The Case for AVAPS

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Stephen Biehl
Stephen Biehl
Respiratory therapist specializing in lung health investigations. If not I’m the unit, find me in the PFT lab, bronch suite, rehab, or taking the stairs.

The Pre-brief

The use of noninvasive ventilation (NIV) continues to be of service for patients.  While there are several different modes to choose from, one that continues to be on the rise is average volume assured pressured support ventilation (AVAPS). There is a good reason that clinicians are opting to choose and prescribe it.

What is AVAPS

Since the production of the V60 by Respironics, AVAPS has been used to treat several chronic conditions. It is used for chronic respiratory insufficiency, chronic respiratory failure, and chronic hypoventilation. Chronic hypoventilation includes COPD, neuromuscular diseases, OHS, and kyphoscoliosis. 

AVAPS is a mode of ventilation that targets a set volume. It works by utilizing both pressure and volume control. It uses a maximum pressure (Max P) and minimum pressure (Min P) instead of a set inspiratory pressure (IPAP). This allows for a changing pressure to guarantee a desired VT for the patient. Other than the set volume, the Max P and the Min P, AVAPS uses settings similar to BiPAP. These settings include EPAP, Rate, I-time, and FiO2. The main difference will be in setting the Max and Min P. 

The main benefit of AVAPS is that it will adjust the pressure as needed to achieve the tidal volume (VT) set. It achieves this by using an algorithm to determine the correct pressure, allowing for changes in inspiratory pressure to ensure VT is delivered. The VT displayed will be a six-breath average. Typically, changes will occur over several minutes. The ever-changing IPAP of AVAPS helps to prevent patient dyssynchrony and improve patient compliance, by adjusting for lung compliance, extrinsic lung resistance, and respiratory effort. One way this is evident is as the patient changes position as they sleep, they may need a greater or smaller inspiratory pressure to maintain the desired VT. This then allows for improved patient outcomes.  

Another benefit of AVAPS would be increased compliance for treatment for patients. As AVAPS has been known to be helpful in treating stable patients with chronic conditions, it has begun to be used in acute respiratory failure. It has been associated with improvement in ABGs, pH, and respiratory rate of patients. AVAPS has led to quicker recoveries for patients. And with the increased comfort for patients, compliance of treatment for patients increases. All of this leading to AVAPS being a possible better treatment than just BiPAP for patients who have acute COPD exacerbations and also OSA.  And AVAPS would not have to be changed to a different mode before discontinuing use. The exception would be for patients with higher Apache II scores who have a greater risk of treatment failure.

What about settings

When setting the pressures for AVAPS, it is important to know what the patient was doing on a S/T mode. You would want to set the Min P at the IPAP setting previously. This number generally will be at least 8, and generally 4 above EPAP setting. The Max P should be in the 20-25 range. At the start, AVAPS will use three different methods to determine what to set the inspiratory pressure to. Of the three methods, the one with the highest value will be picked. Per Respironics, it will choose from Min P, EPAP + 8 cmH2O, or EPAP + (target volume/60 mL/cmH20). Then it will adjust the IPAP between 1-2.5 cmH20 per minute to achieve the desired VT.

Respironics does offer some tips to follow when starting in AVAPS. 

  • When setting the Min P, if after several breaths you have not achieved the set VT, raise the Min P up until the set VT is achieved.
  • When the set VT is achieved, lower the Min P to allow for AVAPS to have the chance to adjust settings in P as needed.
  • Being unable to reach a set VT because of a low Min P setting, change the Min P setting appropriately. This should work unless the set Max P has been reached.
  • When the set VT is surpassed due to a Min P being set too high, lower the Min P if the Min P has not been reached. 
  • Set alarms appropriately, including high and low VT alarms.
  • Remember, EPAP must be set to at least 1 cmH2O lower than the set Min P. 

Contraindications would include:

  • Cardiac/Respiratory arrest
  • Upper airway blockages
  • GI bleeds
  • Encephalopathy
  • Fascial problems

The Debrief

  • AVAPS uses a Min P and Max P instead of set IPAP to deliver a set VT
  • AVAPS improves dyssynchrony and patient compliance, leading to improved patient outcomes
  • AVAPS is not just for chronic conditions anymore and has shown to be highly beneficial in acute COPD and OSA.

References

  1. Hoo, G. W. S. (2020, December 6). Noninvasive Ventilation: Overview, Methods of Delivery, General Considerations. Medscape. 
  2. Asp, K.  (2020, August 10). What is AVAPS Mode? (Settings and Indications). AAST. 
  3. Yarrarapu, S. N. S., Saunders, H., & Sanghavi, D. (2020, August 15). Average Volume-Assured Pressure Support. StatPearls. 
  4. Philips. (2018). Pocket guide – Philips V60 and V60 Plus* ventilators. A comprehensive noninvasive solution. [E-book]. 

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