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Chapter 29

### Introduction

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.

### Definitions and Terms

• ▪  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 respiratory rate
• ▪  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 of gas.
• —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.

### Techniques

• ▪  There are a variety of indications for mechanical ventilation ranging from short term (ie, perioperative) to chronic (ie, chronic respiratory failure).
• —Intraoperative
• —Postrespiratory or cardiac arrest
• —Chronic obstructive pulmonary disease (COPD) exacerbation
• —Asthma
• —Acute respiratory failure
• —Neurologic failure
• —Cardiogenic shock/pulmonary edema
• ▪  Contraindications to mechanical ventilation.
• —Presence of an advanced directive precluding its application
• ▪  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 ...

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