Page 110 - Clinical Application of Mechanical Ventilation

76 Chapter 3

Output Alarms

Output alarms can be further subdivided into pressure, volume, flow, time, inspira-
tory, and expiratory gas.
Pressure alarms include high/low peak and mean and baseline airway pressures.
High and low values may be set for each of these output parameters to alert the
clinician of changes in the patient’s respiratory status. Additionally, an alarm may
be provided to detect failure of the airway pressure to return to the baseline valve.
This could be caused by airway obstructions, circuit obstructions, or ventilator
malfunctions.
Volume alarms include high/low exhaled tidal volumes for both ventilator-
supported breaths and spontaneous breaths. Low volumes may result from sedation
(spontaneous volumes), disconnection, or apnea (spontaneous volumes).
Flow alarms are limited to exhaled minute volume. High and low values may
be set on some ventilators to alert the clinician to changes in the patient’s minute
ventilation.
Time alarms include high/low frequency, excessive or inadequate inspiratory or
expiratory time and inverse I:E ratio. High/low frequency alarms alert the clinician
to changes in the total ventilatory frequency. Inspiratory and expiratory time alarms
may alert the practitioner to circuit obstructions or malfunctions, changes in gas
distribution, or inappropriate ventilator settings.
Inspired gas alarms alert the clinician to changes in oxygen concentration or gas
temperature. Some ventilators incorporate an oxygen analyzer to detect changes in
F O . High/low alarms alert the clinician to these changes. Inspired gas temperature
I
2
may be controlled by a servo-controlled humidifier or monitored by an indepen-
dent ventilator temperature alarm. High/low temperature alarms can alert the clini-
cian to changes in the inspiratory gas temperature.
Exhaled oxygen tension or end tidal carbon dioxide tension can be monitored,
and high/low alarms can be sent to the exhaled gas monitoring system. These moni-
tors can assist the clinician in determining the V /V , gas exchange, and the respira-
D
T
tory exchange ratio (R).

SUMMARY

As computer and medical technologies are getting more advanced, future mechanical
ventilators are likely to have more new features than the current ventilators. No one
knows for certain whether more new features will make the ventilators more complex
and less user-friendly. But no matter what the future ventilators become, the practitioners
who use mechanical ventilators must learn and maintain the theory, skills, and practice
in the use of mechanical ventilation.
The ability to use mechanical ventilation will be enhanced if the practitioners are
able to classify the ventilator properly and apply the unique characteristics of each
ventilator in patient care situations.

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