Weaning patients from the ventilator.

Copyright © 2012 Massachusetts Medical Society. In the United States, almost 800,000 patients who are hospitalized each year require mechanical ventilation.1 This estimate excludes neonates, and there is little doubt that mechanical ventilation will be increasingly used as the number of patients 65 years of age or older continues to increase.2,3 The majority of patients who receive mechanical ventilation have acute respiratory failure in the postoperative period, pneumonia, congestive heart failure, sepsis, trauma, or the acute respiratory distress syndrome (ARDS).4 Our discussion below assumes that physicians have addressed metabolic, inflammatory, and infectious conditions that may be present and have corrected them to the extent possible. As soon as the condition that caused respiratory failure has started to improve, the transition from full ventilatory support to spontaneous breathing may be initiated. This transition requires sufficient respiratory-muscle strength to sustain breathing and maintain acceptable gas exchange. In most patients, this transition also includes the removal of the endotracheal tube. In patients with prolonged respiratory failure, the term “weaning” may be apropos, since it describes a gradual process of improving the strength-to-load ratio of the respiratory system to enable spontaneous respiration. Unfortunately, although this term is widely used, it is somewhat misleading in the vast majority of patients with acute respiratory failure. “Liberation” from mechanical ventilation is a better description, since it implies rapid removal of a burden that is no longer necessary. Figure 1 shows a typical algorithm used by clinicians to discontinue mechanical ventilation. Patients are assessed daily for their readiness to undergo a trial of spontaneous breathing. In many intensive care units (ICUs), protocol-driven assessments of readiness are carried out by nurses or respiratory therapists. Typical readiness criteria include hemodynamic stability, a ratio of the partial pressure of arterial oxygen (measured in millimeters of mercury) to the fraction of inspired oxygen (which is unitless) of more than 200 with the ventilator set to deliver a positive end-expiratory pressure of 5 cm of water or less, and some improvement in the underlying condition that caused the respiratory failure. Trials of spontaneous breathing assess a patient’s ability to breathe while receiving minimal or no respiratory support. To accomplish this, ventilators are switched from full respiratory support modes such as volume-assist control or pressure control to ventilatory modes such as pressure support, continuous positive airway pressure (CPAP), or ventilation with a T-piece (in which there is no positive endexpiratory pressure). Ideally, a trial of spontaneous breathing is initiated while the patient is awake and not receiving sedative infusions.5 For a spontaneous-breathing trial to be successful, a patient must breathe spontaneously with little or no ventilator support for at least 30 minutes without any of the following: a respiratory rate of more than 35 breaths per minute for more than 5 minutes, an oxygen saturation of less than 90%, a heart rate of more than 140 beats per minute, a sustained change in the heart rate of 20%, systolic blood pressure of more than 180 mm Hg or less than 90 mm Hg, increased anxiety, or diaphoresis.