Page 431 - Clinical Application of Mechanical Ventilation

Management of Mechanical Ventilation 397

for the heated humidifier should be placed inside the inspiratory limb of the venti-
lator circuit as close to the patient as possible. Since water vapor saturation depends
on the water content as well as the temperature, the temperature setting should be
adjusted for a distal temperature reading of 37°C. This ensures proper temperature
and humidification to the patient (Burton et al., 1997).

Frequency of Circuit Change

Ventilator circuits should not be changed routinely for infection control purposes.
The maximum duration of time that circuits can be used safely is unknown (Hess
et al., 2003). For circuits with a humidifier or HME, they should be changed only
when visibly soiled (Tablan et al., 2004). Studies have shown that the optimal
The optimal interval for interval for ventilator circuit change is once per week (Fink, 1998; Kotilainen, 1997;
ventilator circuit change is
once per week. Long et al., 1996; Stamm, 1998). When compared to more frequent circuit changes,
weekly circuit change does not increase the incidence of nosocomial infection, in-
cluding ventilator-associated pneumonia. Weekly change also saves manpower and
reduces the direct replacement cost for new ventilator circuits (Kotilainen, 1997).

CARE OF THE ARTIFICIAL AIRWAY

Supplemental humidity must be provided during mechanical ventilation, because
Patency of the ET tube the endotracheal (ET) tube does not receive humidification normally provided by
can only be ensured with
adequate humidification and the upper airway. In addition, secretions must be removed by suctioning, if nec-
prompt removal of retained essary, because the ET tube and the ventilator circuit are a closed system. If not
secretions.
removed, any secretions coughed up by the patient are likely to stay in the ET tube.
Patency of the ET tube can only be ensured with adequate humidification and
prompt removal of retained secretions.

Patency of the Endotracheal Tube

In mechanical ventilation, the primary purpose of an ET tube is to protect the
airway and to provide airflow to the lungs. Since airflow resistance is inversely
related to the diameter of the tube, small tubes cause a tremendous increase in
the work of breathing. In order to maximize airflow, the largest ET tube that is
appropriate to the patient should be used. Mucus in the ET tube should also be
removed frequently in order to minimize airflow obstruction created by retained
secretions.
Poiseuille’s Law shows that when the radius of an airway is reduced by half, the
driving pressure (work of breathing) must be increased 16 times in order to main-
tain the same flow rate. An obstructed airway hinders not only mechanical ventila-
tion, but spontaneous ventilation as well. Airway management should always be an
integral part of mechancial ventilation.

Flow
Pressure change =
r 4

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.