Mechanical ventilation

Abstract

Acute respiratory failure is the most common cause of admission to critical care. Many patients presenting to ICU have pre-existing heart disease and 13.1% will be diagnosed with chronic, NYHA IV heart failure. In addition, global left ventricular hypokinesia frequently occurs in adults with septic shock and around 20% of patients with acute respiratory distress syndrome (ARDS) have acute pulmonary hypertension and right heart failure. The presence of heart failure adds significant challenges for the management of mechanically ventilated patients and increases their morbidity and mortality. Furthermore, positive pressure ventilation can exert profound cardiovascular effects through heart-lung interactions. It is thus essential for the cardiologist to have an appreciation of the assessment and management of patients with respiratory failure, particularly if mechanically ventilated. Mechanical ventilation is used to assist or replace spontaneous respiration. Gas flow can be generated by negative pressure techniques, but it is positive pressure ventilation that is the most efficacious and most commonly used in intensive care. There are numerous pulmonary and extrapulmonary indications for mechanical ventilation, and it is the underlying pathology that will determine the duration of ventilation required. Ventilation modes can broadly be classified as volume- or pressure-controlled, but modern ventilators combine the characteristics of both in order to complement the diverse requirements of individual patients. To avoid confusion, it is important to appreciate that there is no international consensus on the classification of ventilation modes. Ventilator manufacturers can use terms that are similar to those used by others that describe very different modes or have completely different names for similar modes. This chapter provides an introduction on mechanisms of respiratory failure, principles of physiological assessment, modes and strategies of invasive mechanical ventilation. Whenever possible we discuss the heart-lung interactions of relevance to the cardiologist.