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Indications for Mechanical Ventilation

Indications for mechanical ventilation have evolved substantially since widespread use of ventilatory support began in the early 1960s. While the metabolic and blood-gas alterations that mandate institution of ventilatory support have remained unaltered, new noninvasive modes of ventilation have widened the therapeutic options available to patients in acute respiratory failure. An understanding of the effect of mechanical ventilation on other organ systems has clarified the role of mechanical ventilation in the treatment of conditions other than respiratory failure such as stroke or head injury. Studies in patients recovering from major surgery have better defined the benefits and risks of postoperative mechanical ventilation. Finally, a better understanding of disease processes has led to more prognostic information that can help physicians, patients, and families decide on limits to compassionate care. The proper use of mechanical ventilation in disease states that do not involve respiratory failure as their primary manifestation is also important in light of the risks of respiratory support. In patients with CNS injury, the role of hyperventilation is limited to acute control of dangerous elevations of intracranial pressure. Although hypocarbia has been proposed to improve regional cerebral blood flow, studies have not demonstrated an improvement in outcome, suggesting that the risks of intubation, tracheal stimulation, sedation, and inability to examine the mental status outweigh any benefit. Some evidence suggests a detrimental effect from prolonged hyperventilation. The use of mechanical ventilation in postoperative care is another area that requires scrutiny. Numerous studies have shown that with coordination of care between surgeons, anesthesiologists, and nurses, many patients can be extubated significantly sooner than in the past. As techniques for administering anesthesia, performing surgery, and managing pain and mild respiratory insufficiency improve, knowledge in this area will continue to develop. Finally, the relation between mechanical ventilation, quality of life, and patient autonomy has come to play a greater role as the population ages. In many situations, respiratory failure represents the end stage of an irreversible disease. Whereas respiratory failure secondary to pulmonary contusion in young patients does not indicate a poor outcome, progressive respiratory failure in cystic fibrosis or following bone marrow transplantation usually represents a preterminal event. Understanding the epidemiology of respiratory failure in different disease categories is important to physicians, patients, and families in making informed decisions about their care. Mechanical ventilation represents a vital, fundamental form of life support. As the diseases, tools, and treatments change in anesthesia and critical care, careful definition of the role of mechanical ventilation in specific diseases, the route by which it is delivered, and the ability of such a form of life support to affect outcome will continue to be necessary.