COPD patients, whereas a slow ramp increases
the time needed to reach lower peak inspiratory
fl ow, thereby favouring late cycling to expiration.
Expiratory trigger sensitivity
The expiratory trigger sensitivity (ETS) is the
percentage of the inspiratory fl ow peak that
commands the expiratory valve opening and the
cycling to expiration. It can be manually set from
minimum values of 5% to maximum of 60–70% of
the fl ow peak; default setting is usually 25% of
fl ow peak.
Setting the ETS appropriately is essential for
synchronisation. 9,22,23 There is not a ‘one size fi ts
all’ confi guration: each patient needs a
customised setting, based on the respiratory
mechanics and the current respiratory pattern. If
the ETS is too low, the ventilator will continue to
infl ate the patient’s lungs even after the
respiratory muscles have relaxed. In other words,
a certain amount of the inspiratory phase will be
passive, without the participation of the patient’s
muscles. By contrast, if the ETS is too high, the
ventilator will stop aerogating air even if the
respiratory muscles are still contracted: this
‘pliometric’ or ‘eccentric’ contraction can directly
damage the diaphragm 5,24,25 and can lead to
Once identifi ed,
patient’s
spontaneous
activity can
be supported
by optimising
ventilator
settings at the
bedside
double triggering, breath stacking and lung
injury.
An optimised ETS can also positively affect the
triggering phase, allowing a physiologic passive
exhalation, minimising hyperinfl ation and
ultimately facilitating the trigger for the
following breath.
Because COPD patients are prone to late
cycling, whereas restrictive patients can
experience early cycling, a reasonable approach
for initial ETS setting is 25% for patients with
normal mechanics (RCexp 0.4–0.8 s), 10% for
restrictive patients (RCexp <0.4 s) and 50% for
COPD patients (RCexp >0.8 s). Thereafter, the
interpretation of bedside ventilator waveforms
can be used for fi ne tuning of ETS.
Sedation
Most of the patients ventilated in assisted modes
require some sedation, at least for tube
tolerance, 26 but excessive sedation is associated
with diffi cult ventilator triggering and with
ineffective efforts, mainly for respiratory drive
and muscular pressure reduction. 15 Optimising
sedation is mandatory for correct patient–
ventilator interaction management: a lighter
sedative plan promotes a patient’s own muscle
13
HHE 2019 | hospitalhealthcare.com