Weaning parameters
P 0.1, RSB, NIF:
A number of criteria must be taken into account by the
doctor when deciding whether or not a patient is ready
to be weaned off the ventilator. In addition to the results
of examinations and laboratory analyses, ventilation
parameters can also be used to judge whether the
patient can be weaned successfully.
The following weaning parameters are calculated by
Evita 4:
– Occlusion pressure P 0.1
– Rapid Shallow Breathing RSB
– Negative Inspiratory Force NIF
Occlusion pressure P 0.1
Breathing drive can be measured at the start of inspira-
tion by measuring the mouth pressure during a short-term
occlusion: within 100 ms, the pressure is not influenced
by physiological compensation reaction (e.g. reflected
breathing stop or increased breathing drive). This
pressure is always dependent on the muscle strength of
the diaphragm. Therefore, the negative mouth pressure
P 0.1 after 0.1 seconds is a direct measure of neuro-
muscular breathing drive*.
For patients with healthy lungs and regular breathing,
P 0.1 will be about –3 to –4 mbar. A higher P 0.1
signifies a high breathing drive which can only be
maintained for a limited period. P 0.1 values about
–6 mbar, e.g. for a COPD** patient, indicate impending
exhaustion (RMF – respiratory muscle fatigue).
When weaning COPD patients off the Ventilator,
measurement of P 0.1 can define the weaning point.
To measure P 0.1, Evita 4 keeps the inspiratory valve
closed after one expiration and measures the airway
pressure produced by the inspiratory effort during
100 ms (P1).
The 100 ms time interval starts when a negative pressure
of –0.5 mbar is measured as a result of the inspiratory
effort.
A second pressure value (P2) is activated after 100 ms.
Simultaneously, the inspiratory valve is opened so that
the patient can breathe normally again.
The occlusion pressure P 0.1 is the difference between
the pressure values P2 – P1.
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* Bibliography (10), (15), page 182
** COPD = Chronic Obstructive Pulmonary Disease
174
Description
Weaning parameters
Occlusion pressure P 0.1
Paw
CPAP
–0,5 mbar
100 ms
P 0.1
P1
P2
t
Insp. valve closed
Insp. valve open
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