Hamilton - Adaptive Support Ventilation System (ASV)

All Hamilton Medical ventilators feature the intelligent ventilation mode Adaptive Support Ventilation (ASV). ASV adjusts respiratory rate, tidal volume, and inspiratory time continuously depending on the patient’s lung mechanics and effort. ASV adapts ventilation breath-by-breath, 24 hours a day, and from intubation to extubation.

ASV automatically employs lung-protective strategies to minimize complications from AutoPEEP and volutrauma/barotrauma. It also prevents apnea, tachypnea, dead space ventilation, and excessively large breaths. Within the rules of this lung-protective strategy, ASV encourages the patient to breathe spontaneously. 

ASV is a well established mode in critical care since 1998 and has become a standard mode in many units around the world. ASV has been successfully used in a variety of patient groups — including post-operative, COPD, and ARDS patients (Celli 2014, Agarwal 2013, Kirakli 2011, Gruber 2008, Sulzer 2001).

Since its introduction in 1998, ASV has received a lot of interest from the scientific community and has been the topic of well over 30 studies. 

Studies show that:

• In passive patients, ASV selects different tidal volume / respiratory rate combinations for normal lung, COPD, and ARDS patients (Arnal 2008).
• In active patients, ASV decreases work of breathing and improves patient-ventilator synchrony (Wu 2010, Tassaux 2010). 
• In the ICU, ASV decreases the weaning duration in medical patients (Chen 2011) and COPD patients (Kirakli 2011).
• In post-cardiac surgery, ASV allows earlier extubation than conventional modes (Gruber 2008, Sulzer 2001) with fewer manual adjustments (Petter 2003) and fewer ABG analyses performed (Sulzer 2001). 

The bibliography gives an overview of the results of the studies on ASV and of some of the underlying principles.

ASV maintains an operator set minute volume and automatically determines an optimal tidal volume / respiratory rate combination based on the minimal work of breathing principle described by Otis (Otis 1954). ASV takes into account the patient’s respiratory mechanics, which are measured breath-by-breath by the proximal flow sensor. ASV ensures optimal ventilation for each patient during passive ventilation, spontaneous breathing, and weaning.

ASV in passive patients

In passive patients, ASV is a volume-targeted pressure controlled mode with automatic adjustment of inspiratory pressure, respiratory rate, and inspiratory/expiratory time ratio. Maximum tidal volume is controlled by setting a maximum inspiratory pressure. Expiratory time is determined according to the expiratory time constant in order to prevent dynamic hyperinflation.

ASV in active patients

In spontaneously breathing patients, ASV is a volume-targeted pressure support mode with automatic adjustment of pressure support according to the spontaneous respiratory rate. The automatic decrease of pressure support when the patient recovers their inspiratory strength is very useful for weaning. ASV can also be used to perform a weaning trial before extubation.