Page 638 - Clinical Application of Mechanical Ventilation

604 Chapter 18

TABLE 18-11 Changes in Ventilator Parameters under Hypobaric Conditions

Altitude in ft 2,500 5,000 8,500 10,000

P in mm Hg 695 633 554 524
B
Set V in mL (Evita 4 Drager) 500 500 500 500
T
Indicated V in mL (Evita 4 Drager) 371 355 307 353
T
Measured V in mL 512 521 567 647
T
(ASL 5000 lung simulator, Ingmar Medical)
Peak Flow in mL/s 1158 1197 1337 1554

(Data rounded to whole numbers and ranges not included. Reference: Schedler et al., 2007.)
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altitude, the continuing increase in delivered tidal volume (result of gas expansion dur-
ing ascent) can cause hyperinflation and become potentially harmful to the patient.
The increase in tidal volume, airway, and alveolar pressures may produce lung injuries
or volutrauma if the condition is unrecognized. (Abadia de Barbara, 2004).

Pressure-compensated Pressure Compensation
ventilators tend to deliver
stable tidal volume, peak in-
spiratory flow, peak proximal
airway pressure, and minute Since most airplanes cruise at a cabin pressure altitude of up to 8,000 ft, the tidal
ventilation. volume of non-pressure-compensated ventilators should be monitored and adjusted
during airplane ascent and descent.
Pressure-compensated ventilators are better suited for mechanically ventilated pa-
tients who must travel long distance at high altitude. Pressure-compensated ventila-
For ventilators without tors tend to deliver stable tidal volume, peak inspiratory flow, peak proximal airway
the capability of pressure pressure, and minute ventilation (Grissom et al., 1997).
compensation, they may be
recalibrated after significant Use of Non-Pressure-Compensated Ventilators. For ventilators without the capability
changes in cabin altitude.
of pressure compensation, they may be recalibrated after significant changes in
cabin altitude. Manual ventilation is often necessary to maintain adequate ventila-
tion and oxygenation for the patient during the calibration period (Grissom et al.,
pressure compensation: a 1997). Another method of compensation is to monitor the ventilator outputs (tidal
ventilator feature that makes
self-adjustment of pressure or volume, frequency, and minute ventilation) and make necessary adjustments to the
volume output based on changing tidal volume and frequency during ascent and descent. Methods of adjustment will
atmospheric pressure.
be discussed under Adjustment of Tidal Volume in this chapter.

TRAVELING WITH PORTABLE VENTILATORS

Improved technology and miniaturization of ventilator components enable more
ventilator-dependent patients to travel by car or air. The major drawback of traveling
by air is the lack of flexibility. A patient must go by the time schedules determined

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