure the patient is using the device correctly and that the settings remain appropriate.