- • Positive pressure mechanical ventilation is
used to treat acute and chronic respiratory failure.
- • It is important to be alert for complications of
mechanical ventilation including barotrauma, ventilator-induced
lung injury, and hemodynamic compromise.
- • Early assessment of readiness to wean reduces duration
- • Use of noninvasive ventilation lessens infection
and duration of time in intensive care and improves mortality.
Mechanical ventilation has resulted in profoundly improved survival
from acute and chronic respiratory failure. Nevertheless, growing
awareness of the potential for ventilators to worsen patient outcomes
has increased the necessity to understand subtle points of patient/ventilator
interactions. In this chapter the central issues of mechanical ventilation
including indications, modes, settings, complications, patient monitoring,
weaning, and noninvasive ventilation will be discussed.
Mechanical ventilation in the intensive care unit (ICU) is delivered
under positive pressure in contrast to normal human breathing in
which inspiration induces negative pressure in the thorax. This
makes the complications of barotrauma and hypotension predictable.
To achieve ventilation, rate, tidal volume (Vt),
fraction of inspired oxygen (Fio2),
and positive end-expiratory pressure (PEEP) are selected, as discussed
in the section on ventilator setting below. It is useful to track
the product of Vt and rate, the minute
ventilation (V̇e), to assess
for complications and readiness to wean. A normal V̇e is less then 10 L/min.
With the exception of apnea, there are no absolute clinical indicators
for mechanical ventilation, so decisions must be individualized.
In acute respiratory failure associated with disorders such as chronic
obstructive pulmonary disease (COPD), a proven intermediary role
for noninvasive positive-pressure ventilation (NIPPV) has clarified
the indications for intubation to ventilate (invasive positive-pressure
ventilation, IPPV). Importantly, mechanical ventilation does not
mandate endotracheal intubation, nor does intubation require mechanical
ventilation. For example, endotracheal tube placement may be life
saving in a case of impending upper airway obstruction or high risk for
aspiration, without need for a ventilator.
General indications for IPPV are listed in Table 27–1.
With the availability of both high-flow oxygen sources and NIPPV,
isolated oxygenation failure as a reason for IPPV is rare. Intubation
for hypoxia is indicated when NIPPV has failed or is contraindicated.
Contraindications include inability to protect the airway, patient
intolerance, and hemodynamic instability/cardiac arrest. For
hypercapnic ventilatory failure, the absolute value of arterial
carbon dioxide (CO2) tension/pressure (Paco2) is less important than
either the corresponding arterial pH (indicating acid/base
compensation) or the trend in Paco2 (indicating
clinical trajectory). Both the inability to “protect” the
airway from aspiration and the need for pulmonary toilet
for excess secretions are indications for intubation but not ventilation,
and are not listed in Table 27–1.
Indications for Mechanical Ventilation. |Favorite Table|Download (.pdf)
Indications for Mechanical Ventilation.
|Oxygenation deficit refractory to other interventions|
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