CHAPTER 49

#### KEY POINTS

• Effective preventive measures in ventilated patients include raising the head of the bed, employing measures to prevent venous thromboembolism, avoiding unnecessary changes of the ventilator circuit, reducing the amount of sedation, and providing oral care with chlorhexidine.

• Even patients with normal lungs may benefit from limited tidal volumes to reduce the risk of ventilator-induced lung injury causing progression to acute respiratory distress syndrome.

• Critical illness and mechanical ventilation combine to impair strength of respiratory muscles and produce atrophy. This tendency can be reduced by setting the ventilator in a way as to preserve inspiratory muscle contraction.

• Whenever the adequacy of oxygen exchange is in question, the initial fraction of inspired oxygen ($FiO2$) should be 1.0; this will be diagnostic as well as therapeutic, since failure to achieve full arterial hemoglobin saturation identifies a significant right-to-left shunt.

• The choice of ventilator mode is relatively unimportant: more relevant is to use the ventilator with full understanding of the principles of lung protection, ventilator-induced diaphragm dysfunction, autoPEEP, and patient-ventilator synchrony.

• The patient with severe airflow obstruction often develops hypoperfusion after institution of positive-pressure ventilation as a result of autoPEEP; this responds to temporary cessation of ventilation and vigorous volume resuscitation, while measures are employed to reduce airflow obstruction and reduce the total minute ventilation.

• The patient with acute hypoxemic respiratory failure (AHRF) resulting from pulmonary edema benefits from lung-protective ventilation (6 mL/kg ideal body weight and rate approximately 30 breaths/min). The initial $FiO2$ of 1.0 can be lowered to nontoxic levels by raising positive end-expiratory pressure (PEEP), guided by pulse oximetry or measures of recruitment.

Regardless of the underlying process leading to mechanical ventilation, several principles guide ventilator settings and associated management. This chapter emphasizes preventing complications by using the “ventilator bundle”; avoiding lung injury (through overdistention or autoPEEP); limiting ventilator-induced diaphragm dysfunction (VIDD); understanding cardiopulmonary interactions; choosing modes and settings in relation to the underlying cause of respiratory failure; ensuring synchrony between patient and ventilator; and responding to crises.

Other chapters of this book are complementary to the information presented here. The pathophysiology of respiratory failure is broadly reviewed in Chap. 43; monitoring respiratory system waveforms of pressure and flow is delineated in Chap. 48; noninvasive ventilation is covered in Chap. 44; ventilator-induced lung injury is discussed in Chap. 51; and finally, several chapters (eg, Chap. 52, Acute Respiratory Distress Syndrome; Chap. 54, Acute on Chronic Respiratory Failure; Chap. 55, Status Asthmaticus; Chap. 58, Restrictive Disease of the Respiratory System) discuss ventilatory support for specific problems.

#### PREVENTION: THE “VENTILATOR BUNDLE”

Mechanically ventilated patients are at risk for numerous complications related to the presence of the endotracheal tube, most notably ventilator-associated pneumonia (VAP), as well as adverse consequences of sedatives, paralytics, and immobilization. In response, the Institute for Healthcare Improvement promulgated the concept of “bundles,” a structured ...

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