Adaptive Support Ventilation

OVERVIEW

• 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

VENTILATOR SETTINGS

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
• Gender
• % 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)
• PEEP
• FiO2

Then:

• 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

Advantages

• versatile
• can ventilate any patient group
• safe
• 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

Disadvantages

• 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.