Page 264 - Clinical Application of Mechanical Ventilation

230 Chapter 8

pressure limit. Once the alarm is triggered by airflow obstruction, inspiration is
immediately terminated and the ventilator goes into expiratory cycle.
The patient must be evaluated to determine the cause of the airflow obstruction.
Common causes that trigger the high inspiratory pressure alarm include water in the
ventilator circuit, kinking or biting of the endotracheal tube, secretions in the airway,
bronchospasm, mucus plugs, tension pneumothorax, decreases in lung compliance,
increases in airway resistance, and coughing.

Apnea Alarm

The apnea low volume and low pressure alarms are triggered in apnea and circuit
disconnection (i.e., inadvertent disconnection or during endotracheal suctioning).
Inadvertent circuit disconnection is a common event in patients with a tracheos-
tomy tube due to lack of allowance for airway flexibility as with an endotracheal
tube. The apnea alarm should be set with a 15- to 20-sec time delay, with less time
The apnea alarm should delay at higher frequency. On some ventilators, the apnea alarm also triggers an
be set with a 15- to 20-sec
time delay. apnea backup ventilation mode in which the ventilator provides ventilatory support
until the alarm condition no longer exists.

High Frequency Alarm

The high frequency alarm should be set at 10/min over the observed frequency.
The high frequency Triggering of the high frequency alarm may indicate that the patient is experienc-
alarm should be set at
10 /min over the observed ing respiratory distress. See Chapter 12, “Management of Mechanical Ventilation,”
frequency. for a discussion on the causes and management of the high frequency alarm.

High and Low F O Alarms
Set the low and high I 2
F I O 2 alarms at 40% and 50%,
respectively, for an F I O 2 of The high F O alarm should be set at 5% to 10% over the analyzed F O and the
45%. I 2 I 2
low F O alarm should be set at 5% to 10% below the analyzed F O .
I
2
I
2
HAZARDS AND COMPLICATIONS

Mechanical ventilation has many potential hazards (e.g., ventilator disconnection,
nosocomial infection) and complications (e.g., barotrauma, hypotension). The fre-
quency of occurrence is directly related to the length of mechanical ventilation
(Liu et al., 1991; Pierson, 1990). Patients who require mechanical ventilation for
longer periods are likely to develop more complications.
This section summarizes the common hazards and complications of mechanical
ventilation based on several prospective studies. Special emphasis is provided for
barotrauma and decrease in cardiac output and blood pressure since the effects of
these complications are more urgent to the patient’s progress and outcome.

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