After the underlying cause of respiratory failure in critically ill patients has been addressed, the priority is to minimize the duration of mechanical ventilation. The latest review in our Current Concepts series outlines strategies and interventions to reduce this duration.
In the United States, almost 800,000 patients who are hospitalized each year require mechanical ventilation. This estimate excludes neonates, and there is little doubt that mechanical ventilation will be increasingly used as the number of patients older than 65 years of age continues to increase.
• What criteria are used to assess readiness to undergo a trial of spontaneous breathing in a patient on a ventilator?
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.
• What criteria must be met for a spontaneous-breathing trial to be deemed successful?
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. Several additional factors also need to be assessed before removal of the endotracheal tube, including the ability to protect the airway once the tube is removed, the quantity of airway secretions, the strength of cough, and mentation.
Morning Report Questions
Q: How is the transition from mechanical ventilation to spontaneous breathing classified?
A: To better describe the transition from mechanical ventilation to spontaneous breathing, a classification scheme based on the results of spontaneous-breathing trials has been developed. A simple transition to spontaneous breathing is defined as a successful first trial, followed by discontinuation of mechanical ventilation. A difficult transition involves up to three spontaneous-breathing trials but fewer than 7 days between the first unsuccessful trial and successful discontinuation of mechanical ventilation. A prolonged transition is defined as at least three unsuccessful spontaneous-breathing trials or more than 7 days of mechanical ventilation after the initial unsuccessful trial.
Q: What evidence do the authors provide on the importance of early discontinuation of mechanical ventilation?
A: According to the authors, minimizing the duration of mechanical ventilation is an important consideration for all clinicians who care for critically ill patients. As a rule, weaning should start as soon as possible. There is support in the literature for this notion that quick discontinuation of mechanical ventilation is beneficial. In a prospective observational study involving patients with brain injuries, Coplin et al. compared discontinuation of mechanical ventilation within 48 hours after readiness criteria had been met with more than a 48-hour delay in discontinuation. There was higher mortality, an increased risk of pneumonia, and a longer hospital stay in the group with delayed discontinuation than in the group in which ventilation was discontinued in a more timely fashion.