Explains the different modes of non-invasive mechanical ventilation

2.  Ventilation is controlled by setting the volume desired for
each breath or by setting a pressure that will be delivered
to the airway to assist with breathing.
 Changes in volume and pressure are directly
proportional to lung and chest wall compliance.
 Compliance = V / P

3.  When a volume mode is used, tidal volume provided
by the ventilator will be fixed.
 If the compliance of the lung is very low, then a high
amount of pressure will be needed to deliver the set
volume.
 If there is a leak in the system machine, then actual
tidal volume delivered may be lower than prescribed,
as the machine cannot know how much air is delivered
to the patient and how much is lost.

4.  In Pressure mode, pressure will be fixed and tidal
volume vary with compliance.
 Same pressure may generate adequate volumes in a
patient with good chest wall compliance, but would
generate inadequate tidal volumes in a patient with
poor chest wall compliance.
 The machine compensate for leak until set pressure is
reached.

5.  NIV-CPAP – continuous positive airway pressure
 NIV – PS – pressure support

6.  NIV – CPAP
Gives a continuous positive pressure throughout the
respiratory cycle.

7.  NIV – PS
 Gives additional support during inspiration and a
continuous but lower pressure during expiration
 In NIV-PS MODE, with BiPAP machine, the
inspiratory support is termed the IPAP (inspiratory
positive airway pressure), while the expiratory support
is termed the EPAP and the difference between IPAP
and EPAP is the amount of pressure support provided.

8.  In NIV-PS and NIV-CPAP, flow (Q) will depend on set
pressure, patient’s respiratory drive, airway resistance
and presence or absence of leak.
 Q = P / R, where P is the pressure gradient
between airway and alveoli as developed by the patient
(negative pleural pressure) and ventilator (positive
airway pressure) and R is airway resistance.

9.  In spontaneously triggered breaths, the ventilator can
be triggered by either a change in pressure or by a
change in flow.
 Flow triggering is more sensitive than pressure
triggering and reduces the work of breathing in
spontaneous modes.

10.  The trigger for stopping ventilator assistance during
inspiration can be either a decrease in flow to a
percentage of the maximal flow rate (usually 25% of
the maximal flow rate) or a set flow rate.