Page 146 - Clinical Application of Mechanical Ventilation

112 Chapter 4

TABLE 4-10 Characteristics of the Airway Pressure Release Ventilation Mode

Characteristic Description

Type of breath Time-triggered mandatory breaths will continue in this mode and
the patient is allowed to breathe spontaneously between mandatory
breaths.

Triggering mechanism The mandatory breaths are time-triggered, and the patient assumes all
spontaneous breaths.

Cycling mechanism The mandatory breaths are time-cycled by a preset inspiratory time.
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pressure increase should be in accordance with the patient’s breathing pattern to
avoid patient-ventilator dyssychrony.
When bilevel (two-level CPAP) mode on the Puritan Bennett 840 ventilator is in use,
the spontaneous breaths have the option of PSV. This PSV feature helps to augment the
spontaneous tidal volumes in condition of low compliance and high airflow resistance.

Indications for APRV

The primary indication for this mode is similar to that of pressure control, namely,
as an alternative to conventional volume-controlled ventilation for patients with sig-
nificantly decreased lung compliance such as patients with ARDS. Conventional
volume-controlled ventilation in these patients is associated with excessive peak air-
way pressures and barotrauma. APRV can provide effective partial ventilatory support
APRV can provide effec- with lower peak airway pressure than that provided by the PSV and SIMV modes
tive partial ventilatory sup-
port with lower peak airway (Chiang et al., 1994). However, APRV may be less comfortable than the PSV and
pressure than that provided by SIMV modes, and synchronization with mechanical breaths may also be a problem.
the PSV and SIMV modes.
Table 4-10 summarizes the major characteristics of the airway pressure release
ventilation mode.

BIPHASIC POSITIVE AIRWAY PRESSURE (Biphasic PAP)

Biphasic positive airway pressure (biphasic PAP or BiPAP) is a mode that has two
Biphasic positive airway
pressure (BiPAP): A mode that baseline pressure levels (P INSP and PEEP) and it allows spontaneous breathing at any
has two baseline pressures (P insp point in the mechanical ventilation cycle. Biphasic PAP is also called Bilevel (Puritan
and PEEP). It allows spontaneous
breathing at any point in the Bennett), BIPAP (Drager Europe), Bi-Vent (Siemens), BiPhasic (Avea), PCV1
mechanical ventilation cycle. (Drager Medical), and DuoPAP (Hamilton) (Mireles-Cabodevila et al., 2009).
Biphasic PAP is similar to APRV with one exception. In APRV, the patient spends
most of the time at the high pressure level with less than 1.5 sec at the low pres-
sure level. In Biphasic PAP, the patient spends more time at the low pressure level
(Mireles-Cabodevila et al., 2009). Figure 4-12 shows the duration of time at high
and low pressure levels for APRV and Biphasic PAP.

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