- Adaptive support ventilation (ASV) is a positive pressure mode of mechanical ventilation that is closed-loop controlled, and automatically adjusts based on the patient’s requirements
- designed to ensure optimization of the patient’s work of breathing
CLOSED LOOP CONTROL
- closed-loop control involves a positive or negative feedback of the information on the respiratory mechanics of the patient
- it is based on measurements made almost continuously which can be modified or adapted in a more physiological and individualized ventilatory support manner
Two basic methods
- Control between breaths (inter-breath) which refers to the setting of control between each breath, but keeping it constant throughout the breath cycle (e.g. ASV)
- intra-breath control, which does it within the same breath
- see figure here
Other modes are all variations of PSV
- Proportional Assist Ventilation (PAV)
- Neurally Adjusted Ventilatory Assistance (NAVA)
- Knowledge-Based Systems (KBS)
ASV combines modes
- PSV, if RR is higher than the target
- PCV if there is no spontaneous breathing
- SIMV when patient’s RR is lower than target
These are set by the user:
- Height of the patient (cm): Based on this it calculate the ideal body weight and dead space 2.2 ml/kg
- % Min Vol: 25-350%Normal 100%, asthma 90%, acute respiratory distress syndrome (ARDS) 120%, others 110%, Add 20% if T body >38.5°C (101.3°F) or add 5% for every 500 m (1640 feet) above sea level
- Trigger: Flow trigger of 2 l/min
- Expiratory trigger sensitivity: Start with 25% and 40% in Chronic obstructive pulmonary disease COPD
- Tube resistance compensation: Set to 100%
- High pressure alarm limit: 10 cm H2O be the limit of ↓ and ↑ least 25 cm H2O of PEEP/continuous positive airway pressure (CPAP)
- ASV selects the respiratory pattern in terms of RR, VT, Inspiratory:Expiratory time (I:E ratio) for mandatory breathing and reaches the respiratory pattern selected
- Otis equation is used to determine the RR at which work of breathing is optimse
- starts with test breaths to obtain measurements
- ventilation is pressure and volume limited
- % VM can be titrtated by the operator according to clinical criteria and ABG results
PROS AND CONS
- can ventilate any patient group
- prevents tachypnea, autoPEEP and dead space
- less operator dependent and less need for operator involvement
- decreases time on mechanical ventilation
- adjusts to patient inspiratory effort
- cannot directly program VT, RR and I:E ratio
- limited paediatric experience
- algorithm tends to ventilate with low tidal volume and high RR
- only available with Hamilton ventilators
References and Links
- Fernández J, Miguelena D, Mulett H, Godoy J, Martinón-Torres F. Adaptive support ventilation: State of the art review. Indian J Crit Care Med. 2013 Jan;17(1):16-22.PMC3701392.
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.