ABSTRACT
Respiratory failure (RF) is defined by the inability to provide adequate oxygen for consumption by the peripheral tissues and/or the inability to ventilate adequately Four types or pathophysiologic mechanisms of RF are described (Table 2.1): Type I or acute hypoxemic RF is characterized by alveolar airspace flooding and resulting hypoxemia that does not correct easily with supplemental oxygen. Type II or ventilatory failure is characterized by relative alveolar hypo ventilation. Hypoxemia may also be present in type II RF, but it is corrected easily with supplemental oxygen. Type III respiratory failure occurs in the perioperative period and is the end result of progressive atelectasis of dependent lung units. Type IV respiratory failure occurs in the setting of global hypoperfusion due to cardiogenic, hypovolemic, or septic shock. Inadequate cardiac output leads to progressive hypotension and increased work of breathing as the respiratory system attempts to compensate for the metabolic acidosis that often accompanies an underperfused state. In patients with shock, intubation and mechanical ventilation reduces the oxygen consumption of the respiratory muscles and prevents excessive ‘steal’ of the limited cardiac output by the respiratory system.
