Chapter 73. The Pathophysiology of Critical Illness

1. Acute injuries of various etiologies (eg, trauma, infection, shock, etc) cause immediate local and systemic physiologic responses involving all major organ systems.

2. The timing and intensity of the physiologic response to injury is affected by the severity of the injury as well as host factors. An initial activation of the proinflammatory immune responses may be followed by late immunosuppression.

3. Nosocomial infections are a major cause of death of critically ill patients and can be reduced by adopting best practices of infection control.

4. The vascular endothelium is a major organ target of the initial response to injury that activates vasomotor, inflammatory, and procoagulant cascades.

5. Our increased understanding of the molecular biology of the immune response to injury will hopefully lead to new and effective therapies that may include oxygen or nitrogen free-radical scavenging, mitochondrial protection, prevention of apoptosis, and enhancement of the immune response.

The term critical illness defines a variety of clinical situations that are cared for primarily in intensive care units (ICUs) and have in common varying degrees of dysfunction of single or multiple organ systems and a guarded immediate prognosis. Anesthesiologists care for critically ill patients in the operating room, in the ICU, and during procedures in areas outside of the operating room, such as radiologic, endoscopic, and cardiac electrophysiology suites. Thus it is crucial that anesthesiologists have an in-depth understanding of the pathophysiologic processes encountered during critical illness to contribute effectively to the perioperative management of critically ill patients.

This chapter focuses on a number of basic elements of critical illness, including inciting factors, the transition to organ dysfunction, the role of the immune system, and current as well as potential future therapies for various aspects of critical illness. We analyze the progression of critical illness examining common types of primary injuries, the body's response to them, and the progression of the response either toward healing and recovery or to deterioration and death. Epidemiologic and therapeutic considerations are also reviewed. The chapter begins with a case report of a critically ill patient through different stages of her illness that are referred to in subsequent sections of the chapter.

A 77-year-old woman with a history of severe chronic obstructive pulmonary disease and hypertension was admitted to the surgical ICU from a general ward with acute respiratory distress. She had been recovering uneventfully from a pancreatic resection for cancer until that morning when she experienced nausea and malaise, then vomited a large amount of dark fluid, and immediately complained of shortness of breath.

Upon arrival at the surgical ICU, she was in obvious respiratory distress, with a marginal (87%-89%) arterial oxygen saturation (SpO2) on a nonrebreathing oxygen mask. Following a rapid-sequence tracheal intubation, a large amount of dark green material was suctioned from her airways, similar in appearance to that suctioned from her stomach. A bronchoscopy revealed diffuse staining of the tracheobronchial mucosa with biliary material, down to the lobar bronchi ...