Mechanical Ventilation

Mechanical ventilation supports gas exchange when a patient cannot oxygenate, ventilate, protect the airway, or sustain the work of breathing. It does not correct the underlying disease. Pneumonia, pulmonary edema, ARDS, airway obstruction, neurologic injury, shock, and postoperative respiratory failure each require a different parallel treatment plan. Spontaneous breathing draws gas inward by generating negative intrathoracic pressure. Positive-pressure ventilation pushes gas into the thorax. That pressure can improve alveolar inflation, but it also compresses intrathoracic vessels and reduces venous return to the right heart. Less preload can mean lower cardiac output and hypotension, especially in a patient who is hypovolemic, vasodilated, or receiving substantial PEEP. A new fall in blood pressure after intubation or a PEEP increase is therefore not automatically “sedation-related.” Check the timing, assess volume status and perfusion, and consider whether increased intrathoracic pressure is the cause. A patient with severe obstructive disease can become profoundly hypotensive from air trapping even when the set PEEP is low. Ventilator support has two broad jobs: - Oxygenation depends mainly on inspired oxygen concentration, alveolar recruitment, and matching ventilation to perfusion....