Overview of mechanical ventilation

INTRODUCTION

Mechanical ventilation is also called positive pressure ventilation. Air is forced into the central airways, increasing central airway pressure. Air follows the pressure gradient from the central airways to the alveoli, which inflates the lungs. As the lungs inflate and the device stops forcing air into the central airways, the intraalveolar pressure increases and central airway pressure decreases. Expiration occurs when the air follows the newly reversed pressure gradient from the alveoli to the central airways. Mechanical ventilation can fully or partially replace spontaneous breathing.

The types of mechanical ventilation, as well as its benefits, indications, and initiation are discussed in this topic review. Potential complications are described separately. (See "Ventilator-associated lung injury" and "Pulmonary barotrauma during mechanical ventilation" and "Physiologic and pathophysiologic consequences of mechanical ventilation".)

INDICATIONS

Mechanical ventilation is indicated for acute or chronic respiratory failure, defined as insufficient oxygenation, insufficient alveolar ventilation, or both. Some common acute disorders for which mechanical ventilation may be required are listed in the table (table 1).

Mechanical ventilation should be considered early in the course of illness and should not be delayed until the need becomes emergent. Physiologic derangements and clinical findings can be helpful in assessing the severity of illness (table 2). However, the decision to initiate mechanical ventilation should be based on clinical judgment that considers the entire clinical situation [1,2]. Some of the objectives of mechanical ventilation are listed in the table (table 3) [2].

BENEFITS

The principal benefits of mechanical ventilation during respiratory failure are improved gas exchange and decreased work of breathing:
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