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  • • 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 of ventilation.
  • • Use of noninvasive ventilation lessens infection and duration of time in intensive care and improves mortality.

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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.

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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.

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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.

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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.

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Table Graphic Jump Location
Table 27–1. Indications for Mechanical Ventilation.

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