Page 149 - Clinical Application of Mechanical Ventilation

Operating Modes of Mechanical Ventilation 115

AUTOMATIC TUBE COMPENSATION (ATC)

Automatic tube compensation (ATC) is available in the Evita 4 ventilator
automatic tube compensation
(ATC): A mode of ventilation that (Dräger Medical). The PB840 ventilator has a similar feature which is called tub-
offsets and compensates for the ing compensation (TC). This tubing compensation can be applied in all ventila-
airflow resistance imposed by the
artificial airway. tion modes. ATC offsets and compensates for the airflow resistance imposed by
the artificial airway. It allows the patient to have a breathing pattern as if breathing
spontaneously without an artificial airway. With ATC, the pressure delivered by
the ventilator to compensate for the airflow resistance is active during inspiration
and expiration. It is dependent on the airflow characteristics and the flow demand
of the patient. For example, when the airway diameter decreases or flow demand
increases, the pressure is raised to overcome a higher airflow resistance or increased
flow demand.

NEURALLY ADJUSTED VENTILATORY ASSIST (NAVA)

Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventila-
Neurally adjusted ventila-
tory assist (NAVA): A mode of tion in which the patient’s electrical activity of the diaphragm (EAdi or Edi) is
mechanical ventilation in which used to guide the optimal functions of the ventilator (Spahija et al., 2005). The
the patient’s electrical activity
of the diaphragm (EAdi or Edi) neural controls of respiration originated in the patient’s respiratory center are sent
guides the optimal functions of to the diaphragm via the phrenic nerves. In turn, bipolar electrodes are used to
the ventilator.
pick up the electrical activity. The electrodes are mounted on a disposable EAdi
catheter and positioned in the esophagus at the level of the diaphragm (Maquet,
2009).
NAVA is available for adults, children, and neonates, and it has been used suc-
cessfully in the management and weaning of mechanically ventilated patients with
spinal cord injury. Other uses and potential applications of NAVA include patients
with head injury, COPD, and history of ventilator dependency (Maquet, 2011).
The ability to wean these patients rapidly reduces or eliminates the incidence of
disuse atrophy of the diaphragm (Betters et al., 2004).

HIGH-FREQUENCY OSCILLATORY VENTILATION (HFOV)

High-frequency oscillatory ventilation (HFOV) delivers extremely small
High-frequency oscillatory
ventilation (HFOV): HFOV does volumes at high frequency. Its main application is to minimize development
not have a tidal volume setting of lung injury while providing mechanical ventilation. HFOV was patented in
and it delivers extremely small
volumes at high frequency, 1952 by Emerson and was developed for clinical application in the early 1970s
by Lunkenheimer. The U.S. Food and Drug Administration approved HFOV
for clinical use in neonates in 1991, children in 1995, and adults in 2001. The
primary settings of HFOV ventilators are: Airway pressure amplitude (delta P
or power), frequency, mean airway pressure, percent inspiration, inspiratory bias
flow, and F O .
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