After a few years of implementing Adaptive Support Ventilation (ASV), I still receive questions from staff members and physicians regarding the ideal %MinVol target setting when initially setting-up ASV. I usually respond by asking, “do you want to wean or rest the patient”?
If the goal is to rest the patient or decrease WOB, precisely setting the %MinVol may be more time consuming.
At some facilities ASV is used primarily as a weaning modality were patients’ are transitioned to ASV from a conventional ventilator mode (e.g. VC-CMV, PC-CMV). If this is the standard then merely use the measured exhaled minute ventilation from the traditional settings and use this as your %MinVol target. This should adequately off-load the Inspiratory muscles.
Conversely, ASV is becoming the standard mode of ventilation at many institutions, primarily due to the modes specific safety rules (1). Unlike transitioning from a conventional ventilator mode were the practitioner already has a minute ventilation trend, a patient that is placed on ASV from the start needs additional assessment.
The operator manual recommends with initially setting up ASV to set the %MinVol at 100%. You can additionally, add 10% to this if using a Heat Moisture Exchange, and an additional 20% if the patient has a uncompensated metabolic acidosis (Radfords nanogram).
Dr. Wu and colleagues observed in their sampled patients that targeting a %MinVol of 100% is insufficient in decreasing WOB in patients with respiratory failure (2).
From their observations they recommend setting the %MinVol based on what they term as the “ASV Target Point”. The ASV target point is determined when:
1. All baseline breaths were spontaneous.
2. Then 1-to-5 mandatory breaths per minute appear.
3. Measured minute ventilation (VE) remains unchanged however; WOB decreases (as evidence by P0.1 changes).
Basically, increase the %MinVol setting by 10% every five minutes until 1-to5- mandatory breaths appear, and trend P0.1 for comparisons.
Titrating the %MinVol based on the ASV Target point is easy to comprehend and one doesn’t have to wait on additional test (e.g. temperature, ABG’s, CBC, blood culures, etc.) to optimally target a percent minute volume.
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| %MinVol Setting on a Hamilton G5 ventilator.
1. ASV is classified as using “Optimal Control” a ventilator mode that uses multiple mathematical models to prevent tachypnea, prevent auto-PEEP, prevent excessive dead space ventilation, and prevent high pressures.
2. Wu,C.P. et. Al. (2010). Correlation Between the %MinVol Setting and Work of Breathing During Adaptive Support Ventilation in Patients with Respiratory Failure. Respiratory Care. 55 (3).
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