Overview of mechanical ventilation
- Anthony J Courey, MD
Anthony J Courey, MD
- Assistant Professor, Pulmonary and Critical Care
- University of Michigan Medical Center
- Robert C Hyzy, MD
Robert C Hyzy, MD
- Professor of Medicine
- University of Michigan Medical Center
Mechanical ventilation is also called positive pressure ventilation. Following an inspiratory trigger, a predetermined mixture of air (ie, oxygen and other gases) is forced into the central airways and then flows into the alveoli. As the lungs inflate, the intraalveolar pressure increases. A termination signal eventually causes the ventilator to stop forcing air into the central airways and the central airway pressure decreases. Expiration follows passively, with air flowing from the higher pressure alveoli to the lower pressure central airways.
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 "Diagnosis, management, and prevention of pulmonary barotrauma during invasive mechanical ventilation in adults" and "Physiologic and pathophysiologic consequences of mechanical ventilation".)
Mechanical ventilation can fully or partially replace spontaneous breathing. It is indicated for acute or chronic respiratory failure, which is 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 upon clinical judgment that considers the entire clinical situation [1,2]. Some of the objectives of mechanical ventilation are listed in the table (table 3) .
The principal benefits of mechanical ventilation during respiratory failure are improved gas exchange and decreased work of breathing:
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- TYPES OF BREATHS
- Volume control
- Volume assist
- Pressure control
- Pressure assist
- Pressure support
- Invasive versus noninvasive
- Choosing a mode
- Level of support
- - Trigger
- - Tidal volume
- - Respiratory rate
- - PEEP
- - Flow rate
- - Flow pattern
- - Fraction of inspired oxygen
- SUMMARY AND RECOMMENDATIONS