Mechanical ventilation is machine-supported respiratory support
which may completely replace or assist the patient’s spontaneous
efforts. Mechanical ventilation is typically provided through an artificial
airway, although mechanical ventilators may be used as an adjunct
to noninvasive positive pressure ventilation. Negative pressure
mechanical ventilation will not be discussed in this chapter, because
its use is limited and a full discussion of all of the aspects of
mechanical ventilation is beyond the scope of this chapter.
- ▪ Rate: The respiratory rate may be used to indicate
machine or patient rate
- —Machine rate: The rate at which the ventilator
delivers positive pressure ventilation
- —Patient rate: The patient’s spontaneous
- ▪ Tidal volume (TV): The volume of each breath, and
as with rate, this may be used to indicate mechanically delivered
or patient TV
- ▪ Minute ventilation (VE): The total volume of air
breathed (whether spontaneous or mechanical) during 60 sec
- ▪ Fio2: The inspired oxygen concentration
- ▪ Pressure: A variety of pressures are set and measured on
a ventilator including:
- —Inspiratory pressure: Typically the pressure
at which the ventilator delivers a breath, although it may also
mean the pressure reached when the ventilator delivers a set volume
- —Trigger pressure: The negative pressure a patient
mush achieve to initiate a ventilator supported breath.
- —Positive end-expiratory pressure (PEEP): The pressure
the ventilator maintains during the expiratory phase of a breath.
- ▪ Sigh: A larger than normal breath delivered by the
ventilator at preset intervals to expand collapsed alveoli
- ▪ Mode: One of a large number of ventilator settings that
can be set to assist patient ventilation and thereby reduce work
of breathing, including:
- —Control mode: The ventilator is set to deliver
all of the ventilation.
- —Assist control (AC mode): The ventilator has asset
minimum number of breaths and augments every patient respiratory
effort with a preset TV.
- —Intermittent mandatory ventilation (typically synchronized
or SIMV): The ventilator supports a preset number of breaths with
a preset TV, and the patient may generate additional spontaneous TV.
- —Pressure support: Every patient effort is supported
with positive pressure at a preset level—TVs may vary from
supported breath to supported breath.
- —High frequency ventilation: One of a variety of
approaches to ventilatory support wherein mechanical respiratory
rate is supranormal—usually with smaller than normal TVs.
- ▪ There are a variety of indications for mechanical
ventilation ranging from short term (ie, perioperative) to chronic
(ie, chronic respiratory failure).
- —Postrespiratory or cardiac arrest
- —Chronic obstructive pulmonary disease (COPD) exacerbation
- —Acute respiratory failure
- —Neurologic failure
- —Cardiogenic shock/pulmonary edema
- ▪ Contraindications to mechanical ventilation.
- —Presence of an advanced directive precluding
- ▪ The ventilator (Figure 29-1) is connected to the artificial
airway using a standard connector.
- ▪ Initial Fio2, rate, and mode are selected depending
on the patient’s clinical status.
- ▪ Ventilator alarms should be set to ...