Page 632 - Clinical Application of Mechanical Ventilation

598 Chapter 18

TABLE 18-6 Selected Ventilators Suitable for Use in Multiplace Hyperbaric Chambers

Ventilator Testing Conditions and Notes

Bird Avian (Bird Technologies, Palm Springs, USA) VCV only. Tested to 2.5 ATA.

EVITA 4 (Dragerwerk, Germany) VCV and PCV. Tested to 2.8 ATA also in
CPAP and PSV modes.

Impact Uni-Vent Eagle Model 754 (Impact VCV only. Tested to 6 ATA.
Instrumentation, Inc., New Jersey, USA)
Lifecare PLV-100 VCV and PCV. Tested to 6 ATA also in SIMV
and assist modes.
Omni-Vent Series D (Allied Healthcare Products, VCV only. Tested to 6 ATA.
Inc., California, USA)
Servo 900 C (Siemens-Elema, Sweden) VCV and PCV. Tested to 6 ATA.

Reference: Kot, 2006.
© Cengage Learning 2014
Pressure-controlled ventilation (PCV) is preferred when mechanical ventilation is
Pressure-controlled required in a multiplace hyperbaric chamber. Since PCV provides a constant pres-
ventilation provides a con-
stant pressure and delivers sure, it delivers more stable tidal volumes. Volume-controlled ventilation (VCV)
more stable tidal volumes requires frequent adjustments of the tidal volume during compression and decom-
during compression and
decompression. pression (Kot, 2006).
There are many ventilators that can be used safely under hyperbaric conditions.
The ventilators in Table 18-6 offer different modes of ventilation and are capable of
operating under various barometric pressures (Kot, 2006).

Tidal Volume Fluctuations

Boyle’s Law describes the inverse relationship between pressure and volume. In hyper-
baric conditions, pressure causes compression of gases and reduction of gas volume. In
volume-controlled ventilation under hyperbaric conditions, the delivered tidal volume
is therefore less than the set tidal volume. As the pressure increases in the multiplace
hyperbaric chamber, the set tidal volume should be increased to compensate for the ef-
fects of gas compression. In mechanical ventilation, the expired volume approximates
In mechanical ventila- the delivered volume. A mechanical respirometer (e.g., Wright respirometer) may be
tion, the expired volume
approximates the delivered used to monitor the expired tidal volume during gas compression and decompression.
volume. A mechanical The tidal volume setting can be adjusted using the measured tidal volume as a guide.
respirometer (e.g., Wright
respirometer) may be used to In one study, a mechanical respirometer is used to monitor the volume changes of
monitor the changing tidal a ventilator during compression. To compensate for the gas compression, a progres-
volume during gas compres-
sion and decompression. sive increase of set volumes is needed to maintain stable minute and tidal volumes.
At 2.8 ATA pressure, a set tidal volume of 710 mL is needed to deliver a tidal vol-
ume of 500 mL (Table 18-7) (Vazquez et al., 2003).
Ventilators operating under hyperbaric conditions should be evaluated for changes
in pressure, frequency, and other electronic controls. Adjustments of these controls

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