Page 142 - Clinical Application of Mechanical Ventilation

108 Chapter 4

to increasing airway resistance (nonelastic resistance) or decreasing lung compli-
ance (elastic resistance). Since PIP and flow have a direct mathematical relationship,
PRVC lowers the flow to reduce the driving pressure. See Equation (2).
(1) Airflow Resistance (nonelastic or elastic) 5 PIP / Flow
T
T
(2) Airflow Resistance (nonelastic or elastic) 5 PIP / T Flow
T
To compensate for a lower inspiratory flow, PRVC prolongs the inspiratory time
to deliver the target volume (VT 5 Constant Flow 3 TI Time).
T
Automode

Automode is a feature of the Siemens 300A ventilator and it combines PRVC and
automode: This mode provides volume support. This mode alters between time-cycled and flow-cycled breaths
time-triggered, PRVC breaths when
prolonged apnea is detected (12, depending on the degree of patient effort. If there is no spontaneous triggering
8, and 5 sec in adult, pediatric, and
neonatal modes respectively). effort for a time period (i.e., apnea for 12, 8, and 5 sec in adult, pediatric, and
neonatal modes, respectively), the ventilator provides PRVC and the breaths are
time-triggered. The delivered volume is preset with a variable PIP up to the high
pressure limit.
When the patient has two consecutive breaths that trigger the mechanical breaths,
the automode switches to volume support in which all breaths become patient-
triggered, pressure-limited, and flow-cycled.

ADAPTIVE PRESSURE CONTROL (APC)

Adaptive pressure control (APC) offers a dual-control mechanism that combines
adaptive pressure control
(APC): A mode of pressure- the functions of volume ventilation (stable tidal volume) with the functions of pres-
controlled breath that utilizes sure ventilation (via variable flow). Adaptive pressure control is a pressure-controlled
closed-loop control of the pressure
setting to maintain a minimum breath that uses variable inflation pressures (closed-loop control of the pressure) to
delivered tidal volume.
deliver a minimum targeted tidal volume. APC does not guarantee a constant tidal
volume. Since the inflation pressure is variable, as the patient’s inspiratory effort
increases the inflation pressure is reduced. This is a concern because the ventila-
tor cannot distinguish between improved pulmonary compliance and increased
patient effort (Branson et al., 2007, Mireles-Cabodevila et al., 2009). Increasing
patient’s breathing effort due to hypoxia or pain may potentially create a greater
work of breathing (due to decreasing inflation pressure).

VOLUME VENTILATION PLUS (VV1)

volume ventilation plus Volume ventilation plus (VV1) is available in the Puritan Bennett 840® ventilator
(VV1): An option that combines (Tyco Healthcare). It is an option that combines two different dual mode volume-
volume control plus and volume
support. targeted breath types: volume control plus and volume support.

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