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Adaptive Support Ventilation

OVERVIEW

Adaptive support ventilatio n (ASV) is a po sit ive pressure mode of mechanical ventilat ion that is

closed-loop contro lled, and automatically adjust based o n the pat ients requirements

designed to ensure opt imization of the patients WOB

CLOSED LOOP CONTROL

closed-loop contro l involves a pos itive or negative f eedback of the info rmation on t he respiratory

mechanics o f the patient

it is based on measurements made almos t continuously which can be modif ied or adapted in a more

physiological and individualized ventilatory support manner

Two basic methods

Contro l between breaths (inter-breath) which refers to the set ting of contro l between each breath,

but keeping it constant throughout the breath cycle (e.g. ASV)

intra-breath contro l, which does it within the same breath

see f igure here

Other modes are all variations o f 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 patients RR is lower than target

VENTILATOR SETTINGS

These are set by the user:

Height of the pat ient (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 >38.5C (101.3F) or add 5% f or every 500 m (1640 feet) above sea level

Trigger: Flow t rigger of 2 l/min

Expiratory trigger sensitivity: Start with 25% and 40% in Chronic obst ructive pulmonary disease

COPD

Tube resistance compensation: Set t o 100%

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High pressure alarm limit: 10 cm H2O be the limit o f and least 25 cm H2O of PEEP/cont inuous

pos itive airway pressure (CPAP)

PEEP

FiO2

Then:

ASV selects the respiratory pat tern in terms o f RR, VT, Inspiratory:Expiratory t ime (I:E rat io) f or

mandato ry breathing and reaches the respiratory pat tern selected

Otis equation is used to determine the RR at which work of breathing is opt imse

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 f or o perator involvement

decreases time on mechanical ventilation

adjusts t o patient inspiratory eff ort

Disadvantages

cannot directly pro gram VT, RR and I:E rat io

limited paediatric experience

algorithm tends to ventilate with low tidal volume and high RR

only available with Hamilton ventilators

References and Links

Fernndez J, Miguelena D, Mulett H, Godoy J, Martinn-Torres F. Adaptive support

ventilation: State of the art review. Indian J Crit Care Med. 2013 Jan;17(1):16-22. doi:

10.4103/0972-5229.112149. PubMed PMID: 23833471; PubMed Central PMCID:

PMC3701392.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3701392/http://www.ncbi.nlm.nih.gov/pubmed/23833471