Page 266 - Clinical Application of Mechanical Ventilation

232 Chapter 8

Malfunction and Misuse of Alarms

The Joint Commission (TJC) reviewed 23 reported deaths or injuries related to
long-term mechanical ventilation and found 19 deaths and four in coma. Sixty-
five percent of the deaths or injuries were related to the malfunction or misuse of
ventilator alarms. A breakdown of the causes revealed that the alarms were either
turned off or set incorrectly, no alarm was available for certain disconnections,
testing of alarms was not performed, or response to alarm was delayed or absent
(NYSNA, 2002).
These tragedies could be prevented by implementing regular preventive maintenance
and testing of alarm systems on ventilators and monitors. The alarms must also be suf-
ficiently audible with respect to the room design, distance, and noise level of the im-
mediate patient care area. Over dependence on alarms should be avoided and emphasis
should be placed on frequent direct observation and assessment of the patient-ventilator
system.

Barotrauma

Barotrauma is the term used to describe lung tissue injury or rupture that results from the
Risk of barotrauma is shearing force of alveolar over distention. General agreement is that in most cases, peak
high when PIP .50 cm H 2 O,
plateau pressure .35 cm inspiratory pressures greater than 50 cm H O, plateau pressures greater than 35 cm H O,
2
2
H 2 O, mPaw .30 cm H 2 O, and mean airway pressures greater than 30 cm H O, and PEEP greater than 10 cm H O
PEEP .10 cm H 2 O. 2 2
may induce the development of barotrauma (Bezzant et al., 1994; Slutsky, 1994). The
risk of barotrauma also increases with the duration of positive pressure ventilation.
Barotrauma can occur at mean airway pressures lower than 30 cm H O either due to
2
patient susceptibility or due to an uneven distribution of ventilation. COPD patients
are more susceptible to barotrauma presumably due to air trapping and weakened
parenchymal areas (e.g., lung blebs and bullae). Uneven distribution of ventilation
may result in patients with significant airway obstruction and lung parenchymal
changes. A mechanical tidal volume tends to preferentially distribute to areas of low
resistance and high compliance during the early portion of inspiration. This may result
in transient elevated alveolar pressures with resultant over distention and rupture de-
spite what would normally be accepted as a “safe” pressure.
Other lung injuries that may occur as a result of positive pressure ventilation
include pulmonary interstitial emphysema, pneumomediastinum, pneumoperito-
neum, pneumothorax, tension pneumothorax, and subcutaneous emphysema.

Decrease in Cardiac Output and Blood Pressure

Positive pressure ventilation has been implicated in the development of decreased
cardiac output and arterial blood pressure (Bezzant et al., 1994; Franklin et al., 1994).
The reason is that positive airway and alveolar pressures may potentially increase
the normally subatmospheric pleural pressures that surround the heart and vena
cava. The increased pleural pressure tends to compress the right atrium and vena

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