Adaptive servo-ventilation (ASV)
Adaptive Servo Ventilation Algorithms
Resmed ASV Algorithm
Resmed ASV uses a three minute moving average to monitor and determine an appropriate target minute ventilation, set to 90% of their most recent minute ventilation. This target threshold prevents under and over ventilation by dynamically increasing (for hypopneas) or decreasing (for hyperpneas) inspiratory pressure support (IPS) as needed. Together with a back-up respiratory rate 758 Journal of Clinical Sleep Medicine, Vol. 12, No. 5, 2016RN Aurora, SR Bista, KR Casey et al. Adaptive Servo-Ventilation Recommendations (set dynamically at 15 breaths/min), when a patient’s minute ventilation falls below the set target, ResMed’s ASV automatically adjusts the inspiratory pressure support to provide the ventilation needed. As breathing stabilizes, the pressure delivered is rapidly reduced back towards the minimum required. ResMed’s newest ASV device, AirCurve 10 ASV, has a maximum pressure of 25 cmH2O and can be set to an IPS of 0 to 20 cmH2O. *source: Updated Adaptive Servo-Ventilation Recommendations for the 2012 AASM Guideline: “The Treatment of Central Sleep Apnea Syndromes in Adults: Practice Parameters with an Evidence-Based Literature Review and Meta-Analyses”
Philips Respironics ASV Algorithm
The Philips Respironics ASV (BiPAP autoSV Advanced System One) utilizes inspiratory flow as the primary variable to identify and respond to sleep-related breathing disorders (SRBD). In the absence of SRBD, EPAP is automatically determined based on the REMstar Auto algorithm. The algorithm identifies and responds to obstructive sleep disordered breathing events as they occur. During periods of airway stability, the algorithm will proactively assess the airway to minimize pressure while optimizing airway patency. The maximum inspiratory positive airway pressure is 30 cmH2O with a mini-mum EPAP of 4 cmH2O. The Philips Respironics ASV devices are also capable of withdrawing IPS entirely during periods of normal breathing. All Respironics ASV devices have two methods of setting a backup rate: a fixed rate determined by the operator, or an auto mode that synchronize with the patient’s intrinsic rate. *Source Updated Adaptive Servo-Ventilation Recommendations for the 2012 AASM Guideline: “The Treatment of Central Sleep Apnea Syndromes in Adults: Practice Parameters with an Evidence-Based Literature Review and Meta-Analyses”
Adjusting and Optimizing ASV
Titration ASV and ASVauto is based on identifying the EPAP threshold where obstructive apnea is mostly resolved, and setting this as the minimum EPAP pressure.
Obstructive apnea is not resolved by increasing IPAP pressure or pressure support. All auto CPAPs are designed NOT to increase pressure during an apnea, but instead increase pressure after the event. Just as we have seen in positional apnea, an obstructed airway cannot be opened with pressure, instead it is important to prevent the obstruction from happening in the first place. The ASV and ASVauto protocols are shown below. In ASV and ASVauto mode, EPAP min must be increased by 1-cm until OA is eliminated. In auto mode, this will eventually happen, but as I said before, this optimization of the EPAP pressure is an important part of proper titration. Pressure support or raising IPAP will not resolve OA.
In the ***Soft Cervical Collar wiki***, we show examples of someone with positional obstruction. This example was resolved by use of a soft cervical collar rather than pressure, but the effect is the same; the OA event must be prevented, not responded to by the machine.
Adaptive servo-ventilation (ASV) modes of therapy have been developed to manage this central sleep apnea and complex sleep apnea. ASV machines are expensive and insurance will require extensive evidence of medical necessity to approve the purchase and use of ASV. See Justifying ASV backup Info.
Studies have demonstrated marginally superior performance of the adaptive servo ventilators in treating Cheyne-Stokes respiration. Adaptive-servo ventilation adapt to the patient’s ventilatory needs on a breath-by-breath basis, automatically calculating a target ventilation and adjusts the pressure support to achieve it.
Here is a chart posted by a forum member and it shows how the Auto ASV changes pressure to prevent events. In this chart the red pressure line is the pressure the machine is delivering, the blue chart is mask pressure and the flow rate line in black shows the user's breathing flow rate. You can see the machine is set to EPAP min of 6.0, which is the bottom of those pressure charts. The minimum pressure support looks to be 3.0 and that is what is delivered most of the time. The machine frequently increases IPAP pressure to prevent hypopnea and central apnea. In this case there are no events recorded, but the machine is intercepting them by providing as much pressure as is needed to maintain respiratory volume and timing, without getting in the way when that is not needed. In this case the user had limited his maximum pressure support to about 8.0 which was not enough for certain events. The purpose of showing this chart is to show how the ASV adapts to changing needs through the night and on a breath by breath basis.