Chapter 20. Ventilatory Crises

Gregory A Schmidt, MD, FCCP
DOI: 10.1378/critcare.21.20
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  • Review bases for the distressed ventilated patient.

  • Examine the role of patient-ventilator dyssynchrony.

  • Propose analyzing respiratory mechanics to guide diagnosis.

  • Discuss approaches to critical hypoxemia.

  • Introduce ventilator changes in autoPEEP.


The ICU course of mechanical ventilation is characterized by an apparently comfortable patient, silent ventilator alarms, and acceptable gas exchange. This peaceful picture may be punctuated, however, by abrupt crises of distress and alarming or severe hypoxemia or hypercapnia. By their very nature, such crises demand a rapidly paced response. At the same time, the stakes are high: the treatment (eg, needle thoracostomy or a sedative bolus) may be lifesaving (if accurate) or life ending (if wrong). This chapter describes the most common crises during mechanical ventilation; provides a framework for rapid, bedside evaluation; and emphasizes the use of ventilator flow, pressure waveforms, and bedside ultrasonography to guide therapy. This chapter is divided into the following categories: (1) the distressed patient, (2) high-pressure and low-pressure alarms, (3) critically impaired gas exchange, and (4) high levels of auto-positive end-expiratory pressure (autoPEEP), a particular scenario that may provoke distress, alarming, or gas exchange failure.


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